bluuebunny/crossref_metadata_2025_split huggingface dataset:
The causes of change in the diversity and stability of phytoplankton communities in small lakes
Authors: ELBER FREDY , SCHANZ FERDINAND 
Published: May 2006

SUMMARY. 1. A study of the diversity and stability of phytoplankton communities during one vegetation period (February‐October 1984) was carried out in four small lakes in the Pfynwald region of Canton Valais, Switzerland: Kaminsee I, Kaminsee II, Grossee and Rosensee. The diversity was calculated according to Shannon & Weaver (1949). The change in diversity ΔH; and SIMI (similarity index according to Stander. 1970) were used as measures of stability.2. On average, the diversity was highest in the oligotrophic Rosensee (annual mean 3.19) and least in the hypereutrophic Kaminsee I (annual mean 1.34). In Kaminsee I and Grossee, the diversity corresponded in the main to the relative frequency of Cryptomonas erosa Ehrenberg: i.e. the diversity was low when the relative frequency of C. erosa was high and vice versa (Kaminsee I: max. diversity 2.74; min. 0.13. Grossee: max. 3.62; min. 0.28; annual mean 2.21). Kaminsee II and Rosensee exhibited only slight variations in their phytoplankton community structure (Kaminsee II: max. diversity 2.83; min. 1.26; annual mean 2.10. Rosensee: max. 3.79; min. 2.81). High values of diversity, or increases in diversity, were a result of low nutrient availability and grazing pressure. Lower diversity values. or decreases in diversity, were a result of a plentiful nutrient supply, low grazing pressure and grazer selectivity with respect to food organisms.3. Because values of the diversity index vary by different amounts during the course of a year depending on the water body, the characterization of a phytoplankton community on the basis of one value alone is unsatisfactory. It is suggested that the mean and either standard deviation or range of the diversity be cited in order to overcome this drawback at least partially.4. No generally accepted measure exists for the calculation of stability. According to the measure of stability employed, a community may appear to be more or less stable. A statement concerning the stability of a community without mentioning the measure employed is therefore worthless. The factors determining the stability of a phytoplankton community do not have the same effect on all measures of stability.5. The change in diversity ΔH’was influenced in the main by alterations
An ecologically useful classification of mean and near‐bed flows in streams and rivers
Authors: DAVIS J. A. , BARMUTA L. A. 
Published: May 2006

SUMMARY. 1. Mean motion and near‐bed flows in streams and rivers can be described using a classification derived from fairly simple field measurements. Our proposed classification is ecologically useful because it incorporates the combined effects of velocity, depth and substrate roughness to provide a means of quantifying the flow regimes occurring within the microhabitats of stream benthos.2. Mean motion is characterized by the Reynolds number and the Froude number. Both are easily calculated, and because they are dimensionless they provide a means of comparing flows at different sites.3. Five categories of near‐bed flows (i.e. the flow microenvironments of stream benthos) are recognized. Flow may be hydraulically smooth or hydraulically rough and the latter category is subdivided further into: chaotic flow, wake interference flow, isolated roughness flow and skimming flow. Hydraulically smooth flows occur in sections of a river bed with fine sediments (e.g. sands, muds and clays). over flat sheets of bedrock, or in association with the flat blades of submerged macrophytes. Hydraulically rough flows occur where the substrate elements are larger (e. g. pebbles, cobbles and boulders) and are a function of substrate roughness and the depth of flow relative to the height of the roughness elements. Chaotic flows and wake interference flows predominate in riffles whilst isolated roughness flows and skimming flows are more likely to be a feature of runs.4. Conventional stream sampling methods (e.g. the Surber and box or cylinder samplers) may collect across several different flow microhabitats. Our classification should enable different flow microenvironments to be recognized and so sampled more appropriately which, in turn, may reduce apparent clumping and the wide confidence intervals of benthic population estimates. Because our classification identifies ‘patches’ within the flow regime associated with the stream bed it enables stream ecologists to generate testable hypotheses regarding the distribution and abundance of benthic species in response to flow.5. Our classification identifies spatial patterns in the flow regimes associated with the stream bed. Temporal patterns have not been identified: however, predictable changes in spatial patterns will resuh from temporal changes in stream discharge.
Resistance of a cased caddis larva to accidental entry into the drift: the contribution of active and passive elements
Authors: WAR1NGER J. A. 
Published: May 2006

SUMMARY. . 1. The resistance to passive entry into the drift of first to fifth instar larvae of Allogamus auricollis (Pictet, 1834), a case‐bearing caddis‐fly, was investigated in the laboratory using an artifical stream channel.2. Dead larvae in their cases were exposed to different current speeds. When the heads of the larvae were directed towards the water flow (frontal position), the current necessary to wash larvae away ranged from 3 cm s‐l (first instars) to 21 cm s‐1 for fifth instars. When the larvae were at right angles to the current (lateral position), these speeds were 2 and 9cm s‐1, respectively. In terms of force (Newtons), this passive resistance to drift ranged from 0.3x10‐6 N (first instar, frontal position) to 307.0x10‐6 N (fifth instar, frontal position). The data obtained in the experiments were in good agreement with values calculated from hydrodynamic equations, using biometric parameters of the larvae.3. Total resistance to drift was studied by exposing living larvae to different current speeds. The speed just sufficient to wash larvae away ranged from 13 cm s‐1 in the first instar to 27.9 cm s‐1 in the fifth instar (frontal position). In terms of force, the total resistance to drift varied between 5.3x10‐6 N (first instar) and 547.5x10‐6 N (last instar).4. The difference between total and passive resistance to drift was defined as‘active resistance to drift', and is due to the effectiveness of a larva's attachment to the substrate. It ranged from 3.5x10‐6 N (first instar) to 222.8X 10‐6 N (last instar).
Parasitic regulation in a population of Boeckella hamata Brehm (Copepoda: Calanoida)
Authors: BURNS* CAROLYN W. 
Published: May 2006

SUMMARY. 1. The impact of parasitism by a fungus Aphanomyces sp. (Phycomycetes: Saprotegniaceae) on a population of Boeckella hamata in Lake Mahinerangi in New Zealand was studied over 20 months. The incidence of infection among adult female copepods exceeded 12% throughout winter (May‐October) and was highest in autumn (46%) when population birth rates were depressed by 48.8%. During most of the study, parasitism lowered the rates of population recruitment and growth by more than 10%. These effects on the B. hamata population exceeded those of Aphanomyces on Boeckella dilatata Sars in another study.2. It is hypothesized that the high incidence of parasitism by Aphanomyces and its importance at times in regulating populations of Boeckella in New Zealand lakes may be an ecological consequence of life in predator‐poor ecosystems.
Effects of small‐scale sedimentary patchiness on the distribution of tubificid and lumbriculid worms in Lake Geneva
Authors: LANG CLAUDE 
Published: May 2006

SUMMARY. 1. The sediment consists of pillow‐like formations (0.7 m wide) separated by trenches, 0.2 m wide and 0.1 m deep, over large areas of Lake Geneva (Switzerland).2. Biomass and total abundance of tubificid and lumbriculid worms were higher on the pillows than in the trenches. Potamothrix vejdovskyi, P. hammoniensis, P. heuscheri and Tubifex tubifex were more abundant on pillows whereas Peloscolex velutinus and Stylodrilus heringianus were relatively more abundant in the trenches.3. These differences between worm communities suggested that organic sedimentation was higher on the pillows. Sedimentological analyses confirmed this interpretation.4. Results of large‐scale surveys can be biased if sampling design is not adapted to such small‐scale patchiness.
Recent studies on long‐term changes in the sea
Authors: CUSHING D. H. 
Published: May 2006

SUMMARY. 1. Long‐term changes in the sea have been described in fish stock records, the Californian Cooperative Fisheries program (Calcofi) and in the Continuous Plankton Recorder Program (CPR). Links between the recruitments to fish stocks have been established with temperature and they are coherent across broad areas and in time.2. In the western North Sea between the fifties and seventies, phytoplankton and zooplankton declined by a factor of 5, to recover in the eighties. This event was linked to strong northerly winds and gales by which the time of onset of production in spring was delayed. Effects on fishes were shown in the oceanic tuna stocks, North Atlantic demersal stocks, Tasmanian lobsters and on the North Sea herring, all consequent on climatic changes.
Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams
Authors: COLLIER K. J. , WINTERBOURN M. J. 
Published: May 2006

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies (Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.2. Mean densities of larvae (range 234–2318 m−2) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m−2) was always highest at the stable, spring‐fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.3. Annual production was high at the more stable, alkaline site (10.35 gLDW m−2) but much lower at the other sites (2.49–3.77 g m−2).4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.
Interspecific differences in movement and hunting success in damselfly larvae (Zygoptera: Insecta): responses to prey availability and predation threat
Authors: JEFFRIES MICHAEL 
Published: May 2006

SUMMARY. 1. Freshwater invertebrate predators can alter their hunting behaviour in response to prey availability and threat from their own enemies. Movement patterns and hunting success of the larvae of two species of damselfly (Zygoptera: Insecta), Enallagma cyathigerum (L.) and L. sponsa (Hansemann), were monitored in four combinations of prey availability and enemy threat. Aeshna juncea (L.) (Anisoptera: Insecta) larvae acted as predator and Daphnia magna Straus (Cladocera: Crustacea) as prey in the combinations: no predator/no prey; one Aeshna present/no prey; no predator/thirty Daphnia present; one Aeshna present/ thirty Daphnia present.2. E. cyathigerum showed significantly reduced movement in the +Aeshna/no prey treatment but hunting success was not significantly affected. No other treatment effects were noted. L. sponsa movement patterns differed significantly across all four treatments and hunting success was significantly reduced in the presence of Aeshna.Interspecifically, movement patterns of the two species differed markedly in all four treatments. L. sponsa larvae were much more active, and caught many more prey. Despite their activity L. sponsa larvae did not appear markedly more vulnerable than the immobile E. cyathigerum.3. The interspecific differences between the two damselflies reflect predictions based on larval life‐history. Activity patterns and ability to capture adequate prey under varying levels of predation may be important in the ecology of damselfly species.
Short‐term productivity responses of algae and bacteria to zooplankton grazing in two freshwater lakes
Authors: SCHOENBERG STEVEN A. 
Published: May 2006

SUMMARY. 1. The specific productivities of algae and bacteria were measured in short‐term (4 day) experiments consisting of enclosures with natural or reduced zooplankton biomass. Experiments were repeated five times over a season in each of two lakes that differed in the background concentration of dissolved organic carbon (DOC).2. Algal biomass as estimated by chlorophyll a was suppressed in enclosures with ambient grazer levels in six of ten experiments and enhanced in one experiment. Distribution of chlorophyll among net and nanoplankton was not significantly affected by grazing.3. Relative to enclosures with reduced zooplankton, normal grazer biomass (97–466μg 1−1 dry weight) enhanced specific algal productivity in only one of five experiments in the low DOC take and had no effect in all five experiments in the high DOC lake. The main effects of grazers on algae was through removal of biomass rather than through indirect changes in turnover rate.4. Between experiments, bacterial density was either unaffected, or mildly enhanced (4–87%) in enclosures with ambient macrozooplankton compared to those with reduced levels. Bacterial productivity and turnover estimated by incorporation of [3H]thymidine into DNA showed different responses across experiments; increasing, declining or remaining the same with grazer minipulation. This variability was not related to differences in dissolved primary production or to background DOC between lakes or experiments. Comparison of bacterial productivities based on thymidine incorporation rates with changes in cell densities indicated that control of bacterial loss processes by macrozooplankton is more important than control of growth rates.
Simplified methods of estimating daily mean stream water temperature
Authors: CRISP D. T. 
Published: May 2006

SUMMARY. 1. It was assumed that the average of twenty‐four hourly temperature readings is the‘true’daily mean. For a small stream in upper Tees‐dale, northern England, estimates of the daily mean were obtained from: (a) The mean of temperature readings taken at regular but less frequent intervals than hourly (twelve, six and three times per day), (b) The daily mid‐point (=1/2(maximum + minimum)). (c)Spot temperatures at the two times in the day when the daily temperature trace usually crosses the daily mean value. These estimates were then compared with the‘true’mean.2. The accuracy of the estimate of daily mean decreased with reduced frequency of reading but, even at only three readings per day, was always within ±0.5°C of the true value. Consolidation of the daily estimates gave estimates of monthly and annual means within ±0.1°C of the true values.3. Nearly 96% of estimates of the daily mean based on the daily midpoint were within ±0.5°C of the true value. The estimates showed a small but statistically significant positive bias.4. Over 80% of estimates of the daily mean based on the‘first mean crossing’were within ±0.5°C of the true value and no bias could be shown.5. Estimation of daily means from temperature at the time of the 'second mean crossing’was relatively complicated and gave less satisfactory results than did the first mean crossing.6. The daily mid‐point and the temperature at the time of the first mean crossing both gave a good general indication of daily mean temperatures. When consolidated to monthly or annual means the estimates were within ±0.25°C and ±0.10°C, respectively, of the true values.
Population growth rates of two closely related rotifer species: effects of food quantity, particle size, and nutritional quality
Authors: ROTHHAUPT KARL O. 
Published: May 2006

SUMMARY. 1. The relationship between population growth rates and the concentrations of several algal species was determined in laboratory experiments with the rotifers Brachionus rubens and B. calyciflorus.2. The effects of food quantity were well described by a modified Monod model with a threshold for zero population growth. The model parameters depended on particle size and nutritional quality of the food algae. Differences between the rotifer species were significant and reflected their varying food‐size preferences.3. For each rotifer species, thresholds were lowest for algae in the most readily ingested size range. The lowest thresholds were 0.07–0.09 mgC 1−1 with algae of about 5 μm equivalent spherical diameter (ESD) for B. rubens, and 0.19 mgC 1−1 with algae of about 10 μm ESD for B. calyciflorus.4. Maximal growth rates (rmax) were slightly below 0.8 day−1 for both rotifers with most algal species. The highest rmax values for both rotifers were observed when Cyclotella meneghiniana was provided as food. With this alga, B. calyciflorus had a significantly higher rmax (1.02 day−1) than B. rubens (0.838 day−1).5. From a comparison of the relationship between growth rates and ingestion rates, Chlamydomonas reinhardii appeared to be of low nutritional quality for B. rubens.6. Egg ratios were related to growth rate and were not influenced by the algal food used. Egg development times and average mortality rates were estimated from the relationship between egg ratio and growth rate. B. calyciflorus appeared to have a high average mortality rate (0.383 day−1) compared to B. rubens (0.083 day−1).
The impact of the crayfish Orconectes virilis on aquatic macrophytes
Authors: CHAMBERS PATRICIA A. , HANSON JOHN MARK , BURKE JANICE M. , PREPAS ELLIE E. 
Published: May 2006

SUMMARY. 1. The impact of crayfish on the biomass, density and shoot morphology of four submersed plant species was examined under semi‐natural conditions. Male or female crayfish (Orconectes virilis) were held for 5 weeks at biomasses of 0, 5, 10 or 18 g m−2 (live weight) in twelve plastic pools (4.67 m2, surface area) containing Potamogeton richardsonii, Myriophyllum exalbescens, Nuphar variegatum and Sparganium eurycarpum.2. Crayfish significantly affected biomass, density and/or shoot morphology of all four macrophyte species. Differences in the effect of crayfish on macrophyte growth were related to plant species, crayfish sex and activity, and the abundance of alternative foods.3. The effect of female crayfish on macrophyte growth was generally stimulatory. Myriophyllum and Potamogeton biomass, Potamogeton density and Myriophyllum length increased in the presence of female crayfish, possibly due to the reduction in herbivorous snails as a result of crayfish predation. In contrast, plant growth decreased in the presence of male crayfish: Myriophyllum, Nuphar and Potamogeton biomass, Myriophyllum and Sparganium density, and Sparganium and Poiamogeton length were reduced at male crayfish biomasses between 5 and 18 g m−2.4. These results indicate that even relatively low densities of crayfish can greatly affect the growth of submersed aquatic plants. Because of their ability to modify aquatic macrophyte, macroinvertebrate and, ultimately, fish communities, the introduction of crayfish into lakes where they do not occur could have a major effect on the structure and composition of the littoral zone.
The realized food niches of three species of stream‐dwelling triclads (Turbellaria)
Authors: ARMITAGE M. J. , YOUNG J. O. 
Published: May 2006

SUMMARY. 1. The diet of Phagocata vitta, Crenobia alpina and Polycelis felina in a Welsh stream was examined, using a serologicat technique, at monthly intervals over 18 months.2. For each triclad species, dietary composition changed little with time or increasing body size, and overall feeding intensity was greatest in summer and least in winter.3. Alt species fed most heavily on oligochaetes, chironomids and Gammarus. Phagocata vitta fed lightly on Plecoptera, Trichoptera and Ephemeroptera whilst the other two triclad species fed substantially on the first two of these prey categories.4. Food niche breadth indices indicated a wide diet for all species with some specialization in some months. Electivity indices showed positive electivity for oligochaetes and chironomids by all species and for Plecoptera by C. alpina and P. felina.5. Diets overlapped and none had a food refuge: therefore the potential for interspecific competition for food exists.
The ecology of two intermittent streams in Victoria, Australia. I. Multivariate analyses of physicochemical features
Authors: BOULTON A. J. , LAKE P. S. 
Published: May 2006

SUMMARY. 1. Amplitudes in physicochemical features in intermittent streams exceed those in nearby permanent streams and strongly influence macroinvertebrate community structure. Hitherto, seasonal variation in the physicochemistry of intermittent streams has been described only anecdotally; there has been no objective attempt to describe phases of flow that could subsequently be compared with patterns in biotic composition.2. Multivariate techniques of ordination and classification were applied to environmental data collected from pools and riffles at four sites on two intermittent streams in central Victoria during a drought year followed by a wetter year. A cyclical sequence of How phases was usually evident in poo and riffle habitats at all sites over both years: pre‐flow, early flow, main flow, diminishing flow and post‐flow. Several spates that occurred during the sampling period only briefly distorted the cyclical pattern.3. No single variable characterized these phases at each site; instead, the phases represented complex combinations of discharge, current velocity, dissolved oxygen, conductivity, water temperature and time‐related variables. This highlights the advantages of an integrative, multivariate approach to seek patterns in environmental data, especially since physicochemical features are often highly inter‐correlated.
Modelling black fly production dynamics in blackwater streams
Authors: BENKE ARTHUR C. , PARSONS KEITH A. 
Published: May 2006

SUMMARY. 1. Two predictive models were employed along with intensive field sampling to estimate production of black flies (Simulium spp.) on snags (submerged wood) in three blackwater streams on the Georgia Coastal Plain of the southeastern U.S.A. One model predicts daily growth rate from temperature and hydrograph pattern; the other predicts habitat abundance (of snags) from river height.2. In the sixth order Ogeechee River, annual production was twice as high in 1982 (7.1 g dry mass [=DM] m−2 of snag surface) as in 1983 (3.6 g DM m−2). When converted to production per m2 of river bottom, values were 35–40% of the snag surface estimates. Annual production was much lower in fourth order Black Creek (1982, 1.3 g DM m−2 of snag surface) and much higher in the sixth order Satilla River (1975, 15.6–40.0 g DM m−2).3. There was a distinct bimodal pattern of black fly production in the Ogeechee River in both years, with peaks occurring in winter and summer. Similar bimodal patterns of production were found in Black Creek and in the Satilla River. Although there appears to be an intrinsic component to the bimodal pattern, production peaks (growth rate and biomass) appear to be associated with initial stages of flooding.4. Annual production/biomass ratios (37–85) are the highest reported for black fly populations. The variation of annual P/B ratios among sites was more strongly dependent on the temporal distribution of standing stock biomass than on differences in growth rates. Variation in production among sites appears to be due to differences in current velocity, hydro‐graph variability, and abundance of coexisting consumers.