Species invasions and the relationship between community saturation, diversity and ecosystem functioning.
Stachowicz, John*,1, Tilman, David2, 1 University of California, Davis, CA2 University of Minnesota, St. Paul, MN
ABSTRACT- Invasion biology has focused largely on applied problems, rather than the conceptual gains possible from the study of such large scale natural experiments. We discuss the application of the study of invasions in both geological and recent times to understanding the relationship between community saturation, diversity and ecosystem functioning. During large scale biotic interchanges such as have occurred with the opening of the Arctic seaway and the rise of the Isthmus of Panama, species migrations are decidedly unidirectional. More diverse biotas are typically the invaders, with the species poorer biotas generally being the recipient regions. These patterns may result from ecological mechanisms (i.e., species poor regions have more unutilized resources -- empty niches) or from evolutionary ones (species rich areas are more competitive, and thus produce potential invaders with superior competition vs. colonization trade off surfaces). Regardless of the underlying mechanism, these patterns are consistent with the hypothesis that increasing species diversity decreases invasibility. Experimental studies with recent invaders confirm these relationships and suggest that the underlying mechanism is resource competition: all else being equal, increasing diversity decreases invasion success by decreasing resource availability. More complete and/or efficient utilization of resources extends beyond invasion resistance in its contribution to ecosystem functioning, with links to other ecosystem functions such as productivity, nutrient recycling, stability/consistency. Because in the short term invasions may enhance local species diversity, invasion biology also provides the opportunity to test the robustness of the diversity - ecosystem function relationship by addressing whether increasing species richness increases productivity and decreases levels of unused resources, as this hypothesis predicts.
Key words: ecosystem function, resource utilization, invasions, species diversity
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