Factors influencing the distribution of chironomids and oligochaetes in profundal areas of Spanish reservoirs

A canonical correlation analysis was performed in order to explain the distribution and abundance of the profundal macrozoobenthos in 71 Spanish reservoirs. Two sets of variables were considered: one set consisted of subgroups of benthic organisms based on their feeding strategy, and the other consisted of environmental variables related to the trophic state of the reservoir.The results showed that densities of phytophagous chironomids decreased with water depth and increased with oxygen content in the bottom waters, while Tanypodinae densities increased with rising densities of phytophagous chironomids and/or oligochaetes, revealing their strong dependence on the abundance of available prey. The abundance of oligochaetes and phytophagous chironomids showed a disjunct distribution with season and depth, suggesting the importance of food quality and sediment texture.Oxygen availability and water depth acted as governing factors for the zoobenthos. Chlorophyll-a was of secondary importance and correlated inversely with the abundance of benthic fauna, especially in summer. Autogenic production coupled with inputs of allochthonous coarse particulate organic matter and a long stratification period lead to long lasting anoxia that reduces the benthic fauna in Spanish reservoirs.Only up to 18% of the variability in the biological data could be associated with the environmental factors considered. Thus, factors other than the trophic state are much more important in reservoirs. Fluctuations of the water level and inputs of organic and inorganic materials coming from the basin are greater than in lakes and act as stressing factors for the benthic fauna.     

A test of Tyler’s Line – response of chironomids to a pH gradient in Tasmania and their potential as a proxy to infer past changes in pH

1. Tyler’s Line delimits two distinct limnological provinces that reflect differences in climate, geology and vegetation in Tasmania. Lakes west of Tyler’s Line are typically acidic and dystrophic with relatively shallow euphotic zones, whereas eastern lakes are circumneutral and oligotrophic or ultra‐oligotrophic, allowing deeper penetration of light. Consequently, Tyler’s Line defines a boundary where species assemblages change over a relatively short distance. 2. A survey of 48 Tasmanian lakes was undertaken to identify indicator taxa of the two limnological provinces and breakpoints along the pH gradient where shifts in taxa occur. Chironomidae (Diptera) were used because they are ideal candidates for lake classification. 3. Three independent methods (geographical position, piecewise linear regression, two‐way indicator species analysis) verified that chironomids accurately reflect the environmental variables defining Tyler’s Line at lake and catchment scales. Chironomid genera are often speciose, and members of the same genus can have markedly different responses to a given environmental variable. Although the types of taxa changed along the pH gradient, richness did not. This finding contrasts with many studies from the northern hemisphere but accords with other studies from Australia. 4. Models of pH, developed using both partial least squares and weighted averaging partial least squares, can be used to understand past natural variability of pH in Tasmania and to test hypotheses regarding the timing, magnitude and source of contamination in impacted aquatic ecosystems.     

Stratigraphy of Cladocera and Chironomidae in a core from a shallow North German lake

In the subfossil assemblages of chironomids and cladocerans significant changes were found during the late-glacial and postglacial development of a small, shallow North German lake. The successions observed were obviously not related to eutrophication but to factors such as climatic conditions and lake siltation. The absence of species of the subgenus Eubosmina during postglacial times as well as the predominance of Alonella species among the chydorids was due to the small dimensions of the water body.     

Species richness and canopy productivity of Australian plant communities

The species richness (number of vascular plants per hectare) of Australian plant communities (containing a mosaic of gap, regeneration, maturation and senescent phases) is correlated with the annual biomass productivity of the overstorey canopy.The annual production of leaves and stem in the canopy of the plant community is shown to be limited by the requirements of photosynthesis (particularly light and the availability of water) and the length of the growing season.The species richness of Australian plant communities is the product of the blance between the dominance of the overstorey and the response of the understorey to the shading of the overstorey. For all climatic regions and zones the species richness of the overstorey of the plant community is shown to be exponentially related to the annual shoot growth of the overstorey canopy, until the latitudinal or altitudinal tree line is reached. With latitudinal increase outside the tropics, overstorey canopies of forest communities absorb increasingly more of the incident solar radiation. markedly reducing the species richness of the understorey strata. In contrast, in these latitudes the overstorey of plant communities with widely spaced trees or tall shrubs will absorb far less solar radiation, thus enabling the species richness of the understorey to be maintained.     

Species richness and endemism in the Western Australian flora

Aim Estimates of endemic and non‐endemic native vascular plant species in each of the three Western Australian Botanical Provinces were made by East in 1912 and Beard in 1969. The present paper contains an updated assessment of species endemism in the State. Location Western Australia comprises one third of the continental Australian land mass. It extends from 13° to 35° S and 113° to 129° W. Methods Western Australia is recognized as having three Botanical Provinces (Northern, Eremaean and South‐West) each divided into a number of Botanical Districts. Updated statistics for number of species and species endemism in each Province are based on the Census of Western Australian Plants data base at the Western Australian Herbarium ( Western Australian Herbarium, 1998 onwards). Results The number of known species in Western Australia has risen steadily over the years but reputed endemism has declined in the Northern and Eremaean Provinces where cross‐continental floras are common. Only the isolated South‐West Province retains high rates of endemism (79%). Main conclusions With 5710 native species, the South‐West Province contains about the same number as the California Floristic Province which has a similar area. The Italian mediterranean zone also contains about this number but in a smaller area, while the much smaller Cape Floristic Region has almost twice as many native species. The percentage of endemic species is highest at the Cape, somewhat less in south‐western Australia and less again in California. Italy, at 12.5%, has the lowest value. Apart from Italy, it is usual for endemism to reach high values in the largest plant families. In Western Australia, these mainly include woody sclerophyll shrubs and herbaceous perennials with special adaptations to environmental conditions. While those life forms are prominent in the Cape, that region differs in the great importance of herbaceous families and succulents, both of which are virtually absent from Western Australia. In California and Italy, most endemics are in families of annual, herbaceous perennial and soft shrub plants. It is suggested that the dominant factor shaping the South‐West Province flora is the extreme poverty of the area’s soils, a feature that emphasizes sclerophylly, favours habitat specialization and ensures relatively many local endemic species.     

A landscape approach to examining spatial patterns of limnological variables and long-term environmental change in a southern Canadian lake district

1. We explored patterns of limnological variables (physical, chemical and biological) with relation to landscape position (expressed as lake order) in 86 study lakes located on shield bedrock in south‐central Ontario, Canada. 2. Using anova s with lake order as the categorical variable, landscape position explained significant amounts of variation in major ion chemistry, physical and catchment characteristics, hypolimnetic oxygen, and community composition in algal (diatom, chrysophyte) and invertebrate (chironomid) assemblages preserved in surficial sediments. Several nutrient variables (TP, total phosphorus and TN, total nitrogen) and dissolved organic carbon did not have significant relationships with lake order. 3. The strongest relationships with lake order (as a fraction of variation explained in anova s) included silica concentrations (r² = 0.40) and SO₄ (r² = 0.29) concentrations, surface area (r² = 0.50) and hypolimnetic oxygen (r² = 0.29). 4. Bedrock geology (carbonate metasedimentary versus non‐carbonate bedrock) had strong influences on spatial gradients of pH and major ion chemistry. It was difficult to separate geological influences from spatial influences on limnological variables in this study, as drainage patterns in the region are highly influenced by surface features of underlying geological formations because of the very thin glacial till or exposed bedrock that exists in most catchments. 5. Patterns of limnological variables indicated that low‐order, headwater lakes had the lowest concentrations of major ions, and, from algal inferences of pH change, had been most susceptible to acidic deposition. High‐order, downstream lakes were larger and deeper, and had higher concentrations of hypolimnetic oxygen, indicating that optimal lake trout habitat was primarily located in high‐order lakes. 6. Variance partitioning analyses indicated that lake order as a metric of landscape position explained comparable portions of community variation in algal and invertebrate assemblages compared with geographic position (latitude, longitude) and Cartesian coordinate position (e.g. x, y, x², y², etc.) metrics. Lake order explained more community variation in chironomid assemblages compared with other landscape metrics, possibly because of the strong relationships between lake order and lake morphometry variables.     

In search of clinal variation in the period and clock timing genes in Australian Drosophila melanogaster populations

Clinal variation for repeat number in the Thr-Gly region of the period circadian timing gene in Drosophila melanogaster was described in Europe and has subsequently been used as evidence of thermal selection on period alleles. To test for clinal variation in this gene along the east coast of Australia, the period polymorphism was scored on flies from multiple samples collected repeatedly over a 5-year interval, along with variation at another circadian rhythm locus, clock. For period, there was no consistent evidence of clinal variation in the 17 and/or 20 repeat alleles, although when average allele length was examined a weak consistent clinal pattern was detected. For clock there was no evidence of clinal variation in the two most common alleles or in average repeat size. These data are inconsistent with the reported patterns in Europe and suggest that clinal variation in timing genes needs to be re-examined in this region.     

中国伞形科特有属的核型演化及地理分布

首次报道了我国伞形科１０个特有属９种１变种１４个居群的核型,染色体基数分别为ｎ＝６,８,１０和１１,核型类型有２Ａ,３Ａ和４Ａ三种类型。根据各属的核型演化水平并结合其花粉形态,初步确定东俄芹属（Ｔｏｎｇｏｌｏａ）、环根芹属（Ｃｙｃｌｏｒｈｉｚａ）、明党参属（Ｃｈａｎｇｉｕｍ）和川明参属（Ｃｈｕａｍｉｎｓｈｅｎ）是古特有属,其余各属则处于中等或较高的演化水平上。同时初步讨论了各特有属在伞形科分类系统中的核型演化关系并比较了各主要分布区之间核型的演化水平,发现横断山地区不仅特有属数目高,染色体基数变化大,且集中了核型较为原始和演化程度很高的类群,极可能是伞形科特有属的起源和分化中心。     

Effect of watershed land use and lake age on zooplankton species richness

Results of a field survey of southern Wisconsin shallow lakes suggested that watershed (catchment basin) land use has a significant and adverse effect on zooplankton species richness. Zooplankton communities in lakes with no riparian buffer zone, in agriculture-dominated watersheds, contained about half as many species as lakes in least-impact watersheds. In that study, the age of the lake was not taken into account. It is possible that agricultural lakes, often artificial, were so recently-constructed that they had not yet accumulated the equilibrium number of species characteristic of older lakes. In other words, it is possible that the interpretation of the results of the previous study is fatally flawed, if the results were an artifact of lake age, rather than an effect of land use. The major aim of this current study was to determine the ages of agricultural lakes and of lakes in least-impact watersheds, to test for an effect of lake age on zooplankton species richness, using the same sites from the previous study. We used an anova approach to test the null hypothesis that two factors, watershed land use and lake age, had no systematic effect on zooplankton species richness. We determined the age of 35 shallow lakes, using aerial photos, satellite images, and interviews of resource managers and land owners. We identified five artificial agricultural sites and five artificial sites in least-impact prairie watersheds. The artificial sites in this study ranged from 3 to 37 years in age, while natural lakes dated from the melting of the last glacier, about 9500 years ago. Our results suggest, that because artificial lake made up only about a third of the sites, and for the range of lake age and watershed land use, lake age did not have a significant effect on zooplankton species richness, while land use had a highly significant adverse effect. These results pose a larger question for future research. Namely, how quickly do newly-constructed lakes attain the equilibrium number of species seen in the previous study, and what is the quantitative relationship between lake age and zooplankton richness?     

Lake depth and geographical position modify lake fish assemblages of the European 'Central Plains' ecoregion

1. Classification of European lake fish assemblages can be based on fish‐assemblage structure or morphological, geographical, physical and chemical lake attributes. However, substantial gaps in knowledge exist with respect to the correspondence between both classification approaches. 2. Here, we compiled fish assemblage data from 165 lakes situated in the European ‘Central Plains’ ecoregion. Cluster analysis of fish abundances was performed to compare fish assemblage types of the entire ecoregion with those from previous country‐specific studies. Nonparametric group comparisons, classification trees and partial canonical ordinations were used to infer the correspondence between fish assemblage types and morphology, geographical position and nutrient concentration of the lakes. 3. Three distinct fish assemblages were revealed: vendace (Coregonus albula), ruffe (Gymnocephalus cernuus) and roach (Rutilus rutilus) lake types. Both latitude and lake depth were the best determinants of lake type, but total phosphorus (TP) concentrations were also important. Vendace lakes were deep and had low TP concentrations, whereas the shallower ruffe and roach lakes had higher TP values. Roach lakes were more frequent in the north‐west area of the ecoregion, whereas ruffe lakes were more often found south of the Baltic Sea. 4. Controlling for the influence of nutrient concentration showed that lake morphology and geographical position were important determinants of fish assemblages. However, the variance explained was low (<20%), implying that biological interactions may also be important in forming the lake‐specific fish assemblages. 5. The results suggest that fish assemblages differ between deep and shallow lakes, and between the north‐west and south‐east locations within the Central Plains ecoregion. Accordingly, establishment of depth‐related lake morphotypes is needed, and the European ecoregions recommended to be used in evaluation systems according to the Water Framework Directive seem to be too coarse to reflect the subtle differences of fish species richness along geographical gradients.     

Distribution and production of chironomids (Diptera: Chironomidae) in a shallow, alkaline lake (Neusiedler See, Austria)

From July 1990 to July 1991 the benthic community of the open water zone of Neusiedler See, one of the largest shallow lakes in central Europe, was studied with special reference to the chironomids. Only 16 spp. of chironomids inhabited the sediment of the open water zone. The numerically dominant species were Tanypus punctipennis, Procladius cf. choreus, Microchironomus tener and Cladotanytarsus gr. mancus. Most invertebrates showed a distinct horizontal distribution. Species richness and abundance were highest on muddy and organically rich substrates near the reed belt. Chironomid densities in this area reached 54,000 ind m^–2 and biomass was 2.0 g dw m^–2. The two tanypod species accounted for more than 90% of the standing stock of the macrozoobenthos near the reed belt. The sediment of the open lake and of the eastern part of Neusiedler See was composed of compact clay and sand as a result of the erosion of fine material due to strong waves and currents. Individual densities in these areas were much lower. Production of the numerically dominant species T. punctipennis was estimated using the increment-summation method, whereas production of the remaining species was estimated using an empirically derived multiple regression. Mean annual production of chironomids exceeded 6 g dw m^–2 yr^–1 near the reed belt, but it reached only 0.55 g dw m^–2 yr^–1 in the open lake. These values are rather low compared with other lakes and can be explained by unfavourable sediment conditions due to wave action and by physiological stress due to the water chemistry.     

Species richness, rarity and endemicity of European mammals: a biogeographical approach

This paper investigates the distribution of species richness, rarity and endemicity of European land mammals (bats and introduced species excluded). The highest level of species richness was in Central Europe, while Southern areas had the highest rarity and endemicity scores. The distribution of richness was affected by the location of sampling points in islands and peninsulas. After excluding these sampling points, richness continued to decrease Westward suggesting the existence of a large-scale peninsular effect on mammal distribution. These patterns of continental distribution of richness, rarity and endemicity could be the result of the distribution of refuge areas in the southern Mediterranean peninsulas, and the Pleistocene advances and retreats of mammals throughout the Western Palearctic. Thus, European mammal distribution can be interpreted on the basis of two different patterns of abundance distribution in which Palearctic species reduce their abundance from central-Europe outwards, while endemic, rare species show a similar depletion in the North. It should be useful to evaluate the role of the different regions in Europe in conserving the demographic interactions between central and peripheral populations of mammal species. Given the restricted distribution and potential small size of population, these endemic species are most likely to be susceptible to anthropogenic environmental degradation.     

Habitat preferences as patch selection of larval and emerging chironomids (Diptera) in a gravel brook

Four common species of larval and emerging chironomids were investigated during 1981 and between 1984/1985 in an alpine gravel brook. The emergence patterns ofN. dubius, O. rivulorum andH. ornaticollis were significantly affected by fluctuations of the water level, while rises in water temperature tended to trigger the peaks in emergence of the same species and ofO. frigidus. N. dubius exhibited its main emergence activity over areas of bed sediment which had a lower mean water velocity or were discontinuously flooded. On the other hand, the imagines ofO. frigidus, O. rivulorum andH. ornaticollis reached peak densities in zones of the main current channel in the Seebach. The larvae of these species inhabited horizontally and vertically different areas of bed sediment depending on the developmental stage. Early instars ofN. dubius andH. ornaticollis preferred zones near the banks and reached their maximum densities in sediment depths of 10 to 20 cm and 20 to 30 cm, respectively. In contrast, the larvae ofO. frigidus andO. rivulorum reached their highest densities in the first 10 cm of the sediments with significant preferences for the zones of stronger water flow.     

文山国家级自然保护区特有珍稀植物

主要介绍文山国家级自然保护区的地理特点和保护区内丰富的植物资源,重点介绍国家级珍稀濒危保护植物的种类和用途。     

Effects of exported seston on aquatic insect faunal similarity and species richness in lake outlet streams in Montana,USA

The quantity of seston exported from a lake affected the qualitative composition and species richness of aquatic insects in 13 lake outlet streams in northwestern Montana. Mean values for chlorophyll and particulate organic carbon in lake effluent waters ranged from 0.5 to 2.7 and 80 to 601 mg m^-3, respectively. Correlations between a detrended correspondence analysis of faunal similarities in outlet streams and measures of organic export from the lake indicated that distributional patterns were primarily dependent upon the general trophic status of the lakes. A comparison of faunal assemblages at stream stations located at the outlet and 100 m downstream demonstrated that species composition at the two stations was more similar in productive systems.     

Vertical distribution of planktonic rotifers in a karstic meromictic lake

Vertical distribution of planktonic rotifers is described in relation to temperature and oxygen in Lake La Cruz, a single-doline, closed karstic lake (121 m diameter and 25 m maximum depth) which shows iron meromixis. Samples were taken by peristaltic pumping at 10 cm depth intervals in the oxycline zone from June 1987 to September 1988. A model of rotifer vertical structure in stratified lakes is proposed. Rotifers concentrate their populations at the depths with intense gradients. As stratification develops some rotifer populations show a downward migration following the thermocline and some others show an upward migration following the oxycline. The production-respiration balance in the lake, and so the position of the oxycline with respect to the thermocline and the layer of maximum production, depends on meteorological conditions. A shift in the dominance of congeneric or related species can occur in consecutive years. In Lake La Cruz, mixing conditions and subterranean inflow in spring were much more intense in 1988 than 1987, and the distance between production and decomposition depths was smaller in 1988. Anuraeopsis miraclei, an oxycline-bound species with high abundance in 1987, was displaced by A. fissa in 1988. A. fissa, which was a metalimnetic species during early summer, reached peak densities (3 × 10⁴ ind l^–1) at the oxycline, equaling the abundance of A. miraclei the preceeding year.     

Emergence pattern,microhabitat choice,and population structure of the Maghribian endemic Gomphus lucasii Selys, 1849 (Odonata: Gomphidae) in northeastern Algeria

Emergence of Gomphus lucasii Selys, 1849, an unstudied Maghreb endemic, was synchronised by overwintering in the final stadium in the Seybouse River in northeastern Algeria. Regular collections revealed that half of the annual population emerged during 10 days, showing a typical ‘spring species’ emergence pattern. Sex ratio was slightly male biased (51%). Males and females did not differ in vertical stratification. Emergence support choice was not random, but rather depended on support height, body size, and daily population density. Mortality was caused mainly by ants, although deformity of tenerals and bird predation were also important factors. Gomphus lucasii has been assessed as vulnerable (International Union for Conservation of Nature (IUCN) Red List), and the information provided in our study will be helpful in future conservation efforts.     

The effect of tubificids and chironomids on particle redistribution of lake sediment

The effects of chironomid larvae,Chironomus plumosus, and tubificid worms,Limnodrilus spp., on particle redistribution in lake sediment were investigated experimentally using pots containing sediments obtained from Lake Suwa, Japan. The chironomids and tubificids increased the water content of surface sediment. The chironomid larvae had no effect on particle size distribution, while tubificids continuously accumulated small particles on the surface sediment through their selective feeding activity. Particles larger than 0.125 mm were buried at a sediment depth of 6 cm. In Lake Suwa, long diatom frustules, large plant debris and blue-green algal flocs were found to accumulate in the deeper layer of the lake sediment inhabited by tubificids at high density.     

Rapid changes in fish community structure and habitat distribution following the precipitation of lake phosphorus with aluminium

1. Fish community structure and habitat distribution of the abundant species roach, perch and ruffe were studied in Lake Nordborg (Denmark) before (August 2006) and after (August 2007) aluminium treatment to reduce internal phosphorus loading. 2. Rapid changes in fish community structure, abundance and habitat distribution occurred following a decline in in‐lake phosphorus concentrations from 280 to 37 μg P L^?1 and an increase in Secchi depth transparency from 1.1 to 1.9 m (August). The proportion of perch in overnight gill net catches increased, whilst roach decreased, and the average weight of all key species increased. 3. The habitat distribution of perch and roach changed from a high proportion in the upper pelagic and littoral zones in 2006, towards enhanced proportions in the deeper pelagic and profundal zone in 2007. The abundance of large‐bodied zooplankton increased and the abundance of benthic invertebrates decreased in the same period, suggesting that the habitat shift was not induced by food limitation. 4. Ruffe shifted from the littoral and upper profundal zones towards the deep profundal zone, likely reflecting an increased predation risk in the littoral zone and better oxygen conditions in the deep profundal. 5. Our results indicate that enhanced risk of predation in the upper pelagic and the littoral zones and perhaps improved oxygen concentrations in the deeper profundal zone at decreasing turbidity are responsible for the observed habitat shift. The results indicate that fish respond rapidly to changes in nutrient state, both in terms of community structure and habitat use.