bluuebunny/crossref_metadata_2025_split huggingface dataset:
First‐year benthic recovery of a headwater stream following a 3‐year insecticide‐induced disturbance
Authors: WHILES M.R. , WALLACE J. BRUCE 
Published: May 2006

SUMMARY1. A headwater stream (C54) was treated seasonally (twelve times from December 1985 to October 1988) with the insecticide methoxychlor for 3 years, resulting in 72 and 75% reductions of insect abundances and biomass, respectively. Following treatment, monthly benthic abundances and biomass were measured in the treated stream and a nearby reference stream (C55) in order to assess recovery. Seasonal average abundances and biomass were calculated from samples taken from December 1988—December 1989, the first post‐treatment year of C54.2. Non‐insect abundances and biomass were higher in the recovering stream during the winter + spring and summer periods, but were similar to the reference stream by autumn. Abundances and biomass of collector‐filterers, scrapers, and shredders were all lower in the recovering stream during winter + spring; however filterers and scrapers were similar to reference stream values by the end of the recovery year. No distinct differences were seen between collector‐gatherers and predators throughout the year.3. Univoltine and multivoltine taxa, along with treatment‐resistant taxa, were the most important contributors to recovery of C54. Taxa with longer generation times, life histories which were more vulnerable to riming of treatments, and/or poor dispersal abilities were poorly represented during first‐year recovery.4. Abundance data alone were not sufficient for a complete analysis of recovery. Biomass estimates reflected differences in taxonomic composition and developmental stages between streams after 1 year of recovery.
Population dynamics and resource utilization by larval Chironomidae (Diptera) in a backwater area of the River Danube
Authors: SCHMID P.E. 
Published: May 2006

SUMMARY1. The five most abundant species of the larval chironomid community in a backwater area of the River Danube were analysed in terms of population dynamics and utilization of space from July 1985 to July 1986. The life histories of Prodiamcsa olivacea (Meigen), Cryptochironomus defectus (Kieffer), Harnischia curtilamellata (Malloch), Polypedilum laetum (Meigen) and Polypedilum scalaenum Schrank were described; the number of estimated generations per year was two for P. olivacea, H. curtilamellata, P. laetum and P. scalaenum and three for C. defectus.A decline in larval densities of P. olivacea and P. scalaenum was significantly correlated with increasing cumulative water discharge in an area close to a dam (P<0.01).2. Spatial overlap and resource width were estimated for these chironomid species across four ranges of water depth, in three sections of the River Danube. An increasing mean spatial overlap between larval species coincided significantly with higher mean resource utilization in all cross‐sections during the sampling period. Simulations of spatial overlap between randomized species associations were conducted for analyses of coexistence and dispersion between larval populations. On the basis of comparison with a neutral model, in which patches of individuals were randomly reassigned to habitat units, spatial segregation was significantly (P<0.05) different from chance for seventy‐three out of 263 species pairs examined through the year.3. An analysis of the spatial dispersion of each chironomid species (using the standardized Morisita index) suggested temporally and spatially varying patterns of dispersion, whereas the mean spatial segregation between patches of larval species might have resulted from temporary formations of random patches in this backwater area of the River Danube.4. Spatial stability estimated as the minimum positive eigenvalue of the species matrix was significantly positively related to mean spatial segregation, indicating that a lower habitat segregation between patches of larval species pairs may lead to a destabilization of the larval species assemblage.
Induction and inhibition of spine development in the rotifer Keratella tropica
Authors: ZAGARESE HORACIO E. , MARINONE MARÍA C. 
Published: May 2006

SUMMARY1. We analysed the effect of several variables on the morphology of the rotifer Keratella tropica with the aim of accounting for its morphological variability in nature. We used field data from (i) an extensive survey of Argentine lakes, (ii) a 1.5 yr, monthly sampling of Salto Grande Reservoir, and (iii) a 3‐month, outdoor experiment in fish culture tanks. In addition, we performed a series of laboratory experiments aimed at isolating the effects of different variables.2. The increase in crustacean biomass and the amelioration of their nutritional status (measured as the reciprocal of the starvation time) caused spine enlargement. In contrast, the presence of decomposers caused reduction of the spines. These results support the idea that a major proportion of the phenotypic expression of K. tropica depends on the concentration of an inducing factor, which in turn depends on the balance between release and decomposition rates of the chemical.3. Food concentration was identified as a secondary factor affecting morphology. In agreement with records for other rotifers, food concentration and spine length were inversely related. Both factors, crustacean chemicals and food availability, seemed to act independently, at different developmental stages. Our experiments suggest, however, that the most exuberant individuals can only be induced through chemicals released by predators and competitors.4. The presence of backswimmers (Notonectidae) resulted in individuals with very short or non‐existing posterior spines. Filtrates of backswimmer‐conditioned medium also produced a significant, although less striking, spine inhibition. Thus, different chemical factors seem to have opposite effects on K. tropica morphology. Those released by crustaceans induce spine elongation, while those released by backswimmers inhibit spine development.5. Genetic differences were also identified as a source of morphological variability. Under identical laboratory conditions, different clones had spines of different length. Our experiments also suggest an inverse relationship between spine length and growth rate. The latter result, however, is based upon only three clones of K. tropica and is thus preliminary.
Enzymic and molecular analysis of microbial communities associated with lotic particulate organic matter
Authors: SINSABAUGH ROBERT L. , WEILAND TIMOTHY , LINKINS ARTHUR E. 
Published: May 2006

SUMMARY1. Most allochthonous plant detritus moves through stream ecosystems as fine particulate organic matter (FPOM), whose associated microbial communities, unlike those of coarse detritus, have received little scrutiny.2. Benthic POM was collected from a fourth‐order boreal river and two first‐order tributaries in northern New York during July 1991, sorted it into eight size fractions ranging from 38 to >4000 μm, and assayed each fraction for ergosterol, DNA, and the activity of nine extracellular enzymes: β‐1, 4‐glucosidase, endocellulase, cellobiohydrolase, phenol oxidase, peroxidase, β‐N‐acetylglucosaminidase, acid phosphatase, alkaline phosphatase, and aryl sulphatase. In addition, DNA‐DNA hybridization was used to investigate the structural similarity of the microbial communities associated with the FPOM fractions.3. Various enzymes showed distinct activity patterns in relation to particle size as well as among sites. Half of the possible pairwise correlations among enzyme variables were statistically significant, but no enzyme activities were correlated with biomass indices (DNA and ergosterol concentration). DNA‐DNA dot‐blot hybridizations suggested extensive structural similarity among the microbial communities associated with FPOM fractions.4. Cluster analysis was used to compare microbial functional similarity, measured by enzyme assays, and structural similarity, measured by DNA—DNA hybridization. Comparison of cluster coefficients showed a weak correlation between community structural similarity and functional similarity (r= 0.51) with fifteen of eighteen fractions grouped within a narrow range of distance.5. The results suggest a convergence in microbially mediated FPOM processing despite system‐level differences in litter and water quality.
Biovolume as a tool in biomass determination of Oligochaeta and Chironomidae
Authors: SMIT HENK , VAN HEEL ESTI DUDOK , WIERSMA SASKIA 
Published: May 2006

SUMMARY

We used biovolume as a simple non‐destructive means for estimating biomass for several tubificid and chironomid species. Biovolumes were determined by treating the organisms as cylinders and measuring body lengths and diameters; estimates were verified by measuring the displacement of water by live organisms in a 5‐ml burette. In addition, factors were determined for the conversion of biovolume (V) into wet weight (WW), dry weight (DW) and ash‐free dry weight (AFDW).
For six tubificid species, regression functions between the diameter of segment XI (D11) and the biovolume enabled the prediction of any biovolume merely by measuring D11. This method, however, underestimated biovolumes of Branchiura sowerbyi by 38–47% compared with burette measurements. This difference is largely attributable to the mountant we used during identification.
For ten chironomid species a linear relation was found between body length and the diameter of abdominal segment 5. The biovolume of Chironomus muratensis was underestimated by an average of 12% compared with burette measurements.
Specific gravity (WW:V) amounted to 1.07 and 1.05, DW:WW ratios were 0.20 and 0.142 and AFDW:WW ratios were 0.182 and 0.129 for Oligochaeta and Chironomidae, respectively.
The biovolume method is not yet very accurate for Oligochaeta, but to our knowledge, it is the only practical method that can be used in natural polyspecific communities that need to be treated with elucidating media for identification. For those Chironomidae that need no elucidation for identification, this method is time saving and just as accurate as the direct body shape—biomass method.
Macroinvertebrate colonization and biofilm development on leaves and wood in a boreal river
Authors: HAX CAROLYN L. , GOLLADAY STEPHEN W. 
Published: May 2006

SUMMARY

Biofilms, the accumulation of micro‐organisms, exoenzymes, and detritus particles on submerged surfaces, may change the quality of leaves and wood as sources of food and/or habitat for invertebrates. We examined the relationship between macroinvertebrate assemblages and biofilm development on leaves and wood in a boreal river.
Arrays of white birch ice‐cream sticks and sugar maple leaves were placed at fast‐ and slow‐current sites. Samples were collected periodically, and assayed for microbial biomass (ATP, ergosterol, chlorophyll a) and macroinvertebrate colonizers.
Microbial biomass and macroinvertebrate density were consistently greater on wood than leaves. Taxon richness was similar for all substratum/current combinations, but taxon density (number of taxa m−2) was greater on wood. Macroinvertebrate density and taxon richness correlated with all microbial indicators when data from both substrata were pooled.
Leaves did not support as great a density of invertebrates as wood perhaps because of their faster breakdown rate and truncated biofilm development. Greater stability and the potential for surface complexity may make wood a site of higher macroinvertebrate diversity than leaves.
Temporal variability in the impact of river regulation on thermal regime and some biological implications
Authors: WEBB B.W. , WALLING D.E. 
Published: May 2006

SUMMARY

Ten years of hourly water temperature data for three river sites in south‐west England were used to investigate the longer‐term thermal effects of river regulation. The impact of reservoir impoundment on downstream invertebrate and trout development were simulated using daily mean temperature data in conjunction with published biological models.
The main effects of regulation on water temperature were to increase the mean value, eliminate freezing conditions, depress summer maxima, delay the annual cycle and reduce diel fluctuation. These impacts persisted over a distance of at least 5km below the dam but declined downstream, especially for seasonal and diurnal variations.
Simulations suggested that regulation is likely to have had a greater impact on the development of brown trout (Salmo trutta) than on the development of one Ephemeroptera and four Plecoptera species. Trout fry were predicted to emerge up to 57 days earlier, and to weigh up to 67% more by the end of the year following swim‐up, in the regulated compared with the unregulated river.
Marked inter‐annual contrasts in the physical and biological consequences of impoundment were evident, indicating that long‐term studies are required to define properly the effects of river regulation.
Contribution of space remote sensing to river studies
Authors: MULLER ETIENNE , DÉCAMPS HENRI , DOBSON MICHAEL K. 
Published: May 2006

SUMMARY

A review is presented of types of satellite remote‐sensing data currently available, and their recent uses in studies of river systems.
Broad‐scale assessments of relative water quality may be carried out, although precise indication of water quality requires samples to be taken in situ.
In the event of flooding, the extent of inundation may be determined and damage assessed quickly. Some radar data allow measurements of flood water even when obscured by vegetation.
Riparian vegetation may be mapped over large areas, although the recognition of specific tree species remains difficult.
One of the most basic and widely used applications of remote‐sensing data for rivers is that of mapping, both as a single event and over time to follow changes, e.g. channels in a delta. Entire catchments may be mapped, although the efficiency of detection of low‐order streams is dependent upon the characteristics of the system used.
Remote‐sensing data has been widely used in all of the above types of study, but is rarely employed on a long‐term basis. Several factors can explain this situation, including, for example, the absence of reliable absolute relationships between spectral data and ecological parameters.
A clear definition of observational needs (e.g. spectral bands, ground resolution, acquisition frequency) of stream ecologists, together with the identification of ecological parameters that may be collected relatively easily from space, will improve remote sensing as an ecological tool in many restoration and management situations.
Reproductive strategy as population density varies in Daphnia magna (Cladocera)
Authors: GUISANDE C. 
Published: May 2006

SUMMARY

In this study an experiment was carried out to test whether Daphnia magna (Cladocera) changed its reproductive strategy in response to varying population density but constant food supply.
As population density increased there was a reduction in the age at which females reproduced. Early reproduction was offset by smaller body length and clutch size (number of eggs per female) relative to later reproducing females grown at lower population densities.
This pattern was interpreted as a strategy carried out by females to reduce the time at which they release their offspring. One potential advantage of early reproduction is to reduce the risk of severe food limitation for neonates born during a period of rapid population increase.
Quantitative trophic reconstruction from sedimentary diatom assemblages: a cautionary tale*
Authors: FRITZ S.C. , KINGSTON J.C. , ENGSTROM D.R. 
Published: May 2006

SUMMARY

The diatom stratigraphy of 210Pb‐dated sediment cores is used to reconstruct the recent trophic histories of four oligo/mesotrophic lakes in the lower peninsula of Michigan, U.S.A. Quantitative trends in total phosphorus concentrations are reconstructed from the cores with a calibration data set based on modem diatom assemblages and water‐chemistry variables in forty‐two Michigan lakes that span a range of nutrient concentrations and biological productivities.
The total phosphorus reconstructions suggest that phosphorus concentrations have changed very little over the last 200 years, with modern values approximately equal to those at the time of settlement. Three of the four lakes, however, do show a trend to higher phosphorus concentrations at the time of logging and settlement and a subsequent decline.
The quantitative inferences of trophic change are compared with interpretations based on diatom species composition and the accumulation of diatoms, biogenic silica and carbonate in the sediments, and some discrepancies occur among the various lines of evidence. These comparisons are used to discuss the sensitivity of various proxies for reconstructing the nature and magnitude of trophic change.
Inter‐ and intrapopulational variation in time to metamorphosis in a freshwater copepod
Authors: TWOMBLY SARAN 
Published: May 2006

SUMMARY

Adjacent populations of the copepod Cyclops scutifer Sars living in lakes in southern Norway exhibit remarkably different life cycles. A series of laboratory‐common environment experiments were used to partition variance in one life cycle trait—time to metamorphosis—among and within five populations of C. scutifer, to examine the extent to which variation in this trait has a generic basis and to test whether populations are polymorphic for development rates. The experimental populations exhibit a variety of life cycles in the field and occupy environments that represent a broad range of conditions.
Populations with different life cycles in the field continued to express differences in time to metamorphosis in the laboratory, indicating a genetic contribution to life cycle variation. Differences in developmental rates in the laboratory were smaller, however, than differences observed in the field, suggesting that environmental conditions also contribute to observed life cycle variation.
In addition to interpopulation variation, each population maintained substantial intrapopulation variation in time to metamorphosis; differences between individuals from the same population were often as large as or larger than differences between populations.
Individual females in most populations produced highly variable offspring, and there often was little difference in time to metamorphosis among families within a population.
Cyclops scutifer exhibits a hierarchy of variation in time to metamorphosis, with a major portion of this variation expressed among siblings. Intrapopulation life history variation important to natural selection may be maintained by different processes among the major groups of freshwater zooplankton.
The effects of spate‐induced disturbance, predation and environmental complexity on macroinvertebrates in a tropical stream
Authors: DUDGEON DAVID 
Published: May 2006

SUMMARY

The combined effects of fish predation, substrate complexity and flow on benthic macroinvertebrates inhabiting riffles was investigated in a Hong Kong stream. Predation was manipulated using fish inclusion/exclusion cages containing complex (= many refuges) or simple (= few refuges) substrates. Experiments were undertaken during the winter dry season, when disturbance due to flow events was minimal, and repeated during the summer monsoon, when the stream experienced spates of varying intensity and duration.
Predation by the fish, Oreonectes platycephalus, significantly reduced the abundance of macroinvertebrates, especially chironomids and mayflies. Because chironomids (mostly Chironominae) were the dominant cage colonists, there was also a reduction in total macroinvertebrate density.
Predator impacts were significantly lessened during the wet season, when macroinvertebrate densities increased considerably, but significant reductions in the densities of vulnerable taxa and total macroinvertebrate abundance were nevertheless apparent.
Substrate complexity (the presence of prey refuges) had no significant effect on the ability of predators to reduce prey abundance.
Detritus accumulated in cages during the latter part of the study, and densities of most taxa were correlated with detrital standing stocks.
The results of this experiment indicate that biotic interactions such as predation may be suppressed during periods of spate‐induced disturbance, although they can still influence benthic communities significantly. However, the effects of predation are highly taxon specific and may vary among streams in response to changes in predator and prey species composition, or the severity and duration of spates.
The upstream/downstream movement paradox of lotic invertebrates: quantitative evidence from a Welsh mountain stream
Authors: WILLIAMS D. DUDLEY , WILLIAMS NANCY E. 
Published: May 2006

SUMMARY

This study attempts to determine the mechanisms by which the downstream displacement of lotic invertebrates is compensated by the upstream movements of immatures and adults. To this end, submerged and aerial traps were set up at three sites, each 100 m apart on a small mountain stream (Yr Ogof) in North Wales and operated for 12 months.
At Site 1 (the source), 19.3% of the benthic invertebrates lost as drift were replaced by the upstream movement of aquatic stages. At Site 2, the average upstream compensation was 51.1% (although there was a marked difference between the two traps at the site). At downstream Site 3 the average compensation was 55.4%. The net loss of benthos downstream over 1 year was estimated to be 261920 individuals from Site 1, 41891 from Site 2, and 40470 from Site 3.
At Sites 1 and 2, the numbers of invertebrates drifting were positively correlated with both current speed and water depth. At Sites 2 and 3, the numbers moving upstream were positively correlated with water temperature. At all three sites, the numbers of animals drifting were positively correlated with the numbers moving upstream, under water.
In none of the eight common species of stoneffy did females show a strong overall upstream flight preference—however, two species, Leuctra nigra and Nemoura erratica, showed a significant downstream preference.
As with the stonefly nymphs, most of the caddisfly larvae showed a longitudinal distribution. Agapetus fuscipes larvae were most abundant at Site 1, yet females showed no preferred flight direction—this would seem to be inappropriate for maintaining this larval distribution pattern. However, females caught moving upstream at Site 2 were bigger and contained twice as many eggs, which were also larger, than females moving upstream at Site 1. The flight patterns of the other Trichoptera also seemed inappropriate for maintaining their respective larval distributions. Immature insects moved upstream at certain sites and times, but trends were not consistent. There was no correlation between female flight direction and local wind speed and direction.
Downstream displacement of the most abundant non‐insect species, Gammarus pulex, was quite considerable at all three sites. However, at several times during the year the numbers moving upstream approached or exceeded those drifting. Maintenance of benthic population densities in this species is thought to be through a combination of upstream movement (which was highly correlated with benthic density at Sites 1 and 3) and production of young over a long (10 month) reproductive period. Maintenance of the benthic populations of the immature stages of the majority of insect species in Yr Ogof is thought to be through oviposition by females in the vicinity of their emergence sites.
Comment on ‘The nature of the fluid boundary layer and the selection of parameters for benthic ecology’ (Carling, 1992)
Authors: LAMOUROUX NICOLAS 
Published: May 2006

SUMMARY

Near‐bed flow equations and definitions have been reviewed by Carling (1992). The main errors and ambiguities in this contribution are identified.
The hypotheses required to derive the governing equations are usually violated in complex flows of natural streams.