Increasing Dietary Breadth Through Allometry: Bite Forces in Sympatric Australian Skinks

Ecomechanical measures of performance such as bite force may function as an indirect measure of niche. This study proposes that allometric changes in performance may contribute to niche separation, especially in a group where the specific mechanism(s) remains unclear. We surveyed the bite force and morphology of 5 wild caught, sympatric skink species in the Kimberley region of Western Australia. Skinks were collected from trapline fences, weighed, photographed, and maximum bite force was measured with a piezoresistive force sensor. Morphological metrics were derived from photographs of the dorsum. Normalized morphological traits indicate interspecific variability in form, particularly in forelimb length, which may be a result of habitat separation. Bite force showed strong, significantly positive, allometric scaling against most morphological traits. Tail length was the only morphological trait that scaled isometrically. Allometric changes in bite force may increase dietary breadth, allowing larger skinks to supplement their diet with larger, more durable prey. This study reveals that ecologically relevant traits may be explained by allometric differences coupled with size variation. Future work should focus on (1) an increase in sample size, (2) long-term measurement of diet selection, and (3) accessibility of prey items to our focal animals

Dichotomies in perceived predation risk of drinking wallabies in response to predatory crocodiles

Most advances in our understanding of predation risk involve foraging animals, yet animals also trade off predation risk with other essential activities. Drinking under the risk of predation may elicit similar prey behaviours to those in foraging animals, but has been little studied. Agile wallabies, Macropus agilis, manipulate their environment by excavating drinking holes just out of reach of predatory saltwater crocodiles. Paradoxically, however, some wallabies drink from the river's edge despite the immediate availability of the lower-risk drinking holes. We studied the behaviour of wallabies with multiple drinking options to test a series of predictions for animals drinking under the risk of predation. More wallabies drank during the day than at night, regardless of drinking site. However, night-drinking wallabies were much more likely to use the excavated holes than the 'riskier' river. This spatiotemporal dichotomy in perceived predation risk may reflect a mismatch in nocturnal sensory capabilities between predator and prey, and would provide sufficient motivation for wallabies to create low-risk drinking holes. Drinking duration, our surrogate for harvest, was not influenced by drinking site type (hole versus river), drinking time or social context (solitary versus group), suggesting that some animals may not forego drinking during high-risk periods, as predicted and observed for some foraging animals. Compared to wallabies in groups, solitary wallabies were less likely to drink from the river, especially at night, and were more vigilant. Although evidence is limited, our research suggests that vigilance may be ineffective for nocturnally drinking wallabies in the face of this concealed, ambush predator

Conceptual model for thermal limits on the distribution of reptiles

Recent climate change has re-invigorated scientific interest in the dynamics of geographic distributions of organisms. Climate responses and their biogeographical ramifications can be predicted indirectly by studying variation in fitness-related traits across environmental gradients in wide-ranging species. We review evidence for such variation in reptiles. Clinal variation in seasonal timing (onset) of nesting is common but may offer only minor compensation. In contrast, clinal variation in nesting behavior in two wide-ranging species suggests that reptiles can use nest site choice to counter climate differences. We suggest that when range boundaries located at climate extremes are determined by thermal conditions of embryos (vs. the adult stage) they cannot be predicted by the combination of environmental temperatures and thermal tolerances of embryos alone. We propose that nest site choice can reduce or eliminate the environmental variation that would be experienced by embryos in nests selected randomly with respect to temperature or factors influencing temperature. We also hypothesize that this compensation is limited at climate extremes; when temperatures are too cold for behavioral compensation (e.g., due to lack of suitably warm nest sites), reptiles can only invade colder climates by evolving viviparity. Animals with temperature-dependent sex determination (TSD) are more vulnerable to climate change than those with genetic sex determination (GSD) because the complete production of one sex in TSD species would occur before complete embryonic failure in GSD species. Collectively, research on reptiles suggests that range boundaries at climate extremes are determined by: (1) thermal limits and compensatory thermoregulation of free-living adults; (2) thermal limits of embryos; (3) the extent of compensatory nest site choice behavior; (4) mode of sex determination; and in cold climates (5) reproductive mode (oviparity vs. viviparity)

Biological control of the cane toad in Australia: A review

The marine toad Bufo marinus is native to northern South America, parts of Central America and Southern Texas. It was deliberately introduced into Australia's tropical north-east in 1935 in an unsuccessful attempt to control the cane beetle, a damaging insect pest of sugarcane crops. The toads quickly established in the new environment and began to spread. Today, they inhabit most of the Australian tropics and sub-tropics and have reached Western Australia. Models predict that global warming will enable the toads to extend their range further south. They cause severe environmental impacts, as all life stages of B. marinus contain bufadienolides, alkaloid substances toxic to vertebrates, resulting in death of the predators ingesting it. The continental scale of this biological invasion in combination with the remoteness of the areas affected, poses a specific set of challenges to potential control approaches for cane toads. This review covers different biocontrol strategies pursued over the past 8 years, with particular focus on an immunological approach aiming at the disruption of toad metamorphosis. So far, research efforts have failed to produce a tool for large-scale reduction of toad populations. Considerations of future research priorities and efforts are also discussed