Consequences of Long-Term Changes in Fish Community Structure on Ecosystem Functioning in a Subtropical Spring-Fed River
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In this study, I examined patterns of long-term changes in the composition of the fish community in the spring-influenced upper San Marcos River (central Texas, USA) and the ecosystem functioning implications of compositional changes in the fish community. Using a long-term historical data set of fish community composition (Perkin et al. 2011; Kollaus et al. 2015; BIO-WEST, Inc. 2013-2016) and contemporary species- specific fish excretion data from the upper San Marcos River, I examined how temporal changes in the composition and diversity of the fish community were related to changes in the rates and ratios of dissolved inorganic N and P recycled by the fish community and how the sequestration of nutrients into fish biomass changed through time. I hypothesized that temporal changes in fish community composition would lead to changes in which species function as the largest contributors to the community-wide aggregate nutrient recycling rates, as well as changes to the community-wide aggregate ratios of excreted nutrients. Accordingly, I also predicted that temporal changes in fish community composition would be associated with changes to which species sequester the largest amount of C, N, and P, and these changes will alter the community-wide aggregate C:N:P.