Reproductive strategy and the compositional dynamics of crustose lichen communities on aspen (Populus tremula L.) in Scotland

Ecological studies are essential in understanding the response of crustose lichens to habitat dynamics and developing effective conservation strategy. While the combined response of individual crustose species within a community will be tremendously complex, the overall result of individualistic change can be simplified using trait-based analyses. In this paper we examine the response of crustose species with contrasting reproductive traits (predominantly sexual vs asexual reproduction) and which occur within a closely defined habitat (as epiphytes on the lower bole of aspen) to environmental drivers measured at two different scales, i.e. between and within aspen stands. Our results point to the important effect of tree age and subsequent shifts in bark quality (pH) on the composition of the crustose community. However, shifts in community composition putatively controlled by bark quality comprise a change from a community dominated by sexual species to a community with mostly asexual crusts. Our results suggest therefore that variation within this crustose community may be driven by the combined effects of allogenic change (tree age and bark quality) and autogenic processes that are related to a species' adaptive life-history traits.