Distance decay of compositional similarity in multiple taxa across a large latitudinal gradient in european beech forests
Réduction de distance de similarité sur plusieurs taxons à travers un large gradient latitudinal dans hêtraies européennes
Résumé
The exploration of the patterns and the mechanisms that shape organisms distribution along large latitudinal gradients is among the most debated topics in ecology and biogeography due to its implications for conservation in the face of global change. In Europe, beech forests cover a vast surface area, from the southern part of Scandinavia to the mountains of south Italy, providing relatively homogeneous habitat conditions along this latitudinal gradient. This should be reflected by a high similarity in taxonomical composition of its forest biota. However, this hypothesis could be contradicted by the fact that the large-scale distribution of organisms may be hampered by their dispersal capability. This could determine differences in organism spread patterns across European beech forests that should be reflected by a pattern of distance decay of compositional similarity whose magnitude should depend on the dispersal traits of the organisms. To test this hypothesis we assembled a multi-taxon database, including both organisms that are best suited for long-range dispersal (i.e. birds, bryophytes, lichens, fungi) and organisms that are usually less effective in long range dispersal (i.e. beetles and plants). This database consists of 354 plots clustered in 20 forest areas distributed from northern France to southern Italy. Preliminary results reveal a pattern of distance decay of compositional similarity for all organism groups. However, its magnitude reflects the dispersal ability of the organisms, being stronger for those that are less suited for long range dispersal. Only for lichens, results are not consistent with our expectations showing a high rate of compositional dissimilarity over a relatively short distance (i.e. 500 Km). This may reflect their strong sensitivity to local microclimatic conditions. More refined results are expected by an extra close-to-trait analysis considering more in detail the dispersal capability of the single species within each taxonomical group.