University of Tasmania, Australia

Non-lethal effects of predation

There is emerging evidence that predation comprises multiple levels of effects on prey populations. These can be divided into 1) direct (lethal) effects, 2) risk effects, and 3) secondary effects. Risk effects include changes in vigilance and habitat use resulting from predator avoidance behaviour, which can result in reduced survival, growth or reproduction. Recent studies have shown that these risk factors can influence prey dynamics at least as much as direct effects. Secondary effects of predation occur when the loss of the killed individual impacts the remaining individuals. For example, stable social relationships moderate stress responses, immune function and health, and even rate of reproduction. This effect level has been the least studied, and has yet to be incorporated into a model of top-down effects.

In Australia, introduced predators represent a major conservation threat to threatened species survival, and an important limiting factor. Furthermore, the factors leading to the failure of translocations and reintroductions are not clear, often transcending direct predation effects. In some populations, reproduction is inexplicably low. Some recent studies have suggested greater social complexity than previously thought. Therefore, it seems likely that predation may effect populations beyond the direct lethal effects.