Does natural variation in diversity affect biotic resistance?

1. Theories linking diversity to ecosystem function have been challenged by the widespread observation of more exotic species in more diverse native communities. Few studies have addressed the key underlying process by dissecting how community diversity is shaped by the same environmental gradients that determine biotic and abiotic resistance to new invaders. 2. In grasslands on highly heterogeneous soils, we used addition of a recent invader, competitor removal, and structural equation modelling (SEM) to analyse soil influences on community diversity, biotic and abiotic resistance, and invader success. 3. Biotic resistance, measured by reduction in invader success in the presence of the resident community, was negatively correlated with species richness and functional diversity. However, in the multivariate SEM framework, biotic resistance was independent of all forms of diversity, and was positively affected by soil fertility via community biomass. Abiotic resistance, measured by inva...