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Associated data is available at: https://doi.org/10.5061/dryad.595718c; International audience; Habitat destruction is the single greatest anthropogenic threat to biodiversity. Decades of research on this issue have led to the accumulation of hundreds of data sets comparing species assemblages in larger, intact, habitats to smaller, more fragmented, habitats. Despite this, little synthesis or consensus has been achieved, primarily because of non-standardized sampling methodology and analyses of notoriously scale-dependent response variables (i.e., species richness). To be able to compare and contrast the results of habitat fragmentation on species’ assemblages, it is necessary to have the underlying data on species abundances and sampling intensity, so that standardization can be achieved. To accomplish this, we systematically searched the literature for studies where abundances of species in assemblages (of any taxa) were sampled from many habitat patches that varied in size. From these, we extracted data from several studies, and contacted authors of studies where appropriate data were collected but not published, giving us 117 studies that compared species assemblages among habitat fragments that varied in area. Less than one-half (41) of studies came from tropical forests of Central and South America, but there were many studies from temperate forests and grasslands from all continents except Antarctica. Fifty-four of the studies were on invertebrates (mostly insects), but there were several studies on plants (15), birds (16), mammals (19), and reptiles and amphibians (13). We also collected qualitative information on the length of time since fragmentation. With data on total and relative abundances (and identities) of species, sampling effort, and affiliated meta-data about the study sites, these data can be used to more definitively test hypotheses about the role of habitat fragmentation in altering patterns of biodiversity. There are no copyright restrictions. Please cite this data paper and the associated Dryad data set if the data are used in publications.

Alder floodplain forests are a rare and threatened forest type in Europe. These forests can be very rich in mollusc species. The intermediate disturbance hypothesis predicts that species richness should peak at intermediate inundation frequency, that is, at intermediate elevation above the river level. We additionally hypothesized that constantly high soil moisture can distort the usually positive correlation between the amounts of downed deadwood and snail richness, and that tree stems might be more favourable than deadwood because their vertical structure provides a better refuge during inundation events. To this end, we sampled molluscs from a core area of 20 × 20 m from eight alluvial forests with black alder in the surroundings of Łodź, Central Poland. In each core area, substrate was collected from eight random plots (0.25 m2 each). We also recorded soil pH, vascular plant species and mosses diversity, along with other structural variables. Plant indicator values were calculated according ...

Habitat disturbance alters environmental conditions and can affect biotic exchange. While the process of biotic exchange is difficult to quantify in the field, it affects community assembly and thus species abundance distributions, diversity, faunal homogeneity and biogeographic patterns. Here, we provide the first comprehensive assessment of habitat-specific assemblage structure and turnover in slow, active dispersers, namely slugs (Mollusca: Gastropoda). We compare species richness, densities, assemblage homogeneity and spatial turnover from nine differently disturbed habitat types (total: 729 sites) within an area spanning the border between two major European biogeographic regions, the Atlantic and the Continental Regions. Gardens, mesic open habitats and successions tended to harbour many introduced species. The nonmetric multidimensional scaling plot revealed a gap, rather than a transition, between disturbed habitats (including woody successions) and mature forest stands. This gap indicates a tipping point for slug assemblages related to food sources and microclimate. Anthropogenic disturbance blurred the effect expected from the border between the biogeographic regions. When compared with broadleaved forests as the natural vegetation cover, human disturbance doubled the range before spatial faunal dissimilarity occurred in physically highly fragmented gardens, and more than tripled it in continuously-disturbed habitat types such as mesic open habitats. Our results support the idea that continuously-disturbed habitats are associated with altered passive dispersal and colonization dynamics, distorted biogeographic boundaries and faunal homogenization.

Blood-feeding terrestrial leeches of the family Haemadipsidae are a notorious part of the invertebrate diversity in Asian and Australian rain forests. All hitherto published records of terrestrial leeches of Borneo belong to the genus Haemadipsa. Here, a second, poorly known haemadipsid genus is reported from Mount Kinabalu and Crocker Range National Park. The individuals were barcoded and compared to sequences available in GenBank. The results show that the genus Tritetrabdella has representatives in the Indochinese and the Sundaic bioregions. All six specimens from Borneo are from a single new Tritetrabdella lineage, T. kinabaluensis spec. nov. Within the Bornean lineage, two groups differing 4-5% in the COI barcoding sequence were identified. Because 1) it is probable that haemadipsid COI is subjected to base pair substitution rates of 2.5% per Ma, 2) COI protein sequences were the same within the Bornean material, 3) color can change as a response to the environment, 4) the lineages inhabit different altitudes in separate areas and 5) only six individuals were found, a conservative approach was taken and the groups were tentatively given subspecies status: T. k. kinabaluensis ssp. nov. and T. k. inobongensis ssp. nov. The ecology and the conservation status of the Bornean Tritetrabdella warrant urgent assessment because the genus Tritetrabdella is considered as mainly feeding on amphibians and probably small mammals, and thus can be predicted to be sensitive to climatic fluctuations, forest disturbances and fragmentation, and amphibian decline.

Aquatic ecosystems are amongst the most heavily altered ecosystems and exhibit a disproportional loss of biodiversity. Numerous stressors, such as nutrient enrichment, contaminant pollution, sedimentation and alterations in stream hydrology and habitat structure, account for these losses. Understanding these forces is of utmost importance to prevent riverine ecosystems from further deterioration and to provide helpful insights for restoration practices. In the present study, we analyse the response of biological indicators to a large number of environmental factors. For this, benthic invertebrate assemblages from 83 sites in Germany were described based on 25 metrics from four different metric types. The condition of the sites was described using 27 environmental factors: 13 for water quality, 4 for land use in the catchment and 10 for local scale habitat structure. The relative importance of single environmental predictors or predictor combinations for benthic invertebrate assemblages was analysed with single and multiple linear regression models. The results for the latter models were statistically supported via a bootstrap approach. The models revealed the importance of water quality and catchment-scale land use in explaining benthic invertebrate assemblages; in particular, chloride, oxygen, total organic carbon and the amounts of artificial surfaces and arable land were the most important predictors. Models including solely structural variables such as plan form, bank structures and substrate diversity had lower goodness of fit values than those for other variables. Regarding the four different assemblage metric types, functional metrics had on average lower goodness of fit values than composition/abundance, richness/diversity and sensitivity/tolerance metrics. Among the richness/diversity metrics, however, the model results for the Shannon–Wiener and Simpson diversity indices and evenness were poor. Our results show that catchment-related factors and water quality were of overriding importance in shaping biodiversity patterns and causing species loss. In contrast, structural degradation at a local scale was not the most significant stressor. This finding might explain why structural restoration at a reach scale often yields a low benefit–cost ratio and may be considered to represent inappropriate investment prioritisation.

The space-for-time approach is widely used in fundamental and applied ecology but assemblages from some habitats are highly variable. For example, streams may show marked spatio-temporal changes in the taxonomic composition of the macroinvertebrate assemblages. We exemplify the effect of the temporal component ‘season’ on some assemblage-derived stream quality assessment metrics under the assumptions of the space-for-time and the replicated samples approaches. Benthic macroinvertebrates were sampled in spring, summer, and fall from two stream types, namely streams in the Pleistocene sediments of the alpine foothills and small fine substrate dominated siliceous highland rivers in southern and central Germany. As exemplified for ASPT and the German multimetric index (MMI), the data showed no effect of season when samples were regarded as independent, whereas stream quality decreased between spring and fall in the replicated samples approach. The transformation of MMI to rank-ordered stream quality classes depicted a decrease in perceived stream quality in 29% and 54% of the sites by summer and early fall, respectively, when compared to spring samples. We thus suggest (1) to test seemingly robust metrics in a repetitive measures approach for other stream types and regions, and (2) to standardize the sampling season for ecological quality assessment. Based on this example, we assume that many subtle, but significant, environmental trends are still to be detected in highly heterogeneous habitats from various ecosystems.

The open-cast lignite mine “Hambach” (NW-Germany) and the accompanying land reclamation replace a large ancient forest. Reclamation of an 1000 ha large overburden dump started 25 years ago and is still in progress. Reclamation methods comprise combinations of different topsoil dumping techniques and reclamation measures such as seeding or afforestation. In accordance with the spatial heterogeneity hypothesis, we hypothesize that beetle assemblages from sites where the topsoil was left structured are more diverse than those from sites with levelled topsoil, and that richly structured mid-successional sites harbour more heterogeneous assemblages than afforested sites. We tested the influence of environmental variables on assemblage characteristics of pitfall-trapped beetles from 17 sites on the overburden dump. The results are based on 35,588 individuals from 339 species. Species assemblages differed significantly between almost all sites. Habitat age did not affect assemblage characteristics, while species richness was significantly influenced by surface structure. Sites that were not levelled and that additionally included pits that slope down for several meters exhibited the highest species richness. Abundance of beetles increased in parallel to the canopy cover, whereas assemblage heterogeneity (MVDISP) decreased. Successional and grassland sites usually exhibited higher diversity (Fisher's α) than afforested sites, but diversity was not significantly predicted by a single environmental factor. Instead, diversity increased along with increasing MVDISP-values. Afforestations speed up the successional process and some euryecious forest species are already well established, but stenecious forest specialists have not yet been found.

Habitat fragmentation may influence the genetic structure of populations, especially of species with low mobility. So far, these effects have been mainly studied by surveying neutral markers, and much less by looking at ecologically relevant characters. Therefore, we aimed to explore eventual patterns of covariation between population structuring in neutral markers and variation in shell morphometrics in the forest-associated snail Discus rotundatus in relation to habitat fragment characteristics. To this end, we screened shell morphometric variability and sequence variation in a fragment of the mitochondrial 16S rDNA gene in D. rotundatus from the fragmented landscape of the Lower Rhine Embayment, Germany. The 16S rDNA of D. rotundatus was highly variable, with a total of 118 haplotypes (384 individuals) forming four clades and one unresolved group. There was a geographic pattern in the distribution of the clades with the river Rhine apparently separating two groups. Yet, at the geographic scale considered, there was no obvious effect of fragmentation on shell morphometrics and 16S rDNA variation because GST often was as high within, as between forests. Instead, the age of the habitat and (re-)afforestation events appeared to affect shell shape and 16S rDNA in terms of the number of clades per site. The ecologically relevant characters thus supported the presumably neutral mitochondrial DNA markers by indicating that populations of not strictly stenecious species may be (relatively) stable in fragments. However, afforestation after large clearcuts and habitat gain after the amendment of deforestation are accompanied by several, seemingly persistent peculiarities, such as altered genetic composition and shell characters (e.g. aperture size). © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 839–850.

The Rhine floodplain is much modified by human land use. What used to be the hardwood zone of the large floodplain nowadays holds only a few isolated, recent (mostly < 60 years) forest patches. The aim of the study was to check if the circumstances favoured homogeneity of the snail communities, usually observed within floodplains, or if heterogeneity prevailed. We inventoried molluscs (presenceabsence) in 21 sites within and 18 sites adjacent to a stretch of the Lower Rhine floodplain (total 39 sites). Communities from eight of the sites were quantitatively sampled for within-site analyses. Species turnover occurred with distance from the Rhine, partially along with lateral habitat turnover. Introduced species mainly occurred in young forests, in similar numbers within and beyond the floodplain. Old forests beyond the floodplain had a small number of introduced species and a small between-site heterogeneity, suggesting strong habitat filters (selection of species by environmental conditions) which might be associated with the prevalence of detritus-derived food. The occasionally flooded sites had the longest scatter along the first NMDS axis, indicating a local differentiation without a longitudinal gradient. The young forests that were occasionally inundated and those that were never flooded shared many species, resulting in the lack of significant differences based on the presence-absence data. The damp, regularly flooded forests differed from the occasionally inundated ones and the ones beyond the floodplain. Flooding introduces drift material and species to the sites. The drift is associated with an initially increased within-site heterogeneity. During the years after the flooding event, the within-site homogeneity of communities increases (suggesting local selection of species) in tandem with an increase in the between-site differences (local selection plus stochastic extinctions). key worDs: afforestation, drift dispersal, habitat fragmentation, introduced species, land use, snail fauna

Base cation depletion due to soil acidification is a major environmental problem which can disrupt proper ecosystem functioning. We investigated nine mesic broad-leaved forests growing on Devonian sediments of the Rhenish Shield (Germany) and investigated the effect of coarse woody debris (CWD). The forests grow on soils originating from different parent material (graywacke, slates, dolostone) with upper soil pH-values ranging from 3.0 to 7.0. We analyzed soil chemistry, soil microbial parameters and the density of litter-dwelling detritivores (snails, slugs, woodlice and millipedes) to assess the influence of both acidification and CWD. The forests were classified according to their (Ca + Mg + K)/Al molar ratios into groups with ratios of either 2+ and Mg 2+ availability and an improved (Ca + Mg + K)/Al molar ratio. The presence of CWD also enhanced soil microbial biomass, the density of detritivores and species richness of snails, slugs and millipedes. Consequently, coarse woody debris influences nutrient fluxes and decreases the acidification-related risk of tree damage.

Many forest ecosystems have been extensively degraded by acidifying pollutants over the last decades. There is also widespread concern about population decline of a number of songbirds due to acidification-driven calcium limitation. We hypothesize that the carrying capacity of forests decreases with reduced soil calcium content. We analyzed songbird assemblage/habitat relationships by territory mapping at 30 sites in a total of five managed beech forests. The sites harbored 38 songbird species. A canonical correspondence analysis showed that soil acidification, represented by soil calcium content, had a significant influence on the species assemblages of the 14 most frequent songbirds. The vertical complexity of the canopy additionally influenced the assemblages. Multiple regressions revealed that the density of the territories of song thrush (Turdus philomelos) and nuthatch (Sitta europaea) were positively correlated to calcium content. Blackbirds (Turdus merula) seemed to compensate for the negative effect of acidification by selecting breeding sites close to forest edges to forage in less acidified agricultural habitats. In contrast, the territorial density of robin (Erithacus rubecula), chaffinch (Phylloscopus collybita) and coal tit (Parus ater) increased with increasing soil acidification. Contrary to our hypothesis, the overall carrying capacity of songbird was not reduced in forests with acidified soils. However, the nesting success of song thrush and blackbird, as determined by the number of fledglings, was higher in the forest with the highest calcium content when compared to the forest with the lowest calcium content. We conclude that some species are severely affected by acidification, whereas others seem to have evolved successful strategies to meet their calcium demand even in acidified habitats.

The highly invasive giant knotweed (Reynoutria spp.) often displaces nettle (Urtica dioica) dominated stands in European floodplains. Urtica-dominated stands differ from the monospecific Reynoutria stands in plant species richness and stand structure. We thus hypothesize that Reynoutria invasion profoundly alters ecosystem structure and function, with negative effects cascading up through the food chain. We performed a paired sampling design in six sites belonging to two different locations and studied effects on the soil and the litter-dwelling fauna. Reynoutria stands differed in habitat structure and were characterized by decreased soil pH and potassium depletion. The faunal analysis is based on model groups of herbivore generalists (Gastropoda), detritivores (Isopoda and Diplopoda), and predators (Opiliones). The gastropod assemblages from Reynoutria stands were severely impoverished subsets of those from Urtica stands with reduced densities, species richness and diversity. In general, snails were more sensitive to Reynoutria invasion than slugs such as the invasive Arion 'lusitanicus’. Among detritivores, the abundance of the Isopoda decreased, whereas Diplopoda were not affected by Reynoutria invasion. Yet, the relative abundance of detritivores was significantly higher within the Reynoutria stands. Abundance, species richness and diversity of the predatory Opiliones were higher in the relatively sparse Reynoutria stands. We conclude that ecosystem changes associated with Reynoutria invasion are characterized by shifts from a plant-based to a detritus-based food chain and that Reynoutria invasion primarily enhances predators that profit from the simplified vegetation structure.

Tropical mountains are hot spots of biodiversity and endemism,but the evolutionary origins of their unique biotas are poorlyunderstood. In varying degrees, local and regional extinction,long-distance colonization, and local recruitment may all contribute to the exceptional character of these communities. Also, it isdebated whether mountain endemics mostly originate from locallowland taxa, or from lineages that reach the mountain by long-range dispersal from cool localities elsewhere. Here we investigatethe evolutionary routes to endemism by sampling an entire tropical mountain biota on the 4,095-metre-high Mount Kinabalu inSabah, East Malaysia. We discover that most of its unique biodiversity is younger than the mountain itself (6 million years), andcomprises a mix of immigrant pre-adapted lineages and descendants from local lowland ancestors, although substantial shiftsfrom lower to higher vegetation zones in this latter group wererare. These insights could improve forecasts of the likelihood ofextinction and ‘evolutionary rescue in montane biodiversity hotspots under climate change scenarios.

In a managed beech forest a volume of 3 – 5 m 3 /ha deadwood including coarse woody debris (CWD) was found on the forest floor. The influence of CWD on the gastropod fauna was investigated during three seasons (September, March and June). Samples were taken in two different locations (plateau and SWexposed slope); in each location, sites close to CWD (c-CWD) and distant from CWD (d-CWD) were distinguished. The results clearly revealed a strong influence of CWD on the fauna that was observed in all seasons, and a Discriminant Analysis showed that the species assemblages differed both between sites and between locations. A three-way ANOVA with single species revealed a strong influence of CWD, a low influence of location and no influence of season. Two dominant species, Punctum pygmaeum and Nesovitrea hammonis, occurred independent of the three factors analysed. Among those species that clearly preferred c-CWD sites were the other three dominant species, Discus rotundatus, Aegopinella pura and Carychium tridentatum ,a long withEuconulus fulvus, Cochlodina laminata, Monachoides incarnatus and Phenacolimax major. Only three species were also significantly influenced by location, of which C. tridentatum and A. pura preferred the plateau and P. major the slope. Life-stage analysis revealed that C. tridentatum clearly depended on the sheltered microclimate of c-CWD sites for reproduction. The results warrant the change to management practices favouring the availability of CWD as an important structural component, in order to help maintain biodiversity and improve aspects of the biological functioning of the forest floor such as nutrient cycling.

We analysed in how far the decrease of pH, that is part of the ongoing restoration of the softwater Lake Windsborn (conductivity below 30 μS cm−1), may in future influence the occurrence of the two cladoceran species Ceriodaphnia quadrangula and Diaphanosoma brachyurum. In the field, the abundance of Ceriodaphnia was positively correlated with lake water pH, whereas there was no correlation between abundance and pH for D. brachyurum. Experiments on the tolerance against acidification included dynamic (24 h) and static tests (24, 48 h, 30 d), and were conducted with acidified lake water. C. quadrangula tolerated a slight acidification to pH 5.2, but not pH 4.8, whereas the NOEC value seems to be between pH 4.2 and 4.5 for D. brachyurum. Differences between the experimental NOEC values and field data may be explained by diurnal pH fluctuations and the low ion content of Lake Windsborn which puts an additional physiological challenge to its inhabitants.

We evaluate trophic interactions between the rotifer Asplanchna priodonta and the plankton community of Lake Windsborn (Eifel District, Germany). The long-term population dynamics of this species and of the two most abundant zooplankton species, Keratella cochlearis and Bosmina longirostris, were analyzed in relation to hydrochemical and climatic variates. The maximum abundance of A. priodonta was limited to the summer months with temperature being the only significant predictor of abundance. Intrinsic rate of growth and abundance of the three species were independent from each other suggesting the absence of trophic interactions. In Lake Windsborn, A. priodonta was a grazer rather than a predator. Its diet included high proportions of colonial algae and cyanobacteria which cannot be ingested by the other abundant zooplankton species, whereas zooplanktonic food were rarely found. Thus, our study supports the hypothesis that A. priodonta is an opportunistic feeder whose trophic position entirely depends on the structure of the plankton community.

We quantified the mollusc assemblage composition in eight riverine forests inhabited by the door snail Alinda biplicata (Montagu) in Central Poland where it occurs at the north-eastern border of its distribution range. In each location, eight random 0.25 m2 plots were quantitatively sampled from a 400 m2 core area that was searched for additional species. A total of 54 species were found, composed of 46 terrestrial snails and slugs, six freshwater gastropod and two clam species. Abundances ranged from 220 to 4,400 ind.m–2 per location, with a maximum of 2,200 individuals per plot. The number of taxa ranged from 17 to 34 per location and from 3 to 23 per plot. A. biplicata occurred in each randomly sampled plot. The highest number of co-occurrences with Alinda was found for Carychium tridentatum and Nesovitrea hammonis. Additionally, forest-specific, wetland-specific and even dry habitat-specific snails can use the same patch of microhabitat. The lack of narrow ecological specialisation in A. biplicata may favour its presence in man-made habitats where it is sometimes considered an invasive native gastropod. The species list included invasive Arion vulgaris and some other species with a mainly West European distribution, such as Oxychilus draparnaudi, O. alliarius, Arion rufus, Cepaea nemoralis and C. hortensis. The eastern borders of the native ranges of these species reach into the western part of Poland but in the sampled region they seem to be recent arrivals. Our results indicate that “western” (Atlantic) faunal elements benefit from more balanced microclimate in wet floodplain forests, which possibly reduces macroclimatic constraints at their distribution border. key worDS: alder forest, Clausiliidae, diversity, Gastropoda, land snails, Mollusca, stream

The goal of this study is to assess if the reproductive strategy of a brooding land snail shifts along a climatic gradient. We focused on the following traits: timing and length of the reproductive season, brood size, ontogenetic dynamics of embryos, and reproductive mode (viviparity versus egg-laying). We dissected the central European door snail Alinda biplicata, collected monthly from eight populations covering the oceaniccontinental climatic gradient within the species’ distribution range. Forty percent of the 1706 dissected individuals were brooding. The species displayed a spring-summer reproductive activity pattern: intrauterine brooding was recorded between March and September; first embryos of a developmental stage that equals that of live-born neonates appeared in late April. Brooding started approximately when the mean daily temperature of a month exceeds ca. 5°C, thus the ontogenetic development of embryos is advancing earlier in populations under the influence of mild oceanic climate, and later in the eastern, more continental part of the range, or in submontane localities. A range-wide synchrony in reproduction occurred in May, when average temperatures and precipitation display a high rangewide similarity. The mean number of intrauterine eggs decreased between spring and summer in all populations (April: 10.9 ± 2.9; September: 6.4 ± 2.4), suggesting a gradual release of neonates which are not immediately replaced in uteri by new eggs. Snails from areas with long frosty winters do not invest much in a second reproductive period in late summer. Embryos of advanced embryonic stage were found in the reproductive tract of individuals from each population, thus we refute the hypothesis that A. biplicata switches its reproductive strategy towards oviparity under the influence of oceanic climate.

Habitat fragmentation is a major cause for species loss, but its effect on invertebrates with low active dispersal power, like terrestrial gastropods, has rarely been studied. Such species can not cross a hostile habitat matrix, for which the predictions of island theory, such as positive relations between species richness and patch size, should apply. In order to test this prediction, we studied gastropod species diversity by assessing gastropod assemblage characteristics from 35 sites in 19 fragments of deciduous old-growth forests in the Lower Rhine Embayment, Germany. Assemblages differed between larger (¡Ý700 ha) and smaller forests (1,000 ha, i.e., well above the size of most fragments. In conclusion, the prediction is valid only for forest species. The response to fragmentation is species specific and seems to depend on habitat specialization and macroclimatic conditions.

The growth of bivalve gills proceeds at the posterior end of the gill from a meristem-like budding zone, that is, an undifferentiated terminal organ, which continuously proliferates new gill elements in growing bivalves. In representatives of protobranch, filibranch, and eulamellibranch gills (13 species from Protobranchia, Pteriomorphia, Palaeoheterodonta, and Heterodonta), the first growth steps demonstrate a uniform basic pattern. The budding zone produces either transverse folds that split after a transition zone into parallel pairs of lobules (which themselves later differentiate into the inner and outer demibranchs), or it produces the lobules directly, without first forming a transition zone. The lobules elongate, differentiate into lobes, and transform into leaflet-like structures (protobranchs) or into filaments (filibranchs and eulamellibranchs). The filaments represent the differentiated outer margins of each lobe, of which the central tissue (interlamellar septum) becomes incised or fenestrated, or transformed by tissue junctions. A distally located main growth zone for each lobe is suggested. With regard to the delayed onset of the differentiation of the outer demibranch in juvenile unionids, an additional temporary growth zone for filaments is suggested to exist at the anterior end of the outer demibranch.

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 1.0 km per year for most snails and is probably well below 0.1 km 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 3–10 years. 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.