PARENT SESSION
Poster Session #32: Plant Ecology I.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
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Patterns of assembly along a toposequence in pine savannas and baygall gallery forests.
Hawkins, Katherine1, McDonald, John2, Meador, Andrew2, Weiher, Evan1,2, 1 2
ABSTRACT- Rarely have ecologists combined gradient analysis and the search for community assembly rules. We investigated how the strength of assembly rules varies among three plant communities along a soil toposequence, from upland dry-mesic longleaf pine savanna through slash pine - pitcher plant seepage savanna to wet-mesic baygall gallery forests located in southern Mississippi. While strong gradients facilitate comparisons between vegetation types, high species density (up to 40 species per 0.25 m2 quadrat in slash pine savanna) and a significant relationship between mean quadrat species richness and bootstrapped stand-level richness both suggest that assembly rules are probably weak and composition may be random. We found no evidence for assembly rules in the uplands, however in both the seeps and the galleries two of three stands showed significant checkerboard scores (meaning that species are not independent). Moreover, the patterns tended to decrease in strength with elevation, in accordance with Schneider and Kay's thermodynamic model. Species pairs responsible for the significant scores were primarily combinations of woody species or large graminoids and diminutive species. Pairs of ecological equivalents were also noted, but were less common. Guild proportionality (sensu Wilson) was tested, but not found. The replacement of small species by larger competitors helps explain the lack of significant guild proportionality. Evidence of assembly rules in this poor model system suggests that assembly rules may be more common than previously thought
KEY WORDS: assembly, gradient, savanna, baygall