Impacts of introduced European hedgehogs on endemic skinks and weta in tussock grassland

Abstract

Context Control of introduced pest species is based on the premise that there is a relationship between pest abundance and impact, but this relationship is rarely defined. Aim We investigated the impacts of introduced European hedgehogs (Erinaceus europaeus) on two species of small endemic skink (Oligosoma spp.) and flightless, nocturnal endemic orthopteran ground weta (Hemiandrus spp.), using an enclosure-based experimental manipulation of hedgehog density in tussock grasslands in the South Island of New Zealand. Methods We used capture–mark–recapture methods to estimate the densities of skinks before and after exposure to a range of hedgehog densities over a 3-month period and also compared changes in indices of abundance of skink demographic groups and ground weta. Key results Faecal analysis confirmed that hedgehogs consumed skinks and invertebrates in the enclosures. The proportional change between capture sessions in numbers of captured juvenile McCann’s skinks (O. maccanni) declined with increasing hedgehog density. Similarly, the proportional change in the numbers of ground weta encountered in pitfall traps showed a highly significant negative relationship with increasing hedgehog density. Total species abundances and numbers in other demographic skink groups did not change significantly in relation to hedgehog density. For overall skink abundance estimates, there was an apparent trend suggesting that changes in abundance were more negative with increasing hedgehog density, but this did not reach statistical significance for either skink species. Conclusions Our results confirmed that hedgehogs are important predators of small native fauna, but suggested that highly abundant prey populations may be buffered against significant impacts. Implications Less abundant prey and some demographic groups within populations, however, may be at significant risk from hedgehog predation.