ARE INVASIVE SPECIES THE DRIVERS OR PASSENGERS OF CHANGE IN DEGRADED ECOSYSTEMS?

Few invaded ecosystems are free from habitat loss and disturbance, leading to uncertainty whether dominant invasive species are driving community change or are passengers along for the environmental ride. The “driver” model predicts that invaded communities are highly interactive, with subordinate native species being limited or excluded by competition from the exotic dominants. The “passenger” model predicts that invaded communities are primarily structured by noninteractive factors (environmental change, dispersal limitation) that are less constraining on the exotics, which thus dominate. We tested these alternative hypotheses in an invaded, fragmented, and fire-suppressed oak savanna. We examined the impact…