John Llewelyn

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Papers by John Llewelyn

Adaptation Pathways and Opportunities for the Wet Tropics NRM Cluster region: Volume 2. Infrastructure, Industry, Indigenous peoples, Social adaptation, Emerging planning frameworks, Evolving methodologies and Climate adaptation planning in practice.

by James Langston, Karen J Vella, John Llewelyn, and Gary Searle

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Thermal regimes and diel activity patterns of four species of small elapid snakes from south-eastern Australia

by Jonathan Webb and John Llewelyn

Australian Journal of Zoology, 2005

Two of the most basic biological attributes for any ectothermic animal are the times of day that ... more 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 31.3°C during the day and 33.2°C at night). The other three taxagolden-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 (18.1-23.4°C). Thus, mean selected body temperatures differ substantially among sympatric elapid species in south-eastern Australia and are correlated with times of activity.

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Do evolutionary constraints on thermal performance manifest at different organizational scales?

by John Llewelyn and S. Macdonald

Journal of evolutionary biology, 2014

The two foremost hypotheses on the evolutionary constraints on an organism's thermal sensitiv... more The two foremost hypotheses on the evolutionary constraints on an organism's thermal sensitivity—the hotter-is-better expectation, and the specialist-generalist trade-off—have received mixed support from empirical studies testing for their existence. Could these conflicting results reflect confusion regarding the organizational level (i.e. species > population > individual) at which these constraints should manifest? We propose that these evolutionary constraints should manifest at different organizational levels because of differences in their underlying causes and requirements. The hotter-is-better expectation should only manifest across separate evolutionary units (e.g. species, populations), and not within populations. The specialist-generalist trade-off, by contrast, should manifest within as well as between separate evolutionary units. We measured the thermal sensitivity of sprint performance for 440 rainforest sun skinks (Lampropholis coggeri) representing 10 popula...

After the crash: How do predators adjust following the invasion of a novel toxic prey type?

by Lin Schwarzkopf and John Llewelyn

Austral Ecology, 2014

The ability of a native predator to adjust to a dangerously toxic invasive species is key to avoi... more The ability of a native predator to adjust to a dangerously toxic invasive species is key to avoiding an ongoing suppression of the predator's population and the trophic cascade of effects that can result. Many species of anurophagous predators have suffered population declines due to the cane toad's (Rhinella marina: Bufonidae) invasion of Australia; these predators can be fatally poisoned from attempting to consume the toxic toad.We studied one such toad-vulnerable predator, the yellow-spotted monitor (Varanus panoptes: Varanidae), testing whether changes to the predator's feeding behaviour could explain how the species persists following toad invasion. Wild, free-roaming lizards from (1) toad-naïve and (2) toad-exposed populations were offered non-toxic native frogs and slightly toxic cane toads (with parotoid glands removed) in standardized feeding trials. Toad-naïve lizards readily consumed both frogs and toads, with some lizards displaying overt signs of illness after consuming toads. In contrast, lizards from toad-exposed populations consumed frogs but avoided toads. Repeated encounters with toads did not modify feeding responses by lizards from the toad-naïve populations, suggesting that aversion learning is limited (but may nonetheless occur). Our results suggest that this vulnerable predator can adjust to toad invasion by developing an aversion to feeding on the toxic invader, but it remains unclear as to whether the lizard's toad-aversion arises via adaptation or learning.

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Chemoreception and mating behaviour of a tropical Australian skink

by John Llewelyn and Conrad Hoskin

acta ethologica, 2015

Ontogenetic shifts in a prey’s chemical defences influence feeding responses of a snake predator

by Ross Alford, Lin Schwarzkopf, and John Llewelyn

Oecologia, 2012

Foraging theory suggests that predator responses to potential prey should be influenced by prey c... more Foraging theory suggests that predator responses to potential prey should be influenced by prey chemical defences, but the effects of ontogenetic variation in such defences on prey vulnerability to predators remain unclear. Cane toads (Rhinella marina) are toxic to anurophagous snakes, including the keelback (Tropidonophis mairii, a natricine colubrid that occurs within the toads' invasive range in Australia). Toxin levels and diversity change through toad ontogeny, decreasing from the egg stage to metamorphosis, then increasing in postmetamorphic toads. If the toxin content of a prey item influences predator responses, we predict that keelbacks should exhibit selective predation on toads close to metamorphosis. The results of our laboratory trials on adult (field-collected, and thus toad-experienced) and hatchling (laboratory-incubated, and thus toad-naive) keelbacks supported this prediction. The snakes selectively consumed later-stage rather than earlierstage tadpoles, and earlier-stage rather than later-stage metamorphs. Our data are thus consistent with the hypothesis that ontogenetic changes in toxin content can affect individuals' vulnerability to predation.

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Locomotor performance in an invasive species: cane toads from the invasion front have greater endurance, but not speed, compared to conspecifics from a long-colonised area

by Ross Alford, John Llewelyn, and Lin Schwarzkopf

Oecologia, 2010

Cane toads (Bufo marinus) are now moving about 5 times faster through tropical Australia than the... more Cane toads (Bufo marinus) are now moving about 5 times faster through tropical Australia than they did a half-century ago, during the early phases of toad invasion. Radio-tracking has revealed higher daily rates of displacement by toads at the invasion front compared to those from long-colonised areas: toads from frontal populations follow straighter paths, move more often, and move further per displacement than do toads from older (longestablished) populations. Are these higher movement rates of invasion-front toads associated with modified locomotor performance (e.g. speed, endurance)? In an outdoor raceway, toads collected from the invasion front had similar speeds, but threefold greater endurance, compared to conspecifics collected from a long-established population. Thus, increased daily displacement in invasion-front toads does not appear to be driven by changes in locomotor speed. Instead, increased dispersal is associated with higher endurance, suggesting that invasion-front toads tend to spend more time moving than do their less dispersive conspecifics. Whether this increased endurance is a cause or consequence of behavioural shifts associated with rapid dispersal is unclear. Nonetheless, shifts in endurance between frontal and core populations of this invasive species point to the complex panoply of traits affected by selection for increased dispersal ability on expanding population fronts.

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Adaptation or preadaptation: why are keelback snakes (Tropidonophis mairii) less vulnerable to invasive cane toads (Bufo marinus) than are other Australian snakes?

by Ross Alford, John Llewelyn, and Lin Schwarzkopf

Evolutionary Ecology, 2011

Biological invasions can expose native predators to novel prey which may be less nutritious or de... more Biological invasions can expose native predators to novel prey which may be less nutritious or detrimental to predators. The introduction and subsequent spread of cane toads (Bufo marinus) through Australia has killed many anuran-eating snakes unable to survive the toad's toxins. However, one native species, the keelback snake (Tropidonophis mairii), is relatively resistant to toad toxins and remains common in toad-infested areas. Is the keelback's ability to coexist with toads a function of its ancestral Asian origins, or a consequence of rapid adaptation since cane toads arrived in Australia? And does the snake's feeding preference for frogs rather than toads reflect an innate or learned behaviour? We compared keelback populations long sympatric with toads with a population that has encountered toads only recently. Unlike toad-vulnerable snake species, sympatry with toads has not affected keelback toxin tolerances or feeding responses: T. mairii from toadsympatric and toad-naïve populations show a similar sensitivity to toad toxin, and a similar innate preference for frogs rather than toads. Feeding responses of neonatal keelbacks demonstrate that learning plays little or no role in the snake's aversion to toads. Thus, behavioural aversion to B. marinus as prey, and physiological tolerance to toad toxins are pre-existing innate characteristics of Australian keelbacks rather than adaptations to the cane toad's invasion of Australia. Such traits were most likely inherited from ancestral keelbacks that adapted to the presence of bufonids in Asia. Our results suggest that the impact of invasive species on native taxa may be strongly influenced by the biogeographic histories of the species involved.

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Sublethal costs associated with the consumption of toxic prey by snakes

Austral Ecology, 2009

Costs of plant defences to herbivores have been extensively studied, but costs of chemical defenc... more Costs of plant defences to herbivores have been extensively studied, but costs of chemical defences to carnivores are less well understood. We examine the costs to Australian keelback snakes (Tropidonophis mairii, Gray 1841) of consuming cane toads (Bufo [Rhinella] marinus Linnaeus 1758). Cane toads (an invasive species in Australia) are highly toxic. Although keelbacks can consume toads without dying (unlike most Australian snakes), we show that cane toads are poor quality prey for keelbacks. Toads are of low net nutritional value, take longer to consume than do native frogs and reduce the snake's locomotor performance for up to 6 h after ingestion of a meal. These latter effects may increase a snake's vulnerability to predation. Nutritional content of vertebrate prey is not the only factor driving the evolution of foraging behaviour; other more subtle costs, such as risk of predation, may be widespread.

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Behavioural responses of carnivorous marsupials (Planigale maculata) to toxic invasive cane toads (Bufo marinus)

by Ross Alford, John Llewelyn, Lin Schwarzkopf, and Jonathan Webb

Austral Ecology, 2009

The arrival of a toxic invasive species may impose selection on local predators to avoid consumin... more 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-naïve 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-naïve 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.

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Something different for dinner? Responses of a native Australian predator (the keelback snake) to an invasive prey species (the cane toad)

by Lin Schwarzkopf, Ross Alford, and John Llewelyn

Biological Invasions, 2010

Predictions from foraging theory suggest that the probability a native predator will incorporate ... more Predictions from foraging theory suggest that the probability a native predator will incorporate a novel type of prey (such as an invasive species) into its diet depends upon the potential benefits (e.g., nutrient input) vs. costs (e.g., handling time) of ingesting it. Cane toads (Bufo marinus) were introduced to Australia in 1935 and are highly toxic to many frog-eating snakes, thus there was strong selection to delete toads from the diet of these species. What has happened, however, to the feeding responses of an Australian snake species that is able to consume toads without dying? Our field surveys in northeastern Queensland show that, despite their high tolerance to toad toxins (compared to other native snakes), keelbacks (Tropidonophis mairii) feed primarily on native frogs rather than cane toads. This pattern occurs because the snakes show active prey preferences; even under standardized conditions in the laboratory, snakes are more likely to consume frogs than toads. When they are force-fed, snakes frequently regurgitate toads but not frogs. Thus, despite the high availability of the abundant toads, these invasive anurans are largely avoided as prey. This probably occurs because consumption of toads, although not lethal to keelbacks, causes significant sublethal effects and confers little nutritional benefit. Hence, keelback populations are not threatened by toad invasion, but neither do the snakes benefit substantially from the availability of a new type of potential prey.

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