Factors influencing species richness in lacustrine zooplankton

Frequent dispersal events are expected to elevate local species richness in island-like habitats such as lakes. However, the importance of dispersal can be hard to evaluate if other factors cause large background variability in species composition and richness. In this paper, we review empirical studies on ecological factors known or expected to influence species richness in zooplankton communities of inland lakes. We then present summaries of two recent case studies. Our objectives are twofold: we first look for effects of biotic interactions on species richness and species composition, and then evaluate whether the expected effects of dispersal are likely to be detected on a background of large variability caused by other ecological factors and interactions. Species richness within lakes appears to be primarily controlled by factors related to lake size, lake productivity, water quality, and fish predation levels. One case study indicated a slight, but significant, positive effect of lake density and lake area in the surrounding landscape on species richness, suggesting that frequent dispersal events may enhance species richness. This local variation in species richness is superimposed on regional variation in species pools.     

Spatial predictors of fish species composition in European lowland lakes

Composition of animal communities can be shaped by both local and regional processes. Among others, dispersal of organisms links local and regional patterns and determines the similarity of communities at increasing spatial distances. Unique and shared spatial and environmental contributions to fish community composition were calculated for watercourse distances between 49 hydrologically connected lakes in the German lowland area. Variation partitioning indicated a dominant unique effect of spatial predictors on fish community composition, whereas the effects of lake morphometry and productivity were weaker. The spatial effect was attributable to an uneven occurrence of small, littoral fish species found even at the small spatial extension covered here (maximum spatial distance ?550 km). Distance decay of community similarity was moderate, but significant, if all 31 fish species were considered, but the slope of the decay function became steeper if only 11 small‐sized, primarily littoral species were included. These results suggest that fish in European lowland lakes can be considered a metacommunity with limited dispersal along watercourse connections in particular for small‐sized species. The analysis supports that for an appropriate evaluation of spatial effects on fish community similarity, reliable estimates of local richness are required which include in particular also rare, small‐sized species occurring primarily in littoral areas. Furthermore, watercourse distance is a more reliable approximation than Euclidean distance to the real spatial dimension of fish dispersal.     

Regional versus local drivers of water quality in the Windermere catchment,Lake District,United Kingdom: The dominant influence of wastewater pollution over the past 200 years

Freshwater ecosystems are threatened by multiple anthropogenic stressors acting over different spatial and temporal scales, resulting in toxic algal blooms, reduced water quality and hypoxia. However, while catchment characteristics act as a ‘filter’ modifying lake response to disturbance, little is known of the relative importance of different drivers and possible differentiation in the response of upland remote lakes in comparison to lowland, impacted lakes. Moreover, many studies have focussed on single lakes rather than looking at responses across a set of individual, yet connected lake basins. Here we used sedimentary algal pigments as an index of changes in primary producer assemblages over the last ~200 years in a northern temperate watershed consisting of 11 upland and lowland lakes within the Lake District, United Kingdom, to test our hypotheses about landscape drivers. Specifically, we expected that the magnitude of change in phototrophic assemblages would be greatest in lowland rather than upland lakes due to more intensive human activities in the watersheds of the former (agriculture, urbanization). Regional parameters, such as climate dynamics, would be the predominant factors regulating lake primary producers in remote upland lakes and thus, synchronize the dynamic of primary producer assemblages in these basins. We found broad support for the hypotheses pertaining to lowland sites as wastewater treatment was the main predictor of changes to primary producer assemblages in lowland lakes. In contrast, upland headwaters responded weakly to variation in atmospheric temperature, and dynamics in primary producers across upland lakes were asynchronous. Collectively, these findings show that nutrient inputs from point sources overwhelm climatic controls of algae and nuisance cyanobacteria, but highlights that large‐scale stressors do not always initiate coherent regional lake response. Furthermore, a lake's position in its landscape, its connectivity and proximity to point nutrients are important determinants of changes in production and composition of phototrophic assemblages.     

Intraspecific phenotypic variation in a fish predator affects multitrophic lake metacommunity structure

Contemporary insights from evolutionary ecology suggest that population divergence in ecologically important traits within predators can generate diversifying ecological selection on local community structure. Many studies acknowledging these effects of intraspecific variation assume that local populations are situated in communities that are unconnected to similar communities within a shared region. Recent work from metacommunity ecology suggests that species dispersal among communities can also influence species diversity and composition but can depend upon the relative importance of the local environment. Here, we study the relative effects of intraspecific phenotypic variation in a fish predator and spatial processes related to plankton species dispersal on multitrophic lake plankton metacommunity structure. Intraspecific diversification in foraging traits and residence time of the planktivorous fish alewife (Alosa pseudoharengus) among coastal lakes yields lake metacommunities supporting three lake types which differ in the phenotype and incidence of alewife: lakes with anadromous, landlocked, or no alewives. In coastal lakes, plankton community composition was attributed to dispersal versus local environmental predictors, including intraspecific variation in alewives. Local and beta diversity of zooplankton and phytoplankton was additionally measured in response to intraspecific variation in alewives. Zooplankton communities were structured by species sorting, with a strong influence of intraspecific variation in A. pseudoharengus. Intraspecific variation altered zooplankton species richness and beta diversity, where lake communities with landlocked alewives exhibited intermediate richness between lakes with anadromous alewives and without alewives, and greater community similarity. Phytoplankton diversity, in contrast, was highest in lakes with landlocked alewives. The results indicate that plankton dispersal in the region supplied a migrant pool that was strongly structured by intraspecific variation in alewives. This is one of the first studies to demonstrate that intraspecific phenotypic variation in a predator can maintain contrasting patterns of multitrophic diversity in metacommunities.     

Unraveling the effects of water–sediment conditions and spatial patterns on Unionida assemblages in seasonally connected floodplain lakes

Floodplain lakes are good metacommunity systems to study the environmental and spatial processes structuring local assemblages. They are more connected during high-water periods and are more isolated during low-water periods. We evaluated the effects of lake spatial patterning and water and sediment conditions on Unionida species assemblages. Moran Eigenvector Maps were used to generate spatial variables representing spatial patterns at different scales. We sampled 35 lakes from the Pantanal floodplain, Brazil. To understand the effects of environmental and spatial variables, we performed Redundancy Analyses and variation partitioning to separate environmental and spatial pattern effects. Environmental variables explained almost twice the variation in the Pantanal mussel assemblages than did spatial variables. Unionida species presence was driven mainly by variations in sediment coarse sand and silt contents. The weak spatial patterns observed may be related to increased connectivity between lakes during floods, which facilitates mussel host fish dispersal. Mussel abundances were driven mainly by organic matter availability, but varied between species. Changes in lake connectivity can affect the regional sediment dynamics and affect mussel assemblages.

     

Diversity of the Western Carpathian flysch grasslands: Do extremely species-rich plant communities coincide with a high diversity of snails?

Upland fringes of the White Carpathians (Czech Republic) are known to support grasslands with the world’s highest local plant species richness. We investigated whether this unusually high plant richness has a parallel in snail communities, whether patterns of species composition of snail and plant communities in grasslands co-vary and how they are affected by local environment and landscape history. We compared plant and snail communities of dry to mesic grasslands in three neigh bouring regions: (1) hilly lowland of the Central Moravian Carpathians, (2) upland fringes and (3) upland of the White Carpathians. Both snail and plant communities exhibited a strong gradient in species composition associated with altitude, annual temperature and precipitation, soil calcium and pH. However, there was no correlation between local species richness of plants and snails in individual plots. The upland fringes of the White Carpathians were richest in snail species, probably due to intermediate environmental conditions, supporting the occurrence of species with contrasting environmental requirements. The highest local numbers of plant species were also recorded there, although differences among regions were not significant. The regional species richness of plants was also highest in the upland fringes, whereas that of snails was highest in the hilly lowland. Similarities in the diversity patterns of plants and snails among regions suggest the importance of regional factors for local richness, although local abiotic factors, which are partly correlated with the three regions, also influence local species composition and richness.     

Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes

Aiming to elucidate whether large‐scale dispersal factors or environmental species sorting prevail in determining patterns of Trichoptera species composition in mountain lakes, we analyzed the distribution and assembly of the most common Trichoptera (Plectrocnemia laetabilis, Polycentropus flavomaculatus, Drusus rectus, Annitella pyrenaea, and Mystacides azurea) in the mountain lakes of the Pyrenees (Spain, France, Andorra) based on a survey of 82 lakes covering the geographical and environmental extremes of the lake district. Spatial autocorrelation in species composition was determined using Moran's eigenvector maps (MEM). Redundancy analysis (RDA) was applied to explore the influence of MEM variables and in‐lake, and catchment environmental variables on Trichoptera assemblages. Variance partitioning analysis (partial RDA) revealed the fraction of species composition variation that could be attributed uniquely to either environmental variability or MEM variables. Finally, the distribution of individual species was analyzed in relation to specific environmental factors using binomial generalized linear models (GLM). Trichoptera assemblages showed spatial structure. However, the most relevant environmental variables in the RDA (i.e., temperature and woody vegetation in‐lake catchments) were also related with spatial variables (i.e., altitude and longitude). Partial RDA revealed that the fraction of variation in species composition that was uniquely explained by environmental variability was larger than that uniquely explained by MEM variables. GLM results showed that the distribution of species with longitudinal bias is related to specific environmental factors with geographical trend. The environmental dependence found agrees with the particular traits of each species. We conclude that Trichoptera species distribution and composition in the lakes of the Pyrenees are governed predominantly by local environmental factors, rather than by dispersal constraints. For boreal lakes, with similar environmental conditions, a strong role of dispersal capacity has been suggested. Further investigation should address the role of spatial scaling, namely absolute geographical distances constraining dispersal and steepness of environmental gradients at short distances.     

Effects of catchment perturbations by logging and wildfires on zooplankton species richness and composition in Boreal Shield lakes

SUMMARY 1. Forest logging and wildfires are important perturbations of the boreal forest, but their effects on lake biota remain largely unknown. Here, we test whether zooplankton species richness and species assemblages differed among three groups of lakes in Eastern Canada characterised by different catchment conditions: logged in 1995 ( n =9); burnt in 1995 ( n =9); unperturbed ( n =20). Lakes were sampled in June, July and September 1 year after catchment perturbations.
2. Cumulative species richness in reference lakes averaged 46 (33–60) of which 63% were rotifers. Mean cumulative species richness and mean diversity in logged and burnt lakes did not differ from those in reference lakes.
3. Lake species assemblages were described by the density of 62 species (41 rotifers and 21 crustaceans). Among-group differences in species assemblages were not significant. Eighteen per cent of the total variability in species assemblages could be explained by 13 environmental factors, among which dissolved oxygen concentration and cyanobacteria biovolume were the most important. About 5% of species assemblage variability was attributed to covariation between environmental factors and time of sampling, while 4.1% was attributed to temporal variation.
4. Variations in zooplankton species richness and assemblages in Boreal Shield lakes are important, both among lakes and among sampling dates. They seem to depend on environmental factors unrelated to catchment-based perturbations, at least on the short-term of 1 year.     

Lakes in the era of global change: moving beyond single-lake thinking in maintaining biodiversity and ecosystem services

The Anthropocene presents formidable threats to freshwater ecosystems. Lakes are especially vulnerable and important at the same time. They cover only a small area worldwide but harbour high levels of biodiversity and contribute disproportionately to ecosystem services. Lakes differ with respect to their general type (e.g. land-locked, drainage, floodplain and large lakes) and position in the landscape (e.g. highland versus lowland lakes), which contribute to the dynamics of these systems. Lakes should be generally viewed as ‘meta-systems’, whereby biodiversity is strongly affected by species dispersal, and ecosystem dynamics are contributed by the flow of matter and substances among locations in a broader waterscape context. Lake connectivity in the waterscape and position in the landscape determine the degree to which a lake is prone to invasion by non-native species and accumulation of harmful substances. Highly connected lakes low in the landscape accumulate nutrients and pollutants originating from ecosystems higher in the landscape. The monitoring and restoration of lake biodiversity and ecosystem services should consider the fact that a high degree of dynamism is present at local, regional and global scales. However, local and regional monitoring may be plagued by the unpredictability of ecological phenomena, hindering adaptive management of lakes. Although monitoring data are increasingly becoming available to study responses of lakes to global change, we still lack suitable integration of models for entire waterscapes. Research across disciplinary boundaries is needed to address the challenges that lakes face in the Anthropocene because they may play an increasingly important role in harbouring unique aquatic biota as well as providing ecosystem goods and services in the future.     

Pervasive effects of dispersal limitation on within- and among-community species richness in agricultural landscapes

Aim To determine whether the effect of habitat fragmentation and habitat heterogeneity on species richness at different spatial scales depends on the dispersal ability of the species assemblages and if this results in nested species assemblages. Location Agricultural landscapes distributed over seven temperate Europe countries covering a range from France to Estonia. Methods We sampled 16 local communities in each of 24 agricultural landscapes (16 km²) that differ in the amount and heterogeneity of semi‐natural habitat patches. Carabid beetles were used as model organisms as dispersal ability can easily be assessed on morphological traits. The proximity and heterogeneity of semi‐natural patches within the landscape were related to average local (alpha), between local (beta) and landscape (gamma) species richness and compared among four guilds that differ in dispersal ability. Results For species assemblages with low dispersal ability, local diversity increased as the proximity of semi‐natural habitat increased, while mobile species showed an opposite trend. Beta diversity decreased equally for all dispersal classes in relation to proximity, suggesting a homogenizing effect of increased patch isolation. In contrast, habitat diversity of the semi‐natural patches affected beta diversity positively only for less mobile species, probably due to the low dispersal ability of specialist species. Species with low mobility that persisted in highly fragmented landscapes were consistently present in less fragmented ones, resulting in nested assemblages for this mobility class only. Main conclusions The incorporation of dispersal ability reveals that only local species assemblages with low dispersal ability show a decrease of richness as a result of fragmentation. This local species loss is compensated at least in part by an increase in species with high dispersal ability, which obscures the effect of fragmentation when investigated across dispersal groups. Conversely, fragmentation homogenizes the landscape fauna for all dispersal groups, which indicates the invasion of non‐crop habitats by similar good dispersers across the whole landscape. Given that recolonization of low dispersers is unlikely, depletion of these species in modern agricultural landscapes appears temporally pervasive.     

Structuring features of lake districts: landscape controls on lake chemical responses to drought

1. Within a lake district of relatively homogeneous geomorphology, the responses of lakes to climate are influenced by the complexity of the hydrogeologic setting, position in the landscape, and lake‐specific biological and physical features. We examined lake chemical responses to drought in surface water‐ and groundwater‐dominated districts to address two general questions. (1) Are spatial patterns in chemical dynamics among lakes uniform and synchronous within a lake district, suggesting broad geomorphic controls; variable in a spatially explicit pattern, with synchrony related to landscape position, suggesting hydrologic flowpath controls; or spatially unstructured and asynchronous, suggesting overriding control by lake‐specific factors? (2) Are lake responses to drought a simple function of precipitation quantity or are they dictated by more complex interactions among climate, unique lake features, and hydrologic setting? 2. Annual open‐water means for epilimnetic concentrations of chloride, calcium, sulfate, ANC, DOC, total nitrogen, silica, total phosphorus, and chlorophyll a measured between 1982 and 1995 were assembled for lakes in the Red Lake and ELA districts of north‐western Ontario, the Muskoka – Dorset district in south‐central Ontario, and the Northern Highland district of Wisconsin. Within each district, we compared responses of lakes classified by landscape position into highland or lowland, depending on relative location within the local to regional hydrologic flow system. Synchrony, defined as a measure of the similarity in inter‐annual dynamics among lakes within a district, was quantified as the Pearson product‐moment correlation (r) between two lakes with observations paired by year. To determine if solute concentrations were directly related to interannual variations in precipitation quantity, we used regression analysis to fit district‐wide slopes describing the relationship between each chemical variable and annual (June to May) and October to May (Oct–May) precipitation. 3. Among lakes in each of the three Ontario districts, the pattern of chemical response to interannual shifts in precipitation was spatially uniform. In these surface water‐ dominated districts, solute concentrations were generally a simple function of precipitation. Conservative solutes, like calcium and chloride, tended to be more synchronous and were negatively related to precipitation. Solutes such as silica, total phosphorus, and chlorophyll a, which are influenced by in‐lake processes, were less synchronous and relationships with precipitation tended to be positive or absent. 4. In the groundwater‐dominated Northern Highland lakes of Wisconsin, we observed spatial structure in drought response, with lowland lakes more synchronous than highland lakes. However, there was no evidence for a direct relationship between any solute and precipitation. Instead, increases in the concentration of the conservative ion calcium during drought were not followed by a symmetrical return to pre‐drought conditions when precipitation returned to normal or above‐average values. 5. For calcium, time lags in recovery from drought appeared related to hydrologic features in a complex way. In the highland Crystal Lake, calcium concentrations tracked lake stage inversely, with a return to pre‐drought concentrations and lake stage five years after the drought. This pattern suggests strong evaporative controls. In contrast, after five years of normal precipitation, calcium in the lowland Sparkling Lake had not returned to pre‐drought conditions despite a rebound in lake stage. This result suggests that calcium concentrations in lowland lakes were controlled more by regional groundwater flowpaths, which track climatic signals more slowly. 6. Temporal dynamics driven by climate were most similar among lakes in districts that have a relatively simple hydrology, such as ELA. Where hydrologic setting was more complex, as in the groundwater‐dominated Northern Highland of Wisconsin, the expression of climate signals in lakes showed lags and spatial patterns related to landscape position. In general, we expect that landscape and lake‐specific factors become increasingly important in lake districts with more heterogeneous hydrogeology, topography or land use. These strong chemical responses to climate need to be considered when interpreting the responses of lakes to other regional disturbances.     

Connectivity and cladoceran species richness in a metacommunity of shallow lakes

SUMMARY 1. The shallow ponds of the nature reserve 'De Maten' form a metacommunity, in which individual ponds are highly interconnected via a system of overflows and rivulets. This study reports on the relations between cladoceran species richness and (a) connectivity patterns and (b) local environmental variables.
2. No relation was found between local species richness and three connectivity variables or dispersal pathways.
3. Spatial configuration was related to richness, but was confounded by environmental variables for 2 of 3 years. In those 2 years, there was a significant linear relation between Secchi disc depth and species richness, suggesting an important impact of the clearwater/turbid state alternative equilibria in shallow lakes in determining cladoceran richness. Only in the year in which environmental variables were unimportant did connectivity between the ponds influence species richness.
4. These results suggest that local environmental variables related to the clearwater/turbid state alternative equilibria in shallow lakes are important in determining cladoceran species richness. Connectivity and dispersal of individuals between the different ponds only act secondarily by increasing the general species richness within a pond through dispersal from ponds with different environmental conditions.     

Moth assemblages in Costa Rica rain forest mirror small-scale topographic heterogeneity

In many tropical lowland rain forests, topographic variation increases environmental heterogeneity, thus contributing to the extraordinary biodiversity of tropical lowland forests. While a growing number of studies have addressed effects of topographic differences on tropical insect communities at regional scales (e.g., along extensive elevational gradients), surprisingly little is known about topographic effects at smaller spatial scales. The present study investigates moth assemblages in a topographically heterogeneous lowland rain forest landscape, at distances of less than a few hundred meters, in the Golfo Dulce region (SW Costa Rica). Three moth lineages—Erebidae–Arctiinae (tiger and lichen moths), the bombycoid complex, and Geometridae (inchworm moths)—were examined by means of automatic light traps in three different forest types: creek forest, slope forest, and ridge forest. Altogether, 6,543 individuals of 419 species were observed. Moth assemblages differed significantly between the three forest types regarding species richness, total abundance, and species composition. Moth richness and abundance increased more than fourfold and eightfold from creek over slope to ridge forest sites. All three taxonomic units showed identical biodiversity patterns, notwithstanding their strong differences in multiple eco-morphological traits. An indicator species analysis revealed that most species identified as characteristic were associated either with the ridge forest alone or with ridge plus slope forests, but very few with the creek forest. Despite their mobility, local moth assemblages are highly differentially filtered from the same regional species pool. Hence, variation in environmental factors significantly affects assemblages of tropical moth species at small spatial scales.     

Distribution and community-level effects of the Chinese mystery snail (Bellamya chinensis) in northern Wisconsin lakes

Managing invasive species requires information about their distributions and potential effects, but community-level impacts of invasive animals remain poorly understood. The Chinese mystery snail (Bellamya chinensis) is a large invasive gastropod that achieves high densities in waters across North America, yet little is known about its ecological significance in invaded systems. We surveyed 44 lakes to describe the patterns and determinants of B. chinensis distributions in northern Wisconsin, USA, and to assess the likelihood of effects on native snail communities in the invaded systems. B. chinensis was widespread among surveyed lakes (21 of 42 lakes with snails) and its occurrence was correlated with indicators of lake productivity and anthropogenic dispersal vectors (boat landings, distance to population centers, shoreline housing density). Some native snail species tended not to occur at sites where B. chinensis was abundant; among these was Lymnaea stagnalis, which suffered reduced survival in the presence of B. chinensis in a recently published mesocosm study. However, there was no difference in overall snail assemblage structure at either the site or lake level as a function of B. chinensis presence or abundance. Lake occurrences of many snail species have apparently been lost over time, but a comparison to a 1930s survey showed that there was no increased likelihood of species loss in lakes invaded by B. chinensis (or by the invasive crayfish Orconectes rusticus). Although B. chinensis is widespread and sometimes abundant in northern Wisconsin lakes, it does not appear to have strong systematic impacts on native snail assemblages.     

Are distribution patterns linked to dispersal mechanism? An investigation using pond invertebrate assemblages

1. Dispersal ability influences the distribution and abundance of organisms, but empirical investigations of the relationship between dispersal ability and the composition of ecological assemblages are scarce. Here, we compare between-site variation in the species richness and community composition of actively and passively dispersing pond invertebrates.
2. Coleoptera (active dispersers) and microcrustacea (passive dispersers) were sampled over a season from 16 ponds within a 4-km radius in south-west England. Species richness and community composition were related to environmental variables using regression and Canonical Correspondence Analysis (CCA), respectively.
3. Coleopteran species richness was significantly and positively correlated with pond permanence and maximum area, whereas microcrustacean species richness was relatively equal across sites and did not correlate with environmental variables. The frequency of species' occurrence between sites was the same for both groups, which suggests that active and passive dispersers exhibited the same degree of dispersal.
4. Between-site variation in community composition was non-random for both groups, with pond permanence and area, together, explaining similar proportions of between-site variation for Coleoptera. Permanence was correlated most strongly with microcrustacean community composition and a high proportion (25%) of microcrustacean species were more numerous in smaller, more ephemeral ponds.
5. These data suggest that, at small spatial scales, Coleoptera which can undertake multiple dispersal events, are more likely to colonise large, more permanent ponds than passively dispersing microcrustacea. For microcrustacea, other traits (in this case those permitting existence in ephemeral habitats) may over-ride the influences of dispersal in driving between-site variation in species composition.     

Taxonomy and diversity of Afroalpine Chironomidae (Insecta: Diptera) on Mount Kenya and the Rwenzori Mountains, East Africa

Aim Anthropogenic climate change is expected to result in the complete loss of glaciers from the high mountains of tropical Africa, with profound impacts on the hydrology and ecology of unique tropical cold‐water lakes located downstream from them. This study examines the biodiversity of Chironomidae (Insecta: Diptera) communities in these scarce Afroalpine lake systems, in order to determine their uniqueness in relation to lowland African lakes and alpine lakes in temperate regions, and to evaluate the potential of Afroalpine Chironomidae as biological indicators to monitor future changes in the ecological integrity of their habitat. Location Mount Kenya (Kenya) and Rwenzori Mountains (Uganda). Methods The species composition of Afroalpine chironomid communities was assessed using recent larval death assemblages extracted from the surface sediments of 11 high‐mountain lakes between 2900 and 4575 m. Results were compared with similar faunal data from 68 East African lakes at low and middle elevation (750–2760 m), and with literature records of Chironomidae species distribution in sub‐Saharan Africa, the Palaearctic region and elsewhere. All recovered taxa were fully described and illustrated. Results The 11‐lake analysis yielded 1744 subfossil chironomid larvae belonging to 16 distinct taxa of full‐grown larvae, and three taxa of less differentiated juveniles. Eleven of these 16 are not known to occur in African lakes at lower elevation, and eight taxa (or 50% of total species richness) appear restricted to the specific habitat of cold lakes above 3900 m, where night‐time freezing is frequent year‐round. The faunal transition zone coincides broadly with the Ericaceous zone of terrestrial vegetation (c. 3000–4000 m). Snowline depression during the Quaternary ice ages must have facilitated dispersion of cold‐stenothermous species among the high mountains of equatorial East Africa, but less so from or to the Palaearctic region via the Ethiopian highlands. Main conclusions Chironomid communities in glacier‐fed lakes on Africa's highest mountains are highly distinct from those of lowland African lakes, and potentially unique on a continental scale. By virtue of excellent preservation and their spatial and temporal integration of local community dynamics, chironomid larval death assemblages extracted from surface sediments are powerful biological indicators for monitoring the hydrological and ecological changes associated with the current retreat and loss of Africa's glaciers.     

Surface water connectivity drives richness and composition of Arctic lake fish assemblages

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Biome transitions as centres of diversity: habitat heterogeneity and diversity patterns of West African bat assemblages across spatial scales

It is widely accepted that species diversity is contingent upon the spatial scale used to analyze patterns and processes. Recent studies using coarse sampling grains over large extents have contributed much to our understanding of factors driving global diversity patterns. This advance is largely unmatched on the level of local to landscape scales despite being critical for our understanding of functional relationships across spatial scales. In our study on West African bat assemblages we employed a spatially explicit and nested design covering local to regional scales. Specifically, we analyzed diversity patterns in two contrasting, largely undisturbed landscapes, comprising a rainforest area and a forest‐savanna mosaic in Ivory Coast, West Africa. We employed additive partitioning, rarefaction, and species richness estimation to show that bat diversity increased significantly with habitat heterogeneity on the landscape scale through the effects of beta diversity. Within the extent of our study areas, habitat type rather than geographic distance explained assemblage composition across spatial scales. Null models showed structure of functional groups to be partly filtered on local scales through the effects of vegetation density while on the landscape scale both assemblages represented random draws from regional species pools. We present a mixture model that combines the effects of habitat heterogeneity and complexity on species richness along a biome transect, predicting a unimodal rather than a monotonic relationship with environmental variables related to water. The bat assemblages of our study by far exceed previous figures of species richness in Africa, and refute the notion of low species richness of Afrotropical bat assemblages, which appears to be based largely on sampling biases. Biome transitions should receive increased attention in conservation strategies aiming at the maintenance of ecological and evolutionary processes.     

Contrasting responses of arable spiders to the landscape matrix at different spatial scales

Aim Animal communities can be influenced by the composition of the surrounding landscape through immigration. Depending on habitat preferences, however, the effect of the landscape matrix can be positive or negative and can vary with scale. We tested this idea with arable spiders and tried to infer dispersal distances from relationships between local density and landscape composition at different spatial scales. Location Thirty‐eight landscapes around the cities of Göttingen and Giessen, Germany. Methods Spiders were captured with pitfall traps in one field of winter wheat in each landscape. Landscape composition around the fields was characterized at 11 scales from 95 m to 3 km radius by land‐use mapping and subsequent GIS analysis. Correlation tests were performed between landscape composition and local densities or species richness. Results In both study regions, local species richness was enhanced by non‐crop habitats on a landscape scale. The overall densities of wolf spiders (Lycosidae), long‐jawed spiders (Tetragnathidae), crab spiders (Thomisidae), and dwarf sheet spiders (Hahniidae) increased significantly in landscapes with high percentages of non‐crop habitats. Out of the 40 species tested, 19 responded positively to the percentage of non‐crop habitats in the surrounding landscape, and five responded negatively. Depending on the species, the spatial scales with the highest explanatory power ranged from 95 m to 3 km radius around the study fields, potentially reflecting dispersal distances. Main conclusions Arable spider species showed contrasting responses to the landscape context with respect both to the direction and to the spatial scale of the relationship. The variation in landscape requirements among species ensures high spider densities in a wide range of situations, which contributes to ecosystem resilience. However, species richness of arable spiders depends on heterogeneous landscapes with high percentages of non‐crop habitats.