Flood pulsing and metacommunity dynamics in a desert riparian ecosystem

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Jere A. Boudell|J. C. Stromberg
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Questions: 1) Does flood pulsing drive metacommunity dynamics in desert southwestern riparian ecosystems? 2) Do species along a specialist to generalist gradient respond to spatial and/or temporal metacommunity dynamics preferentially? Location: Desert southwestern USA. Methods: We sampled vegetation and propagule banks in four communities located along a hydrogradient in a spatially structured riparian ecosystem. Plant species were classified into a combination of wetland indicator score and Grime's life-history classes, and also into specialist, moderate, and generalist categories. ANOVA was used to test differences between data categories amongst communities (both extant vegetation and propagule banks) and between data categories by soil depth. Sorenson's similarity coefficient was calculated to determine the degree of similarity in communities of specialists and generalists between extant vegetation and propagule banks. Results: Wetland species were found in soils from active channel bar to the outer extent of the floodplain, indicating broad dispersal by flood waters. Specialists, such as wetland ruderals, were found within all soil depths. Specialist communities in propagule banks had little similarity with specialist communities in extant vegetation. Generalists, particularly upland ruderals, were restricted to surface soil layers. Communities of generalists in propagule banks were similar to extant communities of generalists. Collectively, these patterns indicate that specialists and generalists are responding to temporal and spatial dynamics respectively. Conclusions: Flood pulsing is one mechanism that drives metacommunity dynamics in highly dynamic desert southwestern riparian ecosystems. Propagule banks enable many herbaceous species to respond to multidimensional metacommunity dynamics by acting as a storage mechanism that can buffer populations in fluctuating environments.
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