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Environmental drivers of mollusc assemblage diversity in a system of lowland standing water habitats



Druh Další prezentace na konferencích
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Popis The highest diversity of freshwater mollusc is known from lowland shallow standing waters with a rich littoral vegetation and mainly fine substrate. Local populations of aquatic molluscs, relying on passive dispersion, can be highly influenced by human-made habitat degradation, such as pollution and introduction of invasive species. Therefore the understanding the processes shaping their distribution, species richness and composition variation are very important. We studied aquatic mollusc assemblages in 62 pools, ponds and oxbows in the lowland of the lower Dyje River (southeastern Czechia), distributed cross a flat agricultural floodplain landscape, covering ca 50 km2. The environmental heterogeneity among the sites was expressed mainly by a high variation of vegetation cover and the nutrient content. For the analysis, we established 17 environmental variables divided into two groups: plot-specific variables and site-specific variables. In total, 33 species (25 gastropods and 8 bivalves) were recorded at 59 out of 62 studied sites. The abundance and species richness at a site level increased mainly with the increasing length of shoreline and lower nutrition concentration (i.e. chlorophyll a, cyanobacteria and pH). Additionally, at the level of sampling plots, total abundance and species richness increased towards a high vegetation cover, if the counts of the non-native Physa acuta excluded. Assemblage compositional variance was mainly controlled by nutrition concentration, interconnection with running water and substrate roughness. The plot specific and site specific variables explained all together 18.5% of variation in mollusc species composition, with only 3.4% of the variation shared. The pure effect or plot specific variables was 7.7% of species data variance, mostly related to transparency of water and presence of Lemna sp. The site specific variables, such as mainly electric water conductivity and classification site as fish area, explained 4.4% significant variation out of 6.5% of the pure explained variation in species data. The affiliation to site explained other 29.0% of species data, which was not associated with any measured variable. In this study, we determined the main ecological factors shaping the community of aquatic molluscs in a system of lowland water bodies, confirmed the assumption that species are distributed within the site mainly in the association with vegetation cover, and developed a methodology which can be easily applied to a wider area.
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