摘要:

SUMMARY.1. Macro‐invertebrate species lists were obtained for 268 sites on forty‐one river systems throughout Great Britain by qualitative sampling in spring, summer and autumn. Information on twenty‐eight environmental variables was also collated for each site. The sites were ordinated on the basis of their species content using detrended correspondence analysis (DCA) and classified by two‐way indicator species analysis (TWINSPAN). Correlation coefficients between ordination scores and single environmental variables indicated that Axis 1 distinguished between types of rivers and Axis 2 reflected variation along the length of rivers. A preliminary classification of sites into sixteen groups has been proposed, together with a key which allows new sites to be classified. Information on the species and environmental features which characterize each group is also presented.2. Multiple discriminant analysis (MDA) was employed to predict the group membership of the 268 sites using the twenty‐eight environmental variables. 76.1% of sites were classified correctly. An independent assessment of predictive ability using forty test sites yielded a 50% success rate. Predictive ability was higher for the classification presented in this paper than in fifteen additional classifications produced using data from single seasons and/or different taxonomic treatments.3. TWINSPAN and MDA were found to be useful approaches to the classification of running‐water sites by their macro‐invertebrate fauna and the prediction of community type (as indicated by the occurrence of species in the sites comprising the group) using environmental variables. Extension of the scope of the classification, coupled with the use of additional environmental variables to increase predictive ability, is no

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARY.1. Macro‐invertebrate samples were collected from 268 running‐water sites in Great Britain in each of three seasons (spring, summer and autumn). A combined seasons’treatment was generated by amalgamating the individual seasons’data. These four seasonal options were each subjected to four distinct taxonomic analyses differing in level of identification and whether the data were quantitative or qualitative. Thus sixteen data‐sets were available for analysis. Environmental data on physical and chemical variables, macrophyte cover and date of sampling were also recorded for each site.2. All sixteen data‐sets were ordinated by detrended correspondence analysis and classified by two‐way indicator species analysis. There were strong correlations between the sixteen ordinations and significant concordance between classifications.3. The relationships between ordination scores and single environmental variables were investigated. Muhiple discriminant analysis was used to fit environmental data to eight selected classifications covering the full range of seasonal and taxonomic treatments. The environmental variables most useful in distinguishing between rivers were substratum characteristics, alkalinity and total oxidized nitrogen. Within‐river differences were often highly correlated with discharge, distance from source, width and depth. Slope and altitude contributed strongly to both between‐river and within‐river distinctions.4. Between‐site variation (beta diversity), eigenvalues of ordination, the reliability of classifications, the proportion of sites correctly assigned to their biological group using environmental data and the standardized similarity between observed and predicted fauna were all higher when identifications were taken to species level, rather than one of three family treatments. Qualitative data on a reduced list of families gave comparable or better results than more detailed family treatments.5. Combined seasons’data enabled better categorization and prediction than single season's.6. The values of the Czekanowski Index of Similarity between the observed and predicted fauna of test sites were close to realistic maximum values.7. Recommendations are made concerning potential usages of the various classifications. The species level classification has uses in the field of conservation and in the prediction of biological response to environmental change. The family level classifications have value in developing local site inventories and in the interpretation of pollution

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00040.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARY.1. Changes in species composition of the periphyton of an oligotrophic. Sierra Nevada stream continuously dosed for 1 year at three concentrations of copper (2.5, 5 and 10 μg 1−1CuT; approximately 12, 25 and 50 ng 1−1Cu2+) were determined.2. The numerically most abundant taxa were Bacillariophyceae (Achnanthes minutissima, Cocconeis placentula, Cymbella microcephala, C. sinuata, Fragilaria conslruens, F. crotonensis. Naviculaspp.,Synedra acusandS. rumpens), and the CyanophytaLyngbyaspp., a co‐dominant during spring and summer.3. Population densities ofLyngbyaspp. were markedly reduced at all test concentrations of copper. Population densities of the principal Chlorophyta (Spirogyraspp. andCladophoraspp.) and the diatomAmphipleura pellucidawere reduced at 5 μg 1−1CUT. Of the twenty‐two most abundant taxa, sixteen were reduced in abundance by continuous exposure to 10 μg 1−1CuT.4. There was no commensurate reduction in standing crop (total number of individuals of all taxa).Achnanthes minutissima, a co‐dominant in the control, was the primary replacement species. Other taxa that were more abundant at 5 μg1−1CuTthan in the control wereCeratoneis arcus, Cocconeis placentula, Naviculaspp. andSynedra rumpens.OnlyA. minutissimaandCalothrixspp. were more abundant at 10 μg1−1than in the control.5. Three resemblance measures (Canberra metric, Bray‐Curtis and Dice) and diversity (Brillouin's) were evaluated for detecting differences in species composition among experimental stream sections. The Canberra metric, an index sensitive to proportional rather than absolute differences, was the most info

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00041.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARY.1. The results of a survey of thirty‐four stream sites, differing in pH and invertebrate species richness, indicated that the pool of locally available, suitably adapted species was smaller in the acid streams. This plays a part in determining the general pattern of lower species richness at more acid sites.2. Diversity of feeding categories increased with species richness, indicating that a greater range of food resources was available in the less acid, more species‐rich communities.3. The pattern of predation varied with pH and species richness. The numbers of large insect predators were lower in the less acid, more species‐rich communities and this was correlated with the presence of fish.4. A detailed study of the guild of detritivorous stoneflies in four streams differing in species richness provided evidence that density compensation occurs, niche width decreases and niche overlap declines as species richness increases.5. We discuss the roles that competition and predation play in determining the structure and richness of stream invertebrate commun

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00042.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARY.1. During a 2‐year study of the fish and macroinvertebrates of a third‐order montane stream, a severe drought in the first year resulted in a temporary cessation of surface flow. Flow was continuous during the second year.2. Some taxa (e.g.Ophiogomphus severus) exhibited higher density during the drought year, others declined in abundance during low flow (e.g.Baetisspp.), whereas a few (e.g.Tricorythodes minutus) appeared unaffected. Total macroinvertebrate density decreased by 50% during the low flow year compared to the normal flow year. Mayflies were most severely affected, but also exhibited the most dramatic recovery.3. The collector‐gatherer functional feeding group was abundant only during the normal flow year, whereas shredders and predators exhibited increased relative abundance during low flow.4. Fish populations were severely reduced in the low flow year. However, fishes rapidly invaded the area following resumption of normal

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00043.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARY.1. In daylight conditions brown trout preferably attacked head capsules with a contrasting colour pattern compared to those which were more uniformly coloured. This preference was reversed under reduced illumination. It is argued that striped head capsules are cryptic to predators at low light intensities.2. In caddis larvae contrasting head patterns are found mainly in lentic species, whilst the heads of lotic larvae are usually more uniformly coloured. Lentic species dwell in conditions of more diffuse illumination than lotic one, and each category thus achieves high crypsis with respect to head capsule coloration.3. Lentic molannid and phryganeid larvae often dwell at considerable depths, and these species also have the most sharply defined head patterns. These species are predatory and, besides being cryptic to larger predators, may also be cryptic to their prey.4. Intraspecific variation in head capsule coloration in relation to habitat type is also discussed.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00044.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARY.1. Ceilulolytic decomposition, measured by loss of tensile strength in strips of cellulose test cloth, was estimated in thirty‐four stream sites in experiments in summer, autumn and winter.2. The results of multiple regression analyses showed that strength loss was most closely related to temperature in summer, when the model accounted for only 38% of the variation, and to stream pH in autumn and winter, when the models accounted for 52% and 75% of the variation, respectively.3. The relationship between decomposition rate and the structure of invertebrate communities in streams of dissimilar pH is discussed. We argue that a very rapid rate of decomposition of coarse particulate organic matter may profit consumers of fine particulate organic matter at the expense of coarse particle shredder

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00045.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARY.1.Cephalodella for ficula(Ploima, Rotifera) lives in tubes it constructs itself. These tubes are built of mueus in detritus‐rich environments. The tubes are often closed at both ends, arc not used as sieves, and are not eaten directly.2. The rotifer swims back and forth in its tube and apparently lives on bacteria which are shed from the inner walls of the tubes. Because of surface‐to‐volume considerations, this feeding strategy is probably only possible for animals smaller than roughly 1 mm. Under low food conditions, rotifers inside a tube have a distinctly higher fitness than rotifers removed from their tube.3. Given high food conditions, rotifers removed from a tube immediately build another. Grazing on particles outside the tube appears to take place when a tube is being lengthened. Rotifers do not leave the tube for routine feeding, but under conditions of starvation or very low oxygen concentration they will leave the tube and swim

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1984.tb00046.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY