Designer prey: Can controlled predation accelerate selection for anti-predator traits in naïve populations?

Prey naïveté is thought to be a significant factor contributing to the failure of native prey to re-establish in the presence of introduced predators. We tested whether exposing naïve prey to low levels of in situ predation pressure from introduced predators could cause accelerated selection for certain physical or behaviour traits. Such selection could improve the chance of future co-existence between introduced predators and native prey. In 2014, we reintroduced 352 burrowing bettongs (Bettongia lesueur) into a 26 km2 fenced paddock where predation levels could be carefully controlled. Four feral cats (Felis catus) were introduced to the paddock several months after bettong reintroduction and predation events were subsequently recorded. We measured a suite of physical and behavioural traits on the bettongs prior to release and compared these between individuals that survived or were assumed to have died. Population level parameters were also compared between the reintroduced population and the predator-free source population. No a priori measured physical or behavioural traits were significant predictors of individual survival after release and the high survival rate of radio-collared bettongs and the positive population growth rate suggests that the predation pressure from the introduced feral cats may not have been sufficiently high to cause strong selection over a short time period. However, population level comparisons found cat-exposed male bettongs had significantly longer hind feet than the source population at 18-22 months after release. Hind foot length was consistently longer in both older released animals and younger recruits and thus may be an indicator of selection and/or phenotypic change in response to the presence of predators. Our study suggests that predation may cause phenotypic change over short time periods but that higher cat predation pressure may be required to enable the benefits of accelerated natural selection to be adequately assessed.