Synthesis reveals that island species–area relationships emerge from processes beyond passive sampling

Aim The island species–area relationship (ISAR) quantifies how the number of species increases as area an or island-like habitat gets larger and is one most general patterns in ecology. However, studies that measure ISAR often confound variation sampling methodology analyses, precluding appropriate syntheses its underlying mechanisms. Most use only presence–absence data at whole-island scale, whereas we planned to a framework applies individual-based rarefaction synthesize whether differs from null expectation passive hypothesis. Location Five hundred five islands 34 different archipelagos across world, including oceanic islands, lake forest islands. Major taxa studied Local assemblages plants, invertebrates, herpetofauna, birds mammals. Methods We collated local-scale abundance multiple (median 12 per study) used rarefaction-based approach between size (1) sample effort-controlled rarefied richness, (2) effective derived probability interspecific encounter (an index community evenness). Results When applied control for effort, numbers their relative abundances all differed Our evenness also increased with size, suggesting disproportionate effects observed influenced both rarer more common species. found few associations slope this effect type taxon, but did find greater elevational heterogeneity deviated than those less heterogeneity. Main conclusions Using synthetic archipelagos, reject causes instead suggest ecological mechanisms leading (non-random) on smaller are predominant.