Historical and environmental influences on hedgerow snail faunas

In three areas of the English Midlands, composition and diversity of hedgerow snail faunas are influenced both by historical and environmental differences between hedges. Soil aciditv and climate are the most important environmental factors. Hedges originating in or near woodland have richer faunas than those planted in open fields, and some snail species are indicators of woodland origin. Snail diversity also increases with the age of the hedge, but this effect is slight in hedges over 100 years old. It is suggested that these differences are primarily due to the poor dispersal of snails rather than to existing environmental differences between hedges of differing age and origins, and the results are compared with the very similar ones obtained for plants. Historical influences on the distribution ol slow-dispersing organisms may be of very general importance, even in comparisons of adjacent habitats with considerable temporal stability.     

History, island area and habitat availability determine land snail species richness of Aegean islands

Aim We examined the species-area relation of Aegean land snails, comparing different models to describe the relation. By examining those factors other than area that may also affect species richness, we tested whether the Aegean land snail fauna was more influenced by equilibrial migration and colonization processes, or rather is conservative and relictual. Location The Aegean archipelago (Greece). Methods Sixty-five islands were examined. Data were taken from own collections and from literature sources. Multiple regression analysis was used to test the null hypothesis of no relationship between species richness and island area, elevation, distance to the next larger island, and the presence and extent of calcareous substrate. Results The single most important factor determining land snail species number was area. While colonization-extinction dynamics have frequently been cited to explain this result, this conclusion was not tenable in this study as it was contradicted by species number not being related to the islands’ distances to neighbouring larger islands, after accounting for other factors affecting species number. We also found that habitat diversity affected species richness even after accounting for the effects of area: both increased elevation and greater extent of calcareous substrate on islands resulted in higher species number. This effect was most likely due to the fact that particular ecological conditions increased the probability that particular species could survive on an island. We compared the utility of the power and extreme-value function models of the species-area relation and found that both gave substantially the same results. However, fitting the power function model using nonlinear regression was of questionable utility. Main conclusions We conclude that the snail fauna of the Aegean is relictual, not equilibrial. The unusually high number of land snail species found on Crete is consistent with this conclusion. Crete is a currently united island which was separated into at least six smaller islands for 7–9 million years during the Neogene. Our results are consistent with the hypothesis that Crete still hosts a large number of endemic species of these paleoislands, resulting in a total number of species in excess of what would be expected based on area alone.     

Forest snail diversity and its environmental predictors along a sharp climatic gradient in southern Siberia

Diversity patterns of forest snail assemblages have been studied mainly in Europe. Siberian snail faunas have different evolutionary history and colonization dynamics than European faunas, but studies of forest snail diversity are almost missing from Siberia. Therefore, we collected snails at 173 forest sites in the Russian Altai and adjacent areas, encompassing broad variation in climate and forest types. We found 51 species, with a maximum of 15 and an average of seven species per site. The main gradient in species composition was related to soil pH, a variable that also positively correlates with snail abundances. The second gradient was associated with climate characteristics of winter. We observed significant differences in both species richness and composition among six forest types defined based on vegetation classification. Hemiboreal continental forests were the poorest of these types but hosted several species characteristic of European full-glacial stages of the Late Pleistocene. A high snow cover in Temperate coniferous and mixed forests, protecting the soil from freezing, allowed the frost-sensitive large-bodied (>10 mm) species to inhabit this forest type. In contrast to most of the European snail assemblages studied so far we found that the factors responsible for the variation in species richness differed from those driving species composition. This may be attributed to the sharp climatic gradient and the presence of the cold-adapted species typical of the Pleistocene cold stages. We suggest that southern Siberian forests hosting these species can serve as modern analogues of full-glacial forests in periglacial Central and Eastern Europe.     

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.     

THE GEOGRAPHY OF COEVOLUTION: COMPARATIVE POPULATION STRUCTURES FOR A SNAIL AND ITS TREMATODE PARASITE

Gene flow and the genetic structure of host and parasite populations are critical to the coevolutionary process, including the conditions under which antagonistic coevolution favors sexual reproduction. Here we compare the genetic structures of different populations of a freshwater New Zealand snail (Potamopyrgus antipodarum) with its trematode parasite (Microphallus sp.) using allozyme frequency data. Allozyme variation among snail populations was found to be highly structured among lakes; but for the parasite there was little allozyme structure among lake populations, suggesting much higher levels of parasite gene flow. The overall pattern of variation was confirmed with principal component analysis, which also showed that the organization of genetic differentiation for the snail (but not the parasite) was strongly related to the geographic arrangement of lakes. Some snail populations from different sides of the Alps near mountain passes were more similar to each other than to other snail populations on the same side of the Alps. Furthermore, genetic distances among parasite populations were correlated with the genetic distances among host populations, and genetic distances among both host and parasite populations were correlated with “stepping-stone” distances among lakes. Hence, the host snail and its trematode parasite seem to be dispersing to adjacent lakes in a stepping-stone fashion, although parasite dispersal among lakes is clearly greater. High parasite gene flow should help to continuously reintroduce genetic diversity within local populations where strong selection might otherwise isolate “host races.” Parasite gene flow can thereby facilitate the coevolutionary (Red Queen) dynamics that confer an advantage to sexual reproduction by restoring lost genetic variation.     

The influence of recent geography, palaeogeography and climate on the composition of the fauna of the central Aegean Islands

Partial Mantel tests and structural equation models were used to investigate the influence of recent geography, palaeogeography and climate on the composition of the fauna of the central Aegean Islands. The composition of land snail and isopod island faunas was significantly influenced by recent and by Pliocene geography. Only Pleistocene palaeogeography had a significant influence on the composition of tenebrionid beetle island faunas. The composition of butterfly island faunas was influenced by recent and by Miocene geographical distances. The composition of reptile island faunas was correlated with recent and Pliocene geography as well as with Pleistocene and/or Miocene geographical distances. Island area influenced only the composition of the island faunas of the volant butterflies, and not that of the less mobile land snails, land isopods, tenebrionid beetles and reptiles. This might indicate that butterflies are able to colonize large islands with suitable habitats even if such islands are comparatively far from source areas more frequently than can the nonvolant groups. Influence of a climatic parameter, namely annual precipitation, on faunal composition was found only for reptiles.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 785–795.     

The biogeography of land snails in the islands of the Gulf of Guinea

Data on land snail diversity in the Gulf of Guinea islands is presented and the biogeography of the Gulf of Guinea fauna is discussed with reference to island snail faunas in the other areas of the world. Although the land snail faunas of the four islands clearly have west and central African affinities, speciation events following rare colonizations have led to high rates of endemism at the species and generic levels. The influence of island size, altitude, isolation and other factors on the development of the land snail faunas is discussed. The effect of land use changes on the land snail fauna over the last 150 years is evaluated. Current threats include recent changes in agricultural practice leading to the destruction of snail habitats in both forest and plantation areas. The potential threat posed by introduced species is also discussed. The Gulf of Guinea snail faunas appear to be in relatively good health in comparison to many other island snail faunas. However, the uniqueness of the faunas makes it imperative that further ecological and taxonomic research is undertaken both to understand the processes by which they developed and to evaluate the current status of many species in terms of distribution and threats.     

Cambrian to Cretaceous changes in hardground communities

The changing nature of the communities of boring and encrusting taxa found on upward-facing hard-grounds has been studied from the standpoints of (a) diversity, (b) faunal composition, and (c) nature of the niches occupied. After a rapid initial increase in the early Palaeozoic, diversity remained at much the same level from the Middle Ordovician until the late Cretaceous. However, there is a considerable turnover in the identity of the individual taxa between successive sample intervals. The incoming and outgoing of the major groups parallel their fortunes in the marine realm as a whole. Niche analysis suggests that the same feeding levels are occupied for most of the history of hardground communities, but Mesozoic faunas contain a much higher proportion of species with true exoskcletons, or which lived infaunally. The evolution of these forms was probably influenced by the Mesozoic radiation of marine predators and duriphages, but it also resulted in Mesozoic hardground faunas being more resistant than their Palaeozoic counterparts to episodic corrasion. Resulting higher population densities in the Mesozoic were probably one reason why cavity faunas beneath some of these hardground surfaces are more diverse than those beneath Palaeozoic examples. □ Hardground, community, evolution.     

Diversity partitioning in Permian and Early Triassic benthic ecosystems of the Western USA: a comparison

This paper compares the relative contributions of within-habitat diversity [alpha-diversity] and between-habitat-diversity [beta-diversity] to regional diversity [gamma-diversity] in marine benthic communities of the western US before and after the end-Permian mass extinction. We found that presumably cool-water faunas from the Permian Gerster Limestone and the Park City Formation had low alpha- and beta-diversities, comparable to those of low diverse faunas of the Early Triassic. In contrast, tropical Permian faunas had much higher alpha-diversities and a variable pattern of beta-diversity: Whereas faunas of space-limited bioherms show a positive correlation between beta-diversity and gamma-diversity, beta-diversity in level-bottom faunas is elevated only when gamma-diversity is very high (>250 species). This contrasting pattern probably reflects differential effects of interspecific competition on habitat partitioning. In low-competitive level-bottom faunas, species are able to coexist until competition forces species into their ecological optima, thereby increasing beta-diversity. This effect occurs at much lower gamma-diversities in more competitive reef-bound faunas, causing the observed positive correlation between beta- and gamma-diversity. We suggest that differences in the level of interspecific competition and hence diversity partitioning between Permian and Triassic benthic communities result from the higher average metabolic rates in the Mesozoic mollusc-dominated benthos in contrast to their Permian counterparts.     

Chance and necessity: land-snail faunas of Sao Miguel, Azores, compared with those of Madeira

The land-snail faunas of 23 sites from forest, disturbed andopen habitats were sampled on São Miguel, Azores archipelago.Collectively, the samples contained nearly all the known faunaof the island. Forest sites were the richest; while the numberof non-endemic species differed little between habitats, forestsheld more endemic species, many of which were widely distributed.Open habitats have no unique endemic species. These resultsare compared with similar data from Madeira. Although the twoislands are of the same size, and share the same Laurisilvaforest cover, their faunas differ in important aspects of diversity.While many non-endemic species are common to both islands, andoccur in similar numbers, endemic species are more numerouson Madeira, even though the numbers at individual forest sitesare, on average, fewer than on São Miguel. Many endemicsare confined to open, coastal habitats. These differences arediscussed in terms of the islands' histories, the range of habitatsavailable and the ease of dispersal from continental sources.Age, accidents of colonization and the range of natural habitatsavailable must have major effects on the faunas, but presentendemic faunal diversity is more a product of speciation andextinction than of immigration. (Received 13 May 2006; accepted 7 July 2006)     

Mitochondrial DNA phylogeny and morphological diversity in the genus Mastus (Beck, 1837): a study in a recent (Holocene) island group (Koufonisi, south-east Crete)

Three endemic Cretan land snail species of the genus Mastus (Beck, 1837) from the island group of Koufonisi (south-east Crete) and the eastern part of Crete, were studied by multivariate analysis of shell morphology and analysis of mtDNA sequences. The phylogeny of the populations studied and the processes effecting the genetic and morphological diversity of the species were investigated. Extremely high mtDNA sequence divergence was observed both within and between populations. The Cretan populations could not be distinguished morphologically, while the populations of the islets were more distinct. We argue that the active geological past of the area (including sea level changes) and the long-term presence of humans has produced a mixing up of Mastus populations leading to the accumulation of high divergence of mtDNA sequences on a small spatial scale. The limited morphological diversity and the distinct shell 'identity' of the islets' populations can be attributed to the selective pressures of the island group.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 383–399.     

The origin and diversity of Drilus Olivier, 1790 (Elateridae: Agrypninae: Drilini) in Crete based on mitochondrial phylogeny

We investigated the phylogeography and speciation of Drilus in the Mediterranean, with focus on the Aegean and especially Crete. Altogether 12 species were sequenced for two fragments of the cytochrome c oxidase subunit I gene (cox1–3′ and cox1–5′ mtDNA) and provided 1381 nucleotides. Both fragments were analysed under the maximum likelihood criterion and Bayesian inference separately and concatenated as a single dataset. The Drilus species from the Peloponnese, the Ionian islands and Crete did not form a monophylum. Drilus sp. E from the Peloponnese and Zakynthos was sister to D. mauritanicus Lucas from Spain in most cases. The remaining Greek Drilus species formed a robustly supported clade in all analyses; however, the species from Crete do not seem to be monophyletic. Estimating species divergences using BEAST, we found out that the key dates in the west Aegean Drilus phylogeography appeared to be the Tortonian Crete–Peloponnese separation (12–9 Mya), the desiccation of the Mediterranean basin during the Messinian Salinity Crisis (5.96–5.33 Mya), and the repeated fragmentation of Crete during the Pliocene and Pleistocene. Within the Drilus lineages, we obtained a substitution rate estimate of 2.75% divergence per million years, which is in excellent agreement with previous studies. A Generalized Mixed Yule Coalescent (GMYC) analysis suggested the presence of six Drilus species in Crete (seven species in total, since the DNA sequences were not available for D. creticus Pic); however, we formally identified and (re)described only four which can be morphologically defined: D. creticus, D. longulus Kiesenwetter, D. horasfakionus sp. nov. and D. baenai sp. nov. These species are endemic to Crete and surrounding islets. Their diagnostic characters are illustrated and an identification key to males of these species is provided. The intraspecific variability, distribution and ecology of all species are discussed and suggestions for further research are given.

http://zoobank.org/urn:lsid:zoobank.org:pub:F8DDBCC1-C2D1-48F7-BE99-55D9ED4C2234     

Forest snail faunas from Transylvania (Romania) and their relationship to the faunas of Central and Northern Europe

Forty‐three forest sites in seven sampling areas in mountainous parts of Transylvania were sampled to obtain inventories of their snail faunas, and to make comparisons between these and the faunas of similar sites further north along the Carpathian chain. Sampling areas ran from close to the Ukrainian border in the north to Retezat in the south‐west. Altogether, 83 species were found, as well as between 19 and 40 species at individual sites. Sites within the same sampling area had more species in common than in among‐area comparisons, although differences between areas did not relate to the distance between them. Such differences appear to be related more to ecological factors than to geography. Faunas of all areas were very similar to those recorded from the Polish and Ukrainian Carpathians; distance from these northern faunas had little effect on similarity. More broadly, the fauna of these forests shows a much greater affinity to those of countries to the north than to those of countries to the south. Despite the survival of forests through the last glacial period of the Pleistocene, and the greater proximity to potential Mediterranean refugia, these faunas appear to be mainly a subset of those found further north. They represent a rather small proportion of the known Romanian fauna, in which there are many endemics restricted to other habitats. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 471–479.     

Land snail faunas of the Napier and Oscar Ranges, Western Australia; diversity, distribution and speciation

The snail faunas of the Napier and Oscar Ranges, Western Australia have two major components: large camaenid species which are restricted endemics, with tiny geographical distributions and a pattern of geographical replacement within the Ranges, and smaller species of wider distribution, most of which are found throughout the Ranges. Sampling of 55 similar sites, protected from fire, over the length of the Ranges reveals this pattern clearly, with γ diversities being far higher for camaenids than for others, in which there is no pattern of geographical replacement. This difference is not found in temperate and subtropical snail faunas from elsewhere, nor does the camaenid pattern occur in surveys of diversity in other organisms. These results are discussed in terms of dispersal and allopatric speciation related to demonstrable environmental fluctuation. An additional finding is that within one major taxonomic group (Gastropoda), a community may be partly structured by competition and exclusion and partly by accidents of colonization and accumulation: some, but not all niches may be full.     

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.     

Similarity in ectoparasite faunas of Palaearctic rodents as a function of host phylogenetic, geographic or environmental distances: Which matters the most?

Different host species harbour parasite faunas that are anywhere from very similar to very different in species composition. A priori, the similarity in the parasite faunas of any two host species should decrease with increases in either the phylogenetic distance, the distinctness of the environments occupied or the geographical distance between these hosts. We tested these predictions using extensive data on the faunas of fleas (Insecta: Siphonaptera) and gamasid mites (Acari: Parasitiformes) parasitic on rodents across the Palaearctic. For each pair of host species, we computed the similarity in parasite faunas based on both species composition as well as the phylogenetic and/or taxonomic distinctness of parasite species. Phylogenetic distances between hosts were based on patristic distances through a rodent phylogeny, geographic distances were computed from geographic range data, and environmental dissimilarity was measured from the average climatic and vegetation scores of each host range. Using multiple regressions on distance matrices to assess the separate explanatory power of each of the three dependent variables, environmental dissimilarity between the ranges of host species emerged as the best predictor of dissimilarity between parasite faunas, especially for fleas; in the case of mites, phylogenetic distance between host species was also important. A closer look at the data indicates that the flea and mite faunas of two hosts inhabiting different environments are always different, whilst hosts living in similar environments can have either very similar or dissimilar parasite faunas. Additional tests showed that dissimilarity in flea or mite faunas between host geographic ranges was best explained by dissimilarity in vegetation, followed by dissimilarity in climatic conditions. Thus, external environmental factors may play greater roles than commonly thought in the evolution of host-parasite associations.     

Cytochrome b sequences reveal Acomys minous (Rodentia, Muridae) paraphyly and answer the question about the ancestral karyotype of Acomys dimidiatus

Sequences of the cytochrome b (cyt b) mitochondrial gene show that the spiny mouse Acomys from Crete, known as the endemic species A. minous, is composed of two distinct maternal lineages ("A" and "B"). Group "A" sequences cluster with A. nesiotes (Cyprus) and group "B" sequences cluster with A. cilicicus (Turkey), which is evidence of paraphyly of A. minous in regard to these two species. From cyt b sequences, the three taxa are very closely related to A. cahirinus (Egypt): the maximum divergence found among these sequences is 1.6%, which is equivalent to the intraspecific diversity observed in other Acomys species. Paleozoology evidenced that man unintentionally introduced Acomys into Crete and Cyprus during antiquity. The divergence time between Acomys cyt b sequences found in Crete was estimated at 0.4 Myr, which means that the diversity observed did not appear after the introduction but reflects a much more ancient polymorphism. Cytochrome b phylogeny and cytogenetic data together comprise evidence that, within the species A. dimidiatus (Saudi Arabia, Israel, Egypt), it is the karyotypic form with 36 chromosomes that derives from the form with 38 chromosomes, due to a single acrocentric fusion.     

Diversity biases in terrestrial mammalian assemblages and quantifying the differences between museum collections and published accounts: A case study from the Miocene of Nevada

Understanding diversity through time in the fossil record has primarily relied on the raw count of species within a given time interval, or species richness. These estimates are often derived from published fossil data, and standardized for sample size or geographic area. However, most methods that standardize richness by sample size are sensitive to changes in evenness, which introduces a potential problem with relying on published records: published accounts could be more even than the museum collections from which they are drawn. We address this bias in the context of mammalian paleodiversity, comparing published and museum collections of the Hemphillian Thousand Creek fauna to those of the Barstovian Virgin Valley fauna. We rarified specimen data, both number of identified specimens (NISP) and minimum number of individuals (MNI), and presence/absence data to compare published and museum data within and between faunas. Within faunas, published numbers of specimens are more even than museum samples, but the difference for localities in Virgin Valley is not significant. Neither published nor museum numbers of specimens indicate a significant difference between faunas, but the diversity pattern is reversed between the two data sets. Presence/absence rarefactions show no differences between sources; here, published data adequately sample the underlying museum records. Specimen-based evenness is not accurate in the published sample, and therefore we suggest that future studies of diversity in terrestrial mammalian assemblages must assess unpublished collections. Additionally, NISP data for Thousand Creek are more even than MNI data, suggesting that relying solely on NISP for assessing species diversity can also be misleading. Because publication bias alters richness and evenness, diversity estimates using published data must be circumspect about data sources.