Importance of biotic niches versus drift in a plant-inhabiting arthropod community depends on rarity and trophic group

Communities are mostly composed of rare species; yet, the factors that determine their patterns of occurrence remain obscure. Theory predicts that, in contrast with common species, the occurrence of rare species will be poorly correlated with environmental variables (niches) and more affected by stochasticity (ecological drift), but how this pattern varies across different trophic groups is still poorly understood. Here, we compared the ability of environmental variables (bottom-up biotic niches) to predict the occurrence of plant-dwelling arthropods across different abundance classes in the Cape Floristic Region of South Africa. We compared three trophic groups, including 104 herbivorous hemipteran, 171 parasitoid wasp and 84 spider species, totalling 4511 individuals in 48 quadrats. To quantify bottom-up biotic niches, we studied the influences of species composition of plants on hemipterans, and of plants and hemipterans on spiders and wasps. We compared the observed strength of the...