Data from: Species-area relationships in the Andaman and Nicobar islands emerge because rarer species are disproportionately favored on larger islands

The Island Species-Area relationship (ISAR) describes how the number of
species increases with increasing size of an island (or island-like
habitat), and is of fundamental importance in island biogeography and
conservation. Here, we use a framework based on individual-based
rarefaction to infer whether ISARs result from passive sampling, or
whether some processes are acting beyond sampling (e.g., disproportionate
effects and/or habitat heterogeneity). Using data on total and relative
abundances of four taxa (birds, butterflies, amphibians and reptiles) from
multiple islands in the Andaman and Nicobar archipelago, we examine how
different metrics of biodiversity (total species richness, rarefied
species richness, and abundance-weighted effective numbers of species
emphasizing common species) vary with island area. Total species richness
increased for all taxa, as did rarefied species richness controlling for a
given sampling effort. This indicates that the ISAR did not result because
of passive sampling, but that instead, some species were
disproportionately favored on larger islands. For birds, frogs and
lizards, this disproportionate effect was only associated with species
that were rarer in the samples, but for butterflies, both more common and
rarer species were affected. Furthermore, for the two taxa for which we
had plot-level data (reptiles and amphibians), within-island β-diversity
did not increase with island size, suggesting that within island
compositional effects were unlikely to be driving these ISARs. Overall,
our results indicate that the ISARs of these taxa are most likely driven
by disproportionate effects, that is, where larger islands are important
sources of biodiversity beyond a simple sampling expectation, especially
through their influence on rarer species, thus emphasizing their role in
the preservation and conservation of species.