COMPETITIVE PERFORMANCE AND SPECIES DISTRIBUTION IN SHORELINE PLANT-COMMUNITIES - A COMPARATIVE APPROACH

Using a comparative approach, we tested the prediction that relative competitive performance of plant species is correlated with distribution along natural gradients of fertility and standing crop. The mean position of 40 species of herbaceous plants along standing crop, phosphorus, nitrate, magnesium, potassium, pH, and percent organic content gradients was calculated based on data from 217 quadrats from lake and river shorelines in Nova Scotia, Quebec, and Ontario. Competitive performance was measured in an outdoor experiment in which species were grown together with a common phytometer, Lythrum salicaria (n = 5 replicates per species). The relative ability of each species to suppress the growth of the phytometer was used as a measure of relative competitive performance. This measure of competitive performance was significantly correlated with the mean position of species on the standing crop (r = 0.081; P < 0.0001), percent organic content (r = 0.71; P < 0.0001); phosphorus (r = 0.70; P < 0.0001), nitrate (r = 0.67; P < 0.0001), magnesium (r = 0.66; P < 0.0001), and potassium gradients (r = 0.61; P < 0.0001). When monocotyledons and dicotyledons were considered separately, the relationship between distribution along the macronutrient gradients and competitive performance was much stronger for monocotyledons. It is suggested that this may reflect a differential influence of disturbance on distribution.