Eutrophication and fragmentation are related to species’ rate of decline but not to species rarity: results from a functional approach

Due to ubiquitous eutrophication and fragmentation, many plant species are actually threatened in Europe. Most ecosystems face an overall nutrient input leading to changes in species composition. Fragmentation is effectively influencing species survival. We investigate if two different measures of species performance of 91 calcareous grassland species–rate of decline and rarity—are related to comparable traits and hence processes. On the one hand we expected that species rate of decline is mainly determined by the processes of eutrophication and fragmentation. On the other hand we hypothesized that the importance of site characteristics may overwhelm the effect of eutrophication and fragmentation for species rarity. Hence, we compared persistence traits responding to eutrophication, dispersal traits being related to fragmentation and ecological site factors for decreasing and increasing species and for rare and common species. The results suggest that increasing species had better means of long-distance dispersal and were more competitive than decreasing species. In contrast, there were hardly any differences in traits between rare and common species, but site characteristics were related to species rarity. Rare species were in the main those with ecological preferences for warm, dry, light and nutrient poor conditions. This study may represent a basis for the assessment of plant species threat. Applying the deduced knowledge about the life history of decreasing versus increasing species to habitat-scale approaches it is possible to predict which species may become threatened in the future simply from the combination of their trait values.