Deterministic and stochastic factors shape ecological communities.
However, a quantitative synthesis of the factors underlying the balance
among different assembly processes is lacking. Here, we synthesized data
from 149 datasets covering major biotic groups and ecosystem types
globally. We used a null model approach based on Raup-Crick
dissimilarities and Bayesian meta-regression to analyze the data. We
found that communities were more under homogeneous selection than
heterogeneous selection across biotic taxa and ecosystems. Environment
selected species homogeneously more often at small scales while
heterogeneously more often at large scales. Stochasticity also showed
scale-dependence as stochastic community assembly increased with study
scale. Homogeneous and heterogeneous selection were strongest at high
latitudes while stochastic factors were strongest in tropics. Marine
systems had the highest degree of homogeneous selection and the lowest
stochasticity. We provide the first analysis of community assembly
across taxa and ecosystems which should be important for a better
understanding of how communities respond to environmental change.