Assembly Processes Structuring Mammal Metacommunities are not Zero-sum

Metacommunity studies commonly gain insight by partitioning assembly processes into habitat filtering, dispersal and species interactions. These processes are commonly assumed to be zero-sum, such that structuring by one process leads to less structuring by other processes. We predicted that mammal community composition would be strongly affected by species interactions in geographical areas with abundant top predators, while dispersal and habitat selection would be stronger in areas lacking top predators. Unexpectedly, we found that in mammal communities in Northeast China forests, strong environmental/habitat filtering was coincident with strong effects of top-predators (species interactions) on other community members and marked roles of dispersal. In areas with few top predators and less habitat/environmental filtering, species interactions remained important but driven by mesopredators rather than top predators. Multiple types of analysis support our finding that strong habitat structuring of mammal communities can be accompanied by strong effects of species interactions and dispersal.