Evolution, Ecology and Floristics in Northern California - Current Knowledge and Unexplored Realms
Harrison, Susan , Safford, Hugh D. , Grace, James , Viers, Joshua H. , Davies, Kendi F. .
Regional and local species richness in an insular environment: Serpentine plants in California.
WE asked how the richness of the specialized (endemic) flora of serpentine rock outcrops in California varies at both the regional and local scales. Our study had two goals: first, to test whether endemic richness is affected by spatial habitat structure (e.g. regional serpentine area; local serpentine outcrop area; regional and local measures of outcrop isolation); and second, to conduct this test in the context of a broader assessment of environmental influences (e.g., climate, soils, vegetation, disturbance) and historical influences (e.g., geologic age, geographic province) on local and regional species richness. We measured endemic and total richness and environmental variables in 109 serpentine sites (1000 m2 paired plots) in 78 serpentine-containing regions of the state. We used structural equation modeling (SEM) to simultaneously relate regional richness to regional-scale predictors, and local richness to both local-scale and regional-scale predictors. Our model for serpentine endemics explained 66% of the variation in local endemic richness based on local environment (vegetation, soils, rock cover) and on regional endemic richness. It explained 73% of the variation in regional endemic richness based on regional environment (climate and productivity), historical factors (geologic age and geographic province) and spatial structure (regional total area of serpentine, the only significant spatial variable in our analysis). We did not find a strong influence of spatial structure on species richness. However, we were able to distinguish local vs. regional influences on species richness to a novel extent, despite the existence of correlations between local and regional conditions.
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1 - University of California Davis, Environmental Science and Policy, Davis, California, 95616, USA
2 - USDA Forest Service, Pacific Southwest Region, 1323 Club Drive, Vallejo, California, 94592, USA
3 - Usgs Nat Wetlands Research Cnt, 700 Cajun Dome Blvd, Lafayette, Louisiana, 70506, USA
Presentation Type: Symposium or Colloquium Presentation
Date: Tuesday, August 1st, 2006
Time: 4:00 PM