Implementation of a long-term monitoring program of the ocellated lizard (Timon lepidus) population on Oleron Island

Abstract

AbstractThe ocellated lizard Timon lepidus (Sauria; Lacertidae) has declined throughout most of its range. Habitat fragmentation and habitat loss seem to be mainly responsible for the species' decline. The ocellated lizard population of Oleron Island, confined to a longshore dune of 140 ha, is the subject of a long-term monitoring study established in 2007. The monitoring method consists of 70 plots (50 × 50 m) randomly placed within a study area divided into six distinct zones. Three surveys were conducted in the study area over the spring season of 2007. During each survey, we counted the individuals in each plot. These counts were analyzed with the PRESENCE 2.0 and the R package Unmarked software using two different modeling approaches, the 'site-occupancy model' and the 'N-mixture model'. Estimates resulting from our analyses indicated the proportion of occupied plots to be 0.76. Our results indicated that the ocellated lizard has a highly heterogeneous distribution on Oleron Island, with parts of the dune sheltering clusters of lizards, and other areas totally unoccupied. The population size was estimated to be 516 individuals (95% CI 248-783). The relative abundance of ocellated lizards on the island can be principally explained by the presence of permanent shelters (used both during winter and the lizards' active period), including rabbit and rodent burrows and artificial shelters. This monitoring survey will be replicated every three years to enable us to calculate the species' colonization and local extinction probabilities. These results will help in evaluating and guiding management and conservation measures.