A comparative study of clutch size, range size, and the conservation status of island vs. mainland lacertid lizards

Abstract

Whereas the range size of endangered species is undoubtfuly useful to predict risk of extinction, the role of their life-history characteristics is much less clear, and their effects may depend on the nature of the threatening factors. Such factors, for instance, are known to be different on islands and on the mainland. We used phylogenetically based statistical analyses to study the relationships among conservation status, insularity, range size, and life-history traits in a clade of Western Palaearctic lacertids including insular and continental species. These lizards are ecologically similar, but they show wide variation in life-history traits and vulnerability to extinction. Insular species of a given size had smaller clutches than mainland ones. Degree of threat was best predicted by a logistic regression including range size, insularity, clutch size, and the insularity × clutch size interaction. On the mainland, but not on islands, threatened species had smaller clutches than non-threatened ones. On islands, small clutch size is probably an adaptive trait, and it might predispose certain species to extinction, but the intrinsic characteristics of such species remain unclear. However, small clutch size was a good predictor of extinction risk on the mainland, having evolved most frequently in late maturing species from montane habitats in which climatic conditions limit their reproductive output and increase their vulnerability to stochastic hazards or habitat fragmentation.