Waterfowl impacts to zooplankton communities in wetland meta-ecosystems
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The meta-ecosystem concept is an attempt to combine metacommunity, ecosystem and landscape ecology. In meta-ecosystems, both organismal dispersal and material movement between patches can have important effects on communities. This concept provides a more realistic framework of natural systems by considering both processes jointly. My dissertation presents a case-study of natural metaecosystems by studying the role of waterfowl in structuring zooplankton communities in prairie pothole wetlands in South Dakota. I use observations of natural wetlands, microcosm and mesocosm experiments to show how dispersal of materials and organisms by waterfowl can affect zooplankton abundance and community composition. Waterfowl are conspicuous, behaviorally adaptable, highly mobile and economically important members of wetland habitats. They are thought to have possible effects on zooplankton communities either by dispersing zooplankton propagules among wetlands or by moving nutrients into (via defecation) or out of (via consumption of macrophytes and invertebrates) wetlands. In this dissertation, I show evidence that waterfowl disperse a limited subset of locally rare zooplankton species between wetlands. I also provide experimental evidence that these dispersed species may have impacts on zooplankton community assembly. I also show how input of waterfowl excreta may sometimes have strong impacts on the local community. Very large inputs of goose excreta promote abundance and diversity of zooplankton. However, inputs at more modest levels, such as those routinely found in nature, are rarely detectible. Additions of excreta at levels five-times that typically found in nature produce a possible shift in zooplankton community structure away from both no-excreta communities and communities fertilized with comparable amounts of nitrogen and phosphorus. I postulate that most excreta quickly sinks to the benthos and only a small fraction becomes available for use by zooplankton. On the time scales used in my dissertation, it is only with very large additions of excreta that shifts in the zooplankton community become apparent. My dissertation is one of the first to apply the meta-ecosystem concept to a natural system. It also shows that waterfowl impacts on the zooplankton community may be most important in small wetlands or early in community assembly.