Shifts in the foraging tactics of crocodiles following invasion by toxic prey

Richard Shine,Ruchira Somaweera,Abhilasha Aiyer,Tina Bell,Georgia Ward-Fear

doi:10.1038/s41598-021-03629-6

Richard Shine, Ruchira Somaweera + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-03629-6

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Abstract

Biological invasions can modify the behaviour of vulnerable native species in subtle ways. For example, native predators may learn or evolve to reduce foraging in conditions (habitats, times of day) that expose them to a toxic invasive species. In tropical Australia, freshwater crocodiles (Crocodylus johnstoni) are often fatally poisoned when they ingest invasive cane toads (Rhinella marina). The risk may be greatest if toads are seized on land, where a predator cannot wash away the toxins before they are absorbed into its bloodstream. Hence, toad invasion might induce crocodiles to forage in aquatic habitats only, foregoing terrestrial hunting. To test this idea, we conducted standardised trials of bait presentation to free-ranging crocodiles in sites with and without invasive toads. As anticipated, crocodiles rapidly learned to avoid consuming toads, and shifted to almost exclusively aquatic foraging.

Highlights

Biological invasions can modify the behaviour of vulnerable native species in subtle ways
Invasive species can have catastrophic impacts on native wildlife, and in doing so, can induce changes that increase the ability of the native species to tolerate the presence of the invader Even if population declines are modest, the arrival of an invasive species may induce adaptive shifts in the biology of a native s pecies[3]
The spread of cane toads (Rhinella marina) through Australia has led to the fatal poisoning of many predators that ingest this toxic a mphibian[7,8,9]

Summary

Introduction

Biological invasions can modify the behaviour of vulnerable native species in subtle ways. Aquatic predation might buffer amphibious predators against toad-induced poisoning This hypothesis fits with other situations where animals (mostly mammals) employ behavioural mechanisms akin to ‘prey washing’, which enable them to consume toxic p rey[16]. We can test this idea in crocodiles by quantifying foraging locations of individuals in sites with and without cane toads (i.e., behind the toad invasion front, versus in advance of the invasion front). We predict that terrestrial foraging will decrease in frequency after toads have invaded, for two potential reasons: (a) natural selection, if there is a genetic basis to behaviour or foraging-site choice, and (b) learning, if a crocodile with a non-fatal experience when foraging on land thereafter shifts to predominantly aquatic foraging. To test our prediction we deployed baits in a standardised fashion to Scientific Reports | (2022) 12:1267

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