Living in Patchy Habitats: Substrate Selection by Basking Sympatric Lizards in Contrasted Anthropogenic Habitats in Western France

Abstract

The influence of temperature on the physiological processes in reptiles is well known, for example growth, reproduction and muscular energy are all temperature dependent. However, there may be constraints on the ability of a reptile to harness thermal energy, particularly during cold seasons in the temperate zones. Substrate selection is a key factor in enhancing thermoregulation since it can enhance rate of heat uptake. For example, wood substrates are known to increase rates of heat gain in basking reptiles enabling earlier attainment of optimum body temperatures compared to other substrate types, which enables increased time available for other activities. In this paper we describe substrate use for basking in populations of Lacerta bilineata and Podarcis muralis in a hedgerow and a population of Podarcis muralis in a suburban garden in western France. The proportions of substrate used were compared against a null model of substrate availability. When different substrates were pooled based on material similarities both species were recorded in greater frequency on wood based materials in comparison to their availability compared to non-wood substrates. However at a finer level, in comparison to the null model of substrate availability (fallen tree branches, tree stumps, open ground etc), P. muralis showed strong substrate selection whereas L. bilineata did not depart significantly from the null model. We speculate that intra-specific aggression in L. bilineata was one possible cause of this result due to dominant individuals limiting access to prime basking sites in smaller or female lizards. Differences in communal basking between the two species supported this notion.