Resurveyed Island Vegetation Reveals That Species Colonisation and Extinction Probabilities Are Linked to Traits

Abstract

The Equilibrium Theory of Island Biogeography (ETIB) proposes that species richness on islands reflects a balance between extinctions and colonisations. However, ETIB assumes species neutrality, limiting predictions to species richness rather than types. Here, we integrate traits into equilibrium dynamics for 132 Australian islands' native floras sampled repeatedly over six decades. Our analysis shows that both species richness and community mean trait composition remain stable despite continuing turnover. We found evidence for traits being associated with both species' colonisation and extinction. Colonisations were faster for low-stature, small-seeded species, while extinctions were faster in species with low leaf mass per area and annual life history. Our results highlight that species equilibria on islands are maintained by species-specific turnover dynamics linked to traits. This trait dependence in colonisation and extinction helps explain how ecological communities assemble and why some species are more likely to occur on islands than others.