Inverse relation of survival of lizards with island size and avifaunal richness

Abstract

SMALL islands have fewer species than larger islands or mainlands, and the number of species of very large predators, for example raptorial birds, may be disproportionately lower^1,2. This suggests the reasonable but largely untested idea that predation is less important as a determinant of population structure on small islands than on large islands or mainlands, particularly for relatively large potential prey such as songbirds and lizards^3–10. We have compared the survival of three species of the lizard Anolis on two islands differing in size and number of predatory bird species. We report here that annual survival in sites identical in diurnal lizard species and nearly so in vegetation structure is smaller, and usually substantially so, on the larger island. In one species, the size distribution of males parallels this difference in survival: lizards are smaller where survival is lower. Sexual differences in survival between the two islands are especially marked in an intensely territorial, polygamous species.