A global analysis of land snail diversity on islands

Abstract

Explaining spatiotemporal disparities in island species‐richness (ISR) is a fundamental pursuit in (macro)ecology and biogeography. While most research has focused on vertebrates and vascular plants, invertebrates—representing ~70% of global species—remain understudied. Using data from 727 islands worldwide, we evaluate the impact of 14 key biogeographic variables, including island area, isolation, climate, energy, environmental heterogeneity, and human presence, on different insular land snail chorotypes: total indigenous richness, archipelagic endemics, including multiple‐ and single‐island endemics, and native non‐endemics. We find that these variables jointly explain 80%–84% of inter‐island variation in endemic ISR, substantially enhancing explanatory power beyond what can be attributed to traditional species–area and species–energy relationships. In contrast, native non‐endemic ISR, although partially explained by area or energy alone, is predominantly influenced by other unaccounted factors including source‐pool effects. Driver significance varies among chorotypes, illustrating the capture of distinct biogeographic processes (speciation vs. colonization) per chorotype. Our findings show that factors influencing land snail ISR broadly align with those for vertebrates and plants while revealing significant variation in community assembly processes across chorotypes. Thus, our study provides a step towards a unified theory of diversity, encompassing chorotypes as fundamental ISR components, and invertebrates, which comprise most island animal diversity.