From threatened to threatening: Impacts of a reintroduced predator on reintroduced prey

Despite the recent global increase in projects utilizing conservation fencing, reintroductions of predators to fenced conservation reserves are rare. Reintroducing threatened predators into closed ecosystems raises potential issues of overabundance, population viability and inbreeding. In particular, impacts to resident prey species are not well studied across predator reintroductions worldwide, in part due to the difficulties in measuring predator impacts without adequate control areas. Over the 4 years following release, we used multiple lines of evidence and a paired treatment and control area to assess the potential impact of a reintroduced threatened predator, the western quoll, on four reintroduced threatened mammal species in a fenced reserve. Diet analysis, radio-tracking and direct observation suggested that quolls killed and consumed all four reintroduced threatened native prey species, but two of these prey species (bettongs and bandicoots) were preferred prey. Abundance indices of these two prey species declined in parts of the reserve where quolls were present relative to control areas, yet local extinction did not occur. Quoll hunting behaviour suggested that these preferences may be driven, in part, by differences in the detectability and accessibility of similar-sized prey. Dietary selection for threatened prey was reduced at times when native rodents, a highly preferred prey species, were in high abundance. The presence of rodents, coupled with the quoll-exclusion control area and carcass dumps, may have protected reintroduced threatened prey from local extinction. Predator reintroductions to fenced reserves may help maintain ecosystem balance; however, predators may be incompatible with conservation of some threatened prey species unless alternative common prey are present or intensive management actions are implemented. Reintroducing threatened predators into closed ecosystems raises issues of impacts on resident prey species which are not well understood or measured. Over the 4 years following release, we used multiple lines of evidence to assess the potential impact of a reintroduced threatened predator, the western quoll, on four reintroduced threatened mammal species in a fenced reserve. Quolls consumed all four reintroduced prey species but demonstrated a preference for bettongs and bandicoots - which has implications for other reserves planning future reintroductions of western quolls across Australia.image