Resource availability determines the importance of niche-based vs. stochastic community assembly in grasslands

Niche-based selection and stochastic processes can operate simultaneously to generate spatial and temporal variation in species composition. Yet, the conditions under which ecological dynamics are dominated by niche-based vs. stochastic processes are poorly understood. Using a field experiment in early-successional temperate grassland and null models of beta diversity, this study investigates the effects of soil nutrient supply on the relative importance of niche-based selection vs. stochastic dynamics for variation in species composition among sites. Nutrient availability was manipulated experimentally, individual seed mixtures with 25 species were sown in each experimental plot, and then stochastic and deterministic niche-based assembly processes were allowed to happen. We found that compositional variation among grassland plots with low nutrient supply was driven by stochastic immigration and extinctions. In contrast, nutrient enrichment reduced the importance of stochasticity and im...