Ecosystem Consequences of Biological Invasions

Exotic species affect the biogeochemical pools and fluxes of materials and energy, thereby altering the fundamental structure and function of their ecosystems. Rapidly accumulating evidence from many species of both animal and plant invaders suggests that invasive species often increase pool sizes, particularly of biomass, and promote accelerated flux rates, but many exceptions can be found. Ecosystem dynamics are altered through a variety of interacting, mutually reinforcing mechanistic pathways, including species' resource acquisition traits; population densities; ability to engineer changes to physical environmental conditions; effects on disturbance, especially fire; regimes; the ability to structure habitat for other species; and their impact on food webs. Local factors of landscape setting, history, and other sources of disturbance constrain ecosystem responses to invasions. New research directions are suggested, including the need for whole-system budgets, the quantification of abundance-impact relationships for particular ecosystem processes, and a better exploration of food web impacts on ecosystem processes.