INTRODUCTION
Geographical history and stochastic occurrences play a critical role in the species composition of islands (Diamond 1975, Thornton 1996). Islands usually support fewer species than mainlands (MacArthur & Wilson 1967; e.g., butterflies: Dapporto &Dennis 2009). Intrinsic dispersal and competitive ability of species, and the environmental characteristics of is-lands (e.g. climate, geography, humidity) determine the probability that species colonize and persist. It has often been postulated that lower species richness on islands goes along with broader niches (niche expansion) and increased density (density compensa-tion, e.g. MacArthur et al. 1972). “Density compen-sation” describes the constant overall abundance of
ecologically comparable species (ecospecies) on is-lands, despite lower species r
ichness (Gonzalez &Loreau 2009).