Species richness in dry grassland patches of eastern Austria: A multi-taxon study on the role of local, landscape and habitat quality variables

According to island biogeography theory, the species richness of patches is determined by their size and spatial isolation, while in conservation practice, it is patch quality that determines protection and guides management. We analysed whether size, isolation or habitat quality are most important for the species richness in a set of 50 dry grassland fragments in agricultural landscapes of eastern Austria. We studied two plant taxa (vascular plants, bryophytes) and 11 invertebrate taxa (gastropods, spiders, springtails, grasshoppers, true bugs, leafhoppers and planthoppers, ground beetles, rove beetles, butterflies and burnets, ants and wild bees). The species richness of three categories was analysed: (1) dry grassland specialist species, (2) all grassland species and (3) all species. We used regression and hierarchical partitioning techniques to determine the relationship between species richness and environmental variables describing patch size and shape, patch quality, landscape configuration and landscape quality. The area-isolation paradigm was only applicable for dry grassland specialists, which comprised 12% of all species. Richness of all grassland species was determined mostly by landscape heterogeneity parameters. Total species richness was highly influenced by spillover from adjacent biotopes, and was significantly determined by the percentage of arable land bordering the patches. When analysing all taxa together, species richness of dry grassland specialists was significantly related to historical patch size but not to current patch size, indicating an extinction debt. At the landscape scale, the variable ‘short-grass area’ was a better predictor than the less specific variable ‘area of extensively used landscape elements’. ‘Distance to mainland’ was a good predictor for specialists of mobile animal taxa. Plant specialists showed a pronounced dependence on quality measures at the patch scale and at the landscape scale, whereas animal specialists were influenced by patch size, patch quality, landscape quality and isolation measures. None of the taxa benefited from linear structures in the surroundings. In conclusion, high patch quality and a network of high-quality areas in the surrounding landscape should be the best conservation strategy to ensure conservation of dry grassland specialists. This goal does not conflict with the specific demands of single taxa.