THE SPECIES-AREA CURVE AS AN INDEX OF DISTURBANCE IN SAXICOLOUS LICHEN COMMUNITIES

Species-area data were used to compare saxicolous lichen communities differing in species richness and level of disturbance. Three communities in Maryland and Virginia were chosen for study based on previous investigations indicating variations in species number caused by differences in background pollution. Additional data from previously published studies done in central Chile and New Zealand were analyzed for comparison. Regressions of the species-area relationship were determined using three frequently-used models: 1) the power function model, which assumes an equilibrium between immigration and extinction of species on islands; 2) the exponential model, which assumes increases in habitat diversity with area; and 3) the untransformed model, which makes no assumptions about habitat diversity or population processes. Significant regressions were obtained for all data sets and all three models. Slopes of the logS/logA regressions were not significantly different for the six relatively undisturbed communities, this despite differences in species richness and location of these communities. Significant differences among slopes were observed when the species-area data of the disturbed community were included in the analysis, indicating an alteration of community processes by pollution. It is suggested that the species-area curve provides a useful method for assessing pollution damage to lichen communities.