Diversity and turnover in moth assemblages in rainforests on a remote oceanic island

Spatially driven turnover in species composition and relative abundance drives gamma diversity in all ecosystems. Assemblages of nocturnal Lepidoptera in rainforests are powerful tools for estimating and understanding this heterogeneity. There are three fundamental theoretical tools for explaining this place-to-place change: neutral stochasticity, niche-driven opportunity and historical contingency. We sampled moth and woody plant assemblages across the oceanic island landscape of La Réunion to tease apart how these factors shape diversity. We collected a total of ~ 13000 individuals of about 229 species and analyzed how distance and forest habitats shape moth assemblage turnover. We subdivided moth species into endemics and non-endemics. Our results show the local occurrence of the generally more diet-restricted endemic moths is more likely to be niche-driven due to host-plant preferences while occurrence of the generally more polyphagous non-endemic species is most parsimoniously explained by stochastic neutral mechanisms. Spatial patterns in the native flora may also be neutrally assembled sets across the rainforest region (with implications for native moth species) whereas introduced species reflect human-driven historical contingency.