Interference competition following a recent invasion of plague skinks (Lampropholis delicata) into a nationally critical native skink population

Abstract

Context Invasive species can threaten native species through exploitative and interference competition if they occupy similar ecological niches. The invasive plague skink (Lampropholis delicata) has been accidently introduced to New Zealand, Lord Howe Island, and the Hawaiian Islands. Resource usage overlaps between plague skinks and several New Zealand skinks, suggesting the potential for exploitative and interference competition. However, no competitive mechanism or population impact has been identified. In 2014–15, plague skinks colonised Bream Head Scenic Reserve, Northland, New Zealand, where they overlap in occupancy and habitat with the ‘Nationally Critical’ kakerakau skink (Oligosoma kakerakau). Aims We investigated intra- and interspecific interference competition between kakerakau and plague skinks in the wild. Methods We recorded naturally occurring encounters and quantified aggression at a short-lived resource (sun-basking sites). Key results Behavioural interactions were observed in 72% of all encounters with similar proportions of encounters resulting in agonistic interactions between intraspecific kakerakau skink encounters and interspecific kakerakau-plague encounters. Although kakerakau skinks and plague skinks reacted equally aggressively in an interspecific interaction, kakerakau skinks behaved significantly more aggressively in an interaction with a plague skink than with a conspecific. Juvenile kakerakau skinks were more likely than adults to exhibit submissive behaviours such as fleeing during interspecific interactions. Conclusions This is the first evidence of interference competition occurring between plague skinks and a native skink. Our study suggests that kakerakau skinks, particularly juveniles, may experience competitive exclusion at important resources. Implications Our findings indicate that plague skinks may pose a threat to native skink populations when habitat use overlaps.