| Few studies have thoroughly investigated the influence of environmental factors in saxicolous lichen communities and the importance of scale awaits discovery. 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 x 20-cm plots across 16 sites (8 lakeshore and 8 inland). At a macroscale, lakeshore and inland granite rock communities differed considerably in composition with 68-90% species turnover. 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 based on the measured environmental variables. However, individual species differed greatly in their associations with specific habitat variables. A host of micro niches were discovered, with some lichens specializing on rock overhangs, quartz veins, cracks, subtle variations in rock texture, and mafic and felsic types of granite. |
