Loss of epiphytic diversity along a latitudinal gradient in southern Europe.

Latitudinal gradients that involve macroclimatic changes can affect the diversity of several groups of plants and animals. Here we examined the effect of a latitudinal gradient on epiphytic communities on a single host species (Fagus sylvatica) to test the core-periphery theory. The latitudinal span considered, covering two biogeographic regions, is associated with major changes in rainfall during the dry season. Because bryophytes and lichens are poikilohydric, we hypothesized that their species richness and composition might vary at different latitudes. We also speculated how epiphytic communities may respond to future climate change. The present study was carried out in Spain, and three latitudes that cover the distributional range of F. sylvatica were selected. The presence/absence and coverage of epiphytic lichens and bryophytes were identified on 540 trees (180 in each zone). We found consistent south to north change in the total richness and in the richness of bryophytes and of lichens separately, all of which tend to increase at higher latitudes due to the presence of several hygrophytic species. Epiphytic composition also differed significantly among the three latitudes, and the similarity decreased when the latitudinal span was greater. In addition, high species turnover was driven by the increased rainfall at higher latitudes. We conclude that epiphytic communities have a similar pattern to the predictors of the core-periphery theory from populations, and they suffer a great impoverishment in species richness at lower latitudes, coincident with the southern boundary of the F. sylvatica distribution.