Habitat diversity associated with island size and environmental filtering control the species richness of rock-savanna plants in neotropical inselbergs

Disentangling the multiple factors controlling species diversity is a major challenge in ecology. Island biogeography and environmental filtering are two influential theories emphasizing respectively island size and isolation, and the abiotic environment, as key drivers of species richness. However, few attempts have been made to quantify their relative importance and investigate their mechanistic basis. Here, we applied structural equation modelling, a powerful method allowing test of complex hypotheses involving multiple and indirect effects, on an island-like system of 22 French Guianan neotropical inselbergs covered with rock-savanna. We separated the effects of size (rock-savanna area), isolation (density of surrounding inselbergs), environmental filtering (rainfall, altitude) and dispersal filtering (forest-matrix openness) on the species richness of all plants and of various ecological groups (terrestrial versus epiphytic, small-scale versus large-scale dispersal species). We sho...