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Land snails are one of the most diverse groups of terrestrial animals and are commonly used as model organisms in ecology, biogeography and conservation biology. Despite being poor dispersers, they form crucial components of island faunas and exhibit high percentages of endemism. Insular land snails are also among the most threatened animals on Earth, already having suffered extensive human-caused extinctions. However, current estimates of global insular land snail diversity are based on sporadic records published at the scale of individual islands and/or archipelagos. To tackle this shortfall, we herein present the major features of a global inventory of island snails. We recovered full species lists from existing literature and available species checklists for 727 islands across the globe and collated a database which currently includes the occurrence of 11,139 species, that is approximately 48% of all known land snail species (of which there are an estimated 23,000). Seventy-five percent of the species are single-island endemics, underlining the exceptional nature of islands as global biodiversity hotspots. Overall, our attempt is one of few to examine insular invertebrate diversity at coarser scales and a crucial step to the study of global patterns in island biodiversity.

Aim: Island biological communities are considered to comprise non‐random assemblages from surrounding source pools, but whether they converge towards predictable structural properties remains unclear. Here, we (i) test whether insular communities of land snails converge towards similar functional and/or taxonomic properties and (ii) evaluate whether island functional diversity is determined by island biogeographical characteristics such as area and distance to the pool as well as human‐related variables. Location: Sixty‐six continental Aegean islands. Taxon: Land snails. Methods: We compiled a database of two morphological traits with functional significance (shell height and width) for 163 island species and 1529 species from the major species pools. We quantified inter‐specific morphological dissimilarity between pairs of islands (turnover), using a modified index of the mean nearest taxon distance. We tested for functional and taxonomic convergence using null models and assessing whether overall mean turnover among islands and pairwise island‐by‐island turnover were lower than expected by chance. We performed multiple regression analyses to test whether functional diversity metrics scale with island biogeographical characteristics and human‐related variables. Results: Our analyses provide strong evidence that communities of land snails across the Aegean islands converge towards non‐random functional properties and taxonomic structure. At the island level, a wide range of different shell shapes is observed, indicating greater functional richness than expected by chance. Regression analyses showed that island area is the only efficient predictor of functional diversity, indicating that available ecological/resource space is of central importance in driving the assembly of different shell shapes. Main Conclusions: Our findings, consistent with previous studies of other taxa from oceanic islands, highlight that island species communities are not randomly assembled and display convergence in their functional and taxonomic composition. Integrating functional diversity metrics within biogeographic analyses has the potential to further our understanding of island biodiversity patterns. [ABSTRACT FROM AUTHOR]

Understanding the properties of time averaging (age mixing) in a stratigraphic layer is essential for properly interpreting the paleofauna preserved in the geologic record. This work assesses the age and quantifies the scale and structure of time averaging of land snail-rich colluvial sediments from the Madeira Archipelago (Portugal) by dating individual shells using amino acid racemization calibrated with graphite-target and carbonate-target accelerator mass spectrometry radiocarbon methods. Gastropod shells of Actinella nitidiuscula were collected from seven sites on the volcanic islands of Bugio and Deserta Grande (Desertas Islands), where snail shells are abundant and well preserved in Quaternary colluvial deposits. Results show that the shells ranged in age from modern to ~48 cal ka BP (calibrated radiocarbon age), covering the last glacial and present interglacial periods. Snail shells retrieved from two of the colluvial sites exhibit multimillennial age mixing (>6 ka), which significantly exceeds the analytical error from dating methods and calibration. The observed multimillennial mixing of these assemblages should be taking into consideration in upcoming paleoenvironmental and paleoecological studies in the region. The extent of age mixing may also inform about the time span of colluvial deposition, which can be useful in future geomorphological studies. In addition, this study presents the first carbonate-target radiocarbon results for land snail shells and suggests that this novel, rapid, and more affordable dating method offers reliable age estimates for small land snail shells younger than ~20 cal ka BP. [ABSTRACT FROM AUTHOR]

Previously in this journal, Altaba (2015) presented an original hypothesis on the dispersal of small wetland snails in Central Europe after the Last Glacial Maximum, based on the discovery of rare species of the genus Vallonia at the foot of the Devín Hill (Slovakia). On the basis of the evidence available to us, it is our opinion that the existence of Vallonia declivis, Vallonia suevica, Vallonia enniensis, and Vallonia tenuilabris at Devín Gate has not been established, and that the hypothesis advanced in Altaba (2015) is therefore unsubstantiated by hard evidence. [ABSTRACT FROM AUTHOR]

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Aim We collate and analyse data for land snail diversity and endemism, as a means of testing the explanatory power of the general dynamic model of oceanic island biogeography ( GDM): a theoretical model linking trends in species immigration, speciation and extinction to a generalized island ontogeny. Location Eight oceanic archipelagos: Azores, Canaries, Hawaii, Galápagos, Madeira, Samoa, Society, Tristan da Cunha. Methods Using data obtained from literature sources we examined the power of the GDM through its derivative ATT2 model (i.e. diversity metric = b1 + b2Area + b3Time + b4Time2), in comparison with all the possible simpler models, e.g. including only area or time. The diversity metrics considered were the number of (1) native species, (2) archipelagic endemic species, and (3) single-island endemic species. Models were evaluated using both log-transformed and untransformed diversity data by means of linear mixed effect models. For Hawaii and the Canaries, responses of different major taxonomic groups were also analysed separately. Results The ATT2 model was always included within the group of best models and, in many cases, was the single-best model and was particularly successful in fitting the log-transformed diversity metrics. In four archipelagos, a hump-shaped relationship with time (island age) is apparent, while the other four archipelagos show a general increase of species richness with island age. In Hawaii and the Canaries outcomes vary between different taxonomic groups. Main conclusions The GDM is an intentionally simplified representation of environmental and diversity dynamics on oceanic islands, which predicts a simple positive relationship between diversity and island area combined with a humped response to time. We find broad support for the applicability of this model, especially when a full range of island developmental stages is present. However, our results also show that the varied mechanisms of island origins and the differing responses of major taxa should be taken into consideration when interpreting diversity metrics in terms of the GDM. This heterogeneity is reflected in the fact that no single model outperforms all the other models for all datasets analysed. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]