PARENT SESSION
Oral Session 4: Biodiversity I: Communities and Function.
Presiding: C Holzapfel and D Ellsworth
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 110.
Space, heterogeneity, and scale affect diversity partitions in a naturally patchy landscape.
Freestone, Amy*,1, Inouye, Brian2, 1 University of California, Davis2 Florida State University, Tallahassee
ABSTRACT- Both local and regional processes can affect community diversity. We examined the effect of natural habitat patchiness at nested spatial scales on plant diversity partitions by comparing observations with null models of diversity partitions based on randomizations of species' distributions. We studied naturally patchy serpentine seep plant communities across 50 seeps (i.e. patches) in California. 25 seeps were dispersed across a region of five serpentine outcrops, and 25 seeps were clustered on one outcrop. We surveyed seep floral diversity and environmental characteristics between 2001-2002. We then calculated observed and expected diversity partitions for four nested spatial scales using an additive model in which average alpha diversity is added to incremental beta diversities between each hierarchical scale (i.e. quadrats within seeps, seeps within outcrops, outcrops within a region) to sum to regional diversity. Observed within-patch beta diversity (i.e. quadrats within seeps) was significantly lower than expected, while between-patch beta diversities (i.e. seeps within outcrops, outcrops within a region) were significantly greater than expected. We evaluated the relative contributions of environmental heterogeneity and spatial dispersion on between-patch differences in community composition using nonparametric Mantel tests. Differences in species composition between seeps at the regional scale were correlated with soil texture and serpentine characteristics, as well as the spatial distance between seeps. Differences at the outcrop scale were correlated with soil texture and moisture components, but not with distance. Distance effects, such as dispersal limitation, may only be important at the regional scale. Environmental influences may appear at both spatial scales, depending on the scales of heterogeneity.
Key words: patchiness, environmental heterogeneity, diversity partitions, scale