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 within-lake gradients on the distribution of fossil chironomids from maar lakes in western Alaska: implications for environmental reconstructions

We examined fossil chironomids (Diptera: Chironomidae) in the surface sediments of four maar lakes in western Alaska to determine chironomid distribution patterns with respect to within-lake gradients of water depth, LOI (loss-on-ignition), and bottom-water temperature. Linear and non-linear regressions were undertaken to test whether the within-lake distributions of fossil chironomids were uniform. Additionally, water depths where abrupt changes or breakpoints in the assemblages occur were identified using piecewise regression. Direct gradient analysis was then used to examine variation in the assemblages explained by the environmental data. For the shallowest lake, chironomid abundances of individual taxa and inferred temperatures varied little within the lake. For the three deep lakes, seven of the sixteen commonest fossil taxa varied significantly with water depth, although some lake-specific patterns were evident. Water depth was generally identified as the principal environmental variable in explaining variation in the assemblages, although sediment organic matter content and bottom-water temperature were also important. Abrupt changes in assemblages occurred at different water depths in each lake, and at only one lake did the breakpoint occur within the range of water depths defining the thermocline. Chironomid-inferred temperature trends from the lakes also showed depth-related patterns: the warmest inferred temperatures were generally from both the shallowest and deepest water depths, whereas intermediate depths yielded temperature inferences about 0.5 to 1.0°C cooler than the average within-lake value. Nevertheless, we conclude that these patterns had only a slight impact on temperature reconstructions relative to the prediction error of the model. A greater understanding of taphonomic processes is needed to determine their influence on environmental reconstructions based on chironomids. Handling editor: J. Saros     

Environmental gradients determining the distribution of benthic macroinvertebrates in Lake Takkobu, Kushiro wetland, northern Japan

Effects of environmental variables on the distribution of benthic macroinvertebrates inhabiting sediments were studied at 25 sites along the shoreline of Lake Takkobu in the Kushiro wetland of northern Japan in summer 2003. During the last decade, the lake’s status has undergone a drastic shift from clear water dominated by submerged macrophytes to turbid water dominated by phytoplankton. The canonical correspondence analysis showed that four environmental variables explained the significant variation in the macroinvertebrate species composition: submerged plant biomass, bottom sediment organic matter content (OMC), distance from the mouth of the Takkobu River, and bottom-layer pH. Five species of Chironomidae [Chironomus sp. (except plumosus group), Psectrocladius sp., Corynoneura sp., Parachironomus sp. arcuatus group, and Zavreliella sp.] occurred in sites with relatively lower pH and a high submerged plant biomass, whereas three species of Tubificidae (Tubifex tubifex, Aulodrilus limnobius and Aulodrilus sp.) and two of Chironomidae (Nanocladius sp. and Monodiamesa sp.) occurred in sites with high pH and little vegetation. The three Tubificidae species also preferred organic-rich sediments. Irrespective of aquatic vegetation, Sphaerium sp. (Bivalvia) and Monodiamesa sp. (Chironomidae) occurred in low-OMC sites, whereas Tanypus sp. (Chironomidae) preferred high-OMC sites. The number of macroinvertebrate taxa showed the highest correlation with the number of submerged plants, suggesting that macroinvertebrate species richness was related mostly to submerged plant species diversity in this lake. The quantity and species richness of submerged plants and OMC are thus important determinants of the community structure of macroinvertebrates inhabiting sediments in Lake Takkobu.     

Environmental gradients and the structure of freshwater snail communities

A fundamental goal of ecology is to understand the factors that influence community structure and, consequently, generate heterogeneity in species richness across habitats. While niche‐assembly (e.g. species‐sorting) and dispersal‐assembly mechanisms are widely recognized as factors structuring communities, there remains substantial debate concerning the relative importance of each of these mechanisms. Using freshwater snails as a model system, we explore how abiotic and biotic factors interact with dispersal to structure local communities and generate regional patterns in species richness. Our data set consisted of 24 snail species from 43 ponds and lakes surveyed for seven years on the Univ. of Michigan's E. S. George Reserve and Pinckney State Recreation Area near Ann Arbor, Michigan. We found that heterogeneity in habitat conditions mediated species‐sorting mechanism to drive patterns in snail species richness across sites. In particular, physical environmental variables (i.e. habitat area, hydroperiod, and canopy cover), pH, and fish presence accounted for the majority of variation in the species richness across sites. We also found evidence of Gleasonian structure (i.e. significant species turnover with stochastic species loss) in the metacommunity. Turnover in snail species distributions was driven by the replacement of several pulmonate species with prosobranch species at the pond permanence transition. Turnover appeared to be driven by physiological constraints associated with differences in respiration mode between the snail orders and shell characteristics that deter molluscivorous fish. In contrast to these niche‐assembly mechanisms, there was no evidence that dispersal‐assembly mechanisms were structuring the communities. This suggests that niche‐assembly mechanisms are more important than dispersal‐assembly mechanisms for structuring local snail communities.     

Macrozoobenthos patterns along environmental gradients and hydrological connectivity of oxbow lakes

Hydrological connectivity and the frequency and intensity of floods are the key factors determining the structure of macroinvertebrates inhabiting wetland ecosystems in river valleys. In 2007, water and macroinvertebrate samples were collected on four occasions in the middle course of the S?upia River and in five oxbow lakes (Northern Poland) to determine the hydrological relations in a regulated lowland river environment marked by a moderate climate. The water bodies selected for the study featured different types of connections with the main river valley: two of them were completely cut off from the valley, one was connected via a single branch, one featured a forced-flow connection through drainage pipes, and one was connected by a system of drainage channels. Macroinvertebrates, mostly Chironomidae larvae, were predominant in the eutrophic waters of the river. The prevalent macroinvertebrates found in the eutrophicated oxbow lakes isolated from the river were Chironomidae larvae and Crustacea (mainly Asellus aquaticus). In unobstructed oxbow lakes, the main component of benthic fauna was Crustacea, while Ephemeroptera were found mostly in the water body connected to the river via a drainage channel. A canonical correspondence analysis (CCA) showed that hydrological connectivity was the main factor responsible for the structure of invertebrate populations, followed by the physical and chemical parameters of the local environment. A non-conformance analysis revealed that hydrological connectivity enhanced invertebrate abundance and biological diversity, while the overall abundance was marked by unimodal distribution. The developed general model indicates that in the group of measured environmental variables, nitrite concentrations were highly correlated with Shannon diversity and invertebrate composition, while sulphate levels were closely associated with invertebrate abundance in the waters of the analyzed ecosystems.     

An in situ pulse light fluorometer for chlorophyll determination as a monitor for vertical and horizontal phytoplankton distribution in lakes

Methodological problems with in vivo, fluorescence (IVF) measurementusing an in situ pulse light fluorometer were investigated inorder to validate this method for monitoring the vertical andhorizontal chlorophyll a (chl. a) distribution in lakes. Thecorrelation between chl. a and IVF was poor in the upper epilimnion(0–5 m) of a mesotrophic lake. The IVF of algal culturesand natural phytoplankton is very sensitive to changes in thelight environment. The response of the IVF to rapid light fluctuationsdepends on the amplitude of the light intensity and the lightconditions to which the algae were exposed before the onsetof light fluctuations. The variability of the ratio IVF:chl.a concentration makes a permanent calibration of the IVF againstchl. a necessary. ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP), Second International Workshop heldat the National Oceanographic Institute, Haifa, Israel in April–May1984.     

Environmental niches and metabolic diversity in Neoarchean lakes

The diversification of macro‐organisms over the last 500 million years often coincided with the development of new environmental niches. Microbial diversification over the last 4 billion years likely followed similar patterns. However, linkages between environmental settings and microbial ecology have so far not been described from the ancient rock record. In this study, we investigated carbon, nitrogen, and molybdenum isotopes, and iron speciation in five non‐marine stratigraphic units of the Neoarchean Fortescue Group, Western Australia, that are similar in age (2.78–2.72 Ga) but differ in their hydro‐geologic setting. Our data suggest that the felsic‐dominated and hydrologically open lakes of the Bellary and Hardey formations were probably dominated by methanogenesis (δ¹³C_org = ?38.7 ± 4.2‰) and biologic N₂ fixation (δ¹⁵N_bulk =?0.6 ± 1.0‰), whereas the Mt. Roe, Tumbiana and Kylena Formations, with more mafic siliciclastic sediments, preserve evidence of methanotrophy (δ¹³C_org as low as ?57.4‰, δ¹³C_carb as low as ?9.2‰) and NH₃ loss under alkaline conditions. Evidence of oxygenic photosynthesis is recorded only in the closed evaporitic Tumbiana lakes marked by abundant stromatolites, limited evidence of Fe and S cycling, fractionated Mo isotopes (δ^98/95Mo = +0.4 ± 0.4‰), and the widest range in δ¹³C_org (?57‰ to ?15‰), suggesting oxidative processes and multiple carbon fixation pathways. Methanotrophy in the three mafic settings was probably coupled to a combination of oxidants, including O₂ and SO₄^2‐. Overall, our results may indicate that early microbial evolution on the Precambrian Earth was in part influenced by geological parameters. We speculate that expanding habitats, such as those linked to continental growth, may have been an important factor in the evolution of life.     

Canadian wetlands: Environmental gradients and classification

The Canadian Wetland Classification System is based on manifestations of ecological processes in natural wetland ecosystems. It is hierarchical in structure and designed to allow identification at the broadest levels (class, form, type) by non-experts in different disciplines. The various levels are based on broad physiognomy and hydrology (classes); surface morphology (forms); and vegetation physiognomy (types). For more detailed studies, appropriate characterization and subdivisions can be applied. For ecological studies the wetlands can be further characterized by their chemical environment, each with distinctive indicator species, acidity, alkalinity, and base cation content. For peatlands, both chemical and vegetational differences indicate that the primary division should be acidic, Sphagnum-dominated bogs and poor fens on one hand and circumneutral to alkaline, brown moss-dominated rich fens on the other. Non peat-forming wetlands (marshes, swamps) lack the well developed bryophyte ground layer of the fens and bogs, and are subject to severe seasonal water level fluctuations. The Canadian Wetland Classification System has been successfully used in Arctic, Subarctic, Boreal and Temperate regions of Canada.     

Fish community comparisons along environmental gradients in lakes of France and north-east USA

Aim  To assess whether eight traits of fish communities (species richness, three reproductive traits and four trophic traits) respond similarly to environmental gradients, and consequently display convergence between the lakes of France and north-east USA (NEUSA).
Location  75 French and 168 north-east USA lakes.
Methods  The data encompass fish surveys, the assignment of species into reproductive and trophic guilds, and environmental variables characterizing the lakes and their catchments. The analytical procedure was adapted from the recommendations of Schluter (1986 ) [ Ecology , 67 , 1073–1085].
Results  The comparison of the regional pools of lacustrine fishes indicated that NEUSA was about twice as speciose as France, mostly due to higher species turnover across lakes, although NEUSA lakes were consistently about 20% more speciose than French lakes for a given surface area. Warmer environments were consistently inhabited by a higher proportion of phytophilous and guarder species than were colder lakes. Hence there was convergence in community reproductive traits. Conversely, there was no evidence of convergence in the trophic structure of lacustrine fish communities between regions.
Main conclusions  The influence of temperature on the availability and quality of spawning substrates appears to be a major constraint on present-day lacustrine fish communities. In parallel, phylogenetic constraints, past events such as the diversification of the North American fish fauna, and selective extinctions during Pleistocene glaciations and subsequent recolonizations contribute to explaining the dissimilarities between the communities of the two regions and differences in their relationship to the environment.     

The biology and ecology of lotic microcrustaceans

• 1 Copepoda, Ostracoda and ‘Cladocera’ are important meiobenthic Crustacea which can be both numerically abundant and species rich in running waters. Harpacticoids and ostracods are well adapted to benthic life because they are typical crawlers, walkers, and burrowers. Many cladocerans are substratum dwellers, but most benthic species among these can also swim. Cyclopoids which are generally good swimmers are nevertheless often bottom frequenters and actively colonise sediment interstices (the hyporheic zone).
  • 2 The subclass Copepoda includes 10 orders. With 53 families, the order Harpacticoida dominates the benthos. Only five of these families are represented in fresh waters (ca. 1 000 species and subspecies). The order Cyclopoida includes 12 families of which the Cyclopidae is well represented in freshwater habitats with 900 species and subspecies. Freshwater Ostracods belong to the order Podocopida (5 000 species) with three superfamilies occurring in running fresh waters. The group ‘Cladocera’ contains four orders, 12 families, more than 80 genera, and 450–600 freshwater species. Most of the benthic species are found in the families Chydoridae (39 genera), Macrothricidae, Ilyocryptidae and Sididae.
• 3 For each of the three major taxa, morphological characteristics are presented, specimen collection and preparation are described and references to available taxonomical keys are provided.
• 4 Biological characteristics are extremely diverse among and within the three taxa, resulting in a great variety of strategies in meiobenthic crustaceans. Characteristics of reproduction, sexual dimorphism, cyclomorphosis and population parameters (i.e. clutch size, lifespan, growth, moulting) are provided for some of the most common species.
• 5 Important differences between the three main taxa were found at the species level. Ecological requirements such as hydraulic microhabitats and geomorphologic features of the streambed are the major determinants of species diversity and abundance for benthic microcrustacea of lotic habitats. Many studies on the ecology of these communities are limited by a lack of knowledge of the life history characterisitics of lotic (especially interstitial) crustacean populations.

     

Environmental factors influencing the distribution of ammonifying and denitrifying bacteria and water qualities in 10 lakes and reservoirs of the Northeast,China

This study presents seasonal and spatial variations of the ammonifying bacteria (AB) and denitrifying bacteria (DNB) and physicochemical parameters in 10 lakes and reservoirs in the northeast of China. Water samples were collected in winter (January), spring (March), summer (July) and fall (November) in 2011. The study revealed that physicochemical parameters such as pH, dissolved oxygen (DO), NH₄⁺‐N and nitrate as nitrogen were closely related with the distribution of AB and DNB. Seasonally, the levels of AB presents gradually upward trend from winter to summer, and declines in fall and DNB were higher in spring and fall than summer and lowest in winter. Spatially, the annual average of AB among 10 lakes and reservoirs showed insignificant difference (P > 0.05), for DNB, Udalianchi and Lianhuan Lake were lower than others (P < 0.05). Regression correlation analysis showed that the levels of AB and DNB had a close relationship with nitrogen nutrition. Three principal components were identified of total variances which are conditionally classified by the ‘natural’ factor (PC1) and ‘nitrogen nutrients’ (PC2, PC3). According the principal component scores, cluster analysis detected two distinct groups: (C1) mainly affected by nitrogen nutrients and (C2) natural environmental factors.     

Environmental gradients,plant distribution,and species richness in arctic salt marsh near Prudhoe Bay,Alaska

Spatial patterns of plant cover and species composition in arctic salt marsh and salt affected tundra near Prudhoe Bay, Alaska reflect gradients in elevation, soil conductivity, and soil concentrations of the ions prevalent in seawater. Soil conductivity and soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^– were significantly related to site elevation, decreasing as elevation increased. Vascular plant species richness increased significantly as soil conductivity and soil ion concentrations decreased, and site elevation increased. Puccinellia phryganodes was the only species present in low elevation sites with low plant cover, high soil conductivity and high soil concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄ ⁼ and Cl^–. Mid-gradient sites were dominated by Carex subspathaceae. Plant cover at these sites was greater than at lower elevation sites, but bare ground was still present. Higher elevation sites had the lowest concentrations of soil ions and the lowest soil conductivities. These sites had little bare ground, contained as many as 16 species, and were dominated by Dupontia fischeri and Eriophorum angustifolium. Ordinations indicated that a complex topographic gradient related most closely to elevation and site distance from the coast best explains variation in the vegetation cover. Irregular deposition along the coastline partially or completely buried three sites in peat or sand up to 20 cm deep. Such rapid changes in plant cover and species composition contributes to the community patch mosaic typical of these marshes. Results suggest an individualistic response of plant species to the environmental gradients in salt marsh and salt affected tundra and are indicative of successional models developed in other marginal arctic environments.     

Environmental phenology and geographical gradients in moose body mass

Intraspecific body mass in ungulates has often been shown to increase with latitude. The biological basis for such latitudinal gradients is, however, poorly known. Here we examined whether satellite-derived indices of environmental phenology, based on the normalised difference vegetation index (NDVI), as well as variables derived from meteorological stations, altitude, and population density, can explain latitudinal gradients and regional variation in body mass of Norwegian moose. The best model gave a considerably better fit than latitude alone, and included all explanatory environmental variables. Accordingly, heavy moose were found in areas with short and intense summers that were followed by long, cold winters, at low altitude relative to the tree-limit, and with low population density relative to the available plant biomass. This relationship was stronger for yearlings than for calves, except for the effect of population density. This indicates that differences in the characteristics of the vegetation quality and environmental phenology, as well as winter harshness and population density, are important factors that shape both the latitudinal and other geographical gradients in moose body mass.     

Vertical distribution and rotifer concentrations in the chemocline of meromictic lakes

The vertical distribution of planktonic rotifers has been analysed in relation to season in several meromictic lakes; a coastal lagoon with sea-water intrusion and three dissolution lakes from two karstic systems. Two species, Filinia hofmanni and a form of Anuraeopsis fissa have been found to be more or less restricted to the chemocline or adjacent strata any time they occurred. Many species common in the upper water layers developed large populations near or in the chemocline and more strikingly in summer. Some species had two vertical maxima (one in the surface or the thermocline and another near the chemocline), while others successively shifted their maxima between the upper layers and the chemocline. It is hypothetized that these rotifers are either very versatile or are differentiated as ecotypes, one of them adapted to the chemocline environment. This distribution in a peculiar fluctuating, anoxic, H₂S-rich environment poses questions about the biology of those rotifers which there develop extraordinary populations.     

Studies on ciliated protozoa in eutrophic lakes: 2. Field and laboratory studies on the effects of oxygen and other chemical gradients on ciliate distribution

An investigation into the spatial distribution of hypolimnetic ciliates in three small eutrophic lakes during the period of summer stratification was carried out. Peak ciliate densities were found to occur at the oxic/anoxic boundary, ciliate numbers declining with increasing depth within the hypolimnion. The ciliates only occurred in aerobic water where oxygen levels were less than about 0.5 mgl^–1 Laboratory experiments demonstrated that the ciliates swim upwards under anaerobic conditions but swim rapidly downwards under aerobic conditions. Further laboratory experiments showed that although the bulk of the population occured within anaerobic water, the hypolimnetic ciliates are aerobes and cannot survive indefinite anoxia. Despite the demonstrable toxicity of high levels of ammonia and sulphide, it was probably excesive distance from an available source of oxygen that excluded the ciliates from the lowest levels of the hypolimnion. Possible mechanisms which allowed these aerobic ciliates to colonise anaerobic water are considered.     

Energy gradients and the geographic distribution of local ant diversity

Geographical diversity gradients, even among local communities, can ultimately arise from geographical differences in speciation and extinction rates. We evaluated three models—energy-speciation, energy-abundance, and area—that predict how geographic trends in net diversification rates generate trends in diversity. We sampled 96 litter ant communities from four provinces: Australia, Madagascar, North America, and South America. The energy-speciation hypothesis best predicted ant species richness by accurately predicting the slope of the temperature diversity curve, and accounting for most of the variation in diversity. The communities showed a strong latitudinal gradient in species richness as well as inter-province differences in diversity. The former vanished in the temperature-diversity residuals, suggesting that the latitudinal gradient arises primarily from higher diversification rates in the tropics. However, inter-province differences in diversity persisted in those residuals—South American communities remained more diverse than those in North America and Australia even after the effects of temperature were removed.     

Environmental gradients drive physiological variation in Hawaiian corals

Coral Reefs - To evaluate potential coral adaptive mechanisms, we investigated physiological traits (biomass, lipid, protein, chlorophyll, and isotopic proxies for trophic strategy) in eight...