Signatures of autogenic epiphyte succession for an aspen chronosequence

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Question:Is the succession of cryptogamic epiphyte communities (lichens) consistent with autogenic processes and life-history trade-offs?Location:Northern Britain (Scotland).Methods:We subsampled epiphytes from the lower bole of aspen (Populus tremula L.) and tested for two signatures in community succession. First, we used resampling among microhabitats to estimate species richness (sR) and species density (ρ) for trees along a chronosequence. We tested sR and ρ against patterns consistent with autogenic and life history-mediated succession. Second, we constructed null model communities from a regional species pool to test for significant dispersion in multivariate trait diversity.Results:We show that species density (ρ) declined along the tree age chronosequence. This decline was consistent with the observed unimodal pattern in species richness (sR) for a habitat that has a non-stationary area (increasing lower bole habitat area with tree age). We found under-dispersed trait diversity for younger trees, tending towards equilibrium between the regional species pool and local community for mid- and older-aged trees. Over-dispersion was evident for communities with the highest species richness.Conclusions:We conclude that lichen epiphyte communities undergo succession structured by autogenic processes (interference competition) and may also be structured by life-history trends, e.g. the competition–colonization trade-off. However, we suggest that the stochastic extirpation of competitive and dominant species may allow pioneer species to persist in the long term, explaining equilibrium in trait diversity observed for older-aged trees.

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