Discrimination of introduced predators by ontogenetically naïve prey scales with duration of shared evolutionary history

Hypotheses on the discrimination and recognition of predators by prey are divided as to whether the prey species' ability to recognize and avoid predators is proportionate to the duration of evolutionary exposure to specific predators or is a result of more generalized discrimination processes. Moreover, understanding of the timeframes necessary for prey species to maintain or acquire appropriate responses to introduced predators is poorly understood. We studied a population of wild, ontogenetically predator naïve greater bilbies, Macrotis lagotis, living within a large (60 km2) predator-free exclosure, to determine whether they modified their burrow-emergence behaviour in response to olfactory stimuli from introduced predators, dogs, Canis familiaris, and cats, Felis catus. Greater bilbies have shared over 3000 years of coevolutionary history with dogs but less than 200 years with cats. Bilbies spent more time only partially emerged (with at most head and shoulders out) as opposed to fully emerged (standing quadrupedally or bipedally) from their burrows when dog faeces were present, in comparison to faeces of cats, rabbits and an unscented control. Our results were consistent with the 'ghosts of predator past' hypothesis, which postulates that prey species' abilities to respond to the odours of predators scales with their period of coexistence. Our study supports the notion that introduced predators should be regarded as naturalized if prey possess an innate ability to detect their cues and respond accordingly.