Species Interactions Between the Plague Skink, Indigenous Skinks, and Invasive Mammals

Abstract

Plague skinks (Lampropholis delicata) were first introduced to New Zealand (the first incursion occurring in south Auckland) in the 1960s. The species was introduced from Australia, likely in a shipment of railway sleepers. Plague skinks have since spread across lower altitude regions of the North Island and the top of the South Island. Across this range, the species is sympatric with many native skink species, many of which are already under threat from habitat loss and predation by invasive mammals. There appears to be an overlap in niches between plague skinks and indigenous skink species and significant potential for competition. This research aimed to answer some of the questions about species interactions and how they are mediated by external factors such as food and shelter availability and the impacts of predation by invasive mammals. Furthermore, this research aimed to examine various capture methods to find a monitoring tool that could estimate plague skink populations and detect new incursions. Populations of copper, ornate, and moko skinks in the presence of a growing plague skink population were analysed alongside the effects of pest mammal eradication. It was found that despite the presence of plague skinks, native species were slowly recovering and that ornate skinks recovered faster than plague skink numbers could increase following the removal of invasive mammals. Laboratory studies of plague and copper skink behaviours showed marked differences in their habits, where plague skinks were far more active, and copper skinks spent most of their time hidden. Few interactions were observed between the species, likely because copper skinks were hidden for much of the time. Though copper skinks became slightly more active, there were no marked effects of varying plague skink densities. There were no effects of altering leaf litter cover. Finally, detection by hand-capture, pitfall traps, funnel traps, and artificial covers was compared. While hand-capture was the most successful method, the probability of detection was still very low, indicating that these methods would not be appropriate to detect plague skink incursions or monitor existing populations. As in previous research, no apparent indications of competition between plague skinks and select native species were observed in this research. Future research should focus on other mechanisms of potential competition, such as disproportionate predation of local invertebrate populations