Capacity and establishment rules govern the number of nonnative species in communities of ground-dwelling invertebrates

Nonnative species are a key agent of global change. However, nonnative invertebrates remain understudied at the community scales where they are most likely to drive local extirpations. We use the North American NEON pitfall trapping network to docu- ment the number of nonnative species from 51 invertebrate communities, testing four classes of drivers. We sequenced samples using the eDNA from the sample’s storage ethanol. We used AICc informed regression to evaluate how native species richness, productivity, habitat, temperature, and human population density and vehicular traf- fic account for continent-wide variation in the number of nonnative species in a local community. The percentage of nonnatives varied 3-fold among habitat types and over 10-fold (0%–14%) overall. We found evidence for two types of constraints on non- native diversity. Consistent with Capacity rules (i.e., how the number of niches and individuals reflect the number of species an ecosystem can support) nonnatives in- creased with existing native species richness and ecosystem productivity. Consistent with Establishment Rules (i.e., how the dispersal rate of nonnative propagules and the number of open sites limits nonnative species richness) nonnatives increased with au- tomobile traffic—a measure of human-generated propagule pressure—and were twice as common in pastures than native grasslands. After accounting for drivers associ- ated with a community’s ability to support native species (native species richness and productivity), nonnatives are more common in communities that are regularly season- ally disturbed (pastures and, potentially deciduous forests) and those experiencing more vehicular traffic. These baseline values across the US North America will allow NEON’s monitoring mission to document how anthropogenic change—from distur- bance to propagule transport, from temperature to trends in local extinction—further shape biotic homogenization.