Multi‐scale altitudinal patterns in species richness of land snail communities in south‐eastern France (original) (raw)
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Journal of Molluscan Studies, 2013
Although many studies have dealt with the spatial distribution of land-snail species and individuals, the effect of quadrat size on the interpretation of distributional patterns at small scales has rarely been investigated. We studied the spatial pattern of terrestrial snail distributions within a continuously sampled area of homogeneous habitat at very small scales (,1 m 2). The sampling was conducted in two contrasting habitat types: deciduous forests (29 sites) and treeless fens (23 sites) in Central Europe; each site consisted of three nested quadrats (25 Â 25 cm 2 , 50 Â 50 cm 2 and 75 Â 75 cm 2). On average the forest plots harboured higher numbers of species than fen plots and fen assemblages were composed of significantly smaller species in body volume. Numbers of species and individuals in smaller quadrats estimated from those present in larger ones often deviated significantly from those actually observed, showing frequently aggregated distribution of snails. These deviations were most marked for comparisons involving the smallest quadrats, whereas they almost disappeared in comparisons of large and middle-sized quadrats, both for species and individuals in both habitat types. Proportional deviances between collected and estimated numbers were always significantly higher for individuals than for species, with only one exception. Our results extend previous observations of land-snail spatial aggregations and they raise questions about environmental heterogeneity even in visually homogeneous areas or about possible biotic interactions among individual species. The steeper slope of the regression between area and numbers of species in log-log space from the smallest to the middle quadrat than from the latter to the largest quadrat, and the existence of several cases in which the observed richness was significantly greater than that predicted from rarefaction, suggest that even at this scale there are still idiosyncratic variations in the range of microhabitats available within quadrats.
Biological Journal of the Linnean Society, 2006
The latitudinal and altitudinal range sizes of northwest European land-snail species increase with increasing latitude/altitude. These Rapoport effects are not caused by northern/high-altitude species with wider latitudinal/ altitudinal ranges and southern/low-altitude species with narrower latitudinal/altitudinal ranges, as predicted by the climatic variability hypothesis. They are instead caused mainly by different northern/upper borders of species occurring in the south part of the study area or at low and intermediate altitudes, respectively. This pattern indicates that the observed Rapoport effects are the result mainly of differential northward/upward expansion of species that were restricted to southern/low or intermediate altitude refugia during the glacials. Although all species occurring in a refugium experienced the same climatic conditions, there is stochastic variation in their climatic tolerance. Species with broader climatic tolerance were able to expand farer northwards/upwards postglacial. The altitudinal distribution of species richness in the analysed alpine faunas cannot be explained by the Rapoport-rescue hypothesis, because species richness peaks at intermediate altitudes and because there is no negative correlation between the number of range borders and altitude. The Rapoport-rescue hypothesis alone is probably also insufficient to explain the decrease in species richness with increasing latitude.
Journal of Molluscan Studies, 2001
It is difficult to define precisely determinant environmental factors that explain land snail distribution and abundance, and most variables are often interrelated. In addition, studies have generally examined only a limited number of environmental variables, yielding a partial and local habitat description. Recognised determinant factors are: climate, vegetation and soil. Competitive interactions, historical factors and spatial structure are rarely included, although they could generate biogeographic patterns on a local or regional scale. The goal of the present work is to evaluate land snail habitat complexity by examining a wide range of environmental variables. Land snails from open environments were studied in a Provence range, the Grand Luberon, characterised by low variations in pH and calcium content. Grasslands on the ridges are maintained by sheep grazing. A stratified sampling was chosen according to altitude and vegetation structure. Sites were sampled throughout the range. Different vegetation structure types were analysed, from low grasslands to shrublands. Thirty-eight environmental variables were noted for each site. They described: (1) topography and climate, (2) habitat structure, (3) flora, and (4) spatial structure of snail communities. The main analytical method used was the partial Canonical Correspondence Analysis which yielded a partition of species variation into several independent components. The four environmental variable groups were used separately. We obtained a partition of ecological variation which emphasised the predominance of habitat structure over floristic composition and the important role played by environmentally independent spatial variables. Nevertheless, it remains difficult to discriminate between the influence of climatic factors s.s., historic events and/or biotic factors within the altitudinal gradient.
ecologia mediterranea, 2006
A complex of invertebrates (mites, Collembola, earthworms, snails, Diplopoda, Myriapoda, Chilopoda, Isopoda and insects) was uncovered in large breeding mounds made by the blind subterranean mole rat (belonging to the species Spalax carmeli Nevo & Ivanitskaya & Beiles, 2000 of the Spalax ehrenbergi (Nehring, 1898) superspecies) in the Haifa region, situated in the Northern Coastal Plain of Israel. The described properties of this complex were based on the 56 beetle species found there, mostly collected from the outer compact wall of the breeding mounds by forceps and exhausters. Most of the recorded beetle species were xerophiles or mesophiles and carnivores or detritivores. Only few species were phytophages, coprophages or necrophages. Since the invertebrate complex derives from the unique breeding mounds architecture, the mole rats can be considered as ecological architects of this microscale ecosystem.
Land Snail Communities in Mediterranean Upland Grasslands
Journal of Molluscan Studies, 2001
It is difficult to define precisely determinant environmental factors that explain land snail distribution and abundance, and most variables are often interrelated. In addition, studies have generally examined only a limited number of environmental variables, yielding a partial and local habitat description. Recognised determinant factors are: climate, vegetation and soil. Competitive interactions, historical factors and spatial structure are rarely included, although they could generate biogeographic patterns on a local or regional scale. The goal of the present work is to evaluate land snail habitat complexity by examining a wide range of environmental variables. Land snails from open environments were studied in a Provence range, the Grand Luberon, characterised by low variations in pH and calcium content. Grasslands on the ridges are maintained by sheep grazing. A stratified sampling was chosen according to altitude and vegetation structure. Sites were sampled throughout the range. Different vegetation structure types were analysed, from low grasslands to shrublands. Thirty-eight environmental variables were noted for each site. They described: (1) topography and climate, (2) habitat structure, (3) flora, and (4) spatial structure of snail communities. The main analytical method used was the partial Canonical Correspondence Analysis which yielded a partition of species variation into several independent components. The four environmental variable groups were used separately. We obtained a partition of ecological variation which emphasised the predominance of habitat structure over floristic composition and the important role played by environmentally independent spatial variables. Nevertheless, it remains difficult to discriminate between the influence of climatic factors s.s., historic events and/or biotic factors within the altitudinal gradient.
PLoS ONE, 2013
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.
Journal of Molluscan Studies, 2014
We investigated the land-snail fauna of rain forests on the eastern slopes of Pico Biao on Bioko Island in the Gulf of Guinea. Thirty-seven plots were studied along an altitudinal transect reaching from sea level (lowland rain forest) to an altitude of 1,830 m (mossy forest). A total of 1,755 specimens were collected and were assigned to 68 land-snail species. Eleven species were new records for Bioko. At least 15 of the recorded species are endemic to Bioko. The degree of endemism was high in mossy forest (23%) and in lowland rain forest (20%), but lower in montane forest (8%). Species richness showed a humpshaped distribution along the altitudinal gradient with a maximum at 500 m a.s.l. Species richness peaked in forests in which there had been selective logging more than 50 years ago, indicating that some disturbance may have beneficial effects on biodiversity. Species richness was correlated with the thickness of leaf litter. The availability and quality of suitable microhabitats is more important for the occurrence of snail species than gradients of otherwise often decisive environmental parameters like temperature, which are strongly correlated with altitude. A lack of clustering of the occurrences of different snail species along the altitudinal gradient indicated a Gleasonian meta-community structure with individualistic responses of the various species to environmental parameters. No negative co-occurrence patterns that might provide evidence for interspecific competition could be detected. The frequent coexistence of morphologically similar, and presumably ecologically equivalent, congeneric species may indicate that such equivalents do not exclude each other as predicted by the neutral theory of biodiversity. However, current knowledge about individual snail species is too scanty to exclude the possibility that niches of congeneric species differ in some details.
Urban Ecosystems, 2024
may be illuminated through investigations of biotic and abiotic changes across urban-to-rural gradients (McDonnell et al. 1997; Niemelä 1999, 2000). Such gradients, from densely built city cores to increasingly rural surroundings, reflect diminishing intensities of human intervention on originally similar land bases. Such a gradient occurs worldwide and provides a useful framework for comparative work on a global scale, because it reflects similar anthropogenic patterns and processes (Niemelä 2000; Niemelä et al. 2002). Terrestrial gastropods are good subjects to study the impact of urbanisation, because organisms with low dispersal capabilities, like snails and slugs, are very susceptible to anthropogenic activities (Ström et al. 2009). Microsnails (< 5 mm in diameter), in particular, are often more vulnerable to disturbance because of their very limited mobility and dispersal and their strong dependence on microhabitats (Baur and Baur 1988). For these reasons, land-snail community composition, especially where microsnails are included, is a good indicator of the overall health of an ecosystem (Frest 2002). A review by Yanes (2012)