Vendula Polášková

Diversity patterns of aquatic specialists and generalists:contrasts among two spring-fen mesohabitats and nearby streams

Abstract Habitat specialists and generalists are known to differ in their width of environmental tolerance and their representation can vary along with the ecological contrast of habitats. In this study we explore factors shaping patterns of species richness and abundance of aquatic macroinvertebrate habitat specialists and generalists at isolated spring fens, separately for spring patch and spring brook mesohabitats at each site. We also examined habitat contrast of these unique island-like communities by the comparison of spring fen specialists and habitat generalists shared between the two spring fen mesohabitats and the nearest stream to each of 13 selects fen sites. Aquatic macroinvertebrates (Clitellata, Ephemeroptera, Plecoptera, Trichoptera, and Diptera) were investigated at 62 isolated spring fens, with 357 taxa identified in more than 172,000 individuals collected. We found that specialists experienced a stronger relation to local environmental conditions (i.e. the amount of dissolved oxygen and water conductivity) at both spring mesohabitats than generalists, primarily responding to fen habitat size. In contrast, responses of species abundances at spring patches and spring brooks differed as the abundances were controlled by the amount of oxygen in spring patches and by habitat size in spring brooks. Based on Trichoptera and Diptera assemblages we found a similar contrast between both spring fen sites and nearby streams. Our results suggest a higher resilience of specialist populations in well oxygenated sites and their competitive advantage over generalists at these sites, which stresses the importance to prevent any significant decrease of oxygenation (e.g., by eutrophication or drainage), especially in spring patches.

Environmental filtering of aquatic insects in spring fens: patterns of species-specific responses related to specialist-generalist categorization

Environmental factors driving compositional changes of headwater aquatic assemblages have been widely studied as these habitats are among the most vulnerable environments and host diverse and species-rich assemblages. However, responses of individual species to multiple environmental gradients remain poorly known, despite such information being essential for understanding the differences in metacommunity structuring. This study aims to explore species-specific responses to the main environmental gradients in Central European spring fens and to assess the responses in relation to the specialist-generalist categorization of species. In total, the responses of 40 species were analysed by GLM, cluster analysis and PCA. Spring-fen specialists responded predominantly to water temperature and the proportion of fine particulate organic matter in the substratum, while generalists responded mainly to flow conditions and oxygenation in the combination with various substratum characteristics. Our results revealed that it is not easy to find general patterns in species responses to environmental gradients. However, we found a clear distinction between specialist and generalist species in how the local environment affects their successful colonization and establishment of viable population. This result emphasizes the need to consider species specialization in future ecological studies of aquatic spring biota.

Spring-fen habitat islands in a warming climate: Partitioning the effects of mesoclimate air and water temperature on aquatic and terrestrial biota

Climate warming and associated environmental changes lead to compositional shifts and local extinctions in various ecosystems. Species closely associated with rare island-like habitats such as groundwater-dependent spring fens can be severely threatened by these changes due to a limited possibility to disperse. It is, however, largely unknown to what extent mesoclimate affects species composition in spring fens, where microclimate is buffered by groundwater supply. We assembled an original landscape-scale dataset on species composition of the most waterlogged parts of isolated temperate spring fens in the Western Carpathian Mountains along with continuously measured water temperature and hydrological, hydrochemical, and climatic conditions. We explored a set of hypotheses about the effects of mesoclimate air and local spring-water temperature on compositional variation of aquatic (macroinvertebrates), semi-terrestrial (plants) and terrestrial (land snails) components of spring-fen biota, categorized as habitat specialists and other species (i.e. matrix-derived). Water temperature did not show a high level of correlation with mesoclimate. For all components, fractions of compositional variation constrained to temperature were statistically significant and higher for habitat specialists than for other species. The importance of air temperature at the expense of water temperature and its fluctuation clearly increased with terrestriality, i.e. from aquatic macroinvertebrates via vegetation (bryophytes and vascular plants) to land snails, with January air temperature being the most important factor for land snails and plant specialists. Some calcareous-fen specialists with a clear distribution centre in temperate Europe showed a strong affinity to climatically cold sites in our study area and may hence be considered as threatened by climate warming. We conclude that prediction models solely based on air temperature may provide biased estimates of future changes in spring fen communities, because their aquatic and semiterrestrial components are largely affected by water temperature that is modified by local hydrological and landscape settings.

Variation of Clitellata (Annelida) assemblages related to water saturation in groundwater-dependent wetlands

Aquatic invertebrates of groundwater-dependent wetlands can be sensitive to a drop in the groundwater table, which is considered one of the possible impacts of climate change. We investigated whether aquatic clitellate species are able to dwell in waterlogged substrates without surface water, in 27 spring fens studied across the Western Carpathians. A total of 78 clitellate species were recorded in pairs of samples from aquatic and semi-aquatic habitats. Semi-aquatic habitats had 27 species in common with aquatic habitats, but algal and fungal feeders were less frequent and abundant, and predatory leeches and Haplotaxis gordioides completely lacking. Terrestrial enchytraeid species enriched the semi-aquatic assemblages. The main change in clitellate composition was controlled by total organic carbon. The importance of further variables, however, differed between aquatic and semi-aquatic sites. Further analyses of semi-aquatic sites showed that the distribution of primarily aquatic species was mainly driven by physical and chemical variables, while that of soil dwellers was driven by depth. Except Tubifex tubifex and Nais communis, all aquatic species preferred the uppermost layer. Results indicate that, during extreme droughts, when aquatic habitats cease to exist, some aquatic clitellates can persist in the waterlogged substrate, while some aquatic specialists may face the risk of local extinction.