Weak altitudinal pattern of overall chironomid richness is a result of contrasting trends of subfamilies in high-altitude ponds

The decline of species richness with altitude is one of the most obvious patterns in ecology and results from the combination of ecological and evolutionary mechanisms. In harsh high-altitude environments, the effect of altitude usually overrules other environmental variables related to biodiversity. Studies using species richness along altitude gradients in high altitude are relatively numerous for lakes, but not for ponds. However, due to their special features, such as small size, high isolation and regional variability, ponds have been proved to be different systems compared to lakes. In high-altitude waterbodies, species of the family Chironomidae often dominate in benthic invertebrate communities and thus serve as an ideal model to study aquatic community changes along an altitude gradient. However, due to the time-consuming processing and expertise needed to identify the species, chironomids are often excluded from regular surveys. In the present study, we sampled 66 Tatra ponds over a 1100-m altitude gradient for benthic invertebrates, with special attention to chironomids. Out of the total 122 taxa collected, Chironomidae constituted the richest group with 58 taxa, being present in all the study ponds. The most diverse pond supported 13 chironomid taxa, and mean diversity was 6 taxa/pond. While total invertebrate richness decreased with altitude, chironomid richness showed only a weak negative response to altitude. The proportion of total chironomid diversity made up of Tanypodinae and Chironominae subfamilies decreased with altitude, while the opposite trend was recorded for the proportion of Diamesinae and Orthocladiinae.     

Environmental determinants of chironomid communities in remote northern lakes across the treeline – Implications for climate change assessments

Chironomids (Diptera: Chironomidae) in northern lakes are especially sensitive to climate change impacts. In addition, environmental factors other than direct temperature increase might play an important role in functioning of these keystone aquatic communities. We examined 31 lakes at the treeline ecotone in subarctic Finnish Lapland for their surface sediment chironomid fauna to assess the influence of different environmental factors on the communities. We aim to improve understanding of the climate-driven catchment and limnological factors, for the assessment of climate change impacts. Our results indicated that organic content of the sediment, total nitrogen, water depth and pH that are all likely to change under global warming had statistically significant influence on the chironomid assemblages and associated indicator taxa were assigned for these variables. In addition, a dissolved organic carbon (DOC) threshold (4 mg l⁻¹) was observed that divided the study sites based on their chironomid composition. Sites with high DOC concentrations and benthic microbial mats had distinctive chironomid fauna from low-DOC sites without microbial mats indicating the significance of benthic versus planktonic productivity in the structure and functioning of polar lakes. The results provide important knowledge on chironomid-environmental relationships in climate-sensitive subarctic lakes and create basis for chironomid-based environmental change assessments in remote northern areas.     

Environmental controls on the distribution and diversity of lentic Chironomidae (Insecta: Diptera) across an altitudinal gradient in tropical South America

To predict the response of aquatic ecosystems to future global climate change, data on the ecology and distribution of keystone groups in freshwater ecosystems are needed. In contrast to mid‐ and high‐latitude zones, such data are scarce across tropical South America (Neotropics). We present the distribution and diversity of chironomid species using surface sediments of 59 lakes from the Andes to the Amazon (0.1–17°S and 64–78°W) within the Neotropics. We assess the spatial variation in community assemblages and identify the key variables influencing the distributional patterns. The relationships between environmental variables (pH, conductivity, depth, and sediment organic content), climatic data, and chironomid assemblages were assessed using multivariate statistics (detrended correspondence analysis and canonical correspondence analysis). Climatic parameters (temperature and precipitation) were most significant in describing the variance in chironomid assemblages. Temperature and precipitation are both predicted to change under future climate change scenarios in the tropical Andes. Our findings suggest taxa of Orthocladiinae, which show a preference to cold high‐elevation oligotrophic lakes, will likely see range contraction under future anthropogenic‐induced climate change. Taxa abundant in areas of high precipitation, such as Micropsectra and Phaenopsectra, will likely become restricted to the inner tropical Andes, as the outer tropical Andes become drier. The sensitivity of chironomids to climate parameters makes them important bio‐indicators of regional climate change in the Neotropics. Furthermore, the distribution of chironomid taxa presented here is a vital first step toward providing urgently needed autecological data for interpreting fossil chironomid records of past ecological and climate change from the tropical Andes.     

Structure of chironomid assemblages along environmental and geographical gradients in the Bohemian Forest lakes (Central Europe): An exploratory analysis

Eight glacial lakes of the Bohemian Forest (Czech Republic and Germany) were characterised by the distribution of chironomids collected as pupal exuviae. Twenty-eight taxa were identified, including some faunistically interesting species of the region. Two-way indicator species analysis (TWINSPAN) was used to classify lakes according to their taxonomic composition. Canonical correspondence analysis (CCA) and multiple regression were used to relate the chironomid assemblages to two sets of explanatory variables: (i) local environmental variables, and (ii) broad-scale spatial variables. The TWINSPAN classified the lakes into four groups, whereas presence/absence of three taxa was indicative for this classification. The CCA of assemblage composition on environmental variables showed that chironomids respond significantly to altitude and alkalinity. The ordination of composition data on geographical variables revealed strong longitudinal gradient in chironomid distributions. Altitude and alkalinity accounted for 36.2% of the total variation, while the geographic gradient explained 20.5%. As revealed by the variation partitioning procedure, the significant effect of these variables was, in large part, independent of each other. Overall taxonomic richness appeared to be governed by altitude only. Causal ecological and historical factors underlying these results are discussed. This paper may provide a basis for hypothesis testing in future research of the Bohemian Forest lakes.     

Changes in trophic state and aquatic communities in high Arctic ponds in response to increasing goose populations

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Ecological influences on larval chironomid communities in shallow lakes: implications for palaeolimnological interpretations

1. To correctly interpret chironomid faunas for palaeoenvironmental reconstruction, it is essential that we improve our understanding of the relative influence of ecosystem variables, biotic as well as physicochemical, on chironomid larvae. To address this, we analysed the surface sediments from 39 shallow lakes (29 Norfolk, U.K., 10 Denmark) for chironomid head capsules, and 70 chironomid taxa (including Chaoborus) were identified. 2. The shallow lakes were selected over large environmental gradients of aquatic macrophytes, total phosphorus (TP) and fish communities. Redundancy analysis (RDA) identified two significant variables that explained chironomid distribution: macrophyte species richness (P < 0.001) and TP (P < 0.005). Generalised linear models (GLM) identified specific taxa that had significant relationships with both these variables. Macrophyte percentage volume infested (PVI) and species richness were significant in classifying the lake types based on chironomid communities under twinspan analysis, although other factors, notably nutrient concentrations and fish communities, were also important, illustrating the complexities of classifying shallow lake ecosystems. Lakes with plant species richness >10 all had relatively diverse (Hill’s N2) chironomid assemblages, and lakes with Hill’s N2 >10 all had TP <250 μg L⁻¹ and total fish densities <2 fish per m². 3. Plant density (PVI), and perhaps more importantly species richness, were primary controls on the distribution of chironomid communities within these lakes. This clearly has implications for palaeoenvironmental reconstructions using zoobenthos remains (i.e. chironomids) and suggests that they could be used to track changes in benthic/pelagic production and could be used as indicators of changing macrophyte habitat. 4. Measuring key biological gradients, in addition to physicochemical gradients, allowed the major controls on chironomid distribution to be assessed more directly, in terms of plant substrate, food availability, competition and predation pressure, rather than implying indirect mechanisms through relationships with nutrients. Many of these variables, notably macrophyte abundance and species richness, are not routinely measured in such studies, despite their importance in determining zoobenthos in temperate shallow lakes. 5. When physical, chemical and ecological gradients are considered, as is often the case with palaeo‐reconstructions rather than training sets chosen to maximise one gradient, complex relationships exist, and attempting to reconstruct a single trophic variable quantitatively may not be appropriate or reliable.     

CHLfuzzy: a spreadsheet tool for the fuzzy modeling of chlorophyll concentrations in coastal lagoons

Our purpose was to explore relationships of freshwater planktonic and benthic community species richness with water chemistry parameters using a dataset of biological, chemical, and physical data from 550 lakes. This was done using multivariate (ordination), graphical, and correlation analyses. Although the lakes are rather similar in location (Belarus) and in being mostly eutrophic, they do show variations in water chemistry. We ordinated lakes by water chemistry variables, and then looked for correlations between the ordination axes and species richness in 10 taxonomic groups: Cyanobacteria, Chlorophyta, Bacillariophyta, Cladocera, Copepoda, Rotatoria, Mollusca, Trichoptera, Chironomidae, and aquatic macrophytes. The first four Principal Components Analysis (PCA) axes explained about 67% of the total variability in water chemistry. The axes represent water hardness (DIC, dissolved inorganic carbon), organic content (DOC, dissolved organic carbon), nutrients, and chlorides and sulfates. The PCA ordination revealed environmental gradients, but not the distinctive clusters of lakes. Species richness was most strongly correlated with the first PCA axis (DIC), which accounted for 29% of the total variation in water chemistry. Species richness was positively correlated with DIC for eight of 10 taxonomic categories. The second PCA axis (DOC), which accounted for 20% of total variation in water chemistry, was correlated with species richness in the three phytoplankton groups, and with chironomid species richness. The third PCA axis (nutrients, especially nitrogen, 11%) was correlated with species richness of copepoda, chironomids, and macrophytes. The fourth PCA axis (chloride and sulfate) accounted for only 7% of the total variance in water chemistry, and was significantly negatively correlated with species richness of rotifers, molluscs, and chironomids. In addition to these linear correlations, there were several significant non-linear relationships. DIC variables showed curvilinear (hump-shaped) relationship with benthos (all groups combined) and especially with molluscs, and DOC variables—with phytoplankton and benthos. Each community, and often separate taxonomic groups within community have their own optimal ranges of chemical concentrations, and various water chemistry variables showed significant curvilinear relationships with biodiversity, suggesting that the diversity of different major aquatic groups may be influenced by different chemicals. Handling editor: S. Declerck     

Non-biting midges in biodiversity conservation and environmental assessment: Findings from boreal freshwater ecosystems

Non-biting midges (Diptera: Chironomidae) are frequently overlooked in freshwater biodiversity surveys and environmental assessment, yet they are commonly the most abundant and the most diverse taxon in freshwater ecosystems. We reviewed the diversity patterns and assemblage–environment relationships of non-dipterans and chironomids mainly in boreal freshwater ecosystems building on previously reported findings. Although generally the same environmental gradients are correlated with assemblage structure, their relative importance varies between chironomids and non-dipterans. Chironomid assemblage response to and recovery from human impacts are also likely to differ from that of other common benthic taxa. Thus, environmental assessments may be biased if chironomids are not included. Different surrogacy approaches have thus far shown little success in accounting for chironomid species richness and assemblage structure, and there appears to be no easy short-cut for the examination of chironomids as part of freshwater surveys. However, we show that genus-level identification of pupal exuviae provides a reliable and rapid way of estimating chironomid species richness at least in boreal freshwater ecosystems. In addition, we demonstrate that the inclusion of chironomids may increase the signal-to-noise ratio in bioassessment data sets, and that this information can be obtained with modest increases in costs.     

Diversity of chironomid larvae in palustrine wetlands of the coastal plain in the south of Brazil

The Chironomidae of tropical South America are a very rich species, but are scarcely known. The range of environmental conditions under which chironomids are found is more extensive than that of any other group of aquatic insects. The objectives of this study were to carry out a diversity survey of chironomid larvae in wetland systems of the coastal plain in the south of Brazil and to analyze the effects of area, altitude, water conductivity, nitrate and phosphorus concentrations, and the life form of the dominant plant species on chironomid richness and composition. Collections were carried out from March to April in 2002. A total of 30 taxa (23 morphospecies and 7 species) distributed along 23 genera were found, and the Chironominae showed the greatest richness, followed by Tanypodinae and Orthocladiinae. The chironomid richness was higher in the emergent than in the multistratified wetland class. The wetland area, altitude, nitrate and phosphorus concentrations, and water conductivity did not influence the richness of Chironomidae. The Chironomidae genera and species were present in both the wetland classes (emergent and aquatic bed vegetation). However, while Chironominae were more frequent in the emergent than in the aquatic bed wetlands, no difference was observed for Tanypodinae. The aquatic vegetation was an important environmental predictor for chironomid larvae richness in the studied wetlands in the south of Brazil.     

Nematode distributions as spatial null models for macroinvertebrate species richness across environmental gradients: A case from mountain lakes

Nematode species are widely tolerant of environmental conditions and disperse passively. Therefore, the species richness distribution in this group might largely depend on the topological distribution of the habitats and main aerial and aquatic dispersal pathways connecting them. If so, the nematode species richness distributions may serve as null models for evaluating that of other groups more affected by environmental gradients. We investigated this hypothesis in lakes across an altitudinal gradient in the Pyrenees. We compared the altitudinal distribution, environmental tolerance, and species richness, of nematodes with that of three other invertebrate groups collected during the same sampling: oligochaetes, chironomids, and nonchironomid insects. We tested the altitudinal bias in distributions with t‐tests and the significance of narrow‐ranging altitudinal distributions with randomizations. We compared results between groups with Fisher's exact tests. We then explored the influence of environmental factors on species assemblages in all groups with redundancy analysis (RDA), using 28 environmental variables. And, finally, we analyzed species richness patterns across altitude with simple linear and quadratic regressions. Nematode species were rarely biased from random distributions (5% of species) in contrast with other groups (35%, 47%, and 50%, respectively). The altitudinal bias most often shifted toward low altitudes (85% of biased species). Nematodes showed a lower portion of narrow‐ranging species than any other group, and differed significantly from nonchironomid insects (10% and 43%, respectively). Environmental variables barely explained nematode assemblages (RDA adjusted R² = 0.02), in contrast with other groups (0.13, 0.19 and 0.24). Despite these substantial differences in the response to environmental factors, species richness across altitude was unimodal, peaking at mid elevations, in all groups. This similarity indicates that the spatial distribution of lakes across altitude is a primary driver of invertebrate richness. Provided that nematodes are ubiquitous, their distribution offers potential null models to investigate species richness across environmental gradients in other ecosystem types and biogeographic regions.     

The chironomid‐temperature relationship: expression in nature and palaeoenvironmental implications

Fossils of chironomid larvae (non‐biting midges) preserved in lake sediments are well‐established palaeotemperature indicators which, with the aid of numerical chironomid‐based inference models (transfer functions), can provide quantitative estimates of past temperature change. This approach to temperature reconstruction relies on the strong relationship between air and lake surface water temperature and the distribution of individual chironomid taxa (species, species groups, genera) that has been observed in different climate regions (arctic, subarctic, temperate and tropical) in both the Northern and Southern hemisphere. A major complicating factor for the use of chironomids for palaeoclimate reconstruction which increases the uncertainty associated with chironomid‐based temperature estimates is that the exact nature of the mechanism responsible for the strong relationship between temperature and chironomid assemblages in lakes remains uncertain. While a number of authors have provided state of the art overviews of fossil chironomid palaeoecology and the use of chironomids for temperature reconstruction, few have focused on examining the ecological basis for this approach. Here, we review the nature of the relationship between chironomids and temperature based on the available ecological evidence. After discussing many of the surveys describing the distribution of chironomid taxa in lake surface sediments in relation to temperature, we also examine evidence from laboratory and field studies exploring the effects of temperature on chironomid physiology, life cycles and behaviour. We show that, even though a direct influence of water temperature on chironomid development, growth and survival is well described, chironomid palaeoclimatology is presently faced with the paradoxical situation that the relationship between chironomid distribution and temperature seems strongest in relatively deep, thermally stratified lakes in temperate and subarctic regions in which the benthic chironomid fauna lives largely decoupled from the direct influence of air and surface water temperature. This finding suggests that indirect effects of temperature on physical and chemical characteristics of lakes play an important role in determining the distribution of lake‐living chironomid larvae. However, we also demonstrate that no single indirect mechanism has been identified that can explain the strong relationship between chironomid distribution and temperature in all regions and datasets presently available. This observation contrasts with the previously published hypothesis that climatic effects on lake nutrient status and productivity may be largely responsible for the apparent correlation between chironomid assemblage distribution and temperature. We conclude our review by summarizing the implications of our findings for chironomid‐based palaeoclimatology and by pointing towards further avenues of research necessary to improve our mechanistic understanding of the chironomid‐temperature relationship.     

Subfossil chironomid assemblages in deep,stratified European lakes: relationships with temperature,trophic state and oxygen

1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy. 2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P < 0.05) explanatory variables explaining between 11 and 14% of the variance in the chironomid data. 3. Owing to the spatial scale covered by our study, many environmental variables were covarying. Temperature, TP concentration and oxygen availability were positively or negatively correlated with the first axis of a detrended correspondence analysis (DCA) of chironomid assemblages, suggesting that climatic and trophic conditions influenced profundal chironomid assemblages either in a direct (food and oxygen) or in an indirect (temperature) way. Parameters related to local environmental conditions, lake morphology and bedrock geology, such as organic matter content of the sediment, maximum lake depth, Secchi depth and pH, were not significant in explaining the distribution of chironomid assemblages in our study lakes. 4. The strong relationship between chironomid assemblages and summer temperature may be related to the covariation of temperature with parameters, such as nutrient and oxygen availability, known to affect chironomid assemblages in deep, stratified lakes. However, summer temperature explained a statistically significant proportion of the variance in the chironomid assemblages even when effects of oxygen availability and TP concentrations were partialled out. This suggests that summer temperature has an effect on chironomid assemblages in deep lakes, which is not related to its covariation with trophic state. 5. The potential of fossil chironomid analysis for quantitatively reconstructing past nutrient conditions in deep, stratified lakes was examined by calculating the Benthic Quality Index (BQI) based on subfossil chironomids and by comparing BQI values with observed TP concentrations. BQI was linearly related to log‐transformed TP. Applying this relationship to fossil chironomid assemblages from Lake Päijänne (Finland) produced a TP reconstruction in agreement with measured TP during the period 1970–1990, demonstrating that this approach can provide quantitative estimates of past nutrient concentrations in deep, stratified lakes.     

Spatial distribution of subfossil Chironomidae in surface sediments of a large, shallow and hypertrophic lake (Taihu, SE China)

Spatial heterogeneity of benthic communities has clear implications for estimating lake production, biodiversity as well as identifying representative sites for palaeolimnological studies. This study investigates chironomid variability and the controlling factors (i.e., environmental and spatial variables) in surface sediments from Taihu Lake (2,338 km²), a hypertrophic lake in the Yangtze delta in eastern China. The spatial distribution of chironomids shows distinct heterogeneity. Microchironomus tabarui-type and Tanypus dominate the midge communities around the estuaries, while Cricotopus sylvestris-type and Polypedilum nubifer-type are the predominant taxa in the East Bays and the East Taihu Lake. Redundancy analysis was used for exploring the relationships between chironomid variability and environmental and spatial stressors. Four variables were identified as significant factors that influence chironomid community structures. The high nutrient concentrations around the estuarial areas favor the development of nutrient-tolerant taxa. Water depth-related oxygen depletion in the open lake during algae blooms prohibits the survival of many organisms, except for a few hypoxic-resistant species. High transparency in the East Bays and the East Taihu Lake indirectly creates a favorite microhabitat for macrophyte-associated chironomid species through aquatic plants. Space per se is a significant forcing factor for organism community and distribution at scales of >1,000 km². It might be important to consider spatial variables more explicitly in future studies of chironomids in large lakes where multiple stressors make the interactions within the ecosystem more complicated. This study aims to illustrate the ecological characteristics of specific chironomid taxa related to a “microecosystem” which is contributed by the multiple environmental gradients within a large lake, and to provide empirical support for interpretation of palaeochironomid data.     

A primary study on relationships between subfossil chironomids and the distribution of aquatic macrophytes in three lowland floodplain lakes,China

Aquatic macrophytes act as an important substrate for zoobenthos-supporting midge communities (chironomids) that can be used for reconstructing past environmental change. This study selected three macrophyte-dominated lakes in the middle reach of the Yangtze floodplain (central China), to identify relationships between macrophyte characteristics (i.e. communities, richness and biomass) and subfossil chironomid assemblages. One-way ANOSIM tests illustrated that there were significant differences in chironomid community compositions between lakes. Most chironomid taxa were not selective of dominant macrophyte species, but Corynoneura species were found to be associated with the development of Vallisneria as revealed by SIMPER analysis. Multivariate analyses indicate that submerged plant biomass, water depth and secchi depth, conductivity and the concentration of HCO₃ ^? were significantly correlated with midge compositions. Overall, this study corroborates the existing opinions that chironomid species show little selectivity to plant type but are significantly influenced by plant density. As an exception to this general trend, we found strong associations between Corynoneura chironomid larvae and Vallisneria macrophytes, prompting the need for future experimental studies to confirm this association.     

Long-term changes in aquatic plant species composition in North-eastern European Russia and Finnish Lapland,as evidenced by plant macrofossil analysis

Three lake sediment sequences from North-eastern European Russia and one from Finnish Lapland were studied for aquatic plant macrofossils. Ages of sediment sequences varied between 12 800 and ca. 10 500 radiocarbon years. Historical records showed distinct changes in the diversity and abundances of aquatic plant remains in each lake's history. Despite the studied lakes being located in different vegetation and climate zones, the records showed a similar long-term pattern of the early Holocene immigration of aquatics, a subsequent maximum in aquatic species richness, and a decline or disappearance after the mid Holocene. It seems that the warming temperature together with sufficient nutrient status enabled establishment of aquatic plant communities during the early Holocene. Afterwards the presence of the limnophytes was probably mainly controlled by the length of the open-water season (i.e. temperature), with changes in nutrient status and water level possibly being additional minor factors. Climate-driven change is supported by the fact that currently aquatic macrophytes are often absent from the lakes beyond tree lines, which are characterized by a short growing season.     

Phytoplankton richness is related to nutrient availability,not to pool size,in a subarctic rock pool system

In small aquatic ecosystems, communities are strongly affected by environmental filtering such as disturbances and fine-scale heterogeneity of physicochemical properties. Aim of this study was to examine the effects of abiotic variables on phytoplankton richness in 30 subarctic rock pools in Finnish Lapland and further to test species–area and productivity–diversity relationships. We used Moran’s correlograms to examine if phytoplankton richness and explanatory variables show spatial autocorrelation. We then related phytoplankton richness to physical, chemical and spatial variables (derived from Principal Coordinates of Neighbor Matrices based on either overland or water course distances) using generalized linear model (GLM). Correlograms did not indicate clear gradient-like spatial structures in the data. According to the best-approximating GLM, phytoplankton richness showed a highly significant positive relationship with total P concentrations, which differed by one magnitude among the pools, and showed also a marginally significant negative relationship with conductivity. Richness scaled nonsignificantly with pool volume. We conclude that rock pools with higher nutrient availability are capable of supporting more phytoplankton species in this low-energy ecosystem. We did not find any support for the species–area relationship across the pools possibly because the pools were similarly affected by random disturbances irrespective of their volume.     

Microhabitat influence on chironomid community structure and stable isotope signatures in West Greenland lakes

Most functional feeding types are represented within the species rich group of aquatic chironomids. Thus, we hypothesized that different lake types and microhabitats within lakes would (1) host specific chironomid communities and (2) that the individual communities would show specific δ ¹³C stable isotope signatures reflecting the prevailing origin of food source. To test our hypotheses, five lakes in southwest Greenland were investigated at a high taxonomic resolution and with detailed information on δ ¹³C signature of the chironomids and of individual microhabitats (macrophytes, sediment, stones, and profundal). We found that there was a significant difference in δ ¹³C between the chironomid assemblages of freshwater lakes and oligosaline lakes, while assemblages of the littoral microhabitats did not differ significantly. The δ ¹³C of chironomids reflected the wide variety of habitat signals, particularly in the freshwater lakes. Our results indicate that many chironomid taxa are ubiquitous and are found in several microhabitats, suggesting that they can adjust their feeding strategy according to the habitat. The implication is that chironomid assemblage composition has only limited use as indicator of littoral microhabitats in the Arctic. On the other hand, the δ ¹³C signature of fossil chironomids might have a potential as indicator of microhabitats in freshwater lakes.     

Predator diversity effects cascade across an ecosystem boundary

Food webs in different ecosystems are often connected through spatial resource subsidies. As a result, biodiversity effects in one ecosystem may cascade to adjacent ecosystems. I tested the hypothesis that aquatic predator diversity effects cascade to terrestrial food webs by altering a prey subsidy (biomass and trophic structure of emerging aquatic insects) entering terrestrial food webs, in turn altering the distribution of a terrestrial consumer (spider) that feeds on emerging aquatic insects. Fish presence, but not diversity, altered the trophic structure of emerging aquatic insects by strongly reducing the biomass of emerging predators (dragonflies) relative to non‐feeding taxa (chironomid midges). Fish diversity reduced emerging insect biomass through enhanced effects on the most common prey taxa: predatory dragonflies Pantala flavescens and non‐feeding chironomids. Terrestrial spiders (Tetragnathidae) primarily captured emerging chironomids, which were reduced in the high richness (3 spp.) treatment relative to the 1 and 2 species treatments. As a result, terrestrial spider abundance was lower above pools with high fish richness (3 species) than pools with 1 and 2 species. Synergistic predation effects were mostly limited to the high richness treatment, in which fish occupied each level of vertical microhabitat in the water‐column (benthic, middle, surface). This study demonstrates that predator diversity effects are not limited to the habitat of the predator, but can propagate to adjacent ecosystems, and demonstrates the utility of using simple predator functional traits (foraging domain) to more accurately predict the direction of predator diversity effects.     

Environmental controls on benthic food web functions and carbon resource use in subarctic lakes

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