bluuebunny/crossref_metadata_2025_split huggingface dataset:
Allozyme variation among natural populations of Holopedium gibberum (Crustacea; Cladocera)
Authors: THIER EDWARD 
Published: May 2006

SUMMARY

Holopedium gibberum, from twenty lakes in Rhode Island and Maine, were examined for allozyme variation at five loci to determine the pattern and degree of generic variation among sites and the genetic structure within individual lakes.
There were significant differences in allele frequencies among sites. Most populations were fixed for a particular allele at each locus. Only five lakes had polymorphic populations.
Polymorphic populations showed significant deviation from expected Hardy‐Weinberg genotype frequencies. In each case, there was an excess of homozygotes.
Two lakes were examined for intra‐lake allele frequency differences. In one lake there were no differences. The other lake exhibited significant allele frequency differences between stations at the north and south ends of the lake.
Populations were examined for the frequency distribution of composite genotypes over three loci. Most populations were dominated by one or two genotypes.
The results suggest sporadic sexual recruitment and a high degree of genetic isolation among these populations of H. gibberum. In these respects they resemble the permanent pond populations of Daphnia magna examined by Hebert (1974a).
Nutritional suitability of some uni‐algal diets for freshwater calanoids: unexpected inadequacies of commonly used edible greens and others
Authors: HART ROB C. , SANTER BARBARA 
Published: May 2006

SUMMARY

Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Tropodiaptomus spectabilis) were measured on mono‐specific diets of comparably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas sp., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capricornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17°C) and food supply level (1 mgCl−1).
All diets other than Scenedesmus and Selenastrum supported complete naupliar development at broadly comparable times within and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between diet types, and both Chlamydomonas and Cyclotella were inferior or inadequate for copepodid development.
Both naupliar and copepodid stages ingested radiolabelled Scenedesmus and Selenastrum readily. Comparative incorporation rate measures of Selenastrum and Cryptomonas respectively exceeded estimated metabolic maintenance needs of stage 3/4 nauplii of T. spectabilis by some 56% and 790%. Scope for growth (‘surplus’ energy) was accordingly fourteen‐fold greater on Cryptomonas than on Selenastrum /Scenedesmus. The dietary inadequacy of these two green algae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.
Interactions between a stream caddisfly and the algae on its case: factors affecting algal quantity
Authors: BERGEY ELIZABETH A. , RESH VINCENT H. 
Published: May 2006

SUMMARY1. Field experiments were conducted to examine interactions between larvae of the caddisfly Gumaga nigricula and the algae (primarily diatoms) located on their sand grain cases. Floating experimental enclosures were placed in sunlit pools of a California stream. Treatments applied to occupied cases, or to those from which caddisflies had been removed, included variations in grazer density, addition of nutrients, and modification of illumination using shade cloth.2. Neither faecal‐enriched agar in empty cases nor injections of faecal material into plugged cases affected case chlorophyll a concentration; injected nutrients (N and P), however, did increase chlorophyll a concentration. Faecal material may be nutrient poor, or nutrients may not be readily released. In addition, the relatively impermeable case wall may reduce the likelihood that nutrients from caddisflies reach the algae on the outer case surface.3. Although a Gumaga larva may graze algae from its own case, grazing by conspecifics and the caddisfly Helicopsyche borealis causes a greater reduction in the chlorophyll a content of cases.4. Chlorophyll a content of empty cases was decreased by experimental reduction of light. Because of shading associated with burrowing, chlorophyll a content of cases occupied by Gumaga was low and was unaffected by experimental light reduction.5. Removal of Gumaga from its case results in rapid accrual of algae. Thus, the net effect of larval presence is to diminish the algal content of its case.
The effect of sample duration on the quantification of stream drift
Authors: CULP JOSEPH M. , SCRIMGEOUR GARRY J. , BEERS CHRIS E. 
Published: May 2006

SUMMARY1. We performed computer simulations and a field experiment to determine the effect that sample duration and, thus, sample volume had on estimates of drift density and sample variance.2. In computer simulations, when the spatial arrangement of individuals in the water column approximated a random and a contagious‐random distribution, estimated mean drift density was not significantly affected by sample duration, but sample variance decreased curvilinearly as sample duration increased.3. Similar results were obtained in field experiments in habitats of high and low water velocity.4. Our findings from an Albertan stream indicate that the relationship between sample variance (i.e. coefficient of variation) and duration of drift samples is curvilinear. This relationship affected the number of samples required to achieve a specific level of precision (i.e. a standard error within 10% of the mean). For estimates in low and high current velocities, sample variation was halved by increasing the duration of sample collections from 10 to 20 min. The increased precision obtained with samples of 20 min duration reduced the amount of drift material that needed to be processed by approximately 50% compared with an equivalent 10% level of precision for samples of 10 min duration. This reduction in the number of samples required to obtain a given level of precision has important consequences to the cost of processing drift samples.5. Thus to optimize studies of stream invertebrate drift, both in terms of sample precision and processing effort, researchers must consider the effect that sample volume has on the variance of drift density estimates. Because researchers generally use drift nets with similar‐sized apertures (>300cm2), the problem for specific field applications becomes one of optimizing sample duration relative to variance estimates for drift density.
Influence of phytoplankton on the response of bacterioplankton growth to nutrient enrichment
Authors: WANG LIZHU , PRISCU JOHN C. 
Published: May 2006

SUMMARY1. Laboratory experiments were conducted to test the effect of nutrient enrichment on bacterioplankton growth in the presence and absence of phytoplankton.2. In one series of experiments, bacterioplankton growth in terms of specific activity [3H‐thymidine incorporation (cell number)−1] was greater in whole lake water samples than in samples from which phytoplankton had been removed by filtration (1.0 μm), regardless of the nutrient enrichments (control, NH+4 plus PO3‐4 and mannitol). Organic C enhanced bacterioplankton growth in both whole and filtered lake water.3. In another series of experiments (with the same nutrient enrichments as in the first experiment except that glucose replaced mannitol), bacterioplankton growth in whole lake water enriched with PO3‐4 plus NH+4 and incubated in the light was greater than in two treatments designed to inhibit photosynthetic activity (+DCMU and dark). Bacterioplankton response to nutrient addition was greatest in the PO3‐4 plus NH+4 enrichment under all three conditions (light +DCMU, and dark).4. These results indicate that bacterioplankton growth could be directly limited by inorganic P and N when these elements are in short supply. Enhancement of bacterioplankton growth by phytoplankton occurs only under PO3‐4 and NH+4 replete environments.
Origins, structure, and trophic significance of amorphous seston in a blackwater river
Authors: CARLOUGH LESLIE A. 
Published: May 2006

SUMMARY1. The role of suspended organic aggregates in aquatic systems has received much attention, but their origin and function vary between environments and conditions.2. In the Ogeechee River (Georgia, U.S.A.) particles are constructed of clay, organic debris, and microorganisms in a matrix of mucopolysaccharide fibrils. Although these fibrils are probably of bacterial origin, microcosm studies suggest that synthesis of particles from dissolved substances can occur in the absence of microbial processing.3. Processing of organic material and production of amorphous aggregates occurs through a series of microbial events and follows a well‐defined successional cycle that results in a high concentration of protists in sestonic particles.4. Chemical analyses show that the relatively high protein and fat content of this amorphous material is a valuable food resource for filter‐feeding macroinvertebrates that are dense in this system.
Toxicity to Daphnia of a compound extracted from laboratory and natural Microcystis spp., and the role of microcystins
Authors: JUNGMANN DIRK , BENNDORF JÜRGEN 
Published: May 2006

SUMMARY1. The microcystin content of a variety of Microcystis spp., from both laboratory strains and natural blooms, was analysed by HPLC. The microcystin content of laboratory strains ranged from 1.6 to 4.3μgmg−1 dry weight. Yearly and seasonal variation was detected in an analysis of bloom material collected from Bautzen Reservoir over a 3‐year period. The microcystin concentration in bloom material ranged from undetectable to 1.16 μg ml−1 dry weight.2. Toxicity of laboratory and natural Microcystis to Daphnia pulicaria was determined using an established LC50 technique. Partially purified water extracts from different Microcystis samples exhibited a wide range of toxicity. The highest activity was found in natural Microcystis samples, with an LC50 of 36 μgm−1 dry weight of Microcystis, whereas one strain did not appear toxic at 1600 μg ml−1.3. No correlation was found between the concentrations of microcystins of different laboratory and natural Microcystis strains and the toxicity of extracts to Daphnia pulicaria from the same strains. Therefore, we discriminated between hepatotoxic microcystins and the compound(s) that is toxic to Daphnia, here termed DTC (Daphnia‐toxic compound), which is independent of microcystins.
Body size and abundance of benthic animals in Mirror Lake, New Hampshire
Authors: STRAYER DAVID L. 
Published: May 2006

SUMMARY1. There is a strong negative correlation between body mass and population density for 192 species from the zoobenthos of Mirror Lake, a small, oligotrophic lake. This correlation spans seven—nine orders of magnitude in body mass.2. The slopes of both the regression and the upper bound on the distribution of data points are significantly shallower than ‐0.75, the slope that has been suggested to imply that metabolic constraints limit animal abundance.3. The regressions for individual taxonomic groups (i.e. classes, phyla) do not conform closely to the overall regression line.4. It is suggested that metabolic constraints on community structure need not be expressed by a slope of ‐0.75 for regressions (or upper bounds) on body mass—abundance functions.
Relationships between macroinvertebrate communities and environmental variables in metal‐contaminated streams in south‐west England
Authors: GOWER A.M. , MYERS G. , KENT M. , FOULKES M.E. 
Published: May 2006

SUMMARY1. Macroinvertebrate species and information on thirty‐nine variables were recorded at forty‐six sites on twelve Cornish streams affected to varying extents by past metalliferous mining.2. Relationships between macroinvertebrate communities and environmental variables were examined using canonical correspondence analysis (CCA). Copper was the strongest correlate with Axis 1 of the analysis, suggesting that it may have a major role in determining community structure. There were also strong correlations between Axis 1 and aluminium, alkalinity, pH, dissolved organic matter and algal cover, and between Axis 2 and discharge.3. CCA distinguished four site groupings. In spite of seasonal changes in position on the ordination, as revealed through CCA and detrended correspondence analysis (DCA), sites retained their group membership. There were differences in the proportions of the major taxa within the four CCA‐derived groups. In the group with the highest copper concentration, Ephemeroptera were absent, but triclads and chironomids were abundant, with Orthocladiinae the dominant group.4. Changes in the occurrence of species along the metal gradient reflected changes in sensitivity. Tolerance' plots of selected species based on the CCA site ordination diagram were used to identify environmental thresholds.5. As well as direct toxic effects of copper and aluminium on invertebrate communities, co‐precipitation of these two metals could be an important physical factor. Further modifying influences resulting from interactions between toxic metals and pH, alkalinity, hardness and dissolved organic matter contributed to the complexity of conditions affecting the faunal community in metal‐contaminated streams.6. The most severely contaminated sites, with mean copper concentration exceeding 500 μgl−1, were all characterized by a reduced community dominated by the flatworm Phagocata vitta, the chironomids Chaetodadius melaleucus and Eukiefferiella claripennis and the net‐spinning caddis Plectrocnemia conspersa. The necessity for species identification is demonstrated in relation to variation in metal tolerance.
Long‐term effects of PO4 fertilization on the distribution of bryophytes in an arctic river
Authors: BOWDEN WILLIAM B. , FINLAY JACQUES C. , MALONEY PATRICIA E. 
Published: May 2006

SUMMARY1. Each year since 1983, H3PO4 has been added continuously during the ice‐free season to a P‐limited tundra river (Kuparuk River, North Slope, Alaska). Effects on epilithic metabolism, invertebrate community structure and fish production developed quickly.2. In 1990, 7 years after fertilization began, we noted extensive coverage by bryophytes within the fertilized reach of the river, where very little had been noted before. Bryophyte biomass from a limited set of quadrats taken in 1990 and 1991 yielded 17 ± 9 (SE) g dry mass m−2 in control reaches and 322 ± 96 g dry mass m−2 in fertilized reaches.3. An initial survey of macroalgal and bryophyte cover in 1991 suggested that the moss Schistidium (Grimmia) agassizii was distributed in both control and fertilized reaches of the river. No clear difference in coverage by this species was found in either reach.4. In contrast, two species of Hygrohypnum (H. alpestre and H. ochraceum) were found almost exclusively in the fertilized reach. An extensive point transect survey done in 1992, above, within and below the fertilized reach, indicated that increased cover and biomass of Hygrohypnum spp. were confined to the fertilized reach of the river. Detrended correspondence analysis clearly separated the macrophyte and macroalgal communities in the fertilized reach from those in the control and downstream reaches.5. A fourth bryophyte species (Fontinalis neomexicana) also occurred almost exclusively in the fertilized reach, but was much less abundant than the Hygrohypnum species.6. Analysis of total N and P in the tissues of the Hygrohypnum spp., and estimates of average coverage (∼15%) and biomass (∼150g dry weight m−2) over an 8km fertilized reach, suggest that these species alone may have removed two‐thirds of the P added in the fertilizer experiment. The bryophyte community in this river is likely to be the dominant sink for P in the fertilized reach.
Feeding ecology of the diving ducks pochard (Aythya ferina), tufted duck (A. fuligula), scaup (A. mania) and goldeneye (Bucephala clangula) overwintering on Lough Neagh, Northern Ireland
Authors: WINFIELD IAN J. , WINFIELD DEMISE K. 
Published: May 2006

SUMMARY1. The diets of pochard (Aythya ferina), scaup (A. marila) and goldeneye (Bucephala clangula) overwintering on Lough Neagh are dominated by chironomid larvae, while molluscs are more important in that of tufted duck (A. fuligula).2. Inshore areas of Lough Neagh offer poor feeding conditions for these diving ducks because chironomid larvae and molluscs are of small individual body size or low abundance. These factors lead to all four ducks foraging at least in part at depths greater than those usually exploited.3. Due to their common consumption of molluscs, the diet of tufted duck shows a higher overlap with that of an introduced roach (Rutilus rutilus) population than with any other duck or fish species.4. The feeding ecology of tufted duck and roach in Lough Neagh may form an example of distant competition and be at least partly responsible for recent fluctuations in the numbers of tufted duck.
Macroinvertebrate drift in streams of the Nepalese Himalaya
Authors: BREWIN PHILIP A. , ORMEROD S.J. 
Published: May 2006

SUMMARY1. Macroinvertebrate drift was investigated in seven small headwater streams along an altitudinal gradient (600–3350 m) in two adjacent river systems in east‐central Nepal. Study streams in the Likhu Khola were at the lowest altitude and flowed through terraced agriculture. At higher altitudes, Langtang streams flowed through catchments of forest and alpine scrub. Samples were collected every 3h over a 24 h period in each stream.2. Terrestrial macroinvertebrate drift was greatest in streams with semi‐natural catchments, but was scarce in streams where trees were absent.3. At lower altitudes drift was dominated by Hydropsychidae and Baetidae, which were most abundant in night samples, and Hydracarina, which tended to be day active. Baetidae also dominated drift at high altitudes, but here drift was increasingly aperiodic or diurnal. The composition of the drift reflected a significant correlation between the percentage abundance of taxa in the drift and benthos.4. As in other mountain regions of the world, drift was aperiodic in fishless streams (high altitude), but strongly nocturnal in streams where insectivorous fish were present (lower altitude). However, a wide array of potentially important variables along the altitudinal gradient, such as temperature, climate and community structure, might be important influences on these patterns.
International collaboration in freshwater ecology
Authors: RESH VINCENT H. , YAMAMOTO DAVID 
Published: May 2006

SUMMARY1. International collaboration in freshwater ecology was examined using authorship affiliations of articles published in thirty‐three specialized journals. Most are published in Europe.2. Researchers from four to thirty‐seven different countries were represented in the 100 articles examined for each journal. Only 29% of articles were single‐authored; multicountry authors' addresses (indicating international collaboration) were found for 9% (range 0–23% per journal) of articles examined.3. Five of the eighty‐nine countries listed in the addresses of the 3300 articles together contributed >50% of total articles: United States (24.9%), Canada (8.6%), Germany (7.6%), Commonwealth of Independent States (7.0%) and Poland (5.9%). Of the fifteen countries that each produced >2.5% of total articles, the percentage representing international collaboration was highest for France (34.9%) and Canada (24.0%). The seventy‐four countries that each contributed <2.5% of total articles generally had higher rates of international collaboration.4. Researchers in the United States and Canada collaborate internationally almost twice as often in freshwater ecology than in all science. Much of France's extensive international collaboration is with countries that produce few articles in freshwater ecology, and their international collaboration is often exclusively with France.5. Three journals publishing both marine and freshwater ecology articles contain more articles on the former topic, but more countries are represented in the publication of freshwater than marine research.6. The percentage of articles that represent international collaboration is higher in freshwater ecology than in medicine, biology, chemistry and engineering, and approximates that in physics.
The synthesis of long‐term ecological research in the context of concurrently developed ecological theory: design of a research strategy for the Upper Rhône River and its floodplain
Authors: STATZNER BERNHARD , RESH VINCENT H. , ROUX A. LOUIS 
Published: May 2006

SUMMARY

Using sites from the Upper Rhône River, France, as an example, the objective of this paper is to identify the essential elements needed to test current ecological theories with previously collected data. Procedures developed may enable other groups to design comparable research strategies for syntheses of long‐term studies of ecological systems.
Because of the high number (more than 200) and turnover of researchers, the long study period (about 17 years), the evolution of research methods and interests, and the diverse systematic groups that were considered (from micro‐organisms to birds), the data available for a synthesis were quite heterogeneous. The application of a ‘fuzzy coding’ technique allowed such disparate information to be structured for analysis.
The habitat templet concept and the patch dynamics concept were selected for analysis with existing data on the Upper Rhône because theories, such as these, that link ecological responses to habitat templets are a focus of current ecological debate and potentially may serve as a general tool for ecologically orientated river management.
A preliminary trial to structure the existing knowledge, to identify (and manage) gaps in it, and to create and apply the analytical tools in a way that predictions from theory could be tested was an essential element in the design of this project.
Predictions derived from the theoretical concepts had to match the format of the available information on the Upper Rhône; potential bias was avoided by having a priori predictions developed by previously uninvolved colleagues.
Synthesis of the long‐term study of the Upper Rhône in the context of concurrently developed ecological theory required, at times, an unconventional research strategy. Hence, the generation of hypotheses and methods, the presentation of results, and consequently the discussions in papers of this special issue of Freshwater Biology (Statzner, Resh & Dolédec, 1994) represent an innovative approach to testing ecological theory.