Michal Horsák

The age of island-like habitats impacts habitat specialist species richness.

While the effects of contemporaneous local environment on species richness have been repeatedly documented, much less is known about historical effects, especially over large temporal scales. Using fen sites in the Western Carpathian Mountains with known radiocarbon-dated ages spanning Late Glacial to modern times (16 975-270 cal years before 2008), we have compiled richness data from the same plots for three groups of taxa with contrasting dispersal modes: (1) vascular plants, which have macroscopic propagules possessing variable, but rather low, dispersal abilities; (2) bryophytes, which have microscopic propagules that are readily transported long distances by air; and (3) terrestrial and freshwater mollusks, which have macroscopic individuals with slow active migration rates, but which also often possess high passive dispersal abilities. Using path analysis we tested the relationships between species richness and habitat age, area, isolation, and altitude for these groups. When only matrix-derived taxa were considered, no significant positive relation was noted between species richness and habitat size or age. When only calcareous-fen specialists were considered, however, habitat age was found to significantly affect vascular plant richness and, marginally, also bryophyte richness, whereas mollusk richness was significantly affected by habitat area. These results suggest that in inland insular systems only habitat specialist (i.e., interpatch disperser and/or relict species) richness is influenced by habitat age and/or area, with habitat age becoming more important as species dispersal ability decreases.

Land Snail Faunas in Polish Forests: Patterns of Richness and Composition in a Post-Glacial Landscape

ABSTRACT We examine variation in species richness, species composition and distance decay in similarity in forest snail faunas from Poland and a small part of Transcarpathian Ukraine, and their connection with geographical position in relation to Pleistocene refugia. Forest faunas were sampled from sites of standard size in each of ten regions. Data were analysed using DCA and partial CCA, extracting the geographical, climatic and ecological correlates with the major axes. Relationships among site and regional faunas were further examined through the Simpson Index of Similarity. Site species richness shows no significant variation with geographical position or climate, but relates to soil and vegetation characteristics. Composition varies with location; southern highland faunas differ from one another far more than do northern lowland faunas, showing a clear east-to-west pattern of change. The aggregate highland fauna is richer than that of the lowlands, which is a subset of the former. Two intermediate upland regions show different associations, one with the highlands the other with the lowlands. Lowland faunas, even over large distances, are very similar, and all relate more closely to the western end of the highlands than to the east. Disaggregating the fauna into large and small species shows that the former show a stronger geographical pattern than the latter; most universally distributed species are small. Latitudinal variation in regional richness, and longitudinal differentiation among highland faunas relate to distance from glacial refugia. This is not reflected in site species richness, raising questions about the assembly rules for local faunas. The western bias in the relationships of lowland faunas to those of the highlands, the differences between large and small species and the varying rates of faunal turnover within the area studied suggest that patterns of post-glacial dispersal are complex and incompletely understood.

Deterministic assembly of land snail communities according to species size and diet

1. We investigated whether coexisting snail species in 145 treeless fen communities in the Western Carpathian Mountains differed more in size and diet than would be expected by chance, as predicted for traits commonly associated with competition and differential resource acquisition under limiting similarity theory. 2. Contrary to expectations, coexisting snail species were no more different in body size than expected by chance under a null model. However, variation in body size played a significant role in structuring snail communities: coexisting snail species were significantly more similar with respect to body size. 3. We developed two new test statistics to expand our investigation of limiting similarity to include diet, a nominal trait. We tested whether communities of snails were characterized by a greater richness of diet, and whether different diets were represented more or less evenly within communities. Communities of snails were significantly less evenly distributed than expected by chance, with detritivores being over-represented relative to predatory strategies. 4. We also examined the effect of water pH and conductivity, herbaceous cover, and bryophyte and vascular plant richness, on these trends by examining how the effect size of our tests varied across these gradients. Convergence in species size increased with increasing habitat pH. Specifically, smaller snail species were over-represented in fen communities in general, and this effect was accentuated in increasingly calcareous fens. 5. Theory predicts that traits related strongly to environmental conditions are more likely to be convergent. Our findings support this suggestion, as small snail species have an advantage in tolerating freezing conditions over winter when refuges are limited. 6. These results add to the growing body of literature demonstrating that variation in body size and diet play a strong role in structuring communities, although frequently in ways not predicted by limiting similarity theory. Finally, our results increase our understanding of how species are assembled non-randomly into communities with respect to important traits.

Using multi-proxy palaeoecology to test a relict status of refugial populations of calcareous-fen species in the Western Carpathians

The distribution pattern of relict and specialised species in calcareous fens was revealed to be non-stochastic, with ancient fens harbouring more of these species than younger ones. This phenomenon could be caused by long-lasting in situ survivals over millennia, but direct palaeoecological evidence is lacking. We addressed the question whether at least some ancient calcareous fens indeed retained open-fen patches throughout the Holocene, using a palaeoecological approach involving proxies with different taphonomies (pollen, vascular plants, bryophytes, molluscs). We identified three old fens in the Western Carpathians, where several postglacial relict species have recently been found, and we reconstructed their histories with respect to sedimentary processes, vegetation structure and dynamics of relict species. The development at all the sites started with a (semi)-open fen community dominated by sedges and brown mosses. The site with the highest recent number of relict species was reconstructed to harbour open patches continually since the late Glacial to the present, including the middle Holocene when open-fen patches were restricted. By contrast, at the site with the lowest recent number of relict species, a large sedimentary hiatus suggested peat mineralisation or erosion that prevented the survival of light-demanding species. At all the sites, characteristic snails of European Glacial periods occurred during fen initiation, but disappeared around the early/middle Holocene transition. The probability of a relict species being present in a modern fen community increases with fen age, but it also depends on the continual existence of open-fen patches and peat accumulation throughout the middle Holocene.

Woodland mollusc communities along environmental gradients in the East Carpathians

Mollusc communities were sampled quantitatively at eleven sites representing different environmental conditions in the Bieszczady National Park (East Carpathians Mts, Poland). Overall 61 species were recorded. Alder forest in the valleys (AF; Alnetum incanae carpathicum, Caltho-Alnetum, secondary alder forest) hosted the richest fauna, with up to 41 species occurring sympatrically on 100 m2 of forest floor and average density ca. 750 specimens m−2. Three important ecological controllers of species composition and community structure were found. The main predictor of mollusc assemblage composition was calcium content; the first DCA axis of molluscs most significantly and highly correlated with calcium content in the leaf litter and organic matter in the upper layer. The second axis significantly correlated with altitude and negatively with annual temperature, and thus can be explained as an elevational gradient. We observed slope aspect to constitute the third significant gradient. On the basis of forward selection in CCA analysis organic matter in the upper layer of soil was the best predictor of species composition, which explained 26% of total variance. It comes to prove that in mountain forest on non-calcareous bedrock molluscs obtain calcium mainly from leaf litter.

Disjunct Occurrences of Plant Species in the Refugial Mires of Bulgaria

Many mire vascular plant and bryophyte species have disjunct occurrences in Bulgaria despite that most of south-eastern Europe is not suitable for the occurrence of permanently waterlogged and nutrient-limited wetlands due to the current and glacial dry climate conditions as well as prevailing limestone bedrock. Unfortunately, such important distributional data are scattered throughout numerous papers and reports, and are not adequately provided even by national checklists and floras. No attempt to summarize them has been done yet. Therefore, the main aim of this paper is to review and enlarge such data, and to use the resulting data set to address the question whether the disjunctly occurring rare species are concentrated in certain mire complexes or even in particular vegetation plots and if they do characterize such localities. Our current research shows that the phenomenon of isolated occurrences of mire plants in Bulgaria is even more widespread than previously thought. Seventeen species were found as new for Bulgaria with their distribution range limits there, and distributional data of many other species, including some previously considered extinct, were enlarged. Fifty-four mire species were found at only three or fewer sites. Our analyses showed a conspicuous concentration of rare, disjunctly occurring species at a few sites, which are, however, largely unexplored in terms of palaeoecology or ecology, not legally protected and currently threatened by human activities. The distributions of target rare species within Bulgarian mires were significantly nested, which means that more species-poor assemblages were subsets of richer ones. Nestedness was significantly related to the estimated area of mire complex, but not all high-diversity mires were large. Disjunctly occurring rare species were more concentrated in particular vegetation plots at lower altitudes and in mineral-rich fens. Fragmentary data about the ecology and history of Bulgarian refugial mires suggest that these mires harbour specific ecotypes and genotypes, contain specifically distributed biogeographic groups of species, provide an opportunity to test biogeographical hypotheses and shelter crucial information about the history of European mires. Thus, these sites have a potential to become a source of very important information for biogeographical, palaeoecological, and phylogeographical analyses.

Early occurrence of temperate oak-dominated forest in the northern part of the Little Hungarian Plain, SW Slovakia

Using a multi-proxy analysis of a postglacial sedimentary sequence from a lowland wetland, we address the possible drivers of change in the wetland habitats and surrounding landscapes of southwestern Slovakia. A 5 m-deep core in the Parížske močiare marshes was investigated for pollen, plant macro-remains, molluscs, organic content and magnetic susceptibility. The palaeoecological record extends from the Pleistocene–Holocene transition (≥11,200 cal. BP) to the 5th millennium cal. BP and was correlated with a macrophysical climate model (MCM) and archaeological data. Our results show the transformation of an open parkland landscape with patches of coniferous forest to a temperate deciduous forest at the onset of the Holocene. The record is remarkable for an early occurrence of Quercus pollen and macro-remains around 11,200 cal. BP and its early expansion (10,390 cal. BP) in the vegetation. Such an early spread of Quercus has not previously been recorded in the region, where Corylus is usually the first to expand among temperate trees. This unusual development of forest communities was most probably triggered by a short-lived increase in precipitation and decrease in temperature, as reconstructed by the MCM model. Higher moisture availability and low temperature inhibited Corylus and favoured the spread of Quercus. Later, the climate became drier and warmer, which, together with fires, supported the expansion of Corylus. Since 7300 cal. BP, human activities became most likely the dominant influence on the landscape. Deforestation contributed to soil erosion, which halted the accumulation of organic material after 5520 cal. BP, followed by the accumulation of clay sediments.

Diversity and Biotic Homogenization of Urban Land-Snail Faunas in Relation to Habitat Types and Macroclimate in 32 Central European Cities

The effects of non-native species invasions on community diversity and biotic homogenization have been described for various taxa in urban environments, but not for land snails. Here we relate the diversity of native and non-native land-snail urban faunas to urban habitat types and macroclimate, and analyse homogenization effects of non-native species across cities and within the main urban habitat types. Land-snail species were recorded in seven 1-ha plots in 32 cities of ten countries of Central Europe and Benelux (224 plots in total). Each plot represented one urban habitat type characterized by different management and a specific disturbance regime. For each plot, we obtained January, July and mean annual temperature and annual precipitation. Snail species were classified into either native or non-native. The effects of habitat type and macroclimate on the number of native and non-native species were analysed using generalized estimating equations; the homogenization effect of non-native species based on the Jaccard similarity index and homogenization index. We recorded 67 native and 20 non-native species. Besides being more numerous, native species also had much higher beta diversity than non-natives. There were significant differences between the studied habitat types in the numbers of native and non-native species, both of which decreased from less to heavily urbanized habitats. Macroclimate was more important for the number of non-native than native species; however in both cases the effect of climate on diversity was overridden by the effect of urban habitat type. This is the first study on urban land snails documenting that non-native land-snail species significantly contribute to homogenization among whole cities, but both the homogenization and diversification effects occur when individual habitat types are compared among cities. This indicates that the spread of non-native snail species may cause biotic homogenization, but it depends on scale and habitat type.

Patterns of Land Snail Assemblages along a Fine-Scale Moisture Gradient

ABSTRACT We studied changes of terrestrial snail assemblages over a gradient of soil moisture using 60 sampling plots in the White Carpathian Mountains of the south-eastern Czech Republic. We used within-site design to control for confounding effects of site characteristics other than humidity, and we directly measured soil moisture along nine transects at distinct locations. Each transect had from 4 to 16 plots, and it was laid down from wet calcium-rich spring fen habitats to semi-dry meadows in the fen surroundings. We observed a sharp moisture gradient along each transect, with the measured soil moisture varying from 97% in fen plots to 19% in semi-dry grassland plots. Altogether 29 land snail species and 4,213 live individuals were collected. Species richness of land snails varied from 2 to 11 species per plot. However, we did not observe any significant linear or unimodal response of species richness or total abundances to measured soil moisture. In contrast, sharp compositional changes along studied transects were found, suggesting differences in species preference to soil moisture conditions at fine, within-site scale. Among 21 species with the frequency higher than five, 10 (after a Bonferroni correction) showed a significant response to soil moisture. Three species expressed significant affinity to drier plots, five species were more abundant in moister plots and only two species preferred middle values. In several previous studies, both linear and hump-shaped relation between soil moisture and number of land snail species were documented. This raised questions about general response of land snails to soil moisture and the importance of possible bias caused either by using only estimated values of site moisture or sampling in distinct sites differing also in other environmental factors that might potentially overtopped importance of soil moisture for land snail distribution.

Exceptionally poor land snail fauna of central Yakutia (NE Russia): climatic and habitat determinants of species richness

There is an ongoing debate on the causes of the latitudinal diversity gradient, but diversity decline towards high latitudes is poorly documented for many invertebrate taxa. Therefore, we sampled land snail assemblages at 79 sites and in various habitat types in central Yakutia, a region with extremely continental, cool and dry climate. We tested whether habitats lacking suitable shelters for winter survival harbour less species than those with vegetation cover that softens climatic extremes. Both local species diversity and regional species diversity were extremely low: 13 species were recorded in total with an average of 1.4 species per site. While the majority of grassland sites were without snails (26 of 34 sites), forest sites supported at least one snail species in most cases (38 of 45 sites). Within grasslands, snail occurrences were associated with a higher herb-layer biomass. Numbers of snail species correlated with the amount of available calcium only in forests, in which species accumulation towards more favourable habitats was possible due to softening of climate harshness. As minute snails are known to be effective passive dispersers and the study area was not glaciated during the last glacial stage, there was certainly enough time for colonization of all favourable habitats. Our results suggest climatically driven limitations of both local and regional land snail diversity in central Yakutia. We conclude that the hypothesis of climate harshness remains the most probable explanation of a sharp drop in land snail diversity in high-latitude areas with cold climate.