Predators learning to avoid toxic invasive prey: a study on individual variation among free-ranging lizards

Within all wild populations, individuals vary in ways that affect their vulnerability to threatening processes. Understanding that variation may clarify mechanisms of population persistence and/or evolution. In Australia, Yellow-spotted Monitors (Varanus panoptes), decline by >90% when toxic Cane Toads (Rhinella marina) invade an area. Taste-aversion training (exposing animals to nonlethal toads) can buffer impacts; but does pre-existing behavioural variation also influence survival? An individual’s fate can be predicted from its behaviour during aversion-training trials. Lizards presented with small toads either consumed them, rejected them, or fled. When Cane Toads invaded our study site, mortality was lower in lizards that ‘consumed’ (aversion-trained) than in those that ‘fled’ (untrained), but even lower in lizards that ‘rejected’ toads outright. Thus, animals reluctant to consume toads in trials survived despite never being aversion-trained. In this system, lizard vulnerability is driven by boldness, behavioural responses to novel prey types, and the opportunity to learn aversion.