Mollusc diversity patterns in Central European fens: hotspots and conservation priorities

Aim To assess mollusc species composition and diversity patterns of treeless fen sites and to find simple environmental parameters that characterize diversity hotspots and priority sites for conservation.

Location Western Carpathian Mountains, Europe.

Methods Mollusc communities were sampled quantitatively from a homogeneous area of 16 m² in the central part of each of 145 treeless fen sites. Water conductivity and pH, geographical coordinates, altitude and habitat size of the sites studied, mean annual rainfall, mean annual temperature and mean January temperature were compiled for each plot. Nestedness in species composition was tested using the binmatnest program to confirm the ‘nested habitat-quality hypothesis’. Patterns in species diversity were analysed using the regression trees method to isolate the main predictors of species diversity.

Results Nested subset patterns of species composition were found along the gradient of mineral richness. Species distribution was highly nested (T_obs = 11.21, P << 0.001) in mineral-poor sites (with water conductivity < 300 μS cm⁻¹, n = 42) and was highly correlated with the site’s mineral richness (r_s = 0.76, P << 0.001). By contrast, species distribution and richness of mineral-rich sites (c.≥ 300 μS cm⁻¹, n = 103) were not controlled by mineral richness. Variation in species richness was further explained by January temperature, landscape geomorphology, and total habitat area. The southern mineral-rich low altitude fens were the most species rich, especially those of larger total area (23 species on average). These 24 sites (17% of all sites) harboured 90% of all recorded species, including all highly endangered ones. Mineral-rich fens in montane valleys were the second most important group because they hosted the majority of populations of two rare glacial relict species (Vertigo geyeri and Pupilla alpicola).

Main conclusions The significant nestedness raises the possibility of conserving the whole fen-mollusc species pool within the most species-rich sites. Thus, to select the conservation priority sites, easily available site characteristics for the prediction of species richness are needed. This knowledge can help us maintain fen biodiversity, which has become closely dependent on conservation management practices after the cessation of traditional mowing of fens for haymaking.