A habitat analysis and influence of scale in lichen communities on granitic rock

Abstract

Environmental factors in saxicolous lichen communities are scale dependent, yet the influence of scale is not often specifically addressed in ecological studies. This study examined three scales [micro (cm), meso (meters–10s of meters), macro (km)] in granite rock communities and compared species assemblages and disturbance regimes in Lake Superior shoreline and inland habitats. Percent cover of lichens and environmental variables were measured in 1280 20 × 20-cm plots across 16 sites (8 lakeshore and 8 inland). A perMANOVA analysis showed that the composition of lakeshore and inland lichen communities was significantly different (F=17.2, df=1,4, P <0.001). Adjacent lakeshore sites were more similar (F=8.550; df = 1, 26; p=0.007) to each other than they were to sites further away, while inland sites were not (F=0.545; df=1, 26; p=0.467). Variation in disturbance is likely more important in determining inter-site variation in inland areas. Mesoscale environmental variables such as solar radiation, height above Lake Superior, and an aspect/slope index were better predictors of species assemblages than microscale variables. However, individual species differed greatly in their associations with specific habitat variables. A host of microhabitats were discovered, with some lichens specializing on rock overhangs, quartz veins, cracks, subtle variations in rock texture, and mafic intrusions within granite.