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Littoral vegetation predicts mollusc distribution in a network of unconnected small karstic lakes in the Mediterranean zone of Albania
Abstract
Small lakes and ponds in karstic systems have received little attention in terms of mollusc research. Although these systems represent a refuge for lentic biota in most of the Mediterranean, there are virtually no ecological studies from many regions, including Albania. Therefore, we quantitatively studied mollusc assemblages at 58 sampling sites within a compact karstic area of Central Albania and measured a set of potentially important environmental variables. Only nine ubiquitous species, including three non-native mollusc species, were recorded. Gyraulus albus, Radix auricularia and Physa acuta were the most frequent species. Individual sites hosted notably species-poor assemblages, ranging between zero and six species, with more than half of the studied sites being unoccupied. Mollusc presence was predicted mainly by fine substrate, depth of soft sediment and high transparency. Despite the importance of calcium for molluscs, more species were recorded at sites with a low calcium concentration. Regression tree analysis explained 40% of the total variation, defining reed cover and lake surface area as the most important variables for mollusc species richness. Based on mollusc species composition, the sites were clustered into four groups, differing mainly in submerged littoral vegetation cover, depth of soft sediment and reed cover. Our results showed that limited development of littoral vegetation and the area of lakes are the major drivers for mollusc species presence and their distribution in the studied network of unconnected karstic lakes.
Species distribution and assemblage structuring are influenced by a combination of species dispersal mode and the dispersal routes used. Habitat connectivity is particularly important for passively dispersing taxa such as freshwater molluscs. In addition, current anthropogenic eutrophication affects the structure of assemblages by reducing native fauna and promoting the spread of generalist species. Here, we examined mollusc assemblages in two systems of small lakes differing in hydrological connectivity. The assemblages of 22 isolated lakes in Albania were mainly controlled by the distance between the lakes with a lower contribution of environmental conditions and lake area. In contrast, assemblages of 52 interconnected lakes in Czechia were driven primarily by environmental conditions. However, as lake trophic status increased, the assemblages in Czechia became more homogeneous in species composition as high trophic status filtered out all species except generalists. These assemblages from 33 eutrophic lakes were strongly determined by environmental variables, whereas the remaining assemblages from 19 low trophic lakes were structured by a combination of spatial and environmental variables. We conclude that hydrological connectivity between lakes is crucial for the distribution of molluscs, but eutrophication may influence the importance of individual mechanisms structuring mollusc assemblages.
Freshwater mollusc diversity has repeatedly been found to peak in lowland stagnant waters, which are highly exposed to human-made degradation and the spread of non-native species. Despite the increasing loss of these habitats, little is known about the main predictors of their mollusc diversity patterns. Therefore, we aimed to determine the environmental drivers of mollusc assemblage variation between and within sites by sampling 62 water bodies in the Dyje River floodplain (south-eastern Czechia). We measured 14 environmental variables, categorized as site-specific or plot-specific. Species richness and abundances were analysed by GLM and GEE; species compositional variance was assessed by NMDS and db-RDA ordinations. Mollusc species richness, ranging between 0 and 15 species per site, and abundance sharply decreased towards high trophy sites, with the chlorophyll-a concentration and water pH highly correlated with species counts. Species compositional variation was driven mainly by water trophy and the quality of organic detritus. Site heterogeneity turned out to significantly control local assemblages of molluscs, while the presence of individual species seemed to be filtered by site trophy and the shoreline length. Thus, to maintain high regional diversity of aquatic molluscs in lowland agricultural landscapes, the presence of low trophy sites seems to be essential.
During a field trip to the western part of the Balkan Peninsula in 2016, investigations of several caves and karstic springs revealed six new gastropod species living in subterranean waters and resulted in some noteworthy faunistic records. Five of the new species are assigned to the genus Paladilhiopsis Pavlović, 1913, namely P. prekalensis sp. n., P. lozeki sp. n., P. szekeresi sp. n., P. wohlberedti sp. n., P. falniowskii sp. n. and one to the genus Plagigeyeria Tomlin, 1930, namely P. steffeki sp. n. New Albania and Kosovo distribution records are given for Iglica illyrica Schütt, 1975, Plagigeyeria zetaprotogona Schütt, 1960, Vinodolia matjasici (Bole, 1961), and the first georeferenced record is given for Saxurinator schlickumi Schütt, 1960. The most important environmental factors influencing habitat selection of these subterranean freshwater gastropods are briefly discussed.
It is well known that land snails can be dispersed by birds, both by attachment to the body (ectozoochory) and by passing intact and alive through the bird's digestive tract (endozoochory). Endozoochory has, however, only been recorded for very small species. We examined the possibility that larger species (up to c. 17 mm in maximum shell dimension) could survive passage through a bird's digestive system. Live Alinda biplicata, Cochlodina laminata (both Clausiliidae) and Discus rotundatus (Discidae) were fed to 10 bird species (Corvidae, Turdidae, Sturnidae and Columbidae) in 14 experimental trials. Of 720 snails offered, 14 passed intact through the birds, of which nine were alive (eight clausiliids and one D. rotundatus); thus more than 1% of all snails offered survived ingestion. In an additional experiment, some A. biplicata and C. laminata remained attached to birds' legs by pedal adhesion in simulated flight trials where the birds' legs oscillated at the maximum rate achieved during flight.
A short overview of subterranean Balkan hydrobid genera, with special focus on genus Bythiospeum Bourguignat, 1892 and Iglica A.J. Wagner, 1928 is given. In addition, based on recently collected material in Montenegro (Vitoja Spring) and Albania (Krumë), five new species are described, namely: Bracenica vitojaensis n. sp., Islamia montenegrina n. sp., Lanzaia pesici n. sp., Bythiospeum szarowskae n. sp. and Pseudamnicola krumensis n. sp. The holotypes and paratypes are depicted. In addition a re-description of Bythiospeum gittenbergeri (A. & P.L. Reischütz, 2008) is given and the types of the Iglica spp. deposited in the NHMW are depicted, some of them for the first time.
Albania is situated in the western part of the Balkan Peninsula, on the eastern coast of the Adriatic and the Ionian Sea. The karst landscape in Albania covers about 6750 km2, approximately 24 % of the Albanian territory. There are 25 karst regions in the country, 23 in carbonate rocks and 2 in evaporites. The total renewable karst water resources are estimated about 227 m3/s, representing 80 % of the groundwater resources of Albania. About 70 % of the population of the cities, including also part of the capital Tirana, obtains the water from karst springs. However, the negative human impacts often are threatening the karst groundwater resources of Albania. Several bad experiences in Albania have demonstrated that the main human negative impacts on karst water are related to: (a) urbanised areas, (b) agriculture activities, and (c) quarrying activities. Understanding the vital importance of karst waters and the necessity for intensive scientific investigations and monitoring, to evidence their high vulnerability, are still at a low level in Albania.
R package, available on CRAN
Albania, as well as a great part of the Balkan area in general, still suffers a lack of environmental studies especially in limnological research. The Dumre plateau, in Central Albania, is characterized by an extraordinary high number of karst lakes in a small geographic area. Despite their environmental peculiarity, very few biological data are to date available for these lakes, none on the zooplankton. For this reason, 15 water bodies located in the central area of the plateau were selected for a preliminary limnological survey carried out in the years 2008-2011. Neodiaptomus schmackeri (Poppe & Richard, 1892), a diaptomid calanoid copepod characterized by a South-Eastern Palearctic - Oriental distribution, and the most widely spread Neodiaptomus species in Asia, was found in 8 lakes of the Dumre area. This finding represents the first record of the species, and of the entire genus Neodiaptomus, for Europe. Several environmental variables were measured to characterize the lakes, and the co-occurring planktonic crustaceans were also identified. Taxonomical drawings and descriptions of the main morphological features of both sexes are herein provided in order to compare the Albanian populations of N. schmackeri with those of the native distribution area of the species. The possible causes which determined the occurrence of this non-indigenous species in several Dumre lakes are discussed.
We hypothesize that pulmonate gastropods, in comparison to prosobranchs should (1) be better competitors because of finely-toothed radulae, (2) be better adapted to variable habitats because of greater powers of physiological regulation, (3) be better dispersers, but (4) face greater risk of predation. In the Salt River, in western Kentucky, U. S. A., pulmonates were fairly common in headwater streams, and were replaced in larger order tributaries by prosobranch snails. The literature suggests that pulmonates have tolerance and capacity adaptations to variation in physicochemical variables like temperature or dissolved oxygen. Only one of the two pulmonates tested in the laboratory, however, had quicker righting responses and rates of movement, important in recolonizing ephemeral habitats. A competition experiment in an artificial stream indicated that the large-river prosobranch, Lithasia obovata (Say, 1829), suffered less reduction in growth than the pulmonate Helisoma trivolvis (Say, 1817). Both the literature and experiments we have performed suggest that prosobranchs are less vulnerable to predators. We interpret these results to suggest pulmonates are more common in temporary headwater streams, or shallow littoral margins of lotic systems, because of greater physiological adaptation, while prosobranchs are more common in larger rivers (or in spring-fed rivers) because of greater competitive ability, lower risk of predation, or less-variable physicochemical regimes.
The relative contributions of lake characteristics (i.e. alkalinity, chlorophyll A concentration, total phosphorus concentration, conductivity, and morphometry) and site characteristics (i.e. depth, littoral slope, exposure to waves, and underwater light levels) to the variability in submerged biomass were examined in 25 Canadian and American lakes. Lake-average submerged biomass is a function of water alkalinity and the lake-average littoral slope whereas site-specific biomass is a function of both site and lake characteristics. Plant biomass decreased with increasing slope and wave exposure and increased with increasing alkalinity and light levels. However, these relationships are complex because submerged biomass is also influenced by threshold phenomena (e.g. critical littoral slopes and transparency-dependent critical depths) that set limits to macrophyte colonization and because the relative contributions of the most relevant environmental factors studied (i.e. littoral slope, exposure, water transparency, and alkalinity) are depth dependent. By demonstrating the importance of lake-average and site-specific scales of variation and the existence of noncontinuous (e.g. threshold) regulation mechanisms the findings provide a new conceptual framework for the study of the relationship between submerged macrophytes, and their associated biota as well as their environment.
A fundamental goal of ecology is to understand the factors that influence community structure and, consequently, generate heterogeneity in species richness across habitats. While niche-assembly (e.g. species-sorting) and dispersal-assembly mechanisms are widely recognized as factors structuring communities, there remains substantial debate concerning the relative importance of each of these mechanisms. Using freshwater snails as a model system, we explore how abiotic and biotic factors interact with dispersal to structure local communities and generate regional patterns in species richness. Our data set consisted of 24 snail species from 43 ponds and lakes surveyed for seven years on the Univ. of Michigan's E. S. George Reserve and Pinckney State Recreation Area near Ann Arbor, Michigan. We found that heterogeneity in habitat conditions mediated species-sorting mechanism to drive patterns in snail species richness across sites. In particular, physical environmental variables (i.e. habitat area, hydroperiod, and canopy cover), pH, and fish presence accounted for the majority of variation in the species richness across sites. We also found evidence of Gleasonian structure (i.e. significant species turnover with stochastic species loss) in the metacommunity. Turnover in snail species distributions was driven by the replacement of several pulmonate species with prosobranch species at the pond permanence transition. Turnover appeared to be driven by physiological constraints associated with differences in respiration mode between the snail orders and shell characteristics that deter molluscivorous fish. In contrast to these niche-assembly mechanisms, there was no evidence that dispersal-assembly mechanisms were structuring the communities. This suggests that niche-assembly mechanisms are more important than dispersal-assembly mechanisms for structuring local snail communities.
More than 90 karst lakes, oft en smaller than 1ha, and shallower than 10m, can be found sparse over limestone or gypsum in Albanian territory. Th e most famous are the lakes of Dumre, a zone that extends between Shkumbini and Devolli valleys (Elbasani district). These lakes do not have nor inflows or outflows, and are oft en filled by the rainfall; therefore, their water level oscillates drastically during the year. Sporadic samples of peryphyton or phytoplankton were collected in some of Dumre lakes (Belshi, Merhoja, Mulleza, Cepi). Moreover, one sediment core (ca. 38cm) was taken in Belshi lake, in June 2005; based on Pb 210 and Cs 137 , the sediments were the well laminated, dating only to the last 20 years (between 2005-1984), where alternated yellow and black layers might belong to one year. Th e calculated sedimentation rate was 1.76 cm/yr, considered relatively high, due to the strong erosion form the surrounding watershed. Th e diversity of diatoms found in Dumre lakes can be considered high, despite the limited number of samples examined. About 220 taxa of microscopic algae, diatoms (Bacillariophyta), were found in all the collected samples, represented mainly from the genera Navicula (28 species), Nitzschia (23) and Cyclotella (17). More than 170 species were found in the littoral samples of diff erent lakes, where the sample from Cepi, a shallow eutrophic pond was the richest with diatoms, more than 90 species. About 140 species were found in the core sample from Belshi lake, represented mainly from Achnnathes minutissima, Cyclotella ocellata, C. stelligera, Gyrosigma acuminatum, Cymbella affi nis, Gomphonema olivaceum or Hantzschia amphioxys. Centric diatoms Cyclotella ocellata and C. stelligera, and the pennate Achnanthes minutissima were found also relatively abundant in the population community of each sediment layer. Th e calculated Trophic Index of Diatoms (TI DIA) in each sediment layer oscillated from 1.2 (oligotroph) to 3.4 (polytroph), showing a moderate pollution with nutrients (phosphorous and nitrogen). Saprobic index seems to be more stable, oscillating from 1.5 (oligosaprob) to 2 (beta-mesosaprob), corresponding to scarcely polluted (I-II class) to moderately polluted water quality (II class). From the rare and interesting species of the karst lakes here were mentionioned Caloneis cf. aerophila, Gomphonema augur, Neidium bisulcatum var. subampliatum, Nitzschia geitleri, N. lorenziana, Placoneis elginensis, P. clementioides, Sellaphora levissima, Surirella venusta, Surirella cf. tenera. Caloneis sp. and Surirella sp. represent interesting or new species. Th e terrigenous hilly relief, the typical Mediterranean climate characteristics combined also with poor land use activities (land denuding), can be the principal causes of the relatively high rate of sedimentation observed in Belshi lake. Th e decentralized management of wastewater is recommended to prevent the eutrophication processes, and protect the water quality of the lakes. Moreover, forestation activities especially in denuded area would restore the vegetation cover and decrease the erosion.
The Albanian locality data of zoological collectings carried out by the Hungarian Natural History Museum and the Hungarian Academy of Sciences during 30 tours to the Balkans between 2004 and 2010 are enumerated. The localities and methods of collecting are enumerated in chronological order. Sites are marked on the map of Albania.
The present paper focuses on the description of the main evaporite karst areas of Albania, and on their environmental problems.
Even though the majority of the karst areas in Albania is represented by carbonates, evaporites crop out significantly at
several sites, and deserve a specific attention for their morphological, karstic and speleological peculiarities. Vulnerability
of karst is well marked by pollution and degradation problems in regions such as Dumre (central Albania), where some tens
of lakes of karst origin are present in the Permian–Triassic evaporites. Water pollution with negative effects on the local
ecosystems, and anthropogenic changes of the natural karst landscape in the last century resulted in intense environmental
degradation at Dumre. Messinian evaporites crop out in the Kavaja area (near the Adriatic coast), and at other sites in central-southern
Albania. In these areas, surface karst morphology is characterized by a number of dolines, ponors and blind valleys, which
often correspond to inlet points of subterranean drainages and caves. Notwithstanding these peculiarities, and the relevance
of the area for biospeleological studies, many caves have been destroyed by quarrying activities, resulting in severe losses
to the natural heritage. Following a general description of the evaporite karst areas of Albania, the paper focuses on the
present situation of the evaporites in the country, which is frequently affected by degradation and environmental losses in
the karst landscape, and pollution of the aquifers.
The macrozoobenthos taxonomic composition in small karst lakes of Vladimir oblast is studied for the first time. In the structure
of bottom communities, 149 taxa one rank below the genus have been found. Chironomid larvae and other amphibiotic animals,
as well as oligochaetes, prevail. Most of them are species widely distributed in the surface waters of European Russia. The
highest macrozoobenthos species diversity was recorded in neutral lakes, and the lowest diversity was in lakes with weakly
acidic waters.
A large number of eutrophic ponds were surveyed for the presence of freshwater gastropods. Factors thought to influence the distribution of the snails were evaluated. As the investigated area has a homogeneous geological background physicochemical factors probably have a low effect on the local distribution of snails. There was a significant, positive regression between pond area and the number of gastropod species in the pond, but the regression only explained a minor part of the variation in species numbers. Multiple regression of an extended number of variables, associated with habitat complexity and dispersal, indicated that, in addition to area, macrophyte diversity and the mean number of gastropods in the 5 closest ponds (S5) were important in explaining the distribution of gastropods. An increase in the number of macrophyte species increases the number of available microhabitats and refuges from predators. S5 probably influences the dispersal rates between ponds. The gastropods in this area are thought to have additional dispersal modes, besides aerial dispersal with birds, and this probably increases the immigration rates and/or decreases the extinction rate.
The methodology used to construct tree structured rules is the focus of this monograph. Unlike many other statistical procedures, which moved from pencil and paper to calculators, this text's use of trees was unthinkable before computers. Both the practical and theoretical sides have been developed in the authors' study of tree methods. Classification and Regression Trees reflects these two sides, covering the use of trees as a data analysis method, and in a more mathematical framework, proving some of their fundamental properties.
Research on the aquatic molluscs of Lake Skadar has a long tradition, starting with the paper published by Küster in 1843. The Lake Skadar basin consists of the lake itself and a variety of nearby water bodies, including lotic waters, pools, and springs that are inhabited by diverse communities of freshwater molluscs. A total of 53 freshwater mollusc species, ten species of Bivalvia and 43 species of Gastropoda, have been found in the Lake Skadar basin and Lake Šasko, with 15 being endemic. Some of the basin’s endemic species are common and relatively unconfined in terms of depths and zones. A characteristic feature of the lake is the presence of endemic species restricted to sublacustrine spring habitats. The lake’s ongoing process of eutrophication, its use as a water supply, and the ecological disruption caused by non-native species are generally recognized as the main threats to the lake’s mollusc fauna. Future research on the lake’s gastropod fauna should focus on the application of molecular methods and including the endemic species in ongoing national and transboundary conservation programs.
Balkan Biodiversity is the first attempt to synthesise our current understanding of biodiversity in the great European hot spot. The conservation of biodiversity is one of today’s great ecological challenges but Balkan biodiversity is still poorly understood, in a region with complex physical geography and a long history of political conflict. The Balkans exhibit outstanding levels of endemism, particularly in caves and ancient lakes such as Ohrid; lying at the crossroads of Europe and Asia they are also renowned as a focus of Pleistocene glacial refugia. This volume unites a diverse group of international researchers for the first time. Its interdisciplinary approach gives a broad perspective on biodiversity at the level of the gene, species and ecosystem, including contributions on temporal change. Biological groups include plants, mammals, spiders and humans, cave-dwelling organisms, fish, aquatic invertebrates and algae. The book should be read by zoologists, botanists, speleobiologists, palaeoecologists, palaeolimnologists and environmental scientists.
Multiple regression analysis revealed that breeding bird community densities in eleven south Swedish lakes were positively correlated both with total phosphorus concentrations of the water and with the percentage of fen area. Eutrophic lakes support more species than oligotrophic ones, but a man-made increase in productivity does not lead to higher species richness in formerly oligotrophic lakes. Species number correlates positively with pH and shore development. About the same species number occurs in single lakes and in similar sized parts of large lakes. It is suggested that lakes, in northern Europe, appear to the birds as any other major continental habitat. The slopes of species-area relations for lakes are computed for vascular plants, invertebrates, fish, and birds and reasons for the low slopes (z
The relevance of environmental and spatial processes for species distributions varies among environments and types of metacommunities. Here, for the first time, we use modern statistical approaches to test the contribution of these two processes in structuring ecologically unique and threatened biotas of insular spring fens. We applied two species categorisations, common/rare and generalists/specialists, to disentangle the roles of dispersal capacity and habitat specialisation.
In accordance with current understanding of headwater ecosystems, we found that environmental processes played a major role in most of the spring fen taxonomic and functional groups. However, we observed significant spatial structure in passive dispersers (Clitellata, a class of annelid worms), common species and habitat specialists.
Spatial processes played the leading role in structuring the metacommunity of passively dispersing specialists. In contrast, all analysed insect groups, even those known to be poor dispersers, were able to reach virtually all favourable sites.
We conclude that dispersal mode (active versus passive) and, to a lesser extent, habitat specialisation are the main factors determining the mechanism of spring fen metacommunity structuring.
Phosphorus-rich deposits of Eocene volcanic rock have caused some lakes in the interior of British Columbia to become eutrophic without direct human influence. In Black Lake the soluble reactive phosphorus (SRP) usually exceeds 250 mu g P.liter-1. When calcite precipitation occurred during blooms of Aphanizomenon, SRP was completely removed from the photic zone. In blooms with no calcite formation, SRP changed little. Subsequent disappearance of phosphate was correlated with an increase in pH and a reduction of Ca and alkalinity and not necessarily with primary production or algal biomass. -from Authors
Molluscs, vegetation and water chemistry were investigated at 48 spring fens situated in the borderland between the Czech Republic and Slovakia in 1997-2000. The purpose of this study was to test whether the gradient from mineral-poor to mineral-rich fens is reflected in the composition and species richness of mollusc communities, and to determine the importance of vegetation in predicting the mollusc community composition. A cluster analysis of mollusc communities separated the fens studied into five basic Clusters which accord well with the results of detrended correspondence analysis (DCA). These clusters are arranged along the first DCA axis following the poor-rich trophic gradient. Ca, Mg, Fe, K, pH and conductivity are strongly correlated with the first DCA axis of the mollusc data. Similarly, Ca, Mg, Fe, pH and conductivity explain a substantial part of species-data variation, as verified by separated canonical correspondence analyses (CCAs) with a single variable. When sites with Sphagnum spp. were excluded, no significant correlations with K, pH and conductivity were found, whereas the significance of correlation with Fe increased markedly. Site classifications based on mollusc data are applicable to vegetation data and Nice versa. Vegetation composition is a more important factor for explaining the variation in mollusc species than water chemistry when both are included in two separated CCAs as constraining variables. We found a linear correlation between mollusc species richness and water calcium concentration in the poor fens. In the rich fens, such a correlation was not found, and species richness was dependent on other abiotic and biotic factors, namely the Fe concentration and the water regime.
This book is written as a reference on organic substances in natural waters and as a supplementary text for graduate students in water chemistry. The chapters address five topics: amount, origin, nature, geochemistry, and characterization of organic carbon. Of these topics, the main themes are the amount and nature of dissolved organic carbon in natural waters (mainly fresh water, although seawater is briefly discussed). It is hoped that the reader is familiar with organic chemistry, but it is not necessary. The first part of the book is a general overview of the amount and general nature of dissolved organic carbon. Over the past 10 years there has been an exponential increase in knowledge on organic substances in water, which is the result of money directed toward the research of organic compounds, of new methods of analysis (such as gas chromatography and mass spectrometry), and most importantly, the result of more people working in this field. Because of this exponential increase in knowledge, there is a need to pull together and summarize the data that has accumulated from many disciplines over the last decade.
1. Limnologists and landscape ecologists have illustrated how the spatial position of a lake in a landscape influences many of its properties, from the physical to the social. Taking a community ecology perspective, we investigated whether freshwater gastropod assemblages respond to lake landscape position.
2. We determined: (a) whether there is any spatial pattern among lakes in either the species richness or composition of gastropod assemblages; (b) the form of any spatial pattern; and (c) if any explanatory variables (e.g. dispersal corridors and limiting local conditions) show a similar pattern.
3. In three different hydrological catchments, snail species richness increased from isolated highland lakes to stream-connected lowland lakes, probably reflecting increased colonization potential and less limiting local factors for lowland drainage lakes. Catchments appear to differ from one another with regard to relative species abundance, both in terms of macrophyte-associated snail fauna and snails from all habitats aggregated. One or more historical events, such as chance dispersal, may have produced this pattern. Taken together, these results suggest that within-catchment constraints produce repeated gradients in species richness, regardless of what species composition persists in the catchment.
1. In a cuirophic pond in southern England. the snail Lymnaca peregra(Mull.) is associated with submersed macrophyies, mainly Elodea canadensis Michx. In contrast, the snail Planorbis vortex(Linn.) is associated with the emergent macrophyte Glyceria maxima(Hartm.) Holmberg.
2. L. peregra grazed selectively on filamentous green algae found only on E. camtdensis. P. vortex selected diatoms. Detritus, which was 5 times more abundant on G. maxima than on E. canadensis. comprised about 60% of the diet of P. vortex.
3. Results of experiments giving both snail species a choice between periphyton-detritus removed from the two macrophytes were consistent with the field observations. L. peregra c hose pcriphyton-detritus from E. canadensis whereas P. vortex chose that from G. maxima.
4. Although other factors may have influenced the distributions of L. peregru and P mriex in Radley Pond, food choice was probably the most important proximate factor.
A phase diagram for Ca- and Fe-bound phosphate has been calculated based on two criteria:
a)
the adsorption of ortho-phosphate onto iron hydroxide
b)
the solubility product of apatite as measured in two hard water rivers.
The phase diagram explains why ortho-phosphate (o-PO4) in sediments, containing high concentrations of CaCO3 (about 10–30%), is bound onto the iron hydroxide rather than onto the CaCO3. The concentration of the iron hydroxide has an effect on the equilibrium between the two phosphates, whilst the concentration of CaCO3 has no effect whatsoever.
Worldwide ancient lakes have been a major focal point of geological, biological, and ecological research, and key concepts
in, for example, evolutionary biology are partly based on ancient lake studies. Ancient lakes can be found on most continents
and climate zones with most actual or putative ancient lakes in Europe being restricted to the Balkan Region. The arguably
most outstanding of them is the oligotrophic and karstic Lake Ohrid, a steep-sided graben of rift formation origin situated
in the central Balkans. Here, an attempt is made to summarize current knowledge of the geological, limnological, and faunal
history of Lake Ohrid. Additionally, existing data on biodiversity and endemism in Lake Ohrid are updated and evaluated, and
patterns and processes of speciation are reviewed in the context of the Ohrid watershed, including its sister lake, Lake Prespa.
Whereas the geological history of the Ohrid Graben is relatively well studied, there is little knowledge about the limnological
and biotic history of the actual lake (e.g., the age of the extant lake or from where the lake first received its water, along
with its first biota). Most workers agree on a time frame of origin for Lake Ohrid of 2–5 million years ago (Mya). However,
until now, the exact limnological origin and the origin of faunal or floral elements of Lake Ohrid remain uncertain. Two largely
contrasting opinions either favour the theory of de novo formation of Lake Ohrid in a dry polje with a spring or river hydrography
or a palaeogeographical connection of Lake Ohrid to brackish waters on the Balkan Peninsula. Whereas neither theory can be
rejected at this point, the data summarized in the current review support the de novo hypothesis. An assessment of the fauna
and flora of Lake Ohrid confirms that the lake harbours an incredible endemic biodiversity. Despite the fact that some biotic
groups are poorly studied or not studied at all, approximately 1,200 native species are known from the lake, including 586
animals, and at least 212 species are endemic, including 182 animals. The adjusted rate of endemicity is estimated at 36%
for all taxa and 34% for Animalia. In terms of endemic biodiversity, Lake Ohrid is with these 212 known endemic species and
a surface area of 358 km2 probably the most diverse lake in the world, taking surface area into account. Preliminary phylogeographical analyses of
endemic Lake Ohrid taxa indicate that the vast majority of respective sister taxa occurs in the Balkans and that therefore
the most recent common ancestors of Ohrid- and non-Ohrid species likely resided in the region when Lake Ohrid came into existence.
These data also indicate that there is relatively little faunal exchange and overlap between Lake Ohrid and its sister lake,
Lake Prespa, despite the fact that the latter lake is a major water supplier for Lake Ohrid. Studies on selected species flocks
and scatters, mostly in molluscs, point towards the assumption that only few lineages originally colonized Lake Ohrid from
the Balkans and that the majority of endemic species seen today probably started to evolve within the lake during the early
Pleistocene. Within the Ohrid watershed, endemism occurs at different spatial and taxonomic scales, ranging from species endemic
to certain parts of Lake Ohrid to species endemic to the whole watershed and from subspecies to genus level and possibly beyond.
Modes of speciation in the Ohrid watershed are largely affected by its degree of isolation. Observational evidence points
towards both allopatric (peripatric) and parapatric speciation. Though sympatric speciation within a habitat is conceivable,
so far there are no known examples. Today, the lake suffers from increasing anthropogenic pressure and a “creeping biodiversity
crisis”. Some endemic species presumably have already gone extinct, and there are also indications of invasive species penetrating
Lake Ohrid. The comparatively small size of Lake Ohrid and the extremely small range of many endemic species, together with
increasing human pressure make its fauna particularly vulnerable. It is thus hoped that this review will encourage future
research on the ecology and evolutionary biology of the lake’s taxa, the knowledge of which would ultimately help protecting
this unique European biodiversity hot spot.
The distribution and diversity of Danish freshwater snails is discussed in the light of MacArthur and Wilson's theory of island biogeography. Species-area curves for 86 eutrophic and oligotrophic ponds and lakes are made and the variance to mean ratios of species numbers in lakes of identical sizes calculated. These data indicate that the snail fauna represents a dynamic equilibrium sustained by immigration and extinction. Different properties of small and large bodies of water are discussed with regard to probability of immigration and extinction. Oligotrophic lakes show a steeper species-area curve than eutrophic ones. This is explained by a higher extinction probability in the former but the total species pool is the same for both types of lakes.
The freshwater snails are described as a group largely consisting of fugitive species. Physicochemical factors set the ultimative physiological limits to a species but within the main area of distribution biotic interrelations may be of main importance in governing the diversity of local faunas. These considerations probably have a general application to the hololimnic fauna.
Molluscs are the proverbial examples of slow movement. In this review, dispersal distances and speed were assessed from literature
data. Active upstream movement can occur both individually and in groups; and depends on traits such as size, sex and reproductive
status, and on external factors such as flow velocity, temperature, sediment structure, and food availability. The potential
for active dispersal follows the sequence Pulmonata≥Prosobranchia>Bivalvia, although data for Pulmonata originated from
short-term experiments that likely overestimated dispersal capabilities. Active upstream movement may be 0.3 to 1.0km per
year for most snails and is probably well below 0.1km per year for bivalves. Natural passive upstream dispersal increases
the range 10-fold (snails) to 100-fold (bivalves), and anthropogenic vectors can increase upstream dispersal more than 100-fold
(snails) to 1000-fold (bivalves). Three km seems to be the maximal within-stream distance at which many species display regular
population mixing, and at which re-colonisation or successful restoration can be expected within 3–10years. Lateral dispersal
between unconnected water bodies is passive and mostly known from observational reports, but potential distances depend on
vectors, climate and geomorphology. In general, active dispersal seems insufficient to furnish a compensatory mechanism, e.g.,
for the rate of projected climate change. We provide an overview on dispersal strategies in the light of applied issues. More
rigorous field surveys and an integration of different approaches (such as mark-recapture, genetic) to quantify distances
and probabilities of lateral dispersal are needed to predict species distributions across space and time.
KeywordsBiological invasion–Dispersal–Global change–Mollusca–Species distribution modelling (SDM)–Vector
Plant communities were examined in ponds in Brittany (north-west France) and then classified into six types reflecting different trophic levels: oligotrophic, oligodystrophic, mesotrophic, meso-dystrophic, meso-eutrophic an eutrophic. In 45 of these ponds, aquatic snails were sampled in order to determine the relationship between the gastropod species richness and the water trophic levels as indicated by plant community types. The second aim of this study was to determine whether some gastropod species were characteristic of a particular trophic level. The number of plant communities in the ponds was also taken into consideration.A trophic gradient was found along the F1 axis on the principal plane of the correspondence analyses. The species richnesses low or zero and especially the lymneid, Lymnaea glabra were close to the oligo-dystrophic and oligotrophic communities. In contrast, the highest numbers of snail species (5 and above) were found in the most eutrophic ponds where Hippeutis complanatus, Planorbis planorbis, Lymnaea stagnalis and Planorbarius corneus were particularly common. The latter species inhabited the ponds including on average the greatest number of macrophyte communities but no significant differences were found between snail species. The ponds which contained the greatest numbers of plant communities included the richest gastropod communities (7 and more) but also the poorest ones (0 or 1 species). Relationships between freshwater snails, macrophytes and trophic levels are discussed.
About a dozen lakes in the world are up to three orders of magnitude older than most others. Lakes Tanganyika (East Africa) and Baikal (Siberia) have probably existed in some form for 12-20 million years, maybe more. Such lakes can have different origins, sizes, shapes, depths and limnologies, but, in contrast to short-lived (mostly post-glacial) lakes, they have exceptionally high faunal diversity and levels of endemicity. A multitude of and processes accounting for these explosive radiations have recently been documented, most of them based on particular groups in certain lakes, but comparative research can detect repeated patterns. No special speciafion mechanism, exclusive to ancient lakes has been demonstrated, although cases of ultra-rapid speciation have been documented. Extant diversity results not by simple accumulation, but by a complex process of immigration, speciation and extinction.