Moving to suburbia: ontogenetic and evolutionary consequences of life on predator-free islands


  • Daniel T. Blumstein

    1. Department of Organismic Biology, Ecology and Evolution, University of California, Los Angeles, CA, USA, and The Cooperative Research Centre for the Conservation and Management of Marsupials, Macquarie University, Sydney, Australia
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Daniel T. Blumstein, Department of Organismic Biology, Ecology, and Evolution, 621 Charles E. Young Drive South, University of California, Los Angeles, CA 90095-1606, USA. E-mail:



Many species find themselves isolated from the predators with which they evolved. This situation commonly occurs with island biota, and is similar to moving from the dangerous inner-city to the suburbs. Economic thinking tells us that we should expect costly antipredator behaviour to be lost if it is no longer beneficial. The loss of antipredator behaviour has important consequences for those seeking to translocate or reintroduce individuals from predator-free islands back to the predator-rich mainland, but we have neither a detailed understanding of the mechanisms of loss nor information on the time course of relaxed selection. Some antipredator behaviours are experience-dependent: experience with predators is required for their proper performance. In these cases, antipredator behaviour is lost after only a single generation of isolation, but it should be able to be regained following exposure to predators. Other behaviours may be more `hard-wired'. The evolutionary loss of antipredator behaviour may occur over as few as several generations, but behaviours may also persist for many thousands of years of predator-free living.


Australia and New Zealand.


I discuss the results of a series of studies designed to document the mechanisms and time course of relaxed selection for antipredator behaviour in macropodid marsupials. Controlled studies of visual, acoustic and olfactory predator recognition, as well as field studies of antipredator vigilance focused on several species of kangaroos and wallabies.


Visual predator recognition may be retained following 9500 years of relaxed selection, but olfactory and acoustic predator recognition may have to be learned. Insular populations allow humans to approach closer before fleeing than mainland animals. Insular species may retain `group size effects' – the ability to seek safety in numbers – when they are exposed to any predators.

Main conclusions

I suggest that the presence of any predators may be an important factor in maintaining functional antipredator behaviour. Managers should pay particular attention as to the source and evolutionary history of their population when planning translocations or reintroductions.