Print PageTwo classic models exist which attempt to explain how natural communities assemble: Gleason's Individualistic model and Clements' Organismic model. The former model suggests that individuals within a community are distributed according to their physiological needs. The latter suggests that competition is the primary determinant of community formation, which would result in distinct boundaries between species groups. The objective of our study was to test these models by examining assemblage of lichen communities along rocky shorelines in the Boundary Waters Canoe Area Wilderness (BWCAW). To do this, we sampled rocky outcrops along lakeshores in the BWCAW. At each site, we recorded the value of physical variables (slope, canopy cover, aspect, and distance from shoreline), as well as the relative abundance of each species present, at 1-meter increments along a 5-meter transect starting at the shoreline. Relative abundance was determined by recording the number of squares occupied by each lichen species within a 30 cm^2 quadrat with a 6x6 grid overlay.
Results/Conclusions
A multi-dimensional analysis revealed that the observed lichen communities do not generally form discrete species groups. However, some minor clustering of species was apparent on the plot, indicating that some species do share similar environmental preferences. Species richness was also found to slightly, but significantly, increase as both distance from shoreline and slope increased. Canopy cover and aspect did not seem to have any effect on the species richness of rocky shoreline lichen communities. These results suggest that lichen communities in the BWCAW assemble according to their own physiological needs, and that community formation is influenced by physical factors. These observations support the idea that lichen communities on rocky shorelines of the North Woods assemble according to Gleason's Individualistic model.
