No abstract

34In the face of ongoing habitat fragmentation, species-area relationships (SARs) have 35 gained renewed interest and are increasingly used to set conservation priorities. An 36 important question is how large habitat areas need to be to optimize biodiversity 37 conservation. The relationship between area and species richness is explained by 38 colonization-extinction dynamics, whereby smaller sites harbour smaller populations, 39 which are more prone to extinction than the larger populations sustained by larger sites. 40These colonization-extinction dynamics are predicted to vary with trophic rank, habitat 41 affinity and dispersal ability of the species. However, empirical evidence for the effect of 42 these species characteristics on SARs remains inconclusive. 43In this study we used carabid beetle data from 58 calcareous grassland sites to 44 investigate how calcareous grassland area affects species richness and activity density for 45 3 species differing in trophic rank, habitat affinity and dispersal ability. In addition, we 46 investigated how SARs are affected by the availability of additional calcareous grassland 47 in the surrounding landscape. 48Our results demonstrate that beetle species richness and activity density increase 49 with calcareous grassland area for zoophagous species that are specialists for dry 50 grasslands and to a lesser extent for zoophagous habitat generalists. Phytophagous 51 species and zoophagous forest and wet grassland specialists were not affected by 52 calcareous grassland area. The dependence of species on large single sites increased with 53 decreasing dispersal ability for species already vulnerable to calcareous grassland area. 54Additional calcareous grassland in the landscape had a positive effect on local species 55 richness of both dry grassland specialists and generalists, but this effect was restricted to 56 a few hundred meters. 57Our results demonstrate that SARs are affected by trophic rank, habitat affinity 58 and dispersal ability. These species characteristics do not operate independently but 59 should be viewed in concert. In addition, species' responses depend on the landscape 60 context. Our study suggests that the impact of habitat area on trophic interactions may be 61 larger than previously anticipated. In small habitat fragments surrounded by a hostile 62 matrix, food chains may be strongly disrupted. This highlights the need to conserve 63 continuous calcareous grassland patches of at least several hectares in size. 64 65

The impact of atmospheric N-deposition on succession from open sand to dry, lichen-rich, short grassland, and tall grass vegetation dominated by Carex arenaria was surveyed in 19 coastal dune sites along the Baltic Sea. Coastal dunes with acid or slightly calcareous sand reacted differently to atmospheric wet deposition of 5-8 kg N ha -1 y -1 . Accelerated acidification, as well as increased growth of Carex and accumulation of organic matter, was observed only at acid sites with pH NaCl of the parent material below 6.0. At sites with slightly calcareous parent material, increased N-deposition had no effect. A trigger for grass encroachment seems to be high acidification in early successional stages to below pH NaCl 4.0. Metals like Al or Fe become freely available and may hamper intolerant species. At acid sites, N-mineralization increases with elevated N-deposition, which may further stimulate Carex arenaria. Due to high growth plasticity, efficient resource allocation and tolerance of high metal concentrations, C. arenaria is a superior competitor under these conditions and can start to dominate the dune system. Carex-dominated vegetation is species-poor. Even at the moderate Nloads in this study, foliose lichens, forbs and grasses were reduced in short grass vegetation at acid sites. Species indicating these first effects of atmospheric deposition on dry, lichen-rich, short grasslands are identified and recommendations for restoration of grass-encroached sites given.