CRB: Plant Communities on Patchy Serpertine Outcrops: Spatial Structure and Ecological Interactions

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9424137 Harrison Serpentine outcrops in Northern California are ecological islands with a rich native flora. This study examines two related aspects of plant community structure on serpentine soils, with both immediate and general relevance for conservation biology. The first question is how plant community diversity is spatially structured on serpentine versus non-serpentine soils, and how this spatial structure is affected by patchiness and other attributes of serpentine. Spatial turnover in species composition will be compared between serpentine and non-serpentine substrates, and between patchy and continuous serpentine, while holding the size and spacing of sampling areas constant. This well be the first rigorous test of the role of patchiness versus distance alone in producing the spatial component of community diversity. To assess the roles of endemism and lack of invasion, the above analyses will be repeated excluding endemics and alien species, respectively. Species turnover between pairs of sites will be regressed on distance and environmental dissimilarity within each habitat type to further quantify spatial turnover and its causes. The second question concerns biotic causes of patterns of diversity. Experiments will examine how the rates of key biotic interactions vary with the size and isolation of serpentine patches. Pollination and seed predation will be measured in two serpentine endemic plant species, along both natural and experimental gradients of patch isolation. This study will illuminate both how best to conserve plant communities on serpentine soils in California, and the more general issue of how patchiness at several spatial scales affects the structure and function of ecological communities. This research becomes even more important as human activities gradually increase the rate and degree of fragmentation of natural systems.