PARENT SESSION
Oral Session #89: Biodiversity and Ecosystem Function III.
Presiding: R. Washington-Allen
Thursday, August 8. 1:00 PM to 3:45 PM. Coconino Meeting Room, TCC.
Flow history moderates the relationship between algal diversity and productivity in stream ecosystems.
Cardinale, Bradley*,1,2, Palmer, Margaret1, Brooks, Shane1, 1 University of Maryland, College Park, MD2 University of Wisconsin - Madison, Madison, WI
ABSTRACT- Recent studies have suggested that the affect of species diversity on ecosystem productivity can be varied, and often depends on how sources of environmental heterogeneity regulate species interactions and community structure. Here we show that the relationship between species diversity and productivity in stream ecosystems is influenced by the history of environmental variation. Using historical records of discharge, we ordinated 474 streams in the Mid-Atlantic United States according to their long-term (10 yr) variability and predictability of flow. We then measured algal diversity and productivity in 42 streams most characterized by hydrologic variation (variable, unpredictable discharge), and 44 streams most characterized by hydrologic stability (constant, predictable discharge). In hydrologically stable streams, productivity was not significantly related to algal species richness; however, in streams characterized by hydrologic variation, primary production increased by 5% per algal species leading to a strong positive relationship between species richness and productivity. Taxonomic evenness in algal biomass did not change with species richness suggesting results were not due to selection effects. Trends were better explained by increased performance of individual algal taxa in more diverse communities. Correlation coefficients relating productivity of the twenty-four most common taxa to species richness were, on average, significantly greater than zero, and were stronger and more frequently positive in streams characterized by hydrologic variation. These results suggest that ecosystem productivity is more strongly related to biodiversity in harsh and fluctuating environments due to an increased prevalence of positive species interactions.
KEY WORDS: biodiversity, ecosystem functioning, aqautic, periphyton