I don’t like crickets, I love them: invertebrates are an important prey source for varanid lizards

Cross, S.L., Craig, M.D., Tomlinson, S. and Bateman, P.W. (2020), I don’t like crickets, I love them: invertebrates are an important prey source for varanid lizards. Journal of Zoology, vol. 310, pp. 323-333. https://doi.org/10.1111/jzo.12750

Arid habitats have low and unpredictable rainfall, and as a result tend to be low productivity ecosystems and present exceptionally challenging conditions for animals. High order mammalian predators tend to be constrained in arid habitats, largely due to a restricted availability of vertebrate prey items, yet such habitats often support numerous large, carnivorous reptiles. In arid Australia, varanids are often the high order predators, occurring at relatively high species richness, raising the question of how such species can thrive in low productivity ecosystems. Diet is a fundamental component of an animal’s ecology, and understanding feeding ecology is important to understand how populations can persist and thrive in these habitats.

The black-headed monitor (Varanus tristis), Gould’s goanna (Varanus gouldii), and the yellow spotted monitor (Varanus panoptes) are common throughout the arid Mid West region of Western Australia and co-exist sympatrically across the region. Habitats of each species overlap extensively, however V. tristis are primarily arboreal, and V. gouldii and V. panoptes primarily terrestrial. In our study, we investigated the diet of V. tristis, V. gouldii, and V. panoptes specimens collected from the Mid West region of Western Australia, to understand how large co-existing ectothermic predators can persist in arid habitats.

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A yellow spotted monitor (Varanus panoptes) foraging. Photographed by Sophie Cross 

All three Varanus species had broad, generalist diets, with the diet of each species overlapping extensively. Invertebrates, particularly Orthoptera (crickets and grasshoppers), were key to the diet of all three species. Although providing a lower energy food source per individual than vertebrate prey items, invertebrates occur at relatively high abundance within arid habitats. Vertebrates tend to be constrained in hot, low productivity habitats, and we recorded vertebrate prey infrequently in each of our three species. The success of the Varanus in arid Australia is likely attributed to their ability to survive on infrequent feeds and invertebrate prey items, in addition to aestivating in unfavourable conditions. Understanding diet is key to determining how animals can persist in resource-limiting environments. 

Sophie Cross

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