Effects of forest fragmentation on the distribution of the lizard Psammodromus algirus

This study reports the population responses of the lizard Psammodromus algirus to forest fragmentation by comparing its distribution in two contrasting situations of habitat conservation: a well connected mosaic landscape (forest patches larger than 2000 ha and/or connected by corridors that prevent their isolation), and an archipelago of forest remnants embedded within a matrix of cereal fields. The frequency of occurrence of P. algirus was larger in the unfragmented habitats (14 out of 19 censused plots) than in the fragments (two out of of 21 wood-lots). Vegetation structure was a good predictor of lizard occurrence under conditions of no fragmentation, but not in the fragments, where high plant cover seemed a necessary, but insufficient, condition for the survival of lizard populations, and where remnant size was the only variable that differed significantly between wood-lots with and without lizards. Historical fragmentation of the habitat is also crucial for understanding the current distribution of lizards, as shown by their absence from a large forest that was highly fragmented in the past but which has been regenerating for decades. It is hypothesized that the combined effects of fragmentation and predation in small remnants have led to the extinction of P. algirus in fragments smaller than c. 90 ha, recolonization being prevented by the very limited dispersal abilities of these forest lizards.