Variation among European beetle taxa in patterns of distance decay of similarity suggests a major role of dispersal processes
The decay of assemblage similarity with spatial distance can be explained by alternative mechanisms: dispersal limitation and species sorting. To understand their relative contributions, we compare the decay in faunal similarity with spatial distance and, independently, with climatic distance, of 21 beetle taxa with varying dispersal abilities and ecological niches, in southern and northern Europe. Similarity in beetle faunas was associated to spatial but not to climatic distances, pointing to the preponderance of dispersal processes rather than niche constraints. In most taxa, southern faunas were more dissimilar than northern ones: smaller initial similarity and steeper distance decay rate. Distance decay patterns in the north were relatively flat and very similar across taxa, suggesting that only good dispersers would have reached those latitudes after the glacial retreat. The difference in distance decay patterns between north and south is correlated with the taxon's slope of the distance decay pattern in the south and with its latitudinal richness difference. That is, in taxa with distance decay patterns similarly flat in the south and the north, the latitudinal richness gradient is weak. This correlation points again to differences in dispersal ability as a major determinant of biogeographic patterns in European beetles. Both dispersal and niche‐related characteristics explained north‐south slope differences, but dispersal attributes turned out to be more relevant when initial similarity and distance decay strength were considered together. Our results show that, to understand diversity patterns in Europe, closely related biological groups cannot be assumed to be surrogates and regions with different historical biogeography should be analysed separately. Paradoxically, the study of beetle faunas of southern Europe will shed light on the processes controlling the recolonization of northern latitudes.
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