PARENT SESSION
Contributed Oral Session 160: Biodiversity: Communities
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal
Structuring fern communities at local and mesoscales: The roles of environmental determinism and dispersal.
Karst, Justine*,1, Gilbert, Ben1, Lechowicz, Martin2, 1 University of British Columbia, Vancouver, B.C., Canada2 McGill University, Montreal, Q.C., Canada
ABSTRACT- We evaluated the roles of environmental determinism and dispersal in the assembly of fern communities at contrasting spatial scales within an old-growth, temperate deciduous forest. Specifically, we examined correlations among the geographic location of sampling plots separated by either 135 to 3515 m (meso-scale) or 4 to 134 m (local-scale), the abiotic environmental characteristics of the plots, and their constituent fern species. At both spatial scales, ferns had predictable distributions along a soil moisture gradient: six of eight common fern species showed repeatable environmental optima along the soil moisture gradient. By sampling in such a way as to decouple the correlation between distance and environmental variation, we showed the dominant role of environmental variables, notably soil moisture, in determining fern distributions at the meso-scale. At the local-scale, however, strong spatial autocorrelation in the abiotic environment precluded assigning any definitive role for either dispersal or environmental determinism alone in affecting fern distributions. The expectations of neutral theory that are rooted in dispersal limitation and those of niche theory that are rooted in environmental adaptation converge at fine spatial scales where natural environments have strong spatial structure. The structure of the environment at fine spatial scales may foster the persistence of dispersal limited plants in the community; neighboring environments are more likely to be similar, and thus suitable for propagules dispersing short distances. While patterns of fern distribution are not consistent with purely neutral or random models of species coexistence, alternative models that rely on strict niche requirements without accounting for dispersal limitation and the inherent spatial structure of the environment are inadequate as well because they neglect the important interaction of these factors. This outcome supports the relevance of developing theory that considers the joint effects of environmental determinism and dispersal on the distribution and abundance of plant species.
Key words: partial ordinations, niche, spatial structure, neutral theory