Researcher Frank Bradley inspects enclosures where pond experiments are conducted.
Biodiversity has become an increasingly important issue in ecology and for the general public. The loss of diversity raises philosophical and ethical questions ranging from our responsibility as stewards to the intrinsic value of nature. While highly discussed, little is known about the role diversity plays in creating and maintaining ecosystem structure nor about its role in ecosystem functions (e.g., nutrient cycling, systemwide productivity).
Historically, biodiversity questions have centered on how environmental characteristics (e.g., latitude, precipitation, and productivity) drive patterns of species richness. In recent studies, however, the questions have been expanded to how diversity affects the performance of an ecosystem, if at all. Using terrestrial systems, researchers have demonstrated that varying diversity levels can have variable effects on the ecosystem. Results indicate changes to resistance and resilience to disturbance, productivity, and nutrient dynamics as responses to changes in diversity. Other studies, while maintaining the value of diversity, question the degree of influence diversity has on ecosystem functions. However, to our knowledge, none of these studies have examined these questions in an aquatic setting.
The purpose of our study is to examine the relationship between fish species diversity and aquatic ecosystem structure and function. Using three levels of fish species diversity (2, 6, and 9 species) in pond enclosures, we were able to obtain preliminary results that support the hypothesis that diversity affects the ecosystem in some way. We found higher zooplankton (microscopic crustaceans) densities and higher chlorophyll concentrations in treatments with higher fish diversity. A diversity index (a numerical indicator of diversity levels) for the zooplankton assemblage indicates that increased fish diversity increases zooplankton diversity. Water column nutrient levels also appear to increase with increased fish diversity.
Researcher Frank Bradley inspects enclosures where pond experiments are conducted.
These results, while preliminary, suggest an effect of diversity on ecosystem structure and function in aquatic systems. Diversity is an important topic, with laws having been enacted in attempts to stem the loss of species, all without a fundamental understanding of the role of diversity. We hope that future analysis of our work will provide us with a better understanding of the environment and the importance of diversity.
Sean Callahan and David H. Wahl, Center for Aquatic Ecology
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