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Dr Jonathan Webb

Biography

Jonathan is a wildlife ecologist with interests in conservation biology, wildlife management, animal behaviour, and physiological and behavioural ecology. His current research focuses on identifying causal factors responsible for declines of endangered fauna, and developing practical solutions to reverse such declines.

Jonathan and his students work on a range of environmental issues that involve a diversity of native and introduced wildlife, including freshwater crocodiles, snakes, lizards, frogs, mammals, shore nesting seabirds, foxes, and cane toads.

Jonathan took up the role of Lecturer in the School of the Environment in May 2012. For the past decade he has been a Senior Research Fellow at the University of Sydney, where he taught the popular field course “Tropical Wildlife Biology and Management”. Prior to working at the University of Sydney, he was an ARC Postdoctoral Fellow at Charles Darwin University and the ARC Key Centre for Tropical Wildlife Management, where he worked on physiological ecology, indigenous use of native wildlife, and the impacts of cane toads on native wildlife.

He has published 114 articles in peer reviewed journals, and has contributed photographs and articles to popular magazines and websites.

To find out more, please visit Jonathan's webpage.

Professional

Memberships:
American Society of Ichthyologists and Herpetologists
Australian Society Herpetologists
Ecological Society of Australia

Editorial Boards:
Associate Editor, Wildlife Research
Associate Editor, Austral Ecology

Industry Research Partners:

The NT Department of Land and Resource Management

Kakadu National Park

The Australian Wildlife Conservancy

Territory Wildlife Park

Image of Jonathan Webb
Senior Lecturer, School of Life Sciences
B Sc (Hons), PhD
 
Phone
+61 2 9514 4037

Research Interests

  • Restoration of rock outcrops for the endangered broad-headed snake
  • Reintroducing endangered northern quolls to Kakadu National Park
  • Using conditioned taste aversion to mitigate impacts of cane toads on predators
  • Chemical communication in elapid snakes
  • Long-term population ecology of elapid snakes in Morton National Park
  • Evolution of antipredator behavior in nocturnal geckos

Can supervise: Yes

Chapters

Webb, J.K., Harlow, P.S. & Pike, D.A. 2015, 'Australian reptiles and their conservation' in Stow, A., Maclean, N. & Holwell, G.I. (eds), Austral Ark: The State of Wildlife in Australia and New Zealand, Cambridge University Press, UK, pp. 354-381.

Journal articles

Dayananda, B., Gray, S., Pike, D. & Webb, J.K. 2016, 'Communal nesting under climate change: Fitness consequences of higher incubation temperatures for a nocturnal lizard', Global Change Biology, vol. 22, no. 7, pp. 2405-2414.
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Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures regulate nest temperatures. In southeastern Australia, velvet geckos Oedura lesueurii lay eggs communally inside rock crevices. We investigated whether increases in air temperatures could elevate nest temperatures, and if so, how this could influence hatching phenotypes, survival, and population dynamics. In natural nests, maximum daily air temperature influenced mean and maximum daily nest temperatures, implying that nest temperatures will increase under climate warming. To determine whether hotter nests influence hatchling phenotypes, we incubated eggs under two fluctuating temperature regimes to mimic current 'cold' nests (mean = 23.2 °C, range 10-33 °C) and future 'hot' nests (27.0 °C, 14-37 °C). 'Hot' incubation temperatures produced smaller hatchlings than did cold temperature incubation. We released individually marked hatchlings into the wild in 2014 and 2015, and monitored their survival over 10 months. In 2014 and 2015, hot-incubated hatchlings had higher annual mortality (99%, 97%) than cold-incubated (11%, 58%) or wild-born hatchlings (78%, 22%). To determine future trajectories of velvet gecko populations under climate warming, we ran population viability analyses in Vortex and varied annual rates of hatchling mortality within the range 78- 96%. Hatchling mortality strongly influenced the probability of extinction and the mean time to extinction. When hatchling mortality was >86%, populations had a higher probability of extinction (PE: range 0.52- 1.0) with mean times to extinction of 18-44 years. Whether future changes in hatchling survival translate into reduced population viability will depend on the ability of females to modify their nest-site choices. Over the period 1992-2015, females used the same communal nests annually, suggesting that there may be little plasticity in maternal nest-site selection. The impacts of climate change may therefore be es...
Cabrera-Guzmán, E., Crossland, M.R., Pearson, D., Webb, J.K. & Shine, R. 2015, 'Predation on invasive cane toads (Rhinella marina) by native Australian rodents', Journal of Pest Science, vol. 88, no. 1, pp. 143-153.
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The success of an invasive species can be reduced by biotic resistance from the native fauna. For example, an invader that is eaten by native predators is less likely to thrive than one that is invulnerable. The ability of invasive cane toads (Rhinella marina) to spread through Australia has been attributed to the toad's potent defensive chemicals that can be fatal if ingested by native snakes, lizards, marsupials and crocodiles. However, several taxa of native insects and birds are resistant to cane toad toxins. If native rodents are also capable of eating toads (as suggested by anecdotal reports), these large, abundant and voracious predators might reduce toad numbers. Our field observations and laboratory trials confirm that native rodents (Melomys burtoni, Rattus colletti and Rattus tunneyi) readily kill and consume cane toads (especially small toads), and are not overtly affected by toad toxins. Captive rodents did not decrease their consumption of toads over successive trials, and ate toads even when alternative food types were available. In combination with anecdotal reports, our data suggest that rodents (both native and invasive) are predators of cane toads in Australia. Despite concerns about the decline of rodents following the invasion of toads, our data suggest that the species we studied are not threatened by toads as toxic prey, and no specific conservation actions are required to ensure their persistence. © 2014 Springer-Verlag Berlin Heidelberg.
Rees, J.D., Webb, J.K., Crowther, M.S. & Letnic, M. 2015, 'Carrion subsidies provided by fishermen increase predation of beach-nesting bird nests by facultative scavengers', Animal Conservation, vol. 18, no. 1, pp. 44-49.
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&copy; 2014 The Zoological Society of London. Many predators are also scavengers that feed on carrion and human refuse. Therefore, the availability of carrion can elevate the abundance or activity of facultative scavengers, amplifying predation pressure on prey. On Australian beaches, fishermen often discard fish carcasses that could attract facultative scavengers, both native, such as Australian ravens Corvus coronoides, and invasive, such as European red foxes Vulpes vulpes, and result in elevated rates of predation on wildlife. We tested whether the presence of fish carcasses increased the risk of depredation for nearby nests of beach-nesting birds by deploying artificial nests in 12 subsidized and 12 control patches, spaced 1 km apart, on a beach. We placed a fish carcass in each subsidized patch, but not at control patches. In each patch, we placed two artificial nests, which resembled red-capped plover Charadrius ruficapillus nests, 80 m apart and 40m from carcasses at subsidized patches. Nest predators were identified from tracks and predator activity near subsidized and control nests was measured by counting tracks crossing a straight transect (220m). The activity of a native predator, the Australian raven, was 17 times higher near (<80m) nests with fish carcasses than nests without carcasses. After 72h, 96% of nests near carcasses were depredated compared with 30% of nests without carcasses. Ravens were identified as the culprit for 80% of depredated nests. Although other predators were present in the study area, they did not depredate artificial nests in this experiment. Previous studies have highlighted the effects of permanent and/or large-scale food resources on scavenger abundance and impact. A key management implication of our study is that even small, sparsely distributed, temporally irregular food subsidies, provided by humans, can elevate the activity and predatory impacts of facultative scavengers.
Mowat, E.J., Webb, J.K. & Crowther, M.S. 2015, 'Fire-mediated niche-separation between two sympatric small mammal species', Austral Ecology, vol. 40, no. 1, pp. 50-59.
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&copy; 2014 Ecological Society of Australia. Fire is a key ecological process influencing the population dynamics of small mammals. Whilst shifting competitive advantage amongst small mammal species following a single fire event is well-documented, there has been little investigation of the potential influence of fire frequency on small mammal interspecific interactions. In this study, we investigated the effect of fire frequency on the abundance of two small dasyurid mammals, Antechinus stuartii and A. flavipes, which occur sympatrically in some parts of their range. The two antechinus species are known to have different habitat preferences, so it is possible that fire regimes may promote their coexistence in areas of sympatry by altering vegetation structure. To investigate this possibility, we estimated the abundance of both species using replicate sites which differed in the number of times burnt (1-4) during the last four decades, but with identical time-since-fire. Proportionally, we captured greater numbers of A. stuartii in less frequently burnt sites and greater numbers of A. flavipes in more-frequently burnt sites. Hence, fire may mediate niche-separation between these two species. To clarify further this pattern of response to fire frequency, we investigated which structural habitat variables differed between fire frequencies, and compared antechinus abundances with structural vegetation characteristics. We found a trend for lower ground cover density under higher fire frequencies. This offers one potential explanation of the patterns of abundance that we observed. Our study provided insights into the complexities of small mammal responses to fire, and strongly suggests that fire could mediate competitive interactions between species.
Ziembicki, M.R., Woinarski, J.C.Z., Webb, J.K., Vanderduys, E., Tuft, K., Smith, J., Ritchie, E.G., Reardon, T.B., Radford, I.J., Preece, N., Perry, J., Murphy, B.P., McGregor, H., Legge, S., Leahy, L., Lawes, M.J., Kanowski, J., Johnson, C.N., James, A., Griffiths, A.D., Gillespie, G., Frank, A.S.K., Fisher, A. & Burbidge, A.A. 2015, 'Stemming the tide: progress towards resolving the causes of decline and implementing management responses for the disappearing mammal fauna of northern Australia', Therya, vol. 6, no. 1, pp. 169-225.
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Letnic, M., Webb, J.K., Jessop, T.S. & Dempster, T. 2015, 'Restricting access to invasion hubs enables sustained control of an invasive vertebrate', Journal of Applied Ecology, vol. 52, no. 2, pp. 341-347.
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&copy; 2015 The Authors. Biological invasions often occur through expansion of satellite populations that become established at 'invasion hubs'. Invasion hubs can result from random dispersal events, but frequently arise when invading individuals actively choose habitats using cues that signify high-quality environments where the fitness consequences are positive. Theoretical studies suggest that targeted control at invasion hubs can effectively suppress the populations and impacts of invaders. In arid Australia, small dams that provide water for livestock function as invasion hubs by providing an invasive vertebrate, the cane toad Rhinella marina, with refuge from extreme aridity during the annual dry season. Toads are attracted to dams and use them as stepping stone habitats from which they disperse during rainy periods. Here, we ask whether sustained control of this invasive vertebrate can be achieved by converting invasion hubs into ecological traps. We did this by manipulating invasion hub habitats to induce a mismatch between toads' habitat preference and the fitness consequences of their habitat choice to cause high mortality. We constructed fences to exclude toads from dams and maintained these fences for 1 year. This period encompassed periods of dry and wet seasonal climatic conditions. Our manipulation did not alter the attractive cues for invading toads which died en masse while attempting to settle at fenced dams that prevented toads from reaching water. Toad populations at the fenced dams were suppressed by 1-2 orders of magnitude compared to unfenced controls and procedural controls. Toad populations remained suppressed for a year after exclusion. By excluding toads from dams, we converted invasion hubs into ecological traps and effectively thwarted the reinvasion of cane toads. Our research suggests that water exclusion devices could be used to prevent toad invasion or to control cane toad populations in arid landscapes colonized by toads. Synthesis an...
Rees, J.D., Webb, J.K., Crowther, M.S. & Letnic, M. 2015, 'Ravens are a key threat to beach-nesting birds', Australian Field Ornithology, vol. 32, pp. 100-107.
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Webb, J.K., Scott, M.L., Whiting, M.J. & Shine, R. 2015, 'Territoriality in a snake', Behavioral Ecology and Sociobiology, vol. 69, no. 10, pp. 1657-1661.
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Territorial behaviour, whereby dominant animals gain priority access to critical resources, is widespread in some animal lineages, but rare in others. Theory suggests that territoriality will evolve only when animals can economically defend sites that contain critical resources (typically mates, sometimes food). In striking contrast to their close relatives the lizards, male defence of territories for access to mates has not been reported in snakes. In south-eastern Australia, receptive female small-eyed snakes thermoregulate under 'hot rocks, concentrating mating opportunities and thus, potentially allowing males to enhance their fitness by defending these rocks from rivals. We videotaped staged contests between resident and intruder males and analysed data on cohabitation patterns from a long-term (21 years) mark-recapture study. In staged contests, males actively defended hot rocks from intruder males; and thus, larger males actively displaced their smaller rivals. In the wild, larger males were found under rocks with more or larger females. These results suggest that the thermally driven concentration of female small-eyed snakes has rendered hot rocks economically defensible, and thus favoured the evolution of territoriality in a snake.
Cremona, T., Mella, V.S.A., Webb, J.K. & Crowther, M.S. 2015, 'Do individual differences in behavior influence wild rodents more than predation risk', Journal of Mammalogy, vol. 96, no. 6, pp. 1337-1343.
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Prey can enhance their survival by eliciting an appropriate response to predators. Theoretically, prey should distinguish odors of predators and nonpredators. The manifestation of defensive antipredator behaviors has been extensively researched in domestic species (i.e., the relationship between laboratory-bred rats and domestic cats). However, little is known about the expression of these behaviors in wild rodents. Studies have so far focused on quantitative assessments of cost&#8211;benefit trade-offs or giving-up densities. We examined the expression of fine-scale defensive behaviors in Arnhem rock rats (Zyzomys maini) in response to fecal cues from 2 predators (the northern quoll [Dasyurus hallucatus] and the dingo [Canis dingo]), a nonpredator (the short-eared rock-wallaby [Petrogale brachyotis]), and a control (water). We adapted a predator-odor avoidance apparatus that has been widely used for domestic rodent studies to film the behavior of wild rock rats in a captive environment. Rock rats did not alter their behavior in the presence of odors of nonpredators, predators, or controls. In the current study, individual rock rats behaved in a consistent manner across time, and we identified 3 individually consistent behaviors which may suggest the existence of personality traits in this species. We suggest that these individual differences may influence wild rock rat behavior more than predation risk. These differences should therefore be taken into consideration when investigating behavioral responses to predators in wild populations
Jessop, T.S., Dempster, T., Letnic, M. & Webb, J.K. 2014, 'Interplay among nocturnal activity, melatonin, corticosterone and performance in the invasive cane toad (Rhinella marinus)', GENERAL AND COMPARATIVE ENDOCRINOLOGY, vol. 206, pp. 43-50.
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Webb, J.K., Letnic, M., Jessop, T.S. & Dempster, T. 2014, 'Behavioural flexibility allows an invasive vertebrate to survive in a semi-arid environment', BIOLOGY LETTERS, vol. 10, no. 2.
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Pearson, D.J., Webb, J.K., Greenlees, M.J., Phillips, B.L., Bedford, G.S., Brown, G.P., Thomas, J. & Shine, R. 2014, 'Behavioural responses of reptile predators to invasive cane toads in tropical Australia', AUSTRAL ECOLOGY, vol. 39, no. 4, pp. 448-454.
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Letnic, M., Webb, J.K., Jessop, T.S., Florance, D. & Dempster, T. 2014, 'Artificial water points facilitate the spread of an invasive vertebrate in arid Australia', JOURNAL OF APPLIED ECOLOGY, vol. 51, no. 3, pp. 795-803.
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Cremona, T., Crowther, M.S. & Webb, J.K. 2014, 'Variation of prey responses to cues from a mesopredator and an apex predator', Austral Ecology, vol. 39, no. 7, pp. 749-754.
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&copy; 2014 Ecological Society of Australia 39 7 November 2014 10.1111/aec.12138 Original Articles Original Article &copy; 2014 The Authors. Austral Ecology. Detection and avoidance of predator cues can be costly, so it is important for prey to balance the benefits of gaining food against the costs of avoiding predators. Balancing these factors becomes more complicated when prey are threatened by more than one type of predator. Hence, the ability to recognize species-specific predator odours and prioritize behaviours according to the level of risk is essential for survival. We investigated how rock rats, Zyzomys spp. modify their foraging behaviour and giving-up density (GUD) in the presence of an apex predator, the dingo Canis dingo, a mesopredator, the northern quoll Dasyurus hallucatus, a herbivore, the rock wallaby Petrogale brachyotis as a pungency control and water as a procedural control. Both dingoes and quolls consume rock rats, but because quolls can enter small crevices inhabited by rock rats, they pose a greater threat to rock rats than dingoes. Rock rats demonstrated a stronger avoidance to quoll odour than dingo odour, and no avoidance of the pungency control (rock wallaby) and the procedural control (water). GUD values declined significantly over the duration of the study, but did not differ between odour treatments. Our results support the hypothesis that prey vary behaviour according to perceived predator threat, and show stronger responses to potentially more dangerous predators.
Somaweera, R., Shine, R., Webb, J.K., Dempster, T. & Letnic, M. 2013, 'Why does vulnerability to toxic invasive cane toads vary among populations of Australian freshwater crocodiles?', Animal Conservation, vol. 16, pp. 86-96.
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The ecological impact of an invasive species can be heterogeneous through space and time. One such case in Australia involves native freshwater crocodiles Crocodylus johnstoni, which are highly sensitive to invasive cane toads Rhinella marina in some areas, whereas other populations experience little or no mortality from ingestion of the toxic toads. We studied the impact of toad invasion on three crocodile populations: one crashed, one showed a minor decrease and one appeared unaffected. We tested three hypotheses for the cause of this spatial variation in impact: differences among populations in toadcrocodile encounter rates (proximity of toads to crocodiles during spotlight surveys), differences in crocodile feeding responses (trials of prey preference in the laboratory) and differences in crocodile physiology (reduction of swim speed after receiving a dose of toad toxin). We found little divergence among populations in any of these traits: crocodiles from the three populations all encountered cane toads in the wild, and exhibited similar feeding responses and toxin tolerances. Thus, we cannot confidently identify causation for the impact heterogeneity. Reliance on alternative food resources and an ability to rapidly learn taste aversion may have allowed crocodiles to deal with toad arrival in Lake Argyle and the Daly River. Future work could usefully evaluate potential explanations for the failure of these adaptive mechanisms in the severely affected (Victoria River) population. We suggest that spatial variation in the availability of alternative prey (and thus the willingness of crocodiles to attack a novel toxic prey item) may have contributed to that variation in impact.
Croak, B., Crowther, M., Webb, J.K. & Shine, R. 2013, 'Movements And Habitat Use Of An Endangered Snake, Hoplocephalus Bungaroides (elapidae): Implications For Conservation', Plos One, vol. 8, no. 4, pp. 1-10.
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A detailed understanding of how extensively animals move through the landscape, and the habitat features upon which they rely, can identify conservation priorities and thus inform management planning. For many endangered species, information on habitat use either is sparse, or is based upon studies from a small part of the species range. The broad-headed snake (Hoplocephalus bungaroides) is restricted to a specialized habitat (sandstone outcrops and nearby forests) within a small geographic range in south-eastern Australia. Previous research on this endangered taxon was done at a single site in the extreme south of the species geographic range. We captured and radio-tracked 9 adult broad-headed snakes at sites in the northern part of the species distribution, to evaluate the generality of results from prior studies, and to identify critical habitat components for this northern population. Snakes spent most of winter beneath sun-warmed rocks then shifted to tree hollows in summer. Thermal regimes within retreat-sites support the hypothesis that this shift is thermally driven. Intervals between successive displacements were longer than in the southern snakes but dispersal distances per move and home ranges were similar. Our snakes showed non-random preferences both in terms of macrohabitat (e.g., avoidance of some vegetation types) and microhabitat (e.g., frequent use of hollow-bearing trees). Despite many consistencies, the ecology of this species differs enough between southern and northern extremes of its range that managers need to incorporate information on local features to most effectively conserve this threatened reptile.
Croak, B., Webb, J.K. & Shine, R. 2013, 'The Benefits Of Habitat Restoration For Rock-dwelling Velvet Geckos Oedura Lesueurii', Journal Of Applied Ecology, vol. 50, no. 2, pp. 432-439.
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Worldwide, efforts to restore habitat quality are rarely matched by efforts to evaluate the effects of those restoration attempts. Simply documenting usage of the newly created habitats by biota is not enough, because such areas may serve as sink populations. We need to monitor viability (growth, survival, reproduction) of individuals that colonize the newly created habitat, compared with conspecifics in non-restored areas. In the Sydney region in south-eastern Australia, humans have degraded sandstone rock outcrops by removing natural rocks for landscaping urban gardens. We restored degraded rock outcrops by placing artificial rocks at sites where natural rocks had been removed. We measured growth rates and survival in velvet geckos Oedura lesueurii at control and restored sites over a 2-year period. Gecko growth rates were unaffected by habitat restoration, but restoring sites with artificial rocks increased the overall numbers of lizards detected (both adults and juveniles). The apparent survival rates of adult male lizards (as estimated using mark) were not significantly affected by habitat restoration. However, apparent survival rates of juvenile geckos were higher at restored sites than at unrestored sites. Synthesis and applications. Habitat restoration using artificial rocks has had measurable conservation benefits on these degraded rocky outcrops. Quantifying those benefits in terms of species' survival and growth rates enables management decisions about habitat restoration to be based upon evidence rather than wishful thinking or untested intuition.
Scott, M., Whiting, M.M., Webb, J.K. & Shine, R. 2013, 'Chemosensory discrimination of social cues mediates space use in snakes, Cryptophis nigrescens (Elapidae)', Animal Behaviour, vol. 85, no. 6, pp. 1493-1500.
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Snakes have traditionally been viewed as solitary, asocial animals whose habitat use is driven by temperature, prey and predators. However, recent studies suggest that snake spatial ecology may also be socially mediated. We examined the influence of conspecific chemical cues on refuge selection in a small nocturnal snake (the small-eyed snake) that engages in male contest competition. Females preferred refuges containing scent cues from conspecifics (of either sex) rather than scentless refuges. Males preferred female-scented rather than male-scented refuges, and preferred the scent of larger (and hence, more fecund) females than smaller females. Males spent more time in refuges containing the scent of smaller rather than larger males, but males that lost a contest did not avoid the refuge scented by the winner and therefore did not show evidence of the winnerloser effect. Females preferred refuges scented by larger males. Small-eyed snakes can distinguish conspecific sex and body size using chemical cues, and they use these cues to select alternative refuge sites. We suggest that social factors play a significant role in driving snake spatial distribution patterns in the wild and that snakes may exhibit more complex social systems than has generally been believed.
Jessop, T.S., Letnic, M., Webb, J.K. & Dempster, T. 2013, 'Adrenocortical stress responses influence an invasive vertebrate's fitness in an extreme environment', Proceedings Of The Royal Society Of London Series B-biological Sciences, vol. 280, no. 1768, pp. 1-9.
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Continued range expansion into physiologically challenging environments requires invasive species to maintain adaptive phenotypic performance. The adrenocortical stress response, governed in part by glucocorticoid hormones, influences physiological and behavioural responses of vertebrates to environmental stressors. However, any adaptive role of this response in invasive populations that are expanding into extreme environments is currently unclear. We experimentally manipulated the adrenocortical stress response of invasive cane toads (Rhinella marina) to investigate its effect on phenotypic performance and fitness at the species' range front in the Tanami Desert, Australia. Here, toads are vulnerable to overheating and dehydration during the annual hotdry season and display elevated plasma corticosterone levels indicative of severe environmental stress. By comparing unmanipulated control toads with toads whose adrenocortical stress response was manipulated to increase acute physiological stress responsiveness, we found that control toads had significantly reduced daily evaporative water loss and higher survival relative to the experimental animals. The adrenocortical stress response hence appears essential in facilitating complex phenotypic performance and setting fitness trajectories of individuals from invasive species during range expansion.
Kamper, W., Webb, J.K., Crowther, M.S., Greenlees, M.J. & Shine, R. 2013, 'Behaviour and survivorship of a dasyurid predator (Antechinus flavipes) in response to encounters with the toxic and invasive cane toad (Rhinella marina)', Australian Mammalogy, vol. 35, no. 2, pp. 136-143.
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Australia's biogeographical isolation has rendered many endemic species vulnerable to invaders. The recent spread of the cane toad (Rhinella marina) has caused serious population declines for some predatory reptile and mammal species. To determine a priori whether or not cane toad poisoning endangers native species, we can test the fates of predators in laboratory trials. We investigated whether an Australian marsupial whose range is increasingly being occupied by cane toads (the yellow-footed antechinus, Antechinus flavipes) is at risk of toad poisoning by testing (1) whether yellow-footed antechinuses approach or attack cane toads and, if so, whether they die as a result; and (2) if they survive, whether they then learn to avoid toads in subsequent encounters. We also investigated the effects of sympatry with toads on the feeding response. In all, 58% of antechinuses from eastern New South Wales approached or attacked a toad (over 4 or 5 opportunities to do so, on successive nights), and none showed ill effects after doing so. Antechinuses that attacked (killed or ingested) toads rapidly learnt to avoid them. Antechinuses from toad-exposed populations ingested more toad flesh, but otherwise reacted in the same ways as did conspecifics from toad-free areas. Hence, the yellow-footed antechinus is unlikely to face population declines via toad poisoning.
Price-Rees, S.J., Webb, J.K. & Shine, R. 2013, 'Reducing the impact of a toxic invader by inducing taste aversion in an imperilled native reptile predator', Animal Conservation, vol. 16, no. 4, pp. 386-394.
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It is virtually impossible to eradicate invasive organisms once they have spread widely, and even low densities of invaders may have devastating impacts. We need to explore alternative management options that accept the inevitability of encounters between alien and native taxa, but reduce the negative consequences of those encounters. Conditioned taste aversion (CTA) is one approach that offers promise in this respect. The spread of the invasive cane toad Rhinella marina across northern Australia is devastating populations of predators such as the blue-tongued skink Tiliqua scincoides intermedia. Predators unable to tolerate the toads' powerful bufadienolide chemical defences are likely to die if they ingest a toad. We trained field-caught skinks to avoid eating cane toad flesh, by offering them toad sausages laced with a nausea-inducing chemical (lithium chloride). These individuals (and controls) were then released and radio-tracked as toads arrived at our study site in north-western Australia. Skinks that regurgitated after consuming the toad sausage survived after release, whereas most untrained animals were fatally poisoned by toad ingestion. Even if we cannot eradicate invasive cane toads, we can ameliorate their ecological impact by CTA training of vulnerable predators.
Elzer, A.L., Pike, D.A., Webb, J.K., Hammill, K., Bradstock, R.A. & Shine, R. 2013, 'Forest-fire regimes affect thermoregulatory opportunities for terrestrial ectotherms', Austral Ecology, vol. 38, no. 2, pp. 190-198.
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Fire-induced changes in canopy openness may affect sunlight penetration to the forest floor, and thus the operative temperatures available to terrestrial ectotherms. We examined thermal regimes for two types of ectotherms: diurnally active species that utilize sun-exposed patches to regulate their body temperatures, and nocturnally active species that depend upon solar radiation striking the rocks under which they shelter. We measured canopy openness, shrub height, radiation transmission and operative environmental temperatures in the open and inside reptile retreat-sites, at 24 study sites in eucalypt forests in two regions (Gosford and Yengo) in south-eastern Australia. All sites were last burnt in 20002001, but had experienced different fire frequencies (14 fires over the previous 37 years). In Gosford, higher fire frequencies reduced canopy openness and radiation transmission at ground and shrub level, and thus reduced environmental temperatures and the thermal quality of reptile habitats. Our modelling based on thermal preferenda of an endangered snake species (the broad-headed snake Hoplocephalus bungaroides) suggests that increased fire frequency at Gosford halved the amount of time an animal could spend within its preferred (set-point) range, regardless of whether it thermoregulated beneath rocks or basked out in the open. At Yengo, however, fire frequency did not affect the thermal quality of reptile habitats. Thus, the effects of fire frequency on forest structure and the thermal environment at ground level differed between adjacent areas, and relatively small changes in canopy openness translated into major effects on thermoregulatory opportunities for reptiles. Although fire is a useful management tool for creating open habitats, we need to understand more about the effects of fire frequency on vegetation structure and thermal environment before we can use fire to manage habitats for reptiles
Jessop, T.S., Letnic, M., Webb, J.K. & Dempster, T. 2013, 'Adrenocortical stress responses influence an invasive vertebrate's fitness in an extreme environment.', Proceedings. Biological sciences / The Royal Society, vol. 280, no. 1768, p. 20131444.
Continued range expansion into physiologically challenging environments requires invasive species to maintain adaptive phenotypic performance. The adrenocortical stress response, governed in part by glucocorticoid hormones, influences physiological and behavioural responses of vertebrates to environmental stressors. However, any adaptive role of this response in invasive populations that are expanding into extreme environments is currently unclear. We experimentally manipulated the adrenocortical stress response of invasive cane toads (Rhinella marina) to investigate its effect on phenotypic performance and fitness at the species' range front in the Tanami Desert, Australia. Here, toads are vulnerable to overheating and dehydration during the annual hot-dry season and display elevated plasma corticosterone levels indicative of severe environmental stress. By comparing unmanipulated control toads with toads whose adrenocortical stress response was manipulated to increase acute physiological stress responsiveness, we found that control toads had significantly reduced daily evaporative water loss and higher survival relative to the experimental animals. The adrenocortical stress response hence appears essential in facilitating complex phenotypic performance and setting fitness trajectories of individuals from invasive species during range expansion.
Pike, D.A., Webb, J.K. & Shine, R. 2012, 'Hot mothers, cool eggs: nest-site selection by egg-guarding spiders accommodates conflicting thermal optima', Functional Ecology, vol. 26, no. 2, pp. 469-475.
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In oviparous species providing maternal care, the choice of nest site is crucial for the survival of both the eggs and the mother. Most embryos only develop successfully within a narrow range of incubation conditions, which may differ from the mothers own requirements. How, then, do nest-attending mothers select sites that provide suitable conditions for embryonic development, without compromising their own viability? We investigated nest-site selection in flat-rock spiders, Hemicloea major, a species that guards fixed egg sacs in a thermally challenging environment (under sun-exposed rocks). Females glue egg sacs beneath rocks during late spring and guard their eggs during summer, when temperatures beneath rocks often exceed 50 degrees C. Our field surveys show that spiders laid eggs beneath rocks that were larger and thinner, and thus hotter, than were most available rocks. However, the egg sacs almost invariably were glued to the coolest sites on the substrate beneath a rock, rather than to the (hotter, by about 9 degrees C) underside of the rock. By affixing their egg sacs to the coolest locations beneath the hottest rocks, females ensured that their developing offspring experienced moderate temperatures and avoided lethal extremes and, simultaneously, gave themselves access to much hotter areas (that enhance their feeding and growth rates) under the same rock. This strategy allows mobile adult spiders to actively select higher temperatures than can be tolerated by their embryos, while remaining close enough to their eggs for effective nest guarding.
Dubey, S., Sumner, J., Pike, D.A., Keogh, J.S., Webb, J.K. & Shine, R. 2012, 'Genetic connectivity among populations of an endangered snake species from southeastern Australia (Hoplocephalus bungaroides, Elapidae)', Ecology and Evolution, vol. 1, no. 2, pp. 218-227.
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For endangered species that persist as apparently isolated populations within a previously more extensive range, the degree of genetic exchange between those populations is critical to conservation and management. A lack of gene flow can exacerbate impacts of threatening processes and delay or prevent colonization of sites after local extirpation. The broad-headed snake, Hoplocephalus bungaroides, is a small venomous species restricted to a handful of disjunct reserves near Sydney, Australia. Mark-recapture studies have indicated low vagility for this ambush predator, suggesting that gene flow also may be low. However, our analyses of 11 microsatellite loci from 163 snakes collected inMortonNational Park, from six sites within a 10-km diameter, suggest relatively high rates of gene flow among sites. Most populations exchange genes with each other, with one large population serving as a source area and smaller populations apparently acting as sinks. About half of the juvenile snakes, for which we could reliably infer parentage, were collected from populations other than those in which we collected their putative parents. As expected from the snakes reliance on rocky outcrops during cooler months of the year, most gene flow appears to be along sandstone plateaux rather than across the densely forested valleys that separate plateaux. The unexpectedly high rates of gene flow on a landscape scale are encouraging for future conservation of this endangered taxon. For example, wildlife managers could conserve broad-headed snakes by restoring habitats near extant source populations in areas predicted to be least affected by future climate change.
Kovacs, E.K., Crowther, M.S., Webb, J.K. & Dickman, C.R. 2012, 'Population and behavioural responses of native prey to alien predation', Oecologia, vol. 168, no. 4, pp. 947-957.
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The introduction of invasive alien predators often has catastrophic effects on populations of native native prey, but in situations where prey survive the initial impact a predator may act as a strong selective agent for prey that can discriminate and avoid it. Using two common species of Australian small mammals that have persisted in the presence of an alien predator, the European red fox Vulpes vulpes, for over a century, we hypothesised that populations of both would perform better where the activity of the predator was low than where it was high and that prey individuals would avoid signs of the predator's presence. We found no difference in prey abundance in sites with high and low fox activity, but survival of one species-the bush rat Rattus fuscipes-was almost twofold higher where fox activity was low. Juvenile, but not adult rats, avoided fox odour on traps, as did individuals of the second prey species, the brown antechinus, Antechinus stuartii. Both species also showed reduced activity at foraging trays bearing fox odour in giving-up density (GUD) experiments, although GUDs and avoidance of fox odour declined over time. Young rats avoided fox odour more strongly where fox activity was high than where it was low, but neither adult R. fuscipes nor A. stuartii responded differently to different levels of fox activity. Conservation managers often attempt to eliminate alien predators or to protect predator-native prey in protected reserves. Our results suggest that, if predator pressure can be reduced, otherwise susceptible prey may survive the initial impact of an alien predator, and experience selection to discriminate cues to its presence and avoid it over the longer term. Although predator reduction is often feasible, identifying the level of reduction that will conserve prey and allow selection for avoidance remains an important challenge.
Shine, R., Webb, J.K., Lane, A. & Mason, R.T. 2012, 'Familiarity with a female does not affect a male's courtship intensity in garter snakes Thamnophis sirtalis parietalis', Current Zoology, vol. 58, no. 6, pp. 805-811.
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Croak, B.M., Pike, D.A., Webb, J.K. & Shine, R. 2012, 'Habitat Selection in a Rocky Landscape: Experimentally Decoupling the Influence of Retreat Site Attributes from That of Landscape Features', PLOS ONE, vol. 7, no. 6.
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Pike, D.A., Webb, J.K. & Shine, R. 2012, 'Reply to comment on 'chainsawing for conservation: Ecologically informed tree removal for habitat management'', Ecological Management and Restoration, vol. 13, no. 3, pp. e12-e13.
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Somaweera, R., Webb, J.K. & Shine, R. 2011, 'Determinants of habitat selection by hatchling Australian freshwater crocodiles', Plos One, vol. 6, no. 12, p. e28533.
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Animals almost always use habitats non-randomly, but the costs and benefits of using specific habitat types remain unknown for many types of organisms. In a large lake in northwestern Australia (Lake Argyle), most hatchling (<12-month-old) freshwater crocodiles (Crocodylus johnstoni) are found in floating vegetation mats or grassy banks rather than the more widely available open banks. Mean body sizes of young crocodiles did not differ among the three habitat types. We tested four potential explanations for non-random habitat selection: proximity to nesting sites, thermal conditions, food availability, and exposure to predation. The three alternative habitat types did not differ in proximity to nesting sites, or in thermal conditions. Habitats with higher food availability harboured more hatchlings, and feeding rates (obtained by stomach-flushing of recently-captured crocodiles) were highest in such areas. Predation risk may also differ among habitats: we were twice as likely to capture a crocodile after seeing it in open-bank sites than in the other two habitat types. Thus, habitat selection of hatchling crocodiles in this system may be driven both by prey availability and by predation risk.
Kelehear, C., Webb, J.K., Hagman, M. & Shine, R. 2011, 'Interactions between infective helminth larvae and their anuran hosts', Herpetologica, vol. 67, no. 4, pp. 378-385.
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Detailed observations on interactions between parasites and prospective hosts during the infection process can clarify (1) the routes by which parasites enter the host and (2) the ability of prospective hosts to detect, avoid, or resist potential parasites. Such information can clarify determinants of host vulnerability. Infective larvae of the nematode Rhabdias pseudosphaerocephala entered the bodies of their anuran host the Cane Toad (Rhinella marina, formerly Bufo marinus) primarily through the orbit (i.e., by crawling over the surface of the toad's eye) rather than by burrowing through the skin (believed to be the usual route of infection for rhabditid parasites). In our experimental infections, metamorph Cane Toads detected infective R. pseudosphaerocephala larvae but did not avoid them, nor did they manage to restrict rates of infective larvae penetration by using behavioral means (the toads kicked at infective larvae but failed to dislodge them). Rhabdias pseudosphaerocephala cause damage to their toad host during the process of host entry and throughout the ensuing infection. Despite the high cost of infection and the low cost of avoidance, metamorph Cane Toads seem to lack effective parasite avoidance strategies.
Florance, D., Webb, J.K., Dempster, T., Kearney, M.R., Worthing, A. & Letnic, M. 2011, 'Excluding access to invasion hubs can contain the spread of an invasive vertebrate', Proceedings Of The Royal Society B-biological Sciences, vol. 278, no. 1720, pp. 2900-2908.
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Many biological invasions do not occur as a gradual expansion along a continuous front, but result from the expansion of satellite populations that become established at 'invasion hubs'. Although theoretical studies indicate that targeting control efforts at invasion hubs can effectively contain the spread of invasions, few studies have demonstrated this in practice. In arid landscapes worldwide, humans have increased the availability of surface water by creating artificial water points (AWPs) such as troughs and dams for livestock. By experimentally excluding invasive cane toads (Bufo marinus) from AWP, we show that AWP provide a resource subsidy for non-arid-adapted toads and serve as dry season refuges and thus invasion hubs for cane toads in arid Australia. Using data on the distribution of permanent water in arid Australia and the dispersal potential of toads, we predict that systematically excluding toads from AWP would reduce the area of arid Australia across which toads are predicted to disperse and colonize under average climatic conditions by 38 per cent from 2 242 000 to 1 385 000 km(2). Our study shows how human modification of hydrological regimes can create a network of invasion hubs that facilitates a biological invasion, and confirms that targeted control at invasion hubs can reduce landscape connectivity to contain the spread of an invasive vertebrate.
Somaweera, R., Webb, J.K. & Shine, R. 2011, 'It's a dog-eat-croc world: Dingo predation on the nests of freshwater crocodiles in tropical Australia', Ecological Research, vol. 26, no. 5 Special Issue, pp. 957-967.
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Predation on eggs is an important source of mortality for many long-lived organisms, but causes of egg mortality from specific predators remain poorly known in most cases. Understanding the identity of predators, and the rates and determinants of their effects on a cohort of recruits, can provide a valuable background for attempts to exploit, control or conserve populations. We used remotely triggered cameras to study predation on the nests of freshwater crocodiles (Crocodylus johnstoni) inhabiting Lake Argyle, in tropical Australia. We also supplemented our work on natural crocodile nests with artificial nests. Overall, 80 of 111 natural nests were opened by predators, and predation occurred throughout the study period (7 weeks). Unlike in other parts of the species' range, most nest-robbers were dingoes (Canis lupus dingo, responsible for 98% of all predator visits in the northern sites, and 54% in the Ord River site), with minimal additional predation by reptiles and birds. Contrary to expectation, rates of nest predation were not influenced by spatial clumping of nests: the probability of predation per nest did not change with total numbers of nests laid in an area, and artificially aggregated versus dispersed nests experienced similar levels of predation. Nest vulnerability was linked to abiotic features including slope of surrounding banks, compactness of nesting substrate, and distance from the nearest forest. Abundant aquatic food resources support a large crocodile population, but a lack of suitable nest-sites forces the crocodiles to concentrate nesting in small areas readily accessible to wide-ranging nest predators. Collectively, our results suggest that distinctive attributes of the lakeside landscape alter predator guilds and fashion unique predator-prey interactions.
Price-Rees, S.J., Webb, J.K. & Shine, R. 2011, 'School for skinks: Can conditioned taste aversion enable bluetongue lizards (Tiliqua scincoides) to avoid toxic cane toads (Rhinella marina) as prey?', Ethology, vol. 117, no. 9, pp. 749-757.
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The invasion of cane toads (Rhinella marina) through Australia imperils native predators that are killed if they consume these toxic anurans. The magnitude of impact depends upon the predators' capacity for aversion learning: toad impact is lower if predators can learn not to attack toads. In laboratory trials, we assessed whether bluetongue lizards (Tiliqua scincoides) - a species under severe threat from toads - are capable of learned taste aversion and whether we can facilitate that learning by exposing lizards to toad tissue combined with a nausea-inducing chemical (lithium chloride). Captive bluetongues rapidly learned to avoid the 'unpalatable' food. Taste aversion also developed (albeit less strongly) in response to meals of minced cane toad alone. Our data suggest that taste aversion learning may help bluetongue lizards survive the onslaught of cane toads, but that many encounters will be fatal because the toxin content of toads is so high relative to lizard tolerance of those toxins. Thus, baiting with nausea-inducing (but non-lethal) toad products might provide a feasible management option to reduce the impact of cane toad invasion on these native predators.
Pike, D.A., Webb, J.K. & Andrews, R.M. 2011, 'Social and thermal cues influence nest-site selection in a nocturnal gecko, Oedura lesueurii', Ethology, vol. 117, no. 9, pp. 796-801.
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In oviparous species lacking parental care, successful reproduction depends on females selecting nest sites that facilitate embryonic development. Such sites may be limited in the environment, which can lead to multiple females using the same nest site simultaneously. However, there are several alternative explanations for communal nesting, including natal homing, predator satiation, and adaptive benefits to offspring. We used laboratory experiments to evaluate three hypotheses about nest-site selection in velvet geckos (Oedura lesueurii), which often nest communally. We investigated whether the trend to nest communally is influenced by the following: (1) evidence of previous nesting (hatched eggshells); (2) body size; and/or (3) thermal regimes. When given the choice, females laid their eggs in shelters containing hatched eggshells rather than in empty shelters, and this was not influenced by body size. Females selected nest sites that were cooler than their own mean selected body temperatures, suggesting that thermal requirements of their developing embryos could outweigh their own thermoregulatory preferences. Field observations of natal homing and high predation rates on gravid females suggest that imprinting on nest sites and/or predator swamping also play roles in communal nesting. Collectively, our results suggest that female velvet geckos use multiple cues to select appropriate nest sites, and hence that multiple mechanisms result in communal nesting behavior in this species.
Somaweera, R., Webb, J.K., Brown, G.P. & Shine, R. 2011, 'Hatchling Australian freshwater crocodiles rapidly learn to avoid toxic invasive cane toads', Behaviour, vol. 148, no. 4, pp. 501-517.
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Predicting the ecological impacts of invasive species on native fauna is a formidable challenge for conservation biologists. One way to deal with that challenge is to stage encounters between the invader and native species in the laboratory, to illuminate likely outcomes of encounters in the wild. The invasion of the highly toxic cane toad Rhinella marina across tropical Australia threatens many frog-eating predators, including freshwater crocodiles (Crocodylus johnstoni). To predict the impact of cane toads on crocodiles, we need to know whether crocodiles will attack cane toads, and whether predators that survive the toads' poisons will learn to avoid toads. We quantified these traits under laboratory conditions in hatchling freshwater crocodiles from Lake Argyle in Western Australia. All toad-naive hatchling crocodiles attacked toads during their first encounter, and none showed signs of overt illness after consuming toads. However, crocodiles rapidly learnt to avoid toads as prey, and only four out of the 10 crocodiles attacked toads during subsequent encounters. Compared to control (toad-naive) conspecifics, toad-smart crocodiles inflicted fewer bites on toads, held toads in their mouths for shorter time periods, and were more likely to reject toads as prey. In the field, toads were consumed more rarely than native frogs. Our results show that hatchling freshwater crocodiles can rapidly learn to avoid cane toads as prey. Hence, even if toads cause mortality of larger crocodiles (as happens in some areas), populations may recover via hatchling recruitment.
Webb, J.K., Pearson, D. & Shine, R. 2011, 'A small dasyurid predator (Sminthopsis virginiae) rapidly learns to avoid a toxic invader', Wildlife Research, vol. 38, no. 8, pp. 726-731.
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Context. Invasive species are a leading cause of extinctions, yet predicting their ecological impacts poses a formidable challenge for conservation biologists. When native predators are naive to invaders, they may lack appropriate behaviours to deal with
Pike, D.A., Webb, J.K. & Shine, R. 2011, 'Chainsawing for conservation: Ecologically informed tree removal for habitat management', Ecological Management & Restoration, vol. 12, no. 2, pp. 110-118.
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In many ecosystems, increases in vegetation density and the resulting closure of forest canopies are threatening the viability of species that depend upon open, sunlight- exposed habitats. Consequently, we need to develop management strategies that recreate open habitats while minimizing the impacts on non-target areas. Selective logging creates canopy gaps, but may result in undesirable effects in other respects. Thus, chainsaws have not been a popular tool for conservation. We conducted a landscape-scale experiment to test whether selective tree removal can restore patch-level habitat quality for Australias most endangered snake (Hoplocephalus bungaroides) and its main prey (the lizard Oedura lesueurii). We selectively removed canopy trees surrounding 25 overgrown rock outcrops and compared the resultant habitat structure and abiotic conditions to 30 overgrown, shady outcrops and 20 open, sunny outcrops. Removing vegetation decreased canopy cover by 19% in experimental plots and increased incident radiation and thermal regimes. These changes increased the availability of suitable shelter sites for our target species by 131%. At the landscape scale, our manipulations had a trivial effect on forest habitat; by increasing the area of sun-exposed outcrops, we decreased forest cover by <0.1%. Our results show that targeted canopy removal can increase the availability of sun-exposed habitat patches for endangered species in biologically meaningful ways. Thus, selective tree felling may be an effective conservation tool for open-habitat specialists threatened by vegetation overgrowth.
Pike, D.A., Webb, J.K. & Shine, R. 2011, 'Removing forest canopy cover restores a reptile assemblage', Ecological Applications, vol. 21, no. 1, pp. 274-280.
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Humans are rapidly altering natural systems, leading to changes in the distribution and abundance of species. However, so many changes are occurring simultaneously (e.g., climate change, habitat fragmentation) that it is difficult to determine the cause of population fluctuations from correlational studies. We used a manipulative field experiment to determine whether forest canopy cover directly influences reptile assemblages on rock outcrops in southeastern Australia. Our experimental design consisted of three types of rock outcrops: (1) shady sites in which overgrown vegetation was manually removed (n=25); (2) overgrown controls (n= 30); and (3) sun-exposed controls (n= 20). Following canopy removal, we monitored reptile responses over 30 months. Canopy removal increased reptile species richness, the proportion of shelter sites used by reptiles, and relative abundances of five species that prefer sun-exposed habitats. Our manipulation also decreased the abundances of two shade-tolerant species. Canopy cover thus directly influences this reptile assemblage, with the effects of canopy removal being dependent on each species' habitat preferences (i.e., selection or avoidance of sun-exposed habitat). Our study suggests that increases in canopy cover can cause declines of open-habitat specialists, as previously suggested by correlative studies from a wide range of taxa. Given that reptile colonization of manipulated outcrops occurred rapidly, artificially opening the canopy in ecologically informed ways could help to conserve imperiled species with patchy distributions and low vagility that are threatened by vegetation overgrowth. One such species is Australia's most endangered snake, the broadheaded snake (Hoplocephalus bungaroides
Pike, D.A., Croak, B.M., Webb, J.K. & Shine, R. 2010, 'Subtle - but easily reversible - anthropogenic disturbance seriously degrades habitat quality for rock-dwelling reptiles', Animal Conservation, vol. 13, no. 4, pp. 411-418.
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Even apparently subtle disturbance to habitat may have severe long-term consequences if that disturbance alters specific microhabitat features upon which animals depend. For example, in south-eastern Australia, the endangered broad-headed snake Hoplocephalus bungaroides and its prey (velvet geckos Oedura lesueurii) shelter in narrow crevices beneath sun-warmed rocks. Humans frequently displace rocks while searching for snakes and lizards, and these reptiles are rarely found under such displaced rocks (even when the rocks superficially appear suitable). We quantified disturbance to rock outcrops and show that most disturbance was subtle (rocks were typically displaced < 30 cm from their original position), but that disturbed rocks harbored fewer reptiles than undisturbed rocks. In a field experiment, we replaced half of the rocks back to their original positions to test whether crevice structure and microclimates differed between disturbed and restored rocks. Crevices beneath displaced rocks were larger and cooler than those beneath restored rocks, and precise repositioning of rocks enhanced usage by reptiles. Both crevice size and temperature influence reptile retreat-site selection; hence, minor displacement of overlying rocks reduces habitat quality by modifying critical crevice attributes. The subtlety of this disturbance suggests that even well-intentioned researchers could damage habitat during field surveys. Conservation of rock outcrop systems requires efforts to reduce rock disturbance, and to educate those searching for animals beneath rocks about the importance of replacing rocks properly. Encouragingly, if rocks are not completely removed, disturbed outcrops can be quickly and easily restored by returning displaced rocks to their original locations.
Croak, B., Pike, D.A., Webb, J.K. & Shine, R. 2010, 'Using artificial rocks to restore nonrenewable shelter sites in human-degraded systems: Colonization by fauna', Restoration Ecology, vol. 18, no. 4, pp. 428-438.
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Many animals spend much of their time within retreat sites underneath loose surface rocks and may be highly selective in terms of the physical characteristics of the sites that they use. If such shelters are eliminated by anthropogenic activities, such as rock removal for landscaping, the only way to restore these nonrenewable habitats may be to replace them with artificial rocks. To construct artificial rock habitats, we need to understand which rock attributes are important for faunal use and develop methods to mimic these important natural retreat site characteristics. Based on our prior understanding of rocky retreat sites used by reptiles in sandstone outcrops of southeastern Australia, we constructed realistic-looking artificial rocks from fiber-reinforced cement and evaluated (1) the degree to which they mimicked natural retreat sites in both thermal regime and three-dimensional crevice structure and (2) their colonization by fauna after deployment in the field. Our results demonstrate that thermal regimes and crevice structures beneath the artificial rocks were similar to those beneath natural rocks. In addition, 100% of the artificial rocks were colonized (by 45 invertebrate, six lizard, and two snake species, including the endangered Broad-headed snake, Hoplocephalus bungaroides) after only 40 weeks. Together, these results suggest that restoring degraded habitats for rock-dwelling species is feasible and can provide a rapid means of enhancing shelter-site availability for such species.
Webb, J.K., Du, W., Pike, D. & Shine, R. 2010, 'Generalization of predator recognition: Velvet geckos display anti-predator behaviours in response to chemicals from non-dangerous elapid snakes', Current Zoology, vol. 56, no. 3 Special Issue, pp. 337-342.
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Many prey species detect chemical cues from predators and modify their behaviours in ways that reduce their risk of predation. Theory predicts that prey should modify their anti-predator responses according to the degree of threat posed by the predator.
Llewelyn, J., Webb, J.K. & Shine, R. 2010, 'Flexible Defense: Context-dependent Antipredator Responses Of Two Species Of Australian Elapid Snakes', Herpetologica, vol. 66, no. 1, pp. 1-11.
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Snakes exhibit a complex repertoire of defensive responses, shifting from one tactic to another depending upon conditions at the time of encounter with a potential predator. Standardized laboratory trials, controlling factors such,is time of day, tempera
Llewelyn, J., Webb, J.K., Schwarzkopf, L., Alford, R. & Shine, R. 2010, 'Behavioural responses of carnivorous marsupials (Planigale maculata) to toxic invasive cane toads (Bufo marinus)', Austral Ecology, vol. 35, no. 5, pp. 560-567.
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The arrival of a toxic invasive species may impose selection on local predators to avoid consuming it. Feeding responses may be modified via evolutionary changes to behaviour, or via phenotypic plasticity (e. g. learning, taste aversion). The recent arrival of cane toads (Bufo marinus) in the Northern Territory of Australia induced rapid aversion learning in a predatory marsupial (the common planigale, Planigale maculata). Here, we examine the responses of planigales to cane toads in north-eastern Queensland, where they have been sympatric for over 60 years, to investigate whether planigale responses to cane toads have been modified by long-term exposure. Responses to toads were broadly similar to those documented for toad-nave predators. Most Queensland planigales seized (21 of 22) and partially consumed (11 of 22) the first toad they were offered, but were likely to ignore toads in subsequent trials. However, unlike their toad-nave conspecifics from the Northern Territory, the Queensland planigales all survived ingestion of toad tissue without overt ill effects and continued to attack toads in a substantial proportion of subsequent trials. Our data suggest that (i) learning by these small predators is sufficiently rapid and effective that selection on behaviour has been weak; and (ii) physiological tolerance to toad toxins may be higher in planigales after 60 years (approximately 60 generations) of exposure to this toxic prey.
Sumner, J., Webb, J.K., Shine, R. & Keogh, J.S. 2010, 'Molecular and morphological assessment of Australia's most endangered snake, Hoplocephalus bungaroides, reveals two evolutionarily significant units for conservation', Conservation Genetics, vol. 11, no. 3, pp. 747-758.
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The Broad-headed snake Hoplocephalus bungaroides is one of Australia's most endangered vertebrates. Extant populations of H. bungaroides are restricted to several geographically isolated reserves to the north, west, and south of Sydney. We analysed mitochondrial DNA from 184 specimens drawn from across the geographic range of the Broad-headed snake. Phylogenetic analysis demonstrated that H. bungaroides comprises two divergent mitochondrial lineages with a "northern" clade comprising populations west and north of Sydney and a "southern" clade comprising animals in Morton National Park. The two clades differ by an uncorrected genetic distance of 1.7%, which implies a divergence dating to approximately 755,000-850,000 years ago. We complemented our molecular data set with a detailed analysis of morphological variation both between and within the genetic clades. The two H. bungaroides genetic clades are morphologically indistinguishable and show little sexual dimorphism. Our results demonstrate that the populations north and south of this biogeographic split function as two distinct populations with no recent gene flow. There is no reason for separate taxonomic recognition of these two clades, but they do represent distinct evolutionarily significant units (ESUs) that require separate conservation management. In addition, within the northern ESU, populations from Royal National Park, Blue Mountains National Park, Wollemi National Park, and the Sydney Water Catchment supply areas should be considered as separate management units to conserve both evolutionary and ecological processes.
O'donnell, S., Webb, J.K. & Shine, R. 2010, 'Conditioned taste aversion enhances the survival of an endangered predator imperilled by a toxic invader', Journal Of Applied Ecology, vol. 47, no. 3, pp. 558-565.
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Even when we cannot eradicate an invasive species, we may be able to reduce its ecological impact. In Australia, a critically endangered predator, the northern quoll Dasyurus hallucatus is threatened by the invasion of the highly toxic cane toad Bufo marinus. Following toad invasion, quoll populations have become extinct across Northern Australia. Toads are continuing to spread, and will soon invade the Kimberley, one of the quoll's last strongholds. To prevent future local extinctions, we need a new approach for mitigating the impact of cane toads on this iconic predator. We investigated whether conditioned taste aversion (CTA) could be used to modify quoll predatory behaviour and mitigate toad impacts. We successfully induced an aversion to live toads in juvenile northern quolls by feeding them a dead toad containing a nausea-inducing chemical (thiabendazole). To investigate whether CTA enhanced quoll survival, we fitted radiocollars to 31 toad-smart and 31 toad-naive quolls, and monitored their survival after reintroduction to the wild. We analysed telemetry data using the program MARK to investigate whether survival was influenced by sex or experimental treatment (toad-smart vs. toad-naive). Five of 17 (29%) toad-naive male quolls died shortly after release, as soon as they encountered and attacked large cane toads. In toad-naive quolls, apparent survival rates were higher for females (0 center dot 84) than for males (0 center dot 58), reflecting a sex difference in the propensity to attack toads. In both sexes, toad-smart quolls had higher apparent survival rates than did toad-naive conspecifics (mean daily apparent survival rates for females, 0 center dot 94 vs. 0 center dot 84 respectively; for males, 0 center dot 88 vs. 0 center dot 58).
Webb, J.K., Pike, D.A. & Shine, R. 2010, 'Olfactory recognition of predators by nocturnal lizards: safety outweighs thermal benefits', Behavioral Ecology, vol. 21, no. 1, pp. 72-77.
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Many prey species are faced with multiple predators that differ in the degree of danger posed. The threat-sensitive predator avoidance hypothesis predicts that prey should assess the degree of threat posed by different predators and match their behavior according to current levels of risk. To test this prediction, we compared the behavioral responses of nocturnal velvet geckos, Oedura lesueurii, to chemicals from 2 snakes that pose different threats: the dangerous broad-headed snake Hoplocephalus bungaroides that eats geckos and the less dangerous small-eyed snake Cryptophis nigrescens that eats skinks (i.e., does not consume geckos). We also tested whether predator avoidance by prey was modulated by thermal costs associated with retreat-site selection. In both the presence and absence of thermal costs, velvet geckos avoided crevices scented by both dangerous and less dangerous snake species. When given the choice between a crevice scented by a broad-headed snake and a crevice scented by a small-eyed snake, most geckos avoided either retreat site. These results suggest that velvet geckos treat both snake predators as equally dangerous. To further explore these results, we quantified patterns of retreat-site selection by free-living velvet geckos on 2 sandstone plateaux. As in the laboratory, velvet geckos avoided thermally suitable rocks previously used by both snake species. Hence, a gecko's choice of retreat site is influenced by the presence of snake chemicals but is independent of thermal costs or the level of danger posed by the predator. To minimize their risk of predation, geckos may use a simple rule of thumb: "all snakes are dangerous".
Penman, T.D., Pike, D.A., Webb, J.K. & Shine, R. 2010, 'Predicting the impact of climate change on Australia's most endangered snake, Hoplocephalus bungaroides', Diversity And Distributions, vol. 16, no. 1, pp. 109-118.
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Aim To predict how the bioclimatic envelope of the broad-headed snake (BHS) (Hoplocephalus bungaroides) may be redistributed under future climate warming scenarios. Location South-eastern New South Wales, Australia. Methods We used 159 independent locations for the species and 35 climatic variables to model the bioclimatic envelope for the BHS using two modelling approaches - Bioclim and Maxent. Predictions were made under current climatic conditions and we also predicted the species distribution under low and high climate change scenarios for 2030 and 2070. Main conclusions Areas of higher elevation within the current range will be most important for persistence of this species because they will remain relatively moist and cool even under climate change and will match the current climate envelope. Conservation efforts should focus on areas where suitable climate space may persist under climate warming scenarios. Long-term monitoring programs should be established both in these areas and where populations are predicted to become extirpated, so that we can accurately determine changes in the distribution of this species throughout its range. Results Broad-headed snakes currently encompass their entire bioclimatic envelope. Both modelling approaches predict that suitable climate space for BHS will be lost to varying degrees under both climate warming scenarios, and under the worst case, only 14% of known snake populations may persist.
Pike, D.A., Webb, J.K. & Shine, R. 2010, 'Nesting in a thermally challenging environment: nest-site selection in a rock-dwelling gecko, Oedura lesueurii (Reptilia: Gekkonidae)', BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, vol. 99, no. 2, pp. 250-259.
Webb, J.K., Du, W., Pike, D. & Shine, R. 2010, 'Generalization of predator recognition: Velvet geckos display anti-predator behaviours in response to chemicals from non-dangerous elapid snakes', CURRENT ZOOLOGY, vol. 56, no. 3, pp. 337-342.
Pike, D.A., Croak, B.M., Webb, J.K. & Shine, R. 2010, 'Context-dependent avoidance of predatory centipedes by nocturnal geckos (Oedura lesueurii)', BEHAVIOUR, vol. 147, no. 3, pp. 397-412.
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Kelehear, C., Webb, J.K. & Shine, R. 2009, 'Rhabdias pseudosphaerocephala infection in Bufo marinus: lung nematodes reduce viability of metamorph cane toads', Parasitology, vol. 136, no. 8, pp. 919-927.
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Cane toads (Bufo marinus) were introduced to Australia in 1935 and have since spread widely over the continent, generating concern regarding ecological impacts on native predators. Most Australian cane toad populations are infected with lung nematodes Rhabdias pseudosphaerocephala, a parasite endemic to New World (native-range) cane toad populations; presumably introduced to Australia with its toad host. Considering the high intensities and prevalence reached by this parasite in Australian toad populations, and public ardour for developing a control plan for the invasive host species, the lack of experimental studies on this host-parasite system is surprising. To investigate the extent to which this lungworm influences cane toad viability, we experimentally infected metamorph toads (the smallest and presumably most vulnerable terrestrial phase of the anuran life cycle) with the helminth. Infected toads exhibited reduced survival and growth rates, impaired locomotor performance (both speed and endurance), and reduced prey intake. In summary, R. pseudosphaerocephala can substantially reduce the viability of metamorph cane toads.
Pringle, R.M., Syfert, M., Webb, J.K. & Shine, R. 2009, 'Quantifying historical changes in habitat availability for endangered species: use of pixel- and object-based remote sensing', Journal Of Applied Ecology, vol. 46, no. 3, pp. 544-553.
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Establishing medium- to long-term trends in habitat availability for endangered species is important for determining the causes of historical population declines and for designing effective management plans. For some animal species, relative habitat availability can be estimated using time series of aerial photographs, but the limited information in old black-and-white images makes it challenging to estimate accurately at large spatial scales. Australia's most endangered snake, the broad-headed snake Hoplocephalus bungaroides, requires unshaded, exfoliated sandstone rocks for shelter. Using digitized aerial photographs of four sites from 1941 and 1971, and a Quickbird satellite image from 2006, we estimated the trend in habitat availability for a well-studied population of H. bungaroides in New South Wales. We did this using both traditional, pixel-based classifications and a more recently developed object-based approach.
Webb, J.K., Du, W.G., Pike, D.A. & Shine, R. 2009, 'Chemical cues from both dangerous and nondangerous snakes elicit antipredator behaviours from a nocturnal lizard', Animal Behaviour, vol. 77, no. 6, pp. 1471-1478.
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Many prey species use chemical cues to detect predators. According to the threat sensitivity hypothesis, prey should match the intensity of their antipredator behaviour to the degree of threat posed by the predator. Several species of lizards display antipredator behaviours in the presence of snake chemical cues, but how species specific are these responses? In Australia, most snake species eat lizards, and are therefore potentially dangerous. Hence, we predicted that lizards should display generalized rather than species-specific antipredator behaviours. To test this prediction, we quantified the behavioural responses of velvet geckos, Oedura lesueurii, to chemical cues from five species of elapid snakes that are syntopic with velvet geckos but differ in their degree of danger. These five snake species included two nocturnal ambush foragers that eat geckos (broad-headed snake Hoplocephalus bungaroides, and death adder, Acanthophis antarcticus), two active foragers that eat skinks (but rarely eat geckos) and that differ in their activity times (nocturnal small-eyed snake, Cryptophis nigrescens, and diurnal whip snake, Demansia psammophis), and a nocturnal nonthreatening species that feeds entirely on blind snakes (bandy-bandy, Vermicella annulata). Geckos showed similar antisnake behaviours (tail waving, tail vibration), and a similar intensity of responses (reducing activity, freezing), to chemical cues from all five snake species, even though the snakes differed in their degree of danger and foraging modes. Our results suggest that velvet geckos display generalized antipredator responses to chemicals from elapid snakes, rather than responding in a graded fashion depending upon the degree of threat posed by a particular snake species.
Whiting, M.J., Webb, J.K. & Keogh, J.S. 2009, 'Flat lizard female mimics use sexual deception in visual but not chemical signals', Proceedings Of The Royal Society B-biological Sciences, vol. 276, no. 1662, pp. 1585-1591.
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Understanding what constrains signalling and maintains signal honesty is a central theme in animal communication. Clear cases of dishonest signalling, and the conditions under which they are used, represent an important avenue for improved understanding of animal communication systems. Female mimicry, when certain males take on the appearance of females, is most commonly a male alternative reproductive tactic that is condition-dependent. A number of adaptive explanations for female mimicry have been proposed including avoiding the costs of aggression, gaining an advantage in combat, sneaking copulations with females on the territories of other males, gaining physiological benefits and minimizing the risk of predation. Previous studies of female mimicry have focused on a single mode of communication, although most animals communicate using multiple signals. Male Augrabies flat lizards adopt alternative reproductive tactics in which some males (she-males) mimic the visual appearance of females. We experimentally tested in a wild population whether she-males are able to mimic females using both visual and chemical signals. We tested chemical recognition in the field by removing scent and relabelling females and she-males with either male or female scent. At a distance, typical males (he-males) could not distinguish she-males from females using visual signals, but during close encounters, he-males correctly determined the gender of she-males using chemical signals. She-males are therefore able to deceive he-males using visual but not chemical signals. To effectively deceive he-males, she-males avoid close contact with he-males during which chemical cues would reveal their deceit. This strategy is probably adaptive, because he-males are aggressive and territorial; by mimicking females, she-males are able to move about freely and gain access to females on the territories of resident males.
Webb, J.K., Pringle, R.M. & Shine, R. 2009, 'Intraguild predation, thermoregulation, and microhabitat selection by snakes', Behavioral Ecology, vol. 20, no. 2, pp. 271-277.
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Intraguild (IG) predation, the killing and eating of potential competitors, can be a powerful force within faunal assemblages. If both the IG predator and its prey prefer similar microhabitats in spatially structured environments, avoidance of the predator may relegate IG prey to suboptimal habitats. In southeastern Australia, the broad-headed snake (Hoplocephalus bungaroides) is an endangered species sympatric with the small-eyed snake (Cryptophis nigrescens), an abundant and geographically widespread species known to eat other snakes. Both of these nocturnal ectotherms shelter diurnally beneath thermally distinctive "hot rocks," which are in limited supply. When selecting shelter sites, broad-headed snakes thus face a trade-off between predation risk and habitat quality. In laboratory experiments, we allowed broad-headed snakes to choose between retreat sites differing in thermal regimes, in scent cues from predators, and in the actual presence of the predator. Broad-headed snakes displayed an aversion to sites with live predators and predator scent, yet nonetheless frequently selected those sites to obtain thermal benefits. In trials with live predators, adult broad-headed snakes shared hot rocks with small-eyed snakes, but most juveniles did not; data from a 16-year field study likewise suggest that broad-headed snakes only cohabit with small-eyed snakes if the two snakes are similar in body size. Our results suggest that thermoregulatory considerations are sufficient to prompt juvenile (but not adult) broad-headed snakes to risk IG predation, emphasizing the importance of microhabitat quality and body size in mediating IG predator-prey interactions.
Croak, B., Pike, D.A., Webb, J.K. & Shine, R. 2008, 'Three-dimensional crevice structure affects retreat site selection by reptiles', Animal Behaviour, vol. 76, pp. 1875-1884.
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When selecting retreat sites, rock-dwelling animals assess thermal and hydric properties of the rocks under which they shelter. Another obvious, but harder to measure, factor that may affect retreat site selection is the size and structure of the three-d
Webb, J.K., Brown, G.P., Child, T., Greenlees, M.J., Phillips, B.L. & Shine, R. 2008, 'A native dasyurid predator (common planigale, Planigale maculata) rapidly learns to avoid a toxic invader', Austral Ecology, vol. 33, no. 7, pp. 821-829.
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Interactions between invasive species and native fauna afford a unique opportunity to examine interspecific encounters as they first occur, without the complications introduced by coevolution. In northern Australia, the continuing invasion of the highly toxic cane toad Bufo marinus poses a threat to many frog-eating predators. Can predators learn to distinguish the novel toxic prey item from native prey (and thus, avoid being poisoned), or are longer-term genetically based changes to attack behaviour needed before predators can coexist with toads? To predict the short-term impact of cane toads on native predators, we need to know the proportion of individuals that will attack toads, the proportion surviving the encounter, and whether surviving predators learn to avoid toads. We quantified these traits in a dasyurid (common planigale, Planigale maculata) that inhabits tropical floodplains across northern Australia. Although 90% of naive planigales attacked cane toads, 83% of these animals survived because they either rejected the toad unharmed, or killed and consumed the prey snout-first (thereby avoiding the toxin-laden parotoid glands). Most planigales showed one-trial learning and subsequently refused to attack cane toads for long time periods (up to 28 days). Toad-exposed planigales also avoided native frogs for up to 9 days, thereby providing an immediate benefit to native anurans. However, the predators gradually learnt to use chemical cues to discriminate between frogs and toads. Collectively, our results suggest that generalist predators can learn to distinguish and avoid novel toxic prey very rapidly - and hence, that small dasyurid predators can rapidly adapt to the cane toad invasion. Indeed, it may be feasible to teach especially vulnerable predators to avoid cane toads before the toads invade, by deploying low-toxicity baits that stimulate taste-aversion learning.
Webb, J.K., Pike, D.A. & Shine, R. 2008, 'Population ecology of the velvet gecko, Oedura lesueurii in south eastern Australia: Implications for the persistence of an endangered snake', Austral Ecology, vol. 33, no. 7, pp. 839-847.
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Ecological specialization, such as major dependence upon a single-prey species, can render a predator taxon vulnerable to extinction. In such cases, understanding the population dynamics of that prey type is important for conserving the predator that relies upon it. In eastern Australia, the endangered broad-headed snake Hoplocephalus bungaroides feeds largely on velvet geckos (Oedura lesueurii). We studied growth, longevity and reproduction in a population of velvet geckos in Morton National Park in south-eastern Australia. We marked 458 individual geckos over a 3-year period (1992-1995) and made yearly visits to field sites from 1995-2006 to recapture marked individuals. Female geckos grew larger than males, and produced their first clutch at age 4 years. Males can mature at 2 years, but male-male combat for females probably forces males to delay reproduction until age 3 years. Females lay a single clutch of two eggs in communal nests in November, and up to 22 females deposited eggs in a single nest. Egg hatching success was high (100%), and juveniles had high survival (76%) during their first 6 months of life. Velvet geckos are long-lived, and the mean age of marked animals recaptured after 1995 was 6.1 years (males) and 8.4 years (females). Older females (7.5-9.5 years) were all gravid when last recaptured. Like other temperate-climate gekkonids, O. lesueurii has a 'slow' life history, and population viability could be threatened by any factors that increase egg or adult mortality. Two such factors - the removal of 'bush rocks' for urban gardens, and the overgrowth of rock outcrops by vegetation - could render small gecko populations vulnerable to extinction. In turn, the reliance of predatory broad-headed snakes on this slow-growing lizard species may increase its vulnerability to extinction.
Schultz, T.J., Webb, J.K. & Christian, K.A. 2008, 'The physiological cost of pregnancy in a tropical viviparous snake', Copeia, vol. 2008, no. 3, pp. 637-642.
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During pregnancy, the metabolic rate of females may Increase above basal levels to support metabolically active tissues and developing embryos. In mammals, this energetic cost of supporting the pregnancy (MCP) is an important component of reproductive effort, but less is known about the magnitude of this cost in ectothermic vertebrates. We estimated the metabolic cost of supporting pregnancy in a tropical viviparous snake, the Northern Death Adder, Acanthophis praelongus. We measured the metabolic rates of non-gravid and gravid females throughout gestation and following parturition. We also measured the oxygen consumption of a sample of neonates from each clutch within 24 h of birth. The metabolic rate of gravid females rose slowly during pregnancy, but was significantly elevated during the last three weeks of gestation. Considering the late term metabolism of gravid females as 100%, then the baseline metabolism of female Death Adders represented 36.6%, embryo metabolism accounted for 37.0%, and the cost of supporting the pregnancy was 26.4% of the total metabolic rate. Neonate metabolism during the first 24 h of birth was 2.9 times higher than the estimate for embryo metabolism. Thus, our results do not support the assumption that the metabolism of embryos (prior to birth) and neonates is similar in this species. Although gravid female Death Adders maintain high and constant body temperatures during late gestation, the energetic cost of supporting the pregnancy is only a minor component of the total reproductive effort for females of this species.
Webb, J.K. & Shine, R. 2008, 'Differential effects of an intense wildfire on survival of sympatric snakes', Journal Of Wildlife Management, vol. 72, no. 6, pp. 1394-1398.
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We analyzed 16 years of mark-recapture data to investigate whether a wildfire influenced survival of an arboreal ambush-forager (broad-headed snake [Hoplocephalus bungaroides]) and a terrestrial active forager (small-eyed snake Cryptophis nigrescens). We predicted that wildfire would cause direct mortality and reduce subsequent survival of both snake species. Contrary to this prediction, wildfire did not affect abundance of broad-headed snakes, but abundance of small-eyed snakes decreased by 48% after the wildfire. Estimated annual survival of small-eyed snakes was 37% lower after fire (s= 0.47, SE= 0.07) than before fire (s=0.74, SE = 0.05). Prescribed burning maybe a suitable tool for creating open habitat mosaics for the endangered broad-headed snake.
Letnic, M., Webb, J.K. & Shine, R. 2008, 'Invasive cane toads (Bufo marinus) cause mass mortality of freshwater crocodiles (Crocodylus johnstoni) in tropical Australia', Biological Conservation, vol. 141, no. 7, pp. 1773-1782.
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Invasive species are frequently blamed for faunal declines, but there is little direct evidence about the pathways, magnitude and size-selectivity of mortality induced by invaders. Top predators are of particular interest in this context, because their removal can generate substantial cascades of secondary effects on community composition. Cane toads (Bufo marinus) are large South American anurans currently spreading rapidly through tropical Australia. Native predators that attempt to consume these highly toxic toads may die as a result. During surveys of the Victoria River in the semi-arid tropical region of the Northern Territory, we documented massive mortality of freshwater crocodiles (Crocodylus johnstoni) at the toad invasion front. Dead crocodiles spanned a wide size range (0.6-2.1 m long) but with significant biases; intermediate-sized animals (0.6-1.5 m long) were more likely to be found dead. Population densities of crocodiles plummeted by as much as 77% following toad invasion, and population size-structures changed. The negative impacts of toads on crocodiles appear to be greater in these hot semi-arid landscapes than in cooler, higher rainfall areas where crocodiles have access to a wider prey base, and the toads are less prone to desiccation and can rehydrate in small, scattered water bodies rather than in the main river. Hence, the impact of cane toad invasion on this top predator may increase with increasing aridity.
Greenlees, M.J., Brown, G.P., Webb, J.K., Phillips, B.L. & Shine, R. 2007, 'Do invasive cane toads (Chaunus marinus) compete with Australian frogs (Cyclorana australis)?', Austral Ecology, vol. 32, no. 8, pp. 900-907.
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Despite widespread concern about the ecological impacts of invasive species, mechanisms of impact remain poorly understood. Cane toads (Chaunus [Bufo] marinus) were introduced to Queensland in 1935, and have now spread across much of tropical Australia.
Christian, K., Webb, J.K., Schultz, T. & Green, B. 2007, 'Effects of seasonal variation in prey abundance on field metabolism, water flux, and activity of a tropical ambush foraging snake', Physiological And Biochemical Zoology, vol. 80, no. 5, pp. 522-533.
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The responses of animals to seasonal food shortages can have important consequences for population dynamics and the structure and function of food webs. We investigated how an ambush foraging snake, the northern death adder Acanthophis praelongus, respon
Shine, R., Branch, W.R., Webb, J.K., Harlow, P.S., Shine, T. & Keogh, J.S. 2007, 'Ecology of cobras from southern Africa', Journal Of Zoology, vol. 272, no. 2, pp. 183-193.
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Large slender-bodied snakes that forage actively for a generalized array of small vertebrates are conspicuous elements of the terrestrial snake fauna of most continents; the venomous elapid species fill this role in much of Asia, Africa and Australia. Our dissections of eight species of cobras from southern Africa Aspidelaps, Hemachatus, Naja; Serpentes and Elapidae (total of 1290 specimens) provide extensive data on sexual dimorphism, reproductive biology and food habits. Females grow larger than males in Aspidelaps lubricus and Naja nigricincta, but (perhaps reflecting selection on male body size due to male-male combat) males grow as large as females in Naja anchietae, Naja melanoleuca, Naja mossambica, Naja nivea and Hemachatus haemachatus, and males grow larger than females in Naja annulifera. Overall, the degree of male size superiority is higher in species with a larger absolute mean adult body size. Male cobras typically have larger heads and longer tails than conspecific females. Fecundity increases with maternal body size, and is higher in the viviparous rhinkals H. haemachatus than in the oviparous Naja species studied. Diets are broad in all eight species, comprising a wide variety of amphibians, reptiles, mammals and (less often) birds. Ontogenetic (size-related) shifts in dietary composition (amphibian to reptile to mammal) are significant within some taxa (N. annulifera, N. nigricincta) but absent in others (notably N. nivea, the most arid-adapted species). Overall, despite substantial interspecific variation among the eight study species, strong parallels are evident between the cobras of southern Africa and their ecological counterparts in other continents.
Phillips, B.L., Brown, G.P., Greenlees, M., Webb, J.K. & Shine, R. 2007, 'Rapid expansion of the cane toad (Bufo marinus) invasion front in tropical Australia', Austral Ecology, vol. 32, no. 2, pp. 169-176.
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Cane toads (Bufo marinus) are large toxic anurans that have spread through much of tropical Australia since their introduction in 1935. Our surveys of the location of the toad invasion front in 2001 to 2005, and radiotracking of toads at the front near Darwin in 2005, reveal much faster westwards expansion than was recorded in earlier stages of toad invasion through Queensland. Since reaching the wet-dry tropics of the Northern Territory, the toads have progressed an average of approximately 55 km year(-1) (mean rate of advance 264 m night(-1) along a frequently monitored 55-km road transect during the wet season of 2004-2005). Radiotracking suggests that this displacement is due to rapid locomotion by free-ranging toads rather than human-assisted dispersal; individual toads frequently moved > 200 m in a single night. One radiotracked toad moved > 21 800 m in a 30-day period; the fastest rate of movement yet recorded for any anuran. Daily displacements of radiotracked toads varied with time and local weather conditions, and were highest early in the wet season on warm, wet and windy nights. The accelerated rate of expansion of the front may reflect either, or both: (i) evolved changes in toads or (ii) that toads have now entered an environment more favourable to spread. This accelerated rate of expansion means that toads will reach the Western Australian border and their maximal range in northern Australia sooner than previously predicted.
Keogh, J.S., Webb, J.K. & Shine, R. 2007, 'Spatial genetic analysis and long-term mark-recapture data demonstrate male-biased dispersal in a snake', Biology Letters, vol. 3, no. 1, pp. 33-35.
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Dispersal is an important life-history trait, but it is notoriously difficult to study. The most powerful approach is to attack the problem with multiple independent sources of data. We integrated information from a 14-year demographic study with molecular data from five polymorphic microsatellite loci to test the prediction of male-biased dispersal in a common elapid species from eastern Australia, the small-eyed snake Rhinoplocephalus nigrescens. These snakes have a polygynous mating system in which males fight for access to females. Our demographic data demonstrate that males move farther than females (about twice as far on average, and about three times for maximum distances). This sex bias in adult dispersal was evident also in the genetic data, which showed a strong and significant genetic signature of male-biased dispersal. Together, the genetic and demographic data suggest that gene flow is largely mediated by males in this species.
Dubey, S., Croak, B., Pike, D.A., Webb, J.K. & Shine, R. 2007, 'Phylogeography and dispersal in the velvet gecko (Oedura lesueurii), and potential implications for conservation of an endangered snake (Hoplocephalus bungaroides)', BMC Evolutionary Biology, vol. 7.
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Llewelyn, J., Shine, R. & Webb, J.K. 2006, 'Time of testing affects locomotor performance in nocturnal versus diurnal snakes', Journal Of Thermal Biology, vol. 31, no. 3, pp. 268-273.
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Studies of the thermal dependence of locomotor performance in ectotherms have provided extensive data on species differences, but often have neglected the time of day at which the test organism is usually active. To compare performance abilities among sp
Shine, R., Branch, W.R., Harlow, P.S., Webb, J.K. & Shine, T. 2006, 'Biology of burrowing asps (Atractaspididae) from southern Africa', Copeia, vol. 2006, no. 1, pp. 103-115.
Ecological data on poorly-known snake species can suggest novel hypotheses about selective forces for interspecific variation in morphological traits. The nocturnal fossorial snakes of the family Atractaspididae represent an ancient African radiation tha
Kelehear, C. & Webb, J.K. 2006, 'Effects of tail autotomy on anti-predator behavior and locomotor performance in a nocturnal gecko', Copeia, vol. 2006, no. 4, pp. 803-809.
Caudal autotomy is widely employed by lizards to facilitate escape from predators. Despite conferring immediate short-term benefits, tail loss may involve substantial costs, including impaired locomotor performance, loss of energy reserves, and reduced survival during subsequent encounters with predators. We investigated whether tail autotomy influenced the running speeds and anti-predator behaviors of adult male Velvet Geckos, Oedura lesueurii. This nocturnal terrestrial gecko displays a range of anti-predator behaviors (tail waving and vibration, slow movement, and crypsis) in the presence of scent from the predatory Broad-headed Snake, Hoplocephalus bungaroides. Since tailless geckos cannot use tail displays to attract predatory strikes away from the torso, we hypothesized that tailless geckos would spend more time motionless in the presence of Broad-headed Snake scent. Sprint speeds of tailless and tailed Velvet Geckos were very similar over short (0.25 m) and longer distances (I m). During locomotor trials, geckos frequently stopped along the racetrack, but tail autotomy did not affect the frequency of this behavior. Contrary to our predictions, tailless Velvet Geckos did not decrease their activity levels in the presence of Broad-headed Snake scent. Overall, our data support the hypothesis that the locomotor costs associated with tail autotomy are relatively minor in lizard species where the tail plays no functional role in locomotion.
Greenlees, M.J., Brown, G.P., Webb, J.K., Phillips, B.L. & Shine, R. 2006, 'Effects of an invasive anuran [the cane toad (Bufo marinus)] on the invertebrate fauna of a tropical Australian floodplain', Animal Conservation, vol. 9, no. 4, pp. 431-438.
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The ways in which invasive organisms influence native ecosystems remain poorly understood. For example, feral cane toads Bufo marinus have spread extensively through tropical Australia over the last 70 years, but assessments of their ecological impact remain largely anecdotal. We conducted experimental trials to examine the effect of cane toad presence on invertebrate fauna in relatively small (2.4 x 1.2 m) outdoor enclosures on a floodplain near Darwin in the wet-dry tropics. Toads significantly reduced invertebrate abundance and species richness, but only to about the same degree as did an equivalent biomass of native anurans. Thus, if toads simply replaced native anurans, the offtake of invertebrates might not be substantially different from that due to native anurans before toad invasion. However, our field surveys suggest that toads cause a massive (fourfold) increase in total amphibian biomass. The end result is that cane toads act as a massive nutrient sink in the floodplain ecosystem because they consume vast numbers of invertebrates but (unlike native frogs) are largely invulnerable to predation by frog-eating predators.
Brown, G.P., Phillips, B.L., Webb, J.K. & Shine, R. 2006, 'Toad on the road: Use of roads as dispersal corridors by cane toads (Bufo marinus) at an invasion front in tropical Australia', Biological Conservation, vol. 133, no. 1, pp. 88-94.
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Determining the factors that influence the rate of spread of invasive species is an important goal for conservation biology. if invasive species utilize specific landscape features as dispersal corridors, control programs can target such corridors. Radio
Webb, J.K. 2006, 'Effects of tail autotomy on survival, growth and territory occupation in free-ranging juvenile geckos (Oedura lesueurii)', Austral Ecology, vol. 31, no. 4, pp. 432-440.
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Many animals autotomize their tails to facilitate escape from predators. Although tail autotomy can increase the likelihood of surviving a predatory encounter, it may entail subsequent costs, including reduced growth, loss of energy stores, a reduction in reproductive output, loss of social status and a decreased probability of survival during subsequent encounters with predators. To date, few studies have investigated the potential fitness costs of tail autotomy in natural populations. I investigated whether tail loss influenced survival, growth and territory occupation of juvenile velvet geckos Oedura lesueurii in a population where predatory snakes were common. During the 3-year mark-recapture study, 32% of juveniles voluntarily autotomized their tails when first captured. Analysis of survival using the program MARK showed that voluntary tail autotomy did not influence the subsequent survival of juvenile geckos. Survival was age-dependent and was higher in 1-year-old animals (0.98) than in hatchlings (0.76), whereas recapture probabilities were time-dependent. Growth rates of tailed and tailless juveniles were very similar, but tailless geckos had slow rates of tail regeneration (0.14 mm day(-1)). Tail autotomy did not influence rock usage by geckos, and both tailed and tailless juveniles used few rocks as diurnal retreat sites (means of 1.64 and 1.47 rocks, respectively) and spent long time periods (85 and 82 days) under the same rocks. Site fidelity may confer survival advantages to juveniles in populations sympatric with ambush foraging snakes. My results show that two potential fitness costs of tail autotomy - decreased growth rates and a lower probability of survival - did not occur in juveniles from this population.
Webb, J.K. & Whiting, M.J. 2006, 'Does rock disturbance by superb lyrebirds (Menura novaehollandiae) influence habitat selection by juvenile snakes?', Austral Ecology, vol. 31, no. 1, pp. 58-67.
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Vertebrates that destroy or disturb habitats used by other animals may influence habitat selection by sympatric taxa. In south-east Australian forests, superb lyrebirds (Menura novaehollandiae) displace soil, leaf litter and rocks during their daily fora
Shine, R., Branch, W.R., Webb, J.K., Harlow, P.S. & Shine, T. 2006, 'Sexual dimorphism, reproductive biology, and dietary habits of psammophiine snakes (Colubridae) from southern Africa', Copeia, vol. 2006, no. 4, pp. 650-664.
Slender-bodied, diurnal "sand snakes" of the genus Psammophis are widespread and abundant through Africa, but the general biology of these animals remains poorly known. For example, sexual dimorphism is unstudied because it is difficult to determine the sex of live specimens (uniquely among snakes, the male hemipenis is vestigial). Our dissections of 700 preserved specimens provide detailed ecological information on ten psammophiine species from southern Africa. Males grow larger than females in most taxa, especially in species of large absolute body size. However, sex differences in body proportions (relative head size, relative tail length) are minor. Females produce small clutches (generally < 10 eggs), with larger clutches in larger females in some but not all species. Psammophylax tritaeniatus differs from the nine Psammophis species studied in its higher fecundity and its primary reliance on mammalian rather than reptilian prey. Within Psammophis, five species (P. brevirostris, P. jallae, P. leopardinus, P. subtaeniatus, P. trigrammus) fed mostly on scincid lizards, two (P. namibensis, P. notostictus) fed mostly on lacertid lizards, and two (P. trinasalis, P. mossambicus) took approximately equal numbers of lizards and mammals. Although dietary composition thus varied with snake species and body size, conspecific males and females took similar prey types. Thus, despite reports of unusual mating systems in captive psammophiines, these snakes exhibit only minor sexual dimorphism in size, bodily proportions, and dietary habits.
Shine, R., Webb, J.K., Lane, A. & Mason, R.T. 2006, 'Flexible mate choice: a male snake's preference for larger females is modified by the sizes of females encountered', Animal Behaviour, vol. 71, no. Part 1, pp. 203-209.
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Why do males exert strong mate choice in some taxa but not others? Theory suggests that mate discrimination will enhance male fitness when encounter rates with potential mates are high, when those potential mates vary in the fitness consequences likely to accrue from an attempted insemination, and when courting one female reduces the male's opportunity to court other females. One widespread form of mate choice involves a trend for males of many ectothermic species to court larger (and thus, more fecund) females. To test whether such preferences are dynamically adjusted to local conditions, we studied male preference for larger females in red-sided garter snakes, Thamnophis sirtalis parietalis, near a communal den in Manitoba, Canada. Courting a small female imposes a high opportunity cost for a male in the centre of the den, because many large and easily located females are nearby. In the surrounding woodland, in contrast, a male that neglects a small female is unlikely to encounter a larger substitute partner. In arena trials, male snakes from the den selected larger females more than did males from the surrounding woodland. Manipulating a den male's exposure to females (none, large, small) for 60 min led males to adjust their criteria for courtship depending upon the sizes of females encountered. Hence, the local environment can modify courtship criteria, with male garter snakes adjusting their mate choice selectivity based upon spatial and temporal factors that affect the opportunity costs of courtship.
Webb, J.K., Shine, R. & Christian, K.A. 2006, 'The adaptive significance of reptilian viviparity in the tropics: Testing the maternal manipulation hypothesis', Evolution, vol. 60, no. 1, pp. 115-122.
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Phylogenetic transitions from oviparity to viviparity in reptiles generally have occurred in cold climates, apparently driven by selective advantages accruing from maternal regulation of incubation temperature. But why, then, are viviparous reptiles so successful in tropical climates? Viviparity might enhance fitness in the tropics via the same pathway as in the temperate zone, if pregnant female reptiles in the tropics maintain more stable temperatures than are available in nests (Shine's maternal manipulation hypothesis). Alternatively, viviparity might succeed in the tropics for entirely different reasons than apply in the temperate zone. Our data support the maternal manipulation hypothesis. In a laboratory thermal gradient, pregnant death adders (Acanthophis praelongus) from tropical Australia maintained less variable body temperatures (but similar mean temperatures) than did nonpregnant females. Females kept at a diel range of 25-31 degrees C (as selected by pregnant females) gave birth earlier and produced larger offspring (greater body length and head size) than did females kept at 23-33 degrees C (as selected by nonpregnant snakes). Larger body size enhanced offspring recapture rates (presumably reflecting survival rates) in the field. Thus, even in the tropics, reproducing female reptiles manipulate the thermal regimes experienced by their developing embryos in ways that enhance the fitness of their offspring. This similarity across climatic zones suggests that a single general hypothesis-maternal manipulation of thermal conditions for embryogenesis-may explain the selective advantage of viviparity in tropical as well as cold-climate reptiles.
Phillips, B.L., Brown, G.P., Webb, J.K. & Shine, R. 2006, 'Invasion and the evolution of speed in toads', Nature, vol. 439, pp. 803-803.
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Webb, J.K. & Whiting, M.J. 2006, 'Habitat disturbance, not predation, is all that is required to influence habitat choice in juvenile snakes: A rejoinder to Lill', AUSTRAL ECOLOGY, vol. 31, no. 7, pp. 905-906.
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Shine, R., Webb, J.K., Lane, A. & Mason, R.T. 2005, 'Mate location tactics in garter snakes: effects of rival males, interrupted trails and non-pheromonal cues', Functional Ecology, vol. 19, no. 6, pp. 1017-1024.
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The ability to follow substrate-deposited scent trails using sophisticated vomeronasal abilities is a key feature of snake biology. However, previous research on this topic has derived mostly from a highly artificial test situation: captive snakes following continuous trails over structurally simple homogeneous substrates, in the absence of any other cues (e.g. visual or olfactory) either from the target of that search or from other snakes.
Stapley, J., Hayes, C.M., Webb, J.K. & Keogh, J.S. 2005, 'Novel microsatellite loci identified from the Australian eastern small-eyed snake (Elapidae: Rhinocephalus nigrescens) and cross species amplification in the related genus Suta', Molecular Ecology Notes, vol. 5, no. 1, pp. 54-56.
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A total of 15 microsatellite primers pairs were developed for the Australian small-eyed snake Rhinoplocephalus nigrescens. Five primers were used to screen 93 individuals of R. nigrescens and were also tested against eight species of the closely related genus Suta. Allelic diversity in R. nigrescens was high in three loci (12-27) and there was high heterozygosity (0.58-0.82). Observed heterozygosity did not deviate from Hardy-Weinberg expectations for the five loci tested. These primers will be useful in studies of population genetics and mating systems of small-eyed snakes and related species.
Greenlees, M.J., Webb, J.K. & Shine, R. 2005, 'Led by the blind: bandy-bandy snakes Vermicella annulata (Elapidae) follow blindsnake chemical trails', Copeia, vol. 2005, no. 1, pp. 184-187.
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The ability to detect and follow prey chemical trails is important for actively foraging nocturnal snakes. We investigated whether a nocturnal, ophiophagous (snake-eating) predator, the Bandy-Bandy (Vermicella annulata) can detect and follow blindsnake chemical trails. Adult Bandy-Bandys were offered the choice between control trails (distilled water) and chemical trails from three sympatric squamate species. Bandy-Bandys ignored distilled water trails and the trails of the burrowing Yellow-Bellied Three-Toed Skink (Saiphos equalis) and the nocturnal Golden Crowned Snake (Cacophis squamulosus). In contrast, all of the Bandy-Bandys followed chemical trails from the Blackish Blindsnake (Ramphotyphlaps nigrescens), and three snakes followed the blindsnake trails along their entire length (mean distance followed = 0.93 m, range 0.2-1.4 m). Our results suggest Bandy Bandys use chemical cues to locate blindsnakes but do not respond to chemical trails of other sympatric squamate species.
Webb, J.K., Shine, R. & Pringle, R.M. 2005, 'Canopy removal restores habitat quality for an endangered snake in a fire suppressed landscape', Copeia, vol. 2005, no. 4, pp. 894-900.
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In the last two centuries, European fire suppression practices have produced increases in vegetation density and canopy cover in many landscapes. Potentially, increases in canopy cover could negatively affect small populations of nocturnal reptiles that use sun-exposed shelters for diurnal thermoregulation. We hypothesized that vegetation encroachment over rock outcrops might partly explain the recent decline of Australia's most endangered snake, the Broad-headed Snake Hoplocephalus bungaroides. To test this hypothesis, we carried out a field study in Morton National Park, southeastern Australia. We removed overhanging vegetation from above shaded rocks and compared their subsequent usage by reptiles to control (shaded) rocks. In spring, one year after canopy removal, experimental rocks were 10.3 C hotter than control rocks and were used as diurnal retreat sites by three species of reptiles, including the endangered Broad-headed Snake and its prey (Velvet Gecko, Oedura lesueurii). By contrast, no reptiles used control rocks as diurnal retreat sites. Our results show that modest canopy removal (similar to 15% increase in canopy openness) can restore habitat quality for nocturnal reptiles. Future studies are needed to examine whether controlled burns can maintain an open canopy above sandstone rock outcrops. However, until effective fire management measures are in place, sapling removal from overgrown rock outcrops could help to protect small populations of endangered reptiles.
Webb, J.K. & Whiting, M.J. 2005, 'Why don't small snakes bask? Juvenile broad-headed snakes trade thermal benefits for safety', Oikos, vol. 110, no. 3, pp. 515-522.
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Previous studies have suggested that most small Australian elapid snakes are nocturnal and rarely bask in the open because of the risk of predation by diurnal predatory birds. Because the physiology and behaviour of reptiles is temperature dependent, staying in refuges by day can entail high thermoregulatory costs, particularly for juveniles that must grow rapidly to maximise their chances of survival. We investigated whether the risk of predation deters juveniles of the endangered broad-headed snake (Hoplocephalus bungaroides) from basking, and if so, whether there are thermal costs associated with refuge use. To estimate avian attack rates on snakes, we placed 900 plasticine snake replicas in sunny locations and underneath small stones on three sandstone plateaus for 72 h. At the same time we quantified the thermal benefits of basking vs refuge use. On sunny days, juveniles could maintain preferred body temperatures for 4.7 h by basking but only for 2.0 h if they remained inside refuges. Our predation experiment showed that basking has high costs for juvenile snakes. Predators attacked a significantly higher proportion of exposed models (13.3%) than models under rocks (1.6%). Birds were the major predators of exposed models (75% of attacks), and avian predation did not vary across the landscape. By trading heat for safety, juvenile H. bungaroides decreased the potential time period that they could maintain preferred body temperatures by 57%. Thermal costs of refuge use may therefore contribute to the slow growth and late maturation of this endangered species. Our results support the hypothesis that nocturnal activity in elapid snakes has evolved to minimise the risk of avian predation.
Webb, J.K., Shine, R. & Christian, K.A. 2005, 'Does intraspecific niche partitioning in a native predator influence its response to an invasion by a toxic prey species?', Austral Ecology, vol. 30, no. 2, pp. 201-209.
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The introduced and highly toxic cane toad (Bufo marinus) is rapidly spreading across northern Australia where it may affect populations of large terrestrial vertebrate predators. The ecological impact of cane toads will depend upon the diets, foraging modes and habitat use of native predators, and their feeding responses to cane toads. However, intraspecific niche partitioning may influence the degree of vulnerability of predators to toxic prey, as well as the time course of the impact of alien invaders on native species. We studied the diet of the northern death adder Acanthophis praelongus and their feeding responses to cane toads. In the laboratory, death adders from all size classes and sexes readily consumed frogs and cane toads. Diets of free ranging A. praelongus from the Adelaide River floodplain were more heterogeneous. Juvenile snakes ate mainly frogs (39% of prey items) and small scincid lizards (43%). Both sexes displayed an ontogenetic dietary shift from lizards to mammals, but adult males fed on frogs (49%) and mammals (39%) whereas adult females (which grew larger than males) fed mainly on mammals (91%) and occasionally, frogs (9%). Feeding rates and body condition of adult snakes varied temporally and tracked fluctuations in prey availability. These results suggest that cane toads may negatively affect populations of northern death adders in the Darwin region. However, we predict that different size and sex classes of A. praelongus will experience differential mortality rates over different timescales. The initial invasion of large toads may affect adult males, but juveniles may be unaffected until juvenile toads appear the following year, and major affects on adult female death adders may be delayed until annual rainfall fluctuations reduce the availability of alternative (rodent) prey.
Llewelyn, J., Shine, R. & Webb, J.K. 2005, 'Thermal regimes and diel activity patterns of four species of small elapid snakes from south-eastern Australia', Australian Journal Of Zoology, vol. 53, no. 1, pp. 1-8.
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Two of the most basic biological attributes for any ectothermic animal are the times of day that it is active and the body temperatures that it exhibits. Published studies on reptile biology display a heavy bias towards diurnal lizards from Northern Hemisphere habitats. To help redress this imbalance, we quantified thermal regimes and activity times in four species of small Australian elapid snakes. Mean selected body temperature in a thermal gradient was affected by the time of testing ( i. e. night v. day), with snakes choosing higher body temperatures at night than by day. In outdoor enclosures, whip snakes ( Demansia psammophis) were shuttling heliotherms active only during daylight hours at relatively high body temperatures; in a laboratory thermal gradient these animals selected high body temperatures ( mean 31.3degreesC during the day and 33.2degreesC at night). The other three taxa - golden- crowned snakes ( Cacophis squamulosus), small- eyed snakes ( Cryptophis nigrescens) and marsh snakes ( Hemiaspis signata) - were active mostly at night at relatively low body temperatures, and selected low body temperatures in a thermal gradient ( 18.1 - 23.4degreesC). Thus, mean selected body temperatures differ substantially among sympatric elapid species in south- eastern Australia and are correlated with times of activity.
Webb, J.K., Pringle, R.M. & Shine, R. 2004, 'How do nocturnal snakes select diurnal retreat sites?', Copeia, vol. 2004, no. 4, pp. 919-925.
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Theoretical and empirical studies of habitat selection suggest that reptiles should use "fixed" structural features (perch diameter, vegetation) or light intensity (sun and shade) to select thermally suitable microhabitats. But how do nocturnal species select thermally suitable diurnal retreat sites at night in the absence of visual cues? To investigate this question, we studied habitat selection by two sympatric nocturnal snakes, the endangered Broad-Headed Snake Hoplocephalus bungaroides and the common Small-Eyed Snake Cryptophis nigrescens. In the field, we investigated whether snakes selected diurnal retreat sites nonrandomly with respect to vegetation structure and rock temperature. In the laboratory, we offered snakes a choice between rocks with different crevice sizes, temperatures, and degree of shading. In the field, rocks used by snakes received significantly higher levels of incident radiation intensity (and therefore had higher temperatures) than random rocks but had similar levels of canopy cover. This apparent paradox reflects differences in the position of canopy gaps relative to the path of the sun, the most important determinant of a rock's diurnal temperature profile. In the laboratory, snakes chose rocks with narrow crevices but did not discriminate between shaded and exposed rocks. Snakes consistently chose hot rocks over cold rocks, even though the nocturnal temperature difference between the two retreat sites was less than 4 C. Our results show that these nocturnal snakes use a fixed structural cue (crevice size) to select potential retreat sites but then use a temporally variable cue (substrate temperature) to choose among potential retreat sites.
Webb, J.K. 2004, 'Pregnancy Decreases Swimming Performance Of Female Northern Death Adders (acanthophis Praelongus)', Copeia, vol. 2, no. 2, pp. 357-363.
Reduction in locomotor performance during pregnancy is a potential cost of reproduction for female lizards and snakes. Most previous studies have suggested that reduced locomotor performance is a direct result of carrying a physical burden (the clutch).
Webb, J.K., Brook, B.W. & Shine, R. 2003, 'Does foraging mode influence life history traits? A comparative study of growth, maturation and survival of two species of sympatric snakes from south-eastern Australia', Austral Ecology, vol. 28, no. 6, pp. 601-610.
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Theory predicts that compared with active searchers, ambush foragers should have lower rates of energy intake, slower growth, and higher survival rates. We tested these predictions with data on two species of sympatric, saurophagous, small-bodied, viviparous elapid snakes: the broad-headed snake, Hoplocephalus bungaroides, and the small-eyed snake, Rhinoplocephalus nigrescens. Demographic parameters and growth curves for both species were estimated from a long-term (9 years) mark-recapture study in Morton National Park, south-eastern Australia. The ambush predator (H. bungaroides) displayed slower juvenile growth and later maturation (5 years for males, 6 years for females) than did the active forager (R. nigrescens, 3 years). Litter sizes were similar in both species, but reproductive frequency was higher in R. nigrescens (90-100%) than in H. bungaroides (50%). Juvenile survival was lower in the active searcher (31%) than in the ambush forager (55%), but adult survivorship was similar (74% vs 82%). Our results support the hypothesis that ambush foragers display 'slow' life history traits, but additional phylogenetically independent comparisons are needed to evaluate the generality of this pattern.
Pringle, R.M., Webb, J.K. & Shine, R. 2003, 'Canopy structure, microclimate, and habitat selection by a nocturnal snake, Hoplocephalus bungaroides', Ecology, vol. 84, no. 10, pp. 2668-2679.
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Forest structure strongly influences ambient environmental conditions such as light and temperature, but most studies on habitat selection by mobile organisms have either ignored canopy structure or treated it as a dichotomous variable (e.g., "shady" or "sunny"). Furthermore, the predominance of active diurnal species as model organisms in such studies has left many unanswered questions about the importance of vegetation-related variables for nocturnal and sedentary species (e.g., what does "shade" mean to an organism that moves at night and sits in a cave all day?). We used hemispherical photography to quantify canopy structure and examine its role in determining the thermal microenvironments available to a rock-dwelling nocturnal snake (Hoplocephalus bungaroides) across two different spatial scales. The narrow plateaus inhabited by the snakes in southeastern Australia are highly heterogeneous with respect to vegetation: east-facing aspects are densely covered whereas west-facing aspects are patchy mosaics. We found that temperatures of potential retreat sites increased with increasing canopy openness, but the definitive determinant of retreat-site temperature was incident radiation intensity, which depended upon the location of canopy gaps relative to the sun path. This factor restricted the snakes to west-facing cliff tops, and there only to an optimal subset of rocks that received adequate irradiance. Moreover, thermal regimes of retreat sites displayed higher maxima and were evening shifted relative to randomly sampled rocks in the same area. Our results suggest that thermally suitable retreat sites are a limiting resource, and that local increases in vegetation density might contribute to the decline of this endangered species.
Christian, K.A., Webb, J.K. & Schultz, T.J. 2003, 'Energetics of bluetongue lizards (Tiliqua scincoides) in a seasonal tropical environment', OECOLOGIA, vol. 136, no. 4, pp. 515-523.
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Webb, J.K., Christian, K. & Fisher, P. 2002, 'Fast Growth And Early Maturation In A Viviparous Sit-and-wait Predator, The Northern Death Adder (acanthophis Praelongus), From Tropical Australia', Journal Of Herpetology, vol. 36, no. 3, pp. 505-509.
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Webb, J.K., Brook, B.W. & Shine, R. 2002, 'Collectors endanger Australia's most threatened snake, the broad-headed snake Hoplocephalus bungaroides', Oryx: the international journal of conservation, vol. 36, no. 2, pp. 170-181.
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The collection of reptiles for the pet trade is often cited as a potential problem for threatened species, but quantitative data on the effects of this trade on wild populations are lacking. In south-eastern Australia the decline of the threatened broad-headed snake Hoplocephalus bungaroides has been blamed on habitat destruction and the collection of snakes for pets, but there was little evidence to support the latter hypothesis. During 1992-2000 we studied one of the last extant southern populations of broad-headed snakes in Morton National Park, New South Wales, where <600 individuals remain on an isolated plateau. Analysis of 9 years of mark-recapture data reveal that the activities of snake collectors seriously endanger the viability of this species. The study population of H. bungaroides was stable over 1992-1996, but declined dramatically in 1997, coincident with evidence of illegal collecting, possibly stimulated by a government amnesty that allowed pet owners to obtain permit,, for illegally held reptiles. Survivorship analyses revealed that 85% of adult females disappeared from the population in 1997. There was no such effect on male survivorship, suggesting that snake collectors, selectively removed adult females, which are the largest snakes in the population. Humans caused significant damage to fragile rock outcrops in three of the 9 years of the study, and a second bout of habitat disturbance in 1999 coincided with a second decline in the H. bungaroides, population, We recommend that locked gates be placed on fire trails to protect existing populations of broad-headed snakes.
Webb, J.K., Brook, B.W. & Shine, R. 2002, 'What makes a species vulnerable to extinction? Comparative life-history traits of two sympatric snakes', Ecological Research, vol. 17, no. 1, pp. 59-67.
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Although it is well known that species vary in their vulnerability to extinction, the reasons are poorly understood. Theory predicts that long-lived species with 'slow' life histories (small litters, slow growth, late maturation) should be at greater risk than short-lived species with high potential rates of increase. This hypothesis was tested by comparing life-history traits of two species of sympatric, elapid snakes: the endangered broad-headed snake, Hoplocephalus bungaroides, and common small-eyed snake, Cryptophis nigrescens. From 1992 to 2000 a mark-recapture study of both species was undertaken in Morton National Park, south-eastern Australia, and this information was used to construct transition matrices for each species. The endangered H. bungaroides was found to mature late (6 years of age), had a high juvenile (54.7%) and adult (81.6%) survival rate, and a long generation length (10.4 years). In striking contrast, the common C. nigrescens matured early (within 3 years), had a lower juvenile (30.4%) and adult (74.4%) survival rate (but higher recruitment rate), and a substantially shorter generation length (5.9 years). Elasticity analyses revealed that H. bungaroides was considerably more sensitive to survival past the age of 2 years (68.6%) than C. nigrescens (37.4%). These results provide support for the hypothesis that species with slow life histories are more vulnerable to extinction.
Webb, J.K., Branch, W. & Shine, R. 2001, 'Dietary Habits And Reproductive Biology Of Typhlopid Snakes From Southern Africa', Journal Of Herpetology, vol. 35, no. 4, pp. 558-567.
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We studied diets, sexual dimorphism, and reproductive biology of six taxa of poorly known African blindsnakes (Rhinotyphlops lalandei, Rana mucruso, Rana schlegelii petersii, Rana schlegelii schlegelii, Typhlops bibronii, and Typhlops fornasinii) by diss
Webb, J.K., Brown, G.P. & Shine, R. 2001, 'Body size, locomotor speed and antipredator behaviour in a tropical snake (Tropidonophis mairii, Colubridae): the influence of incubation environments and genetic factors', Functional Ecology, vol. 15, no. 5, pp. 561-568.
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The physical conditions experienced by reptile embryos inside natural nests can influence the size, shape and behaviour of the resultant hatchlings. Although most reptiles are tropical, the effects of incubation temperatures on offspring phenotypes have received little attention in tropical species. The consequences of differences in thermal variance during incubation on offspring were studied in a tropical natricine snake (the Keelback Tropidonophis mairii), which lays eggs in soil cracks of varying depths. Some 253 eggs from 19 clutches were incubated under two thermal regimes with identical mean temperatures (25.6 degreesC), but temperatures in the 'variable' treatment fluctuated more (21.8-29.6 degreesC) than those in the 'constant' temperature treatment (25.2-26.5 degreesC). These thermal regimes were similar to those of shallow (20 cm deep) and deep (40 cm deep) soil cracks, respectively, and represent thermal conditions inside natural nests and potential nest sites. Incubation temperatures affected body size, shape and antipredator behaviour of hatchling snakes. Snakes from constant temperature incubation were longer and thinner than snakes from high variance incubation. Clutch effects influenced all offspring traits, with significant interactions between clutch of origin and incubation treatment for body size, but not swimming speed or behaviour. 4. There was a significant interaction between incubation treatment and offspring sex on neonate swimming speed. Incubation under cycling thermal regimes significantly increased swimming speeds of females, but had little effect on males. Such sex differences in phenotypic responses of hatchling snakes support a major assumption of the Charnov-Bull hypothesis for the evolution of temperature-dependent sex determination.
Scott, I.A.W., Hayes, C.M., Keogh, J.S. & Webb, J.K. 2001, 'Isolation and characterization of novel microsatellite markers from the Australian tiger snakes (Elapidae : Notechis) and amplification in the closely related genus Hoplocephalus', MOLECULAR ECOLOGY NOTES, vol. 1, no. 3, pp. 117-119.
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Webb, J.K., Shine, R., Branch, W. & Harlow, P. 2000, 'Life Underground: Food Habits And Reproductive Biology Of Two Amphisbaenian Species From Southern Africa', Journal Of Herpetology, vol. 34, no. 4, pp. 510-516.
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Examination and dissection of 216 museum specimens of two species of amphisbaenians (the shovel-snouted Monopeltis anchietae and round-headed Zygaspis quadrifrons) from southern Africa provided data on morphology, sexual dimorphism, reproduction, and die
Webb, J.K. & Shine, R. 2000, 'Paving the way for habitat restoration: can artificial rocks restore degraded habitats of endangered reptiles?', Biological Conservation, vol. 92, no. 1, pp. 93-99.
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The addition of artificial resources (nest boxes, shelter sites) to degraded habitats may help reverse the decline of species that rely on these structures. In south-eastern Australia, the endangered broad-headed snake (Hoplocephalus bungaroides) and its major prey, the velvet gecko (Oedura lesueurii), use exposed sandstone rocks for diurnal shelter sites. Removal of these sandstone "bush-rocks" for landscaping urban gardens has contributed to the decline of both species, and recent studies suggest that rock removal affects broad-headed snakes indirectly, via a decline in prey numbers. Thus, one way to restore degraded sandstone habitat is to provide artificial rocks for the snakes' major prey, the velvet gecko. To investigate this possibility, we placed 128 square concrete pavers (19 cm wide, 5 cm thick) at three study sites in Morton National Park, where velvet geckos and broad-headed snakes are relatively common. We manipulated crevice width (4 vs 8 mm) and temperature of concrete pavers (shaded vs exposed) to determine how these factors influence retreat-site selection by velvet geckos. We monitored the usage of these artificial habitats by geckos and invertebrates over a 1-year period. During the cooler months most velvet geckos selected exposed pavers with narrow crevices. Larger geckos used wider crevices than did smaller conspecifics. Our results show that habitat restoration with appropriate-sized concrete pavers may be a feasible conservation technique for degraded rock outcrops. We recommend the use of large pavers (30-45 cm wide, 5-10 cm thick) with a variety of crevice sizes (up to 10 mm) to maximize the diversity of retreat-sites for broad-headed snakes and saxicolous lizards
Webb, J.K., Shine, R., Branch, W.R. & Harlow, P.S. 2000, 'Life-history strategies in basal snakes: reproduction and dietary habits of the African thread snake Leptotyphlops scutifrons (Serpentes: Leptotyphlopidae)', Journal Of Zoology, vol. 250, pp. 321-327.
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Information on the biology of 'primitive' blind snakes can help clarify the origin of ecological traits typical of 'higher' snakes. We examined and dissected 360 museum specimens to obtain information on morphology, dietary habits, and reproduction of two subspecies of an African thread snake, Leptotyphlops s. scutifrons and L. s. conjunctus. These small (to 225 mm long), slender-bodied (body diameters < 5 mm) burrowing snakes are common throughout southern Africa. In both subspecies, females grow larger than males and have relatively shorter tails. Reproduction is seasonal, with vitellogenesis in spring (October), oviposition in summer (December-February), and hatching in autumn (April-May). Clutch sizes are small (1-3 eggs), and hatchling thread snakes are large relative to maternal body size. Despite the abundance of termites on the African continent, L. scutifrons feeds almost entirely on the larvae and pupae of small ants. Both races fed infrequently, and took large numbers of prey (up to 350 items) in a single meal. A shift from 'lizard-like' to 'snake-like' trophic biology is evident within the Scolecophidia: two species of North American thread snake feed frequently on a taxonomically diverse array of small prey; African L. scutifrons feed infrequently on small prey, but take large meals composed of numerous prey items; and one highly derived Melanesian typhlopid (Acutyphlops subocularis) feeds infrequently on large elongate prey. In contrast to popular theory, our data suggest that the evolutionary shift to infrequent feeding among snakes did not initially require a change from small to large prey.
Webb, J.K., Shine, R., Branch, W.R. & Harlow, P.S. 2000, 'Life-history strategies in basal snakes: Reproduction and dietary habits of the African thread snake Leptotyphlops scutifrons (Serpentes: Leptotyphlopidae)', Journal of Zoology, vol. 250, no. 3, pp. 321-327.
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Information on the biology of 'primitive' blind snakes can help clarify the origin of ecological traits typical of 'higher' snakes. We examined and dissected 360 museum specimens to obtain information on morphology, dietary habits, and reproduction of two subspecies of an African thread snake, Leptotyphlops s. scutifrons and L. s. conjunctus. These small (to 225 mm long), slender-bodied (body diameters < 5 mm) burrowing snakes are common throughout southern Africa. In both subspecies, females grow larger than males and have relatively shorter tails. Reproduction is seasonal, with vitellogenesis in spring (October), oviposition in summer (December-February), and hatching in autumn (April-May). Clutch sizes are small (1-3 eggs), and hatchling thread snakes are large relative to maternal body size. Despite the abundance of termites on the African continent, L. scutifrons feeds almost entirely on the larvae and pupae of small ants. Both races fed infrequently, and took large numbers of prey (up to 350 items) in a single meal. A shift from 'lizard-like' to 'snake-like' trophic biology is evident within the Scolecophidia: two species of North American thread snake feed frequently on a taxonomically diverse array of small prey; African L. scutifrons feed infrequently on small prey, but take large meals composed of numerous prey items; and one highly derived Melanesian typhlopid (Acutyphlops subocularis) feeds infrequently on large elongate prey. In contrast to popular theory, our data suggest that the evolutionary shift to infrequent feeding among snakes did not initially require a change from small to large prey.
Webb, J.K. & Shine, R. 1998, 'Using thermal ecology to predict retreat-site selection by an endangered snake species', Biological Conservation, vol. 86, no. 2, pp. 233-242.
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Many ectotherms spend long periods in retreat-sites, where thermal conditions may strongly influence key physiological or behavioural processes (e.g. locomotion, digestion, growth rates etc). Species that rely upon specific thermal regimes may be restric
Webb, J.K. & Shine, R. 1998, 'Ecological Characteristics Of A Threatened Snake Species, Hoplocephalus Bungaroides (serpentes, Elapidae)', Animal Conservation, vol. 1, no. 3, pp. 185-193.
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Species with ecological (habitat, dietary) specialization and low reproductive output may be at particular risk from anthropogenic habitat disturbance. We studied growth, reproduction and diet of the threatened broad-headed snake (Hoplocephalus bungaroid
Shine, R., Branch, W., Harlow, P. & Webb, J.K. 1998, 'Reproductive Biology And Food Habits Of Horned Adders, Bitis Caudalis (viperidae), From Southern Africa', Copeia, vol. 2, no. 2, pp. 391-401.
Kerned adders (Bitis caudalis) are small heavy-bodied viperid snakes widely dis tributed across a range of habitat types in southern Africa. Measurement and dissection of 580 preserved specimens in museum collections provided information on morpholopy, f
Shine, R., Webb, J.K., Fitzgerald, M. & Sumner, J. 1998, 'The Impact Of Bush-rock Removal On An Endangered Snake Species, Hoplocephalus Bungaroides (serpentes : Elapidae)', Wildlife Research, vol. 25, no. 3, pp. 285-295.
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We examined the impact of habitat degradation (removal of surface rocks) on an endangered snake species (Hoplocephalus bungaroides, Elapidae) at 23 sites in south-eastern Australia, by quantifying the impact of rock removal on (i) the availability of sui
Webb, J.K. & Shine, R. 1998, 'Thermoregulation by a nocturnal elapid snake (Hoplocephalus bungaroides) in southeastern Australia', Physiological And Biochemical Zoology, vol. 71, no. 6, pp. 680-692.
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Studies of reptilian thermoregulation have tended to focus on diurnal heliothermic taxa that display overt thermoregulatory behavior, with nocturnal reptiles attracting less attention. We studied thermoregulation by the broad-headed snake (Hoplocephalus bungaroides), a small (mean snout-vent length = 57 cm) nocturnal elapid that spends long periods sequestered in diurnal retreat sites. The snakes selected body temperatures of 28.1 degrees-31.1 degrees C in laboratory thermal gradients. Prey-capture ability (strike speed and accuracy) increased at higher body temperatures over the range 20 degrees-30 degrees C. Using temperature-sensitive radio transmitters, we obtained 7,801 body-temperature measurements of 19 free-ranging snakes. Information on operative environmental temperatures was obtained at the same time. From these data, we quantified the degree to which the snakes exploit the environmental thermal heterogeneity available to them (i.e., the time they spent within their setpoint range, relative to the total time that these body temperatures were available to them). Mean body temperatures (both diurnally and nocturnally) differed among seasons but not among different types of retreat sites. Inclement weather prevented snakes from attaining "preferred" body temperatures on 30% of days. However, even when preferred temperatures were available, the snakes exploited this opportunity for only 26% of the time: they remained within retreat sites and rarely emerged to bask. Nonetheless, judicious retreat-site selection resulted in snakes being within their set-point range for 60% of the time at the most crucial time of day (i.e., the 2-h period around dusk, when the opportunity to capture prey is highest).
Webb, J.K. & Shine, R. 1997, 'Out On A Limb: Conservation Implications Of Tree-hollow Use By A Threatened Snake Species (hoplocephalus Bungaroides: Serpentes, Elapidae)', Biological Conservation, vol. 81, no. 40940, pp. 21-33.
Habitat requirements of arboreal reptiles may determine their vulnerability to anthropogenic disturbance, but have attracted little research. We studied habitat use by the broad-headed snake Hoplocephalus bungaroides, a threatened species from southeaste
Webb, J.K. & Shine, R. 1997, 'A field study of spatial ecology and movements of a threatened snake species, Hoplocephalus bungaroides', Biological Conservation, vol. 82, no. 2, pp. 203-217.
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Information on movement patterns, home range sizes and site fidelity of endangered fauna may provide a basis for conservation planning (size and location of reserves; vulnerability to habitat fragmentation; feasibility of natural recolonisation of 'restored' habitats, etc.). To obtain such information, we surgically implanted miniature radio transmitters in 25 individual broad-headed snakes Hoplocephalus bungaroides, a small (mean snout-vent length = 57 cm, mean mass = 51 g) viviparous elapid snake reliant upon sandstone outcrops in southeastern Australia. We also carried out a mark-recapture study of this threatened species. Our telemetered snakes spent long periods of time sequestered inside retreat-sites (rocks, crevices, tree hollows) and thus were active on only 21% of days. Gravid females had small home ranges (mean size = 0.05 ha, convex polygon method) and remained near Cliffs during summer, whereas most males and non-gravid females moved long distances (up to 780m) away from cliff tops during summer and had larger home ranges (mean size=3.3 ha). Movements by the snakes were more frequent and extensive when they were in the woodland (mean interval between successive moves = 2.9 days; mean displacement per move = 159m) than when they were in the rock outcrops (means = 63 days, 37m). Home ranges were larger in summer than in spring, and were larger in 1994-95 than in other years. Home ranges of males showed little spatial or temporal overlap in spring, but females were found within the areas used by males. During summer there was little temporal or spatial overlap of home ranges of adults, which suggests that snakes may actively avoid conspecifics of either sex while foraging in the forest. Many adult snakes showed strong site fidelity, frequently returning to the same rocks where they were initially captured. Dispersal of juvenile snakes front their birth sites was relatively limited (maximum recorded distance = 375 m after 6 months).
Webb, J.K. & Shine, R. 1997, 'Out on a limb: Conservation implications of tree-hollow use by a threatened snake species (Hoplocephalus bungaroides: Serpentes, Elapidae)', BIOLOGICAL CONSERVATION, vol. 81, no. 1-2, pp. 21-33.
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Shine, R., Haagner, G., Branch, W., Harlow, P. & Webb, J.K. 1996, 'Natural History Of The African Shieldnose Snake Aspidelaps Scutatus (serpentes, Elapidae)', Journal Of Herpetology, vol. 30, no. 3, pp. 361-366.
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Examination and dissection of museum specimens, combined with observations of free-ranging and captive snakes, provided original data on morphology, sexual dimorphism, feeding habits, and reproductive biology of shieldnose snakes (Aspidelaps scutatus) fr
Shine, R., Harlow, P., Branch, W. & Webb, J.K. 1996, 'Life On The Lowest Branch: Sexual Dimorphism, Diet, And Reproductive Biology Of An African Twig Snake, Thelotornis Capensis (serpentes, Colubridae)', Copeia, vol. 2, no. 2, pp. 290-299.
Measurement and dissection of 144 twig snakes (Thelotornis capensis) from southern Africa provided data on morphology, sexual dimorphism, food habits, and reproductive biology of this species. Twig snakes are extremely elongate arboreal species that rema
Shine, R., Branch, W.R., Harlow, P.S. & Webb, J.K. 1996, 'Sexual dimorphism, reproductive biology, and food habits of two species of African filesnakes (Mehelya, Colubridae)', Journal Of Zoology, vol. 240, no. Part 2, pp. 327-340.
The ecology and general biology of African snakes remains virtually unstudied, even in highly distinctive species such as the filesnakes (genera Mehelya and Gonionotophis). Our measurements and dissections of preserved specimens provided information on body sizes, sexual dimorphism in size and bodily proportions, clutch sizes, and food habits of two Mehelya species. In both M. capensis and M. nyassae, females attain sexual maturity at the same size as conspecific males, but grow to much larger sizes. Mehelya capensis displays extreme differences in body shape between males and females at the same body length: females have longer and wider heads, thicker bodies, and larger eyes (relative to both head length and head width) than do conspecific males. Dimorphism in body proportions is less marked in M. nyassae. Female reproductive cycles are seasonal in M. capensis, and clutch sizes are larger in this species than in its smaller congener (5-11 eggs in M. capensis, 2-6 eggs in M. nyassae).
Webb, J.K. & Shine, R. 1994, 'Feeding-habits And Reproductive-biology Of Australian Pygopodid Lizards Of The Genus Aprasia', Copeia, vol. 2, no. 2, pp. 390-398.
We dissected 615 preserved specimens of eight species of wormlike burrowing pygopodid lizards of the genus Aprasia, to document the basic natural history of this poorly known Australian taxon. Females grow larger than males but are less common in museum
Webb, J.K. & Shine, R. 1993, 'Dietary Habits Of Australian Blindsnakes (typhlopidae)', Copeia, vol. 3, no. 3, pp. 762-770.
Dissection of 1423 specimens of 11 species of small fossorial Australasian blindsnakes (Ramphotyphlops) provided extensive information on dietary differences among species, on the seasonality of feeding, and on intra- and inter-specific correlations betw
Webb, J.K. & Shine, R. 1993, 'Prey-size selection, gape limitation and predator vulnerability in Australian blindsnakes (Typhlopidae)', Animal Behaviour, vol. 45, no. 6, pp. 1117-1126.
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Blindsnakes, Ramphotyphlops nigrescens, are small wormlike fossorial snakes that feed principally on the larvae and pupae of ants. Examination of stomach contents showed that larger blindsnakes consumed larger prey items than, and different prey species from, smaller blindsnakes. Only the largest snakes consumed brood of the large and formidable 'bulldog ants', Myrmecia. Three hypotheses for the causal basis of this size-related shift in dietary habits were tested. Observations on captive snakes suggested that they are gape-limited predators, and the prey items eaten by small snakes in the field are as large as they could physically ingest in the laboratory. Hence, the absence of large prey items from small snakes may be due simply to gape-limitation. However, medium-sized blindsnakes were capable of ingesting items larger than those that they take in the field. The absence of Myrmecia in the diets of these snakes is not due to prey choice (Myrmecia were readily eaten in the laboratory) or to an inability to locate or follow pheromonal trails of this ant genus, because all size classes of blindsnakes readily followed Myrmecia trails in the laboratory. Instead, the absence of Myrmecia from the diets of smaller snakes is probably due to the snakes' size-dependent vulnerability to nest defence by the bulldog ants. In laboratory encounters, Myrmecia workers were able to bite and sting (and eventually kill) small blindsnakes, but larger snakes were relatively invulnerable to attack.
Webb, J.K. & Shine, R. 1992, 'To Find An Ant - Trail-following In Australian Blindsnakes (typhlopidae)', Animal Behaviour, vol. 43, no. 6, pp. 941-948.
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Webb, J.K. & Shine, R. 1992, 'To find an ant: trail-following in Australian blindsnakes (Typhlopidae)', Animal Behaviour, vol. 43, no. PART 6, pp. 941-948.
The ability of small fossorial myrmecophagous Australian blindsnakes, Ramphotyphlops nigrescens, to follow scent trails was studied in the laboratory. Blindsnakes ignored trails of non-prey items (earthworms, isopods, termites) and control trails, but followed trails laid by four species of worker ants. Trails of Campanotus consobrinus and Iridomyrmex purpureus, two ant species that use well defined communal foraging trails, were readily followed by blindsnakes, as were trails of two species of Myrmecia that forage singly but are large and occur in large colonies (and, hence, may leave detectable trails in the field). Trails of two smaller solitary foraging ant species (Rhytidoponera enigmatica and R. metallica) were not followed, even though blindsnakes frequently consume the brood of these species in the wild. Hence, blindsnakes apparently use trail-following to locate some potential prey species, but rely on other cues to find nests of small solitary foraging ants. Blindsnakes followed week-old trails as well as day-old trails, but were apparently unable to follow trails left by single ants. These results reveal behavioural similarities between Australian blindsnakes and a previously studied American leptotyphlopid species, and suggest that chemoreception plays an important role in the foraging biology of these small fossorial snakes. &copy; 1992.
Shine, R. & Webb, J.K. 1990, 'Natural-history Of Australian Typhlopid Snakes', Journal Of Herpetology, vol. 24, no. 4, pp. 357-363.
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