Snail Assemblages Research Articles

Animals and their epibiota as net autotrophs: size scaling of epibiotic metabolism on snail shells

AbstractAnimals are heterotrophic by definition, but species from many taxonomic groups are hosts to epibiota that may alter their net metabolism. We tested the degree to which snail-shell epibiota can generate net ecosystem productivity for snails and their epibiota (snail–epibiota ecosystems; SEEs) after accounting for snail respiration. We focused on 3 species from the Lavigeria snail assemblage in Africa’s Lake Tanganyika and quantified the scaling of SEE metabolism with shell size under light and dark conditions. The metabolism of snails and their epibiota shifted significantly across the size gradient. SEEs of large snails (>20 mm) were consistently autotrophic during the daytime, reflecting increases in shell algae as snails move into well-lit microhabitats after reaching a size refuge from predation by crabs. We extrapolated daytime individual SEE metabolism patterns to snail assemblages at 11 sites and found that SEEs range from heterotrophic to autotrophic in aggregate, reflecting spatial differ...

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

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.

Compositional variability of Pleistocene land snail assemblages preserved in a cinder cone volcano from Tenerife, Canary Islands

A Pleistocene land snail rich scoria sequence was studied to determine if it was influenced by taphonomic bias, climate change, or both, using a multifaceted approach that combines taphonomic, ecological, body size, and stable isotope data. Shell assemblages were sampled from two layers (Units A and B) in a cinder cone volcano of southern Tenerife (Canary Islands), dated to the glacial interval MIS 8 (~299–302ka). The two units differed in taphonomy, species composition, and abundance, with the upper Unit B showing higher diversity, abundance, and lower alteration than the lower Unit A. Larger bodied species dominated Unit A and were better preserved than smaller species. These mismatches likely resulted from physical differences in the sediment matrix surrounding fossils, with larger scoria grains of Unit A enhancing destruction rates and thus favoring preservation of larger (more durable) taxa than smaller scoria grains of Unit B. Comparisons with modern assemblages from the coastal scrub, the plant biome in which the Pleistocene site currently resides, indicates that no modern analogue exists for these fossil assemblages within this biome. Shell oxygen isotope values reveal that the local climate was colder/wetter during MIS 8 than at present, which also may explain variations in species composition through time. These data suggest that both taphonomic and climatic factors appear to have induced temporal variations in taxonomic composition, but it is difficult to determine which of these has more significantly influenced the observed results.

The role of dispersal and local environment in urban land snail assemblages: an example of three cities in Central Italy

Ecologists increasingly appreciate the central role that urban biodiversity plays in ecosystems, however much urban biodiversity is neglected, especially some very diverse groups of invertebrates. For the first time in southern Europe, land snail communities are analysed in four urban habitats along a geographical gradient of three cities, using quantitative methods and assessing the relative roles of local environmental conditions (“distance from sea”, “distance from city centre”, “vegetation cover”) and spatial effects by principal coordinate analysis of neighbour matrices, redundancy analysis and variation partitioning. A total of 53 species was recorded, a richness similar to that of natural areas. At habitat level, species richness did not show a clear increasing trend from more to less urbanized habitats, but rather a homogeneous pattern. At city level, study areas hosted rather heterogeneous species assemblages and biotic homogenization did not seem to have any impact; indeed, only three species could be considered alien. Variation partitioning showed that land snail communities were mostly structured by environmental factors, even when spatial structures independent of measured environmental variables were included: “vegetation cover” and “distance from city centre” were the environmental variables that explained most of the variation in species composition. The lack of strong spatial structure also unexpectedly suggested that transport by humans aids dispersal of organisms with low mobility, which are usually limited by spatial constraints in natural environments. These results provide ecological and conservation implications for other invertebrate groups, suggesting to set priorities in management strategies that include habitat conservation at local scale.

Snail (Mollusca: Gastropoda) assemblages as indicators of ecological condition in freshwater wetlands of Northeastern China

The utility of aquatic macroinvertebrates as indicators of the ecological conditions has long been established in rivers and streams. However, useful invertebrate indicators of wetland conditions remain more poorly developed probably because wetland macroinvertebrates have many attributes that reduce their ability to reflect wetland environmental quality. Snails, however, possess several attributes that should make them useful as potential environmental indicators. In this study, we sampled snail assemblages in 16 wetlands across a range of conditions, from relatively pristine “best available” reference sites to obviously human-impacted sites in Northeastern China’s Sanjiang Plain. We aimed to investigate the utility of snail taxa for indicating environmental variation across these wetland habitats. Results showed that study wetlands divided into three major groups using multivariate analyses: the five wetlands provided the most protection and having the least impacts grouped as apparent “references”, and ten other wetlands in obviously developed areas separated into two other groups of wetlands. Overall snail abundance was higher in the reference wetlands than the impacted wetlands. Seven of the snail species were indicators of specific wetland types. Five pulmonate species including Segmentina nitida, Segmentina hemisphaerula, and Planorbis corneus, Aplexa hypnorum (Physidae), and Galba pervia (Lymnaeidae) were indicators of reference wetlands. Non-pulmonate Bithynia ussuriensis (Bithyniidae) and Valvata sibirica (Valvatidae) were indicators of one of the categories of impacted wetlands. In NE China, snail assemblages and certain indicator species may provide a robust and rapid indicator of environmental impacts on wetlands. Because snails are distributed widely and are generally easy to sample and identify, this overall approach should have applicability in the many wetlands worldwide where diverse snail assemblages naturally occur.

Un village chasséen dans le Sud de la France: Cazan «le Clos du Moulin», Vernègues (Bouches-du-Rhône)

Une fouille réalisée en 2013 à Cazan «le Clos du Moulin » Vernègues (Bouches-du Rhône) a permis de mettre en évidence une importante occupation du Chasséen récent en fond de vallon. Aucun niveau de sol n’a été retrouvé, mais plus de 600 structures en creux permettent de documenter un des premiers sites d’habitat structuré de cette période dans le Sud de la France. Les attributions chronologiques reposent sur huit datations au 14C comprises en 4100 et 3800 avant notre ère et sur un abondant mobilier archéologique qui concorde avec l’attribution à une étape récente du Chasséen. Le gisement livre plusieurs fosses, des puits et une concentration de structures à pierres chauffées, mais aussi et surtout de nombreux trous de poteau et fosses d’implantation qui permettent de restituer les plans d’environ quinze bâtiments. Ces derniers correspondent notamment à dix édifices standards ; trois ensembles architecturaux plus imposants s’insèrent au sein de cette organisation et traduisent sans doute la présence d’édifices socialement plus valorisés. L’analyse du mobilier archéologique ne permet pas de déterminer assurément de chronologies relatives au sein de ces structures et aménagements, mais elle met en évidence plusieurs zones d’activités privilégiées en particulier pour le travail du silex et de l’obsidienne. Ces activités signent une occupation domestique a priori pérenne au sein d’un paysage largement anthropisé et maitrisé d’après les observations anthracologiques et malacologiques. L’ensemble de ces résultats tend à prouver l’attachement des populations chasséennes à ce territoire où elles se sont installées et ont vécues. Ce site permet donc enfin d’approcher pleinement la notion de village pour le Chasséen récent.

Longitudinal and lateral variation in snail assemblages along a floodplain continuum

Emerging theory suggests that biotic communities in floodplain wetlands should change longitudinally along a river’s length and be affected by lateral connectivity of floodplain habitats with main river channels. However, useful invertebrate indicators of floodplain condition remain poorly developed. Snails as a group possess several attributes that should make them useful as potential environmental indicators. In this study, we sampled snail assemblages in 12 floodplain wetlands along Wusuli River (headwater, mid, and downstream reaches) in Northeastern China’s Sanjiang Plain. In addition, at 10 sites, comparisons between river-connected and levee-isolated wetlands were performed. Results demonstrated that snail assemblages were concurrently being impacted by river reach, and whether the wetlands were isolated from the river, or not. Using multivariate analyses, the studied wetlands were divided into three major groups based on snail assemblages: downstream, mid, and headwater reaches. Seven snail species were significant indicators of these wetland groups. Because snail assemblages vary strongly both longitudinally along and laterally across floodplain habitats of Northeastern China, management of floodplains should recognize that landscape position plays an important role in local habitat ecologies, and that efforts to limit hydrologic connectivity across floodplains will have important consequences for resident biota.

Měkkýši přírodní rezervace U Nového hradu a přilehlé zříceniny (Česká republika) [Molluscs of the U Nového hradu Nature Reserve and the nearby castle ruins (Czech Republic)

This study deals with the land snails in the U Nového hradu Nature Reserve and the nearby castle ruins. The main goal was to make an inventory of the snail fauna and to determine factors affecting species diversity and snail abundance. Further, species richness and composition of the assemblages in the Nature Reserve and the castle ruins were analysed and compared. Snails were collected in summer 2015 by hand picking and litter sampling at 14 quadrats; 10 in the Nature Reserve and four in the castle ruins. In each quadrat plant cover, amount of coarse trees and stones were recorded. Soil pH and conductivity values were measured at each plot. In total, 50 species and 675 individuals of snails were found in all quadrats combined. In the Nature Reserve, 43 species and 406 individuals were recorded. In the castle ruins, there were 33 species and 264 individuals found. On average, higher number of species and individuals per plot were found in the castle ruins than in the reserve. Soil pH was the only variable significantly and positive correlating with the number of snail species recorded. This variable also predicted higher local species richness in the castle ruins than that of the reserve. Based on MDS ordination there was no clear segregation of snail assemblages recorded in the reserve and the castle ruins, though sites from the ruins were more similar to each other that those from the reserve.

Residential yards as designer ecosystems: effects of yardmanagement on land snail species composition.

Residential yards comprise the majority of green space in urban landscapes, yet are an understudied system because of access issues and because yards may be considered biologically depauperate. Yards are purposely created and managed and, hence, qualify as designer ecosystems, a term borrowed from restoration ecology. We investigated whether yard management (watering regime, mulching, and chemical use) or dog presence affected land snail assemblage composition and described the pattern of native vs. nonnative species among yards. Land snails form an appropriate model system for yard-scale studies because snails are speciose, common, and have limited mobility. We found 32 land snail species in our survey of 61 yards in Norman, Oklahoma, USA (population size of 118,000). Snail richness in individual yards averaged nine species, with a range of three to 14 species. Native snails were found in all yards and nonnative snails were found in all but one yard. Although some of the nine nonnative species were rare, the most frequently encountered species was the nonnative Triodopsis hopetonensis. All encountered nonnative species also occur in Oklahoma plant nurseries, indicating possible introduction through the plant trade. Yard-scale watering regime and the presence of dogs were associated with differences in snail species composition but not species richness. Pesticide use and mulch type had little, if any, association with snail composition. Effects may have been diluted by treating yards as units, whereas snails were concentrated in specific microhabitats, such as under shrubs. Soil type also influenced snail assemblages and acted at a scale larger than individual yards. Considering yards as designer ecosystems facilitates investigation of how local variation in management affects biota within yards and across the residential landscape, and highlights the importance of variation among residential yards in understanding patterns of urban biodiversity.

Drivers of Central European urban land snail faunas: the role of climate and local species pool in the representation of native and non-native species

The importance of macroclimate and dispersal limitation in the broad-scale variation of European urban land snail assemblages is likely to differ between native and non-native species because of the southern origin of many non-native snails, often spread by humans. We sampled land snails in each of 32 European cities and compiled from the literature a list of land snail species reported from the surroundings of each city. To quantify the predictive power of climate and local species pools, beta-sim dissimilarity matrices of both native and non-native species were explored using MDS and RDA ordination methods, Mantel tests with bootstrapping of each dataset, and multivariate homogeneity analysis of group variances. We observed no significant relation between the numbers of non-native species found in the cities and their surroundings (p > 0.133), while the percentage of native species in the cities derived from their local species pools decreased significantly with the increasing species richness of local faunas (rS = −0.75, p < 0.001). Assemblage variation of urban native species was explained mostly by the difference between mean January and July temperatures (21.3 %), with the major role of July temperature (18.0 %). In contrast, variation of non-native species assemblages was mainly explained by January temperature (19.9 %). The congruence in faunal similarities between the cities and the surrounding areas was higher in native (r = 0.46, p < 0.001) than in non-native species (r = 0.36, p < 0.001). Overall native faunas were significantly more homogeneous than the non-native faunas. Our results suggest that recent climate warming may foster geographical expansions of many non-native land snail species as their distributions are controlled mainly by January temperature.

Native and introduced land snail species as ecological indicators in different land use types in Java

We investigated the effects of different land use types and environmental parameters on the number and abundance of native and introduced land snail species in East Java. 2919 specimens were sampled and assigned to 55 species of which 8 are introduced. Whereas species richness was highest in primary forest, the highest number of introduced species was found in agroforest. The snail assemblages in different habitat types differ much clearer in composition than in total species richness. Plantations and agroforest are dominated by introduced pulmonates with regard to number of individuals, while primary forest is dominated by native prosobranchs. The habitat requirements of the introduced pulmonates differ from those of the native species. In the study area, the abundance of native as well as introduced pulmonate species increased with increasing human impact. However, the abundance of introduced pulmonate species decreased with increasing density of the canopy cover, whereas the abundance of native pulmonate species increased with increasing canopy cover. The abundance of native prosobranch land snails also tends to increase with increasing canopy cover and with the availability of deadwood, but decreased with increasing human impact. Improving the canopy cover and retaining deadwood in plantations and agroforests might help to control the populations of introduced species or even prevent their establishment in these habitats. Land snails are good indicators for the long-term stability of natural habitats, because several species are restricted to undisturbed natural habitats and because of their low dispersal abilities. However, complete inventories of land snail species are costly. Therefore we propose two indices that can be scored with much less effort, namely the percentage of prosobranch individuals and the percentage of individuals of introduced species. Both indices are significantly correlated with the number of native species. Dense plantations and agroforests bordering primary forests may protect the latter from introduced species and help to conserve the native fauna by reducing desiccation and buffering the human impact on the primary forests.

Semi-naturally managed forests support diverse land snail assemblages in Estonia

Snails are an integral part of most forest ecosystems where their sensitivity to timber harvesting depends on insufficiently understood interactions of multiple factors. Some snail species have been reported to indicate natural forest conditions, and deadwood-rich old growth stands are known to be particularly species rich. Other studies demonstrate rich snail fauna in young forests and hypothesize that clear-cutting is less detrimental on wet soils. We investigated forest management impacts on snail assemblages in hemiboreal Estonian forests. We sampled 100 stands using a balanced design of five site types and four management stages (old growth; mature forest; retention cuts and clear-cuts 4–19years post harvest). The material comprised ca. 12,500 live individuals and included 52 species of terrestrial shelled snails. Snail assemblages differed mostly among site types, and less among management stages. Dry boreal site type with a thick moss carpet, pine stands and little woody debris had the most distinct, impoverished assemblages. Harvesting-caused assemblage shifts were restricted to nutrient-rich and wet sites, but the assemblages recovered during maturing of the regrowth. We did not detect ‘life-boating’ function of solitary retention trees on cutover sites. One species, Vertigo alpestris, preferred old growth and abundant coarse woody debris appeared to be a reason for that. We conclude that seminatural forest management approach can sustain relatively intact snail assemblages in humid temperate climate and on calcium poor to moderately rich sites. The clearest long-lasting impact is the decline of some wetland species after draining.

Local and regional scale biodiversity patterns of forest snail assemblages in Tuscany (central Italy)

The land mollusc faunas of three forest areas of Tuscany (central Italy) were sampled to test the effect of geographical and environmental factors on the structure of biodiversity. A total of 60 sites were surveyed in the years 2009-2011, recording species richness and abundance of snails in 400 m2 plots randomly selected in beech and oak woods. Sampling strategy relied on a combination of visual search and litter analysis. Environmental variables (topsoil pH and altitude) and UTM coordinates were recorded to detect relationships with species richness and number of individuals per plot. Abundance data were analyzed using non-metric multidimensional scaling and canonical correspondence analysis; faunal similarity within and between areas was computed by the Bray Curtis index and snail assemblages of the two forest types were compared. A total of 55 species were recorded, with low values of local richness and abundance per site compared to other forest sites in central and northern Europe. Total richness was similar in the three areas, but composition and local richness varied significantly between them. Geographical factors explained the highest percentage of variance, while habitat type, altitude and pH only accounted for a minor part. Internal similarity was greater than between-area similarity in two out of three areas. Beech forests had richer and more heterogeneous faunas, but lower levels of abundance than oak woods. The results are discussed in terms of historical biogeography and local environmental conditions, and compared with those from similar surveys across Europe.

Land Snails, Sand Dunes, and Archaeology in the Outer Hebrides

Although the Western Isles have been subject to a number of recent archaeological investigations, there has been limited recent work on molluscan assemblages, despite the very good degree of preservation to be expected in a number of deposits and the significant work in the 1970s and 1980s on a number of sites such as Northton, Baleshare, and Hornish Point. In the meantime, land snail analysis has flourished in southern England and elsewhere in Europe, with the development of new techniques of numerical analysis such as the taxocene framework, the use of land snail assemblages in climate reconstruction, and recent refinements in amino acid dating. This paper provides a brief summary of the work to date on Hebridean snail assemblages, and presents preliminary results from work in progress, exploring aspects of site-formation processes, middening, land use, and relative dating that can be explored using land snails.

Invader–invader mutualism influences land snail community composition and alters invasion success of alien species in tropical rainforest

Mutualism between invaders may alter a key characteristic of the recipient community, leading to the entry or in situ release of other exotic species. We considered whether mutualism between invasive yellow crazy ant Anoplolepis gracilipes and exotic honeydew-producing scale insects indirectly facilitated land snails (exotic and native) via the removal of a native omnivore, the red land crab Gecarcoidea natalis. In plateau rainforest on Christmas Island, Indian Ocean, the land snail community was surveyed at 28 sites representing four forest states that differed in the density of red crabs, the abundance of yellow crazy ants and management history. One-way ANOVAs and multivariate analyses were used to determine differences in land snail species abundance and composition between forest states. Sample-based rarefaction was used to determine differences in species richness. The removal of the red land crab by supercolonies of yellow crazy ants was associated with a significant increase in the abundance of both invasive (14 species) and native (four species) land snails. Compositional differences in the land snail community were driven most strongly by the significantly greater abundance of a few common species in forest states devoid of red crabs. In forest where the crab population had recovered following management for ants, the land snail assemblage did not differ from intact, uninvaded forest. The land snail community was dominated by exotic species that can coexist alongside red crabs in rainforest uninvaded by exotic ants and scale insects. However, the ant–scale mutualism significantly increased land snail abundance and altered their composition indirectly though the alteration of the recipient community. We suggest these constitute ‘population-release’ secondary invasion in which the impacts of previously successful invaders facilitate a significant increase in abundance of other exotic species already established at low density within the community. Understanding facilitative interactions between invaders and indirect consequences of impacts will provide invaluable insights for conservation in heavily invaded ecosystems.

Comparison of plant and snail diversity patterns in the White Carpathian Mts (Czech Republic) across forest and grassland habitats

AbstractThe Bile Karpaty Mountains belong to the best-explored areas of the Czech Republic for both land snails and vascular plants, providing a unique opportunity for cross-taxa comparison of their diversity patterns. A total of 1,181 plant and 101 snail species, recorded in 45 grid cells of 2.8 × 3.1 km in size, were used for the analysis. We aimed to investigate the responses of forest and grassland assemblages separately, and to determine relative roles of environmental and spatial predictors on the compositional variation. We observed no significant correlation between the number of plant and snail species across the cells. While land snails showed a negative response to human-made habitats, a positive response was found for plants due to a high proportion of species confined to disturbed and ruderal habitats. Such differences can be attributed to different species pools of forest and grassland species and a high sensitivity of most land snails to habitat degradation and deforestation. In contrast, a positive correlation was found between grassland species as both groups positively responded to the same variables related to habitat diversity. Using the variance partitioning approach, we found a notably higher importance of spatial variables for grassland and forest plant assemblages, in contrast to snail assemblages, which were driven mainly by environmental conditions. These differences emerged especially for grasslands, most likely due to a long-term survival of several relict steppe plants and a notably higher species pool of grassland plants than that of snails.

COMPARISON BETWEEN DEATH AND LIVING LAND MOLLUSK ASSEMBLAGES IN SIX FORESTED HABITATS IN NORTHERN ITALY

In order to assess taphonomic pathways leading to preservation of land snail assemblages, the agreement between the death (DAs) and living assemblages (LAs) of land mollusk communities was evaluated in six forest habitats along an altitudinal and soil acidity gradient in Northern Italy, using data obtained by visual search and sorting of leaf litter and soil. Death assemblages were considered both as overall DAs and as DAs consisting solely of pristine (i.e., fresh) shells. Both calcareous and acidic soils showed high fidelity in richness and evenness, in particular leaf litter and soil samples, as can be expected in depositional environments with reduced time averaging. Lack of rank-order agreement in species relative abundance was observed in visual search (r = 20.37-0.45), while significantly high rank-order agreement (r = 0.61-0.89) in leaf litter and soil. Time averaging and interspecific variation in life span and in shell durability appear to determine the observed live-dead mismatch, which, in contrast, was probably not affected by between-habitat transport and temporal changes in community composition. Between-habitat differences are generally preserved in the DAs. DAs based on pristine shells do not show higher rank abundance correlations and smaller differences in ordinations than DAs based on all shells. But in terms of species richness and evenness, DAs composed only of pristine shells were more similar to the LA, in particular in leaf litter and soil, supporting terrestrial ecologists' approach in considering pristine shells in inventories of species richness. Distinguishing between pristine and worn empty shells is especially useful for actualistic studies in highly calcareous sites, where DAs are expected to encompass a longer temporal duration.

Quaternary perspectives on the diversity of land snail assemblages from northwestern Europe

The land snail assemblages in NW Europe exhibit marked gradients in diversity related to both latitude and longitude. These gradients, in turn, are linked to regional differences in temperature and moisture, although other non-climatic factors may be involved. Such diversity patterns have been described for the modern land snail faunas of NW Europe, especially those that inhabit forest. Here we provide an historical perspective on the development and composition of comparable land snail assemblages from various interglacials from the Middle and Late Pleistocene, and from the Holocene. We review the land snail assemblages from tufa sequences, which provide the best faunal records for each of the temperate periods. Data from 32 Quaternary sites in 7 NW European countries are considered. Assemblages from ‘forest optima’ of Pleistocene interglacial periods are richer in species compared with those from the Holocene. Correspondence analysis (CA) of data from 25 Quaternary sites in the regions where both Pleistocene and Holocene sites occur (i.e. southern England, northern France and Germany) resulted in a geographical separation of the assemblages into a western and eastern group. CA on each geographical group resulted in chronological divisions separating Pleistocene sites from the Holocene sequences. This separation results from the occurrence of numerous Central and Eastern European species in the Pleistocene faunas, whereas Holocene assemblages are characterized by species with mostly Western and Northern European modern ranges. This difference appears to reflect climatic influences, rather than resulting from anthropogenic effects. CA of 19 Holocene tufas produced geographical clusters clearly related to their position on a west-east gradient, presumably linked to some effect of ‘continentality’. During the mid Holocene, the diversity of forest snails from tufas in southern England exceeded the totals from the richest calcareous woodland sites in the region today. Further work is needed to establish whether this pattern holds for other regions of NW Europe.

Responses of forest snail assemblages to soil acidity buffer system and liming

Physiological constraints from harsh environmental conditions, such as from calcium limitation on acidic soils, is expected not only to affect species richness, but also species abundance distributions. Also, the effects of amendments by calcium addition (soil liming) on these assemblage characteristics are poorly understood. Because of their sensitivity towards calcium availability, we use snails as model organisms and integrate field surveys and literature data. Temperate forest snail data supported a rule-of-thumb calibration with pH measurements in water being one unit higher than in KCl buffer. The resulting large data set suggests stepwise changes in snail richness that occur at transitions in soil buffer systems, especially at pH 3.2. Species abundance distributions follow the logseries model in most soil buffer systems, except for the iron buffer range (pH ≤3.2) where they swap to the geometric model. Our findings thus suggest several smaller soil pH thresholds for snail assemblages associated with shifts between soil buffer systems, and a tipping point at the threshold to pH ≤3.2. Liming with ground carbonate rocks is a technique to temporarily increase soil pH and calcium availability in forest soils, but its effects on snail assemblages produced inconsistent results that did not meet expectations from the ameliorated soil pH and might warrant a re-evaluation of liming applications.

Effects of land‐use change on a diverse pleurocerid snail assemblage

AbstractThe highest worldwide diversity of snails in the family Pleuroceridae (Caenogastropoda) is found in the Mobile River Basin, Alabama, USA. Here 76 species of pleurocerids have been described and 31 species are now considered extinct due primarily to impoundments in the Alabama River Basin. Of the major basins, only the mainstem of the Cahaba River remains free‐flowing and so provides a refuge for pleurocerid diversity. Using collections, descriptions, and museum vouchers, the impact of changing land‐use on pleurocerid diversity was explored in the Cahaba River Basin.Decadal scale (10 to 20 years) and century scale (70 to100 years) changes in snail diversity within the Cahaba River were determined using information on species distributions based on historical (1880–1940) collections and from 1992, and 2005–2006 surveys.Before 1940, 20 species of pleurocerid snails were reported from the basin, but in 1992 and 2005–2006, only 15 species were recovered. Conversion of the lower portion of the Cahaba River Basin from forest to agriculture before 1940, followed by silviculture and severe downcutting of the channel from headcutting, may have caused the loss of these species. However, two species historically recorded in the basin are thought to be erroneous identifications and reflect the necessity of a complete taxonomic revision of this group.No basin‐wide changes in species richness and composition were detected between 1992 and 2005. Declines in richness among several reaches, however, resulted in the population fragmentation of five species which were reflected in differences in mean richness at the catchment scale. A significant, negative relationship between richness and urban cover between surveys best explained species losses.Despite taxonomic difficulties, these results indicate that land‐use conversion during the last century has had significant, adverse effects on pleurocerid diversity. Continued threats are expected given the projections of increasing human population density for the south‐eastern USA which may lead to further land‐use alterations and instream modifications.Copyright © 2014 John Wiley &amp; Sons, Ltd.