Plant Zonation on Lakeshores in Nova Scotia: A Test of the Resource Specialization Hypothesis

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Abstract
There are 2 contrasting approaches to understanding the coexistence of plant species. One emphasizes the differential use of, for example, space or nutrients as a mechanism for avoiding competitive exclusion, the other emphasizes physical disturbance and temporary co-existence. This study uses lakeshore vegatation to test whether, within a single lake, increasing species richness of a shoreline is correlated with more specialized use of resources, as measured by the range of depth colonized in different parts of the lake. There was no significant correlation between the number of species in a transect and the mean depth-range colonized; if anything, shorelines with the most species had the least specialized species. The number of species was greatest at or just above the water line, and at intermediate levels of exposure to wave energy. Although exposure affected species composition and the number of species per transect, specialization was not significantly correlated with exposure. Although water depth and exposure influence distributions of lakeshore species, specialization along the water-depth gradient does not explain the variation in the number of species on a lakeshore. Disturbance from waves and fluctuating water levels remains an alternaive hypothesis consistent with the data presented.