A niche-based theory of Island Biogeography

Abstract

AbstractThe Equilibrium Theory of Island Biogeography (ETIB) is a widely applied dynamic theory proposed in the 1960s to explain why islands have coherent differences in species richness. The development of the ETIB was temporarily challenged in the 1970s by the alternative static Theory of Ecological Impoverishment (TEI), which suggests that the number of species on an island is determined by its number of niches or habitats. With no clear evidence relating species richness to the number of niches however, the TEI has been almost dismissed as a theory in favour of the original ETIB. Here, we show that the number of climatic niches on islands is an important predictor of the species richness of plants, herpetofauna and land birds, and we therefore propose a model called the Niche-based Theory of Island Biogeography (NTIB) that successfully, merges the ETIB and TEI into a unifying concept. To account for greater species turnover at the beginning of colonisation, we include higher initial extinction rates. When we test our NTIB for resident land birds in Krakatau Islands it reveals a good correspondence with observed species richness, immigration and extinction rates. We estimate that current species richness at equilibrium is ~48 species (range between 47.76 and 51.36) provided the environmental regime remains unchanged.