Vít Syrovátka

The distribution of chironomid larvae and oligochaetes within a stony-bottomed river stretch: the role of substrate and hydraulic characteristics

Combined oligochaete and chironomid data were analyzed to search for main gradients and the separate data sets were analyzed to identify the most important variables determining the structure of the communities. Preferences for particular hydraulic conditions, expressed as Froude number, were calculated for 29 most abundant taxa. The results of Correspondence Analysis (CA) indicated that the main gradient in the data could be explained by hydraulic conditions and, inversely, by the amount of sedimented particulate organic matter (POM). The second CA axis probably reflected the quantity of the available food and space resources. Canonical Correspondence Analysis (CCA) showed the amount of sedimented POM as the most important variable explaining 21 and 24 % of the variance in the oligochaete and chironomid data respectively. Among the other variables, the occurrence of aquatic vegetation, variability of nearbottom current velocity and substrate roughness were the most important.

Selection of indicative taxa for river habitats: a case study on benthic macroinvertebrates using indicator species analysis and the random forest methods

The aim of the study was to evaluate the exclusivity and/or preference of macroinvertebrate taxa for river habitats. Indicator species analysis and random forests methods were applied to the data set of macroinvertebrate samples taken from 58 sampling points. Samples were classified according to habitat types defined by the position in a river channel and local hydraulic characteristics. 86 macroinvertebrate taxa were included in the analyses. High indicative values for habitats (importance value ≥50 and/or indicator value ≥40) were identified for 26 taxa. The results of both methods can be considered similar. Merged habitats of channel margin (margin of main channel and side arms) were mainly defined by “negative” indicator taxa (correct classification of given samples was caused by non-occurrence and low abundances of certain taxa in this habitat). In general, there was only a small group of taxa preferring these habitats. Taxa were not fully habitat specific because they mostly occurred in two or three habitat types. This could be the result of autecological plasticity of individual taxa and the connectivity among habitats. According to the experience from this case study, it can be concluded that both random forests and IndVal methods are suitable for the detection of indicative species, and random forests method has some additional advantages.

Patterns of bryophyte and vascular plant richness in European subalpine springs

The diversity of spring habitats can be determined not only by local environmental conditions, but also by large-scale biogeographical effects. The effects can differ across various groups of organisms. We compared α-, β- and γ-diversity patterns of bryophytes and vascular plants of (sub)alpine springs in three contrasting mountain ranges: Alps (Switzerland), Balkans (Bulgaria), Western Carpathians (Slovakia, Poland). We used univariate and multivariate statistics to test for the effects of pH, conductivity, altitude, slope, mean annual temperature and annual precipitation on diversity patterns of both taxonomic groups and compared diversity patterns among the regions for particular pH and conductivity classes. We identified acidophyte and basiphyte, calcifuge and calcicole species using species response modelling. All regions displayed significant relationship between conductivity and α-diversity of vascular plants. Bulgaria showed the highest α-diversity of vascular plants for the middle part of the conductivity gradient. For both taxonomic groups, the β-diversity in the middle part of gradient was highest in Swiss Alps. The total species pool was lowest in Bulgaria. The percentage of basiphyte and calcicole species was highest in the Alps. In (sub)alpine springs, mineral richness was a better determinant of vascular plant α-diversity than pH, and the extent of the alpine area did not coincide with α-diversity. Observed inter-regional differences in diversity patterns could be explained by the different proportion of limestone bedrock and different biogeographic history. The differences in α-diversity between both taxonomic groups are presumably result of the different rates of adaptation processes.

Temporal and spatial macroinvertebrate variance compared: crucial role of CPOM in a headwater stream

The aim of the present study was to estimate the extent to which macroinvertebrate assemblages in a headwater stream are determined by environmental conditions and temporal dynamics. Six mesohabitats defined by substratum were sampled monthly throughout one year, environmental conditions at each sampling point being precisely described. Environmental variables could be truncated into two main gradients related to (a) the availability of food and space resources (CPOM) and (b) hydraulic conditions. The response of the macroinvertebrate assemblage to the environmental gradients and temporal dynamics were analyzed using GAM and (p)RDA. Twice as high portion of variance in the faunal data was attributed to environmental gradients compared to temporal dynamics. Total abundance, as well as the abundance of almost all feeding groups, was dependent on the availability of food and space resources (CPOM), while their proportions were determined by the quality of food resources driven by hydraulic conditions. Temporal dynamics was of lower importance. Our results suggest the role of CPOM be crucial in woodland headwater streams, as it greatly enhances habitat quality, serving both as a food source to dominant shredders and a space source to most macroinvertebrates.

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.

The response of chironomid assemblages (Diptera: Chironomidae) to hydraulic conditions: a case study in a gravel-bed river.

The response of chironomid assemblages to hydraulic conditions was analyzed within a gravel-bed river reach in central Europe. Multiple linear regression was used to quantify changes in the taxonomic composition along the hydraulic gradient. The results revealed that 47 % of the variability in the taxonomic compositional dis- similarity between pairs of samples could be explained by hydraulic conditions. Values of assemblage dissimilarity naturally increased with the increasing hydraulic difference between pairs of samples, however, the taxonomic composition of the assemblages changed faster at the beginning of the hydraulic gradient. According to the model, the assemblages of two streambed patches with the same hydraulic conditions differed in about 30 % of taxa, while the most hydraulically distant patches in about 65 % of taxa. To identify the taxa responsible for the shift in the chironomid assemblage, presence/absence and abundance of frequent taxa, as well as the proportions and number of taxa of chironomid subfamilies and the proportions of functional feeding strategies were modelled in relation to hydraulic conditions using Generalized Linear Models (GLM). The presence/absence of 15 taxa and abundance of 22 taxa (of the 29 taxa tested) showed a signifi cant response to hydraulic conditions. Of these taxa, all Orthocladi- inae showed a preference for hydraulically rough, while all Chironominae for hydraulically smooth conditions. The proportions and number of taxa of these subfamilies closely followed the responses of their individual taxa, when increased (in Orthocladiinae) and decreased (in Chironominae) along the hydraulic gradient. Tanypodinae showed a weak unimodal response. The proportions of feeding strategies were signifi cantly related to hydraulic conditions too. However, their responses were not in absolute agreement with the expected distribution of food resources - they probably rather indicated feeding potential of the assemblages than gave exact information about actually utilized food resources.

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.

Small ones and big ones: cross-taxon congruence reflects organism body size in ombrotrophic bogs

The monitoring of currently changing bogs has triggered a need to improve our understanding of correlations between different taxa. We analysed the cross-taxon congruence of six contrasting groups of organisms (vascular plants, bryophytes, fungi, diatoms, desmids and testate amoebae) in permanent plots located in differently polluted summit ombrotrophic bogs in two regions of the Czech Republic. In the suboceanic region, whose bogs are more uniformly polluted, the congruence was generally lower. Vascular plants, bryophytes and fungi showed the same gradient structure, while three groups of protists behaved rather independently of one another. In the subcontinental region where recent aerial liming created a new pH gradient, the congruence was generally higher. The main difference among different taxa corresponded clearly with body size and life span (microorganisms versus macroorganisms), conforming the previous results of a faster response of microorganisms to the artificially created pH gradient. Generally, vascular plants, bryophytes and fungi provided similar information, while diatoms behaved most independently. The major division among the study taxa coincided with body size rather than with nutrition or propagule size.

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.

The Chironomidae of the Western Carpathian helocrenes: Metacommunity structuring and its drivers in unique habitats

Springs are unique and vulnerable habitats, which have always been rather out of focus of the scientist interest. Nevertheless, they frequently host very diverse and species-rich assemblages with high proportion of species more or less adapted to their unique environment and can act as biodiversity hotspots in some areas. The Western Carpathian springs are helocrene springs and represent wide variety of different habitat types, from mineral rich sparsely-vegetated or bryophytes-rich covered helocrenes to acidic peaty sites. Such diversification allows the creation of highly diverse assemblages, in which Chironomidae usually dominate in both species richness and abundance. The aim of this study was to provide a comprehensive overview of chironomid assemblages inhabiting the unique environment of spring fens and factors driving the metacommunity structuring and populations of individual taxa. We examined chironomid assemblages of 62 small, treeless helocrenes sites, which are highly isolated from each other by the terrestrial environment constituting dispersal barriers such as the east-west oriented mountain ridges and valleys. The sampling was performed to cover mesohabitat heterogeneity of study sites. Two main mesohabitats were sampled, the plot with flowing water and coarser substratum near water source (the lotic mesohabitat), and water-logged soil with standing water (the lentic mesohabitat). Study sites hosted nearly 100 chironomid taxa, both mesohabitats were inhabited by chironomid assemblages similar in number of species and abundances and the local environment was proved to be the main driver of compositional changes in chironomid assemblages as expected. Moreover, the significant spatial structure of assemblages was found at the lentic mesohabitat, while biotic interactions described by the abundance of Gammarus fossarum and taxa richness and abundances of predators did not significantly contribute to compositional changes in assemblages at any mesohabitat. Nevertheless, taxa-specific responses revealed populations of many taxa significantly affected by biotic interactions, especially at the more stable lotic mesohabitat, which is in concordance with suggested greater importance of biotic interactions at stable environment. Our results emphasized the importance of multilevel approach in community ecology for proper distinction between different mechanisms of metacommunity structuring. Biotic interaction such as competition can result into the same community patterns as environmental filtering, thus the involvement of detailed analyses of species requirements and interactions is necessary.