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The identification of trophic linkages and quantification of interaction strengths among consumers and resources within food webs is critical if we are to understand how human-induced stressors impact the structure and function of ecosystems. In Florida, freshwater springs and associated river runs are increasingly under threat due to variety of factors including, but not limited to, nutrient enrichment, reduced discharge, and exotic species. While myriad research studies have assessed the role of abiotic factors in driving patterns of primary producer abundance and distribution; we understand relatively little about pathways of energy flow and material transport through the food webs operating within these systems.
We employed stable isotope and dietary analyses of consumers inhabiting Silver River, Florida to elucidate food web structure and identify important trophic interactions. Through sampling of food web constituents and resource pools along the entire length of Silver River we determined that submerged macrophytes and their epiphytes contributed the majority of energy to upper trophic levels, while benthic filamentous algae contributed relatively little. Results indicate a high degree of omnivory among taxa, but also some surprising examples of dietary specialization. Stable isotope analysis coupled with other diet information indicates that redear sunfish and kinosternid turtles are primary predators on gastropods that are known to have the potential to exert control on nuisance filamentous algae production. Finally, we note that alligators in the Silver River rely heavily on both gastropods and crustaceans to support metabolism and growth. These predator-prey interactions to date have received little attention, but merit further study to understand more fully the strength of the relationships as they are likely to have a profound influence on ecosystem function. Integration of these novel data and insights will help to refine our understanding of predation and top-down pressures in influencing community dynamics within these complex ecosystems.
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