Document: JOH-3-82-39

Biodiversity and species invasions in marine invertebrate communities.

STACHOWICZ, J.J.* ¹ and R.B.WHITLATCH ²

University of California at Davis, Davis CA 95616 USA ¹
University of Connecticut, Groton CT 06340 USA ²

Abstract:
Along with habitat modification, the intentional or accidental introduction of new species by humans is a leading cause of the global biodiversity crisis. Because biological invasions can dramatically alter community composition and ecosystem function and cause considerable economic damage, there is significant interest in understanding why and how successful invasions occur. Theory first proposed by Elton predicts that species-rich communities should be less susceptible to invasion, but the evidence has been equivocal and often contradictory. Small-scale experimental studies tend to support the Eltonian hypothesis, whereas larger scale, observational studies often show the opposite relationship. We studied the invasion of subtidal marine invertebrate communities in coastal New England by exotic tunicates and bryozoans from Asia and Europe. In local 0.25 by 0.25 m neighborhoods within these communities, native species richness was negatively correlated with the species richness of introduced species. When we manipulated species richness in experimentally assembled 10 by 10 cm communities, we found that more diverse communities were more resistant to invasion by both colonial (Botrylloides diegensis) and solitary (Ascidiella adspersa) species. This appeared to be the result of a more complete utilization of resources (primary space) in communities with a greater number of native species. Despite a high degree of functional redundancy among the native species, increased numbers of species provided "insurance" against fluctuations in the abundance of any one species. Our experimental manipulation demonstrates that diversity, per se, does increase community resistance to invasion by exotic species, but factors correlated with diversity (e.g., larval supply, current regime, microhabitat diversity, etc.) may facilitate invasion, producing positive correlations between native and introduced species diversity on larger scales in the field. This apparent contradiction has important implications for management of marine communities and the selection of sites for marine reserves.

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This abstract is being presented at: 10:30 AM in session:
Oral Session #7: Aquatic Ecology: Shellfish to Snails.