Correlated recovery of five lizard populations following eradication of invasive mammals

Abstract

Many conservation decisions rely on the assumption that multiple populations will respond similarly to management. However, few attempts have been made to evaluate indicators of population trends (i.e. population indicator species). Eradication of introduced mammals from offshore islands is a commonly used management technique for conservation of native taxa in New Zealand. Pacific rats and rabbits were eradicated from Korapuki Island in 1986/1987 enabling population recovery of native species that had been suppressed by predation or competition. However, the degree to which species’ responses were correlated has not been evaluated. We investigated correlations among lizard population trends on Korapuki Island as a test of the population indicator species concept. Our dataset consisted of captures of the five resident lizard species (three skinks, two geckos) from biannual pitfall trapping over a 10 year period (1986–1995) immediately following rodent eradication. We used a Bayesian modelling approach to examine correlations in population trends (based on mean annual counts) between species. Population trends were positively correlated for all species pairs (substantively for 90 % of pairs) and we detected no negative correlations. Systematic searches for single lizard species may indicate correlated recovery of lizard populations following rodent eradication and provide a cost-effective alternative to traditional ‘whole community’ monitoring. Our findings support evidence-based use of the population indicator species concept in cases where a shared ecological driver can be identified.