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Calcareous forest seepages acting as biodiversity hotspots and refugia for woodland snail faunas

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Abstract

Land-snail species richness has repeatedly been found to increase with the increasing site calcium content and humidity. These two factors, reported as the main drivers of land-snail assemblage diversity, are also among the main habitat characteristics of calcareous seepages. Here we explore local species richness and compositional variation of forest spring-fed patches (i.e. seepages), to test the hypothesis that these habitats might act as biodiversity hotspots and refugia of regional snail faunas. In contrast to treeless spring fens, only little is known about land snail faunas inhabiting forest seepages. Studying 25 isolated calcareous forest seepages, evenly distributed across the White Carpathians Protected Landscape Area (SE Czech Republic), we found that these sites, albeit spatially very limited, can harbour up to 66% of the shelled land-snail species known to occur in this well-explored protected area (in total 83 species). By comparing land snail assemblages of the studied seepages with those occurring in the woodland surroundings of each site as well as those previously sampled in 28 preserved forest sites within the study area, we found the seepages to be among the most species rich sites. Although the numbers of species did not statistically differ among these three systems, we found highly significant differences in species composition. Seepage faunas were composed of many species significantly associated with spring sites, in contrast to the assemblages of both surrounding and preserved forest sites. Our results highly support the hypothesis that calcareous forest seepages might serve as refugia and biodiversity hotspots of regional land snail faunas. Protection of these unique habitats challenges both conservation plans and forest management guidelines as they might act as sources for the recolonization and restoration of forest snail assemblages particularly in areas impoverished by harvesting and clearcutting.

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The Evolutionary species pool hypothesis (ESPH) predicts that historically more common habitats will be richer in species because they have had greater opportunity for the evolution of suitably adapted species. We explored the relationship between mire species richness and pH, an important environmental variable in mires, in two regions that differ in habitat pH distribution: the West Carpathians and Bulgaria. Mire habitats in both the West Carpathians and Bulgaria demonstrate support for the ESPH prediction that habitats with more common pH values host more species. We also explored the influence of habitat history by examining the distribution of generalists and specialists along gradients of habitat pH, using extensive community-level vegetation data from European mires in these two regions. We found a striking pattern with the distribution of pH-specialists having three distinct peaks in both regions, whereas the total species pool peaked in near neutral pH habitats in both regions. Because the peaks in specialist richness do not correspond to regional pH distribution patterns, we hypothesize that historical explanations may be important, and that habitats currently rich in pH-specialists may have historically acted as pleniglacial refugia for many mire species. Our findings support the general predictions of the ESPH, but further suggest that historical processes such as patterns of glacial refugia, may significantly influence contemporary species distributions and the diversity of plant species in mire habitats.
Article
Aim To acquire general quantitative data on the molluscan faunas of floodplain pastures, assessing the influence of (minor) topographic variation on molluscan distribution. Additionally, to examine the potential for analogous comparison with fossil dataLocation The study was located within a relic watermeadow system currently used as floodplain pasture near Wylye, Wiltshire, U.K.Methods Mollusca were extracted from forty turf samples collected from relic carriers (cf. ridges) and relic drains (cf. furrows). Molluscan faunal differences between carriers and drains were assessed using TWINSPAN and diversity indices.Results The dry relic carriers, characterized by a short grassy sward, showed a low-diversity Trichia-Vallonia-Cochlicopa-Nesovitrea fauna. The damper relic drains, characterized by longer vegetation comprising both rushes and grasses, additionally contained other molluscan species indicative of wetter and/or more sheltered conditions and had significantly more diverse faunasMain conclusions Intra-site variability of molluscan faunas can be demonstrated with relatively minor changes in topography, hydrology and/or vegetation structure. In addition, the study clearly aids in the analogous interpretation of Holocene subfossil assemblages from the same region.
Article
Aim The goals of this study were to: (1) compare water conductivity and pH as proxy measures of mineral richness in relation to mollusc assemblages in fens, (2) examine the patterns of mollusc species richness along the gradient of mineral richness based on these factors, (3) model species–response curves and analyse calcicole–calcifuge behaviour of molluscs, and (4) compare the results with those from other studies concerning non-marine mollusc ecology. Location Altogether, 135 treeless spring fen sites were sampled within the area of the Western Carpathians (east Czech Republic, north-west Slovakia and south Poland; overall extent of study area was 12,000 km2). Methods Mollusc communities were recorded quantitatively from a homogeneous area of 16 m². Water conductivity and pH were measured in the field. The patterns of local species diversity along selected gradients, and species–response curves, were modelled using generalized linear models (GLM) and generalized additive models (GAM), both using the Poisson distribution. Results When the most acid sites (practically free of molluscs) were excluded, conductivity expressed the sites’ mineral richness and base saturation within the entire gradient, in contrast to pH. In the base-rich sites, pH did not correlate with mineral richness. A unimodal response of local species diversity to mineral richness (expressed as conductivity) was found. In the extremely mineral-rich, tufa-forming sites (conductivity > 600 μS cm−¹) a decrease in species diversity was encountered. Response curves of the most common species showed clear differentiation of their niches. Significant models of either unimodal or monotonic form were fitted for 18 of the 30 species analysed. Species showed five types of calcicole–calcifuge behaviour: (1) a decreasing monotonic response curve and a preference for the really acid sites; (2) a skewed unimodal response curve with the optimum shifted towards the slightly acid sites; (3) a symmetrical unimodal model response curve with the optimum in the base-rich sites, with no or slight tufa precipitation; (4) a skewed unimodal response curve but with the optimum shifted to the more mineral-rich sites; and (5) an increasingly monotonic response curve, the optimum in the extremely base-rich sites with strong tufa precipitation. Main conclusions Conductivity is the only reliable proxy measure of mineral richness across the entire gradient, within the confines of this study. This information is of great ecological significance in studies of fen mollusc communities. Species richness does not increase with increasing mineral richness along the entire gradient: only a few species are able to dwell in the extremely base-rich sites. The five types of calcicole–calcifuge behaviour seen in species living in fens have a wider application: data published so far suggest they are also applicable to mollusc communities in other habitats.
Article
Aim The term relict refers to a formerly widespread species currently occurring in refugia that provide a persistent combination of specific ecological conditions. In peatlands, direct palaeoecological evidence of relict status exists for some plant species and, in the case of calcareous sediments, for some snail species. We tested whether some species are significantly linked to old calcareous fens at the millennial scale independent of the effect of recent fen area. We focused on three organism groups – vascular plants, bryophytes and land snails – that differ in the degree of preservation of their remains in calcareous fen sediments and in their dispersal ability.
Article
Aim The objectives were to (1) analyse the combined effects of soil pH, Ca content and soil moisture on total density and species richness of land snails in forest ecosystems, (2) explore relationships between the quantitative composition of snail assemblages and habitat characteristics, (3) investigate the relationships between soil pH and density of some of the most frequent species, and (4) compare the data with those from studies conducted in other temperate-humid regions of Europe. Location Study sites were selected from 15 landscape types including different lithologies within the area of Baden-Württemberg (35,000 km2), SW Germany. Methods Snails were recorded quantitatively from 83 study sites, with four plots representing a total of 0.25 m2 per site. Topsoil samples from each site were analysed for pH, exchangeable Ca, and Ca content of carbonates. Three categories of soil moisture (dry, intermediate and wet) were established and defined according to the (climatic) water balance. Numbers of individuals and species were brought in relation to soil moisture and soil pH. Cluster analyses were conducted to identify groups of quantitatively similar snail species assemblages. Results Topsoil pH (2.7–7.5) and soil Ca contents were closely correlated. On dry soils, total snail density and species richness are generally low and do not change with pH, but clearly increase with increasing pH on intermediate moisture soils and on wet soils. On the latter, numbers of individuals and species are generally much higher compared with intermediate moisture sites at the same value of soil pH. Changes of density in relation to soil pH vary between species. Depending on the species, density increases only in the lower or only in the higher range of pH, is not related to pH, or decreases with increasing pH. Furthermore, these patterns vary within the same species depending on the region. This became evident from comparisons with other studies, particularly between sites in SW Germany and southern Scandinavia. From cluster analyses, subgroups of snail assemblages of high quantitative similarity were identified. Group formation is explained by soil pH to some extent, and one subgroup showed a connection with coniferous woodland sites on acidic soils. No further environmental factors available from our data could explain the clustering of snail assemblages more detailed. Main conclusions Soil moisture is the strongest determinant of snail density and species richness at undisturbed woodland sites, but effects of soil moisture and soil pH on these patterns are closely interrelated on intermediate moisture soils and wet soils. However, the quantitative species composition of the land snail assemblages is related to soil properties to a lower degree than snail density and species richness, and other habitat characteristics such as vegetation or litter quality, can be important for species dominance in addition.
Article
Mire terminology, subdivision and gradient structure have been subjected to an intense debate intensified in the last years. The conception of Wheeler and Proctor (J. Ecol. 88, 187–203), which divides mires into bogs, having pH<5.5, and fens, having pH>5.5, becomes generally accepted despite a certain critique from the Scandinavian perspective and despite the fact that few contributions to the debate have come from central and southern Europe and from other than botanical disciplines. In this paper, we demonstrated that the bog-fen boundary is clearly determinable not by pH, but by a set of nutrient-requiring species that avoid truly ombrotrophic conditions in central Europe. We therefore defined fens as groundwater-fed wetlands that host low productive nutrient-limited vegetation dominated by Cyperaceae and bryophytes. The fertility gradient within fens, another controversial point in the ongoing debate, is easily distinguishable using both plant and animal data, but it appears primarily within calcium-richer fens. We suggest defining fen grasslands by the high abundance of nutrient-requiring grasses and forbs rather than purely by fen origin and management. Concerning pH/calcium gradient, there is large variation in plant, mollusc, algal, fungal and testacean assemblages within fens with a pH>5.5 in central Europe even though some authors named all mires having such pH ‘(rich) fens’. This clear and extended poor–rich (pH/calcium) gradient in floristical data is independent of the fertility gradient. Conductivity (approximating water mineral richness) contributes significantly to the pH in explaining the vegetation variation. Vegetation composition accounts for a larger amount of the variation in algal, molluscan, testacean and fungal assemblages than even long-term measured environmental data. The chemical limit of the occurrence of any Sphagnum species, even the calcitolerant ones, is the most important and easily recognised natural boundary between major functional fen types, although it varies among regions and hydrological situations. We therefore believe that fen classification based exclusively on floristic data is necessary to avoid circular argumentation and provides the best basis for the characterization of habitats. We propose to subdivide fens into five standard vegetation types with defined boundaries: poor fens (Sphagno recurvi-Caricion canescentis), moderately rich fens (Caricion fuscae), rich fens (Sphagno warnstorfii-Tomenthypnion), extremely rich fens and calcareous fens (both corresponding to Caricion davallianae). Calcareous fens were neglected during the ongoing debate due to its relative scarcity in some traditionally explored regions. Its ecological boundary is the point at which calcium carbonate starts to precipitate, which is connected with marked change in plant and animal species composition. The ecological differentiation of all proposed fen types was tested using a data set from two different regions (Carpathians and Bulgaria). Both conductivity and pH differ significantly between pairs of vegetation types. All proposed fen types also markedly differ in molluscan assemblages.
Article
I propose and develop a new classification system to explain diversity patterns in habitat fragments, equally applicable to islands and other inherently patchy ecosystems. My primary goal is to provide an inclusive model to improve the comparability of studies and enhance future efforts to synthesize their findings, yielding a generalized basis for understanding species composition in patchy ecosystems. Differentiating islands from fragments and incorporating patch age and patch: matrix contrast, eight classes of patch are distinguished, spanning a range of geographical features. To compare studies of diversity patterns among and between patch types, patch biota are divided into three categories based on their origin—relict species (present before fragmentation), matrix-derived species and interpatch dispersers. Applying this novel scheme to existing data, the effects of insularization are synthesized. Direct comparisons among fragments revealed broad similarity in the long-term effects of habitat fragmentation compared with highly divergent patterns in younger landscapes (<200 years). Holding patch: matrix contrast and age constant, fragments and islands were compared. Despite initial differences in community assembly, the biota of islands and fragments converge in several properties over time, as diversities stabilize and patch biotas become distinct from the surrounding matrix. Although necessarily broad, this framework provides an explicit context within which to test forty-four specific predictions regarding the distribution of diversity in patchy landscapes and thereby gain a clearer understanding of the long-term biological consequences of insularization. I propose that the fragments-as-islands analogy be revisited, potentially yielding valuable insight into the long-term future awaiting anthropogenically altered ecosystems.
Article
The aims of this study were to analyse whether land snail assemblage patterns reflect the gradient of calcium content on a very small scale within a site. We chose two sites differing in their calcium richness and source of the calcium. The "Tufa site" had abundant tufa in the soil, while the "Boulder site" was on chemically inert chert bedrock where calcium originated from vegetation. On each site a set of 20 quadrats from which snails were extracted was laid down in a line from the calcium rich patch to the calcium poorer surround matrix. At the both sites, available calcium contents of topsoil decreased significantly with samples' position from the patch centre. For the Tufa site, calcium content was a strong controller not only of species composition but also species richness, total abundance, and abundances of almost all species. At the Boulder site only species composition was significantly driven by calcium. Species composition was highly nested along calcium gradient at the Tufa site contrary to the Boulder site where the species had an almost random distribution. We conclude that the best predictor of species composition was in both cases content of carbonate calcium in topsoil. Topsoil pH was positively correlated with calcium content only at the Tufa site.
R: a Language and Environment for Statistical Computing. R Foundation for Statistical Computing
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Maltz, T.K., 2003. Life cycle and population dynamics of Helicodonta Obvoluta (O.F. Müller, 1774) (Gastropoda: Pulmonata: Helicidae). Folia Malacol. 11, 63e88.
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