摘要:

1. The influence of coarse substratum and flow, coarse substratum and food, and predation risk and flow on habitat use byGammarus pulexwas studied in three experiments conducted in artificial stream channels. Each stream channel consisted of a riffle and pool habitat.2. Location of coarse substrata and food was manipulated by placing cobbles (coarse substratum) and leaf packs (food) in different habitats. Predation risk was varied by running experiments in the presence and absence of sculpins (Cottus gobio), and flow was varied by pumping water with one or two pumps.3. In all experimentsGammaruswere most abundant in pools but placement of cobbles in riffles increased use of the latter. An even greater percentage ofGammarusused riffles if leaf packs were also placed there. Decreased discharge and the presence of sculpins (Cottus gobio) also causedGammarusto increase use of riffles. These data indicate thatGammarusis able to evaluate differences in habitat quality and respond accordingly.

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00096.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Temperature dependence of embryogenesis of the three perlid stonefliesDinocras cephalots,Perla grandisandP. marginatawas investigated by means of incubation experiments. Special emphasis was laid on the effect of fluctuating temperatures and on intraspecific differences between populations from two different field sites in the Swiss prealps (i.e. River Necker and River Thur).2.Dinocras cephalotesembryos develop between 6.3 and 26.6 °C. The lower threshold temperature is lower than has been reported for more northern populations (i.e. from England and Norway), indicating the existence of a latitudinal gradient.Perla grandiseggs only developed between 9.9 and 18.4 °C. InP. marginata, successful embryogenesis was observed between 9.9 and 18.4 °C, but not enough eggs were available to explore the threshold temperatures.3. Embryogenesis ofD. cephalotesandP. grandiswas significantly faster at a 12/16 °C daily fluctuating temperature regime than at a constant 14 °C. However, no significant difference was found between the development under simulated field temperature regimes (with less distinct daily amplitudes) and constant temperatures.4.D. cephalotes, hatching of eggs from the Necker population was much less synchronous than that in the Thur population. Since the Necker discharge regime is harsher than the Thur regime, it is possible that this asynchrony spreads the risk of destruction during bed‐moving

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00100.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Habitat partitioning has been extensively studied in terrestrial plant communities. By comparison, few studies have examined habitat partitioning in riverine macrophyte communities. Riverine environments are often highly heterogeneous with respect to current speed, depth, bottom sediment fertility and other biologically important properties. Thus, the potential for habitat partitioning in riverine macrophyte communities is great.2. The objective of this study was to investigate how, or if, macrophyte species are differentially distributed with respect to abiotic gradients in a large river in central British Columbia, Canada.3. A survey of macrophyte biomass and associated measures of current speed, depth and sediment texture showed that coexistence occurred both with and without habitat partitioning.4. Coexistence in the absence of habitat partitioning was depicted byPotamogeton gramineus,Potamogeton berchtoldii,Myriophyllum exalbescens,Callitriche hermaphroditicaandPotamogeton pectinatussuch that they had a minimum and average niche overlap (NO) of 65% and 84%, respectively, for all measured abiotic variables. Similarly, the spatial niche ofE. canadensiswas close to that ofCeratophyllum demersumandM. exalbescens.5. While several taxa seemed to occupy the same spatial niche, some taxa were distinguished from one another in terms of the types of microhabitats they utilized. Mosses, for example, were often the only occupants of sites having current speeds greater than 0.6 m s–1and substrates of bare rock.Ranunculus aquatiliswas most abundant at sites having current speeds between 0.4 and 0.6 m s–1whereas most other taxa were restricted to slower waters. Habitat partitioning across depth contours, which occurred between several taxa, was most evident betweenP. pectinatusandC. demersum(NO = 17%),C. hermaphroditicaandC. demersum(NO = 3%),C. demersumandP. richardsonii(NO = 19%) andC. hermaphroditicaandE. canadensis(NO = 2

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00105.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. We have studied the numerical and functional responses of campanulate morphs ofAsplanchna intermediafed five species of rotifer (Brachionus rubens,B. patulus,B. calyciflorus,Hexarthra miraandFilinia longiseta). The vulnerability of the prey varied with their morphology and mode of swimming.2. To test the numerical and functional responses, prey species differing in their morphology and mode of swimming were provided. Responses were also tested with mixtures of evasive and non‐evasive prey provided in three different ratios.3.A. intermediashowed a type II functional response to all the prey species provided.4. The population growth rate ofA. intermediaon the various prey species provided ranged from a minimum of –0.24 to a maximum of 0.68. There was a significant correlation between the capturability of a prey species and the population growth rate of the predator feeding on it. The capturability of a prey species also has a significant influence on the maximal predator density but not on the time taken to reach it.5. Observations from a field study undertaken over a 10‐month period to study the prey preferences ofA. intermediain nature were corroborated by the laboratory fin

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.d01-510.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Field experiments were undertaken in a small Danish lowland stream to study the role of invertebrate grazing, phosphorus concentration and irradiance in the regulation of benthic algal biomass on stones.2. Algal biomass was regulated by invertebrate grazing. The gastropodAncylus fluviatilisprevented algal biomass build up in early spring at a density of about 900 ind. m–2, and reduced algal biomass to very low levels during the algal growth period at a density of about 6000 ind. m–2. Grazing pressure therefore might regulate the magnitude of peak algal biomass in Gelbæk stream, a finding in agreement with earlier field observations.3. As phosphorus enrichment to around 152 μg l–1during the period when irradiance was not limiting did not result in any further increase in algal biomass, it can be concluded that algal growth in spring was not controlled by phosphorus limitation.4. Algal biomass development differed significantly in a shaded and in a non‐shaded reach of the stream. Only very low algal biomass accumulation was evident in the shaded reach, while in the non‐shaded reach an algal biomass peak of about 800 mg chlorophyll m–2was evident after 6 weeks of colonization. The shaded reach represented the light condition in Gelbæk stream after leaf proliferation of the overhead canopy and high bank vegetation. The findings therefore suggest that irradiance available to the algal community after shading from riparian vegetation prevents further algal biomass increase and hence determines the timing of peak algal biomass in the stream.5. The irradiance experiment also suggests that if not regulated by invertebrate grazing or shading by an overhead canopy in the summer, then the magnitude of peak biomass in Gelbæk stream will be regulated by self‐shading in the algal community.6. These field experiments support theories, derived from laboratory experiments and field studies, that regulation of algal biomass is a complex interaction of top‐down and b

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00111.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The chief objective was to develop a functional model for growth of stone loach,Barbatula barbatula, using immature fish from three populations. The growth model had been developed previously for brown trout,Salmo trutta, but new estimates of the five parameters for the stone loach had to be obtained from laboratory experiments.2. Fish from four size groups (initial arithmetic mean live weights 0.053 g, 0.231 g, 0.840 g, 1.612 g, with five fish per group) from Great Oaks Wood Beck were acclimatized to constant temperatures of either 3, 5, 10, 15, 20 or 25 °C. Each fish was kept in a separate tank and fed to satiation on freshwater shrimps. Weights and lengths of each fish were recorded at the start and finish of a growth period of 35 days. For each of the other populations (Black and Ford Wood Becks), there were only three temperatures(5, 10, 20 °C) with ten fish per temperature.3. The growth model was an excellent fit (P0.99) for the 120 fish from Great Oaks Wood Beck. Growth rates were negative at 3 °C, close to zero at 5 and 25 °C, and positive at 10, 15 and 20 °C, with an optimum value of 19 °C. When growth rates were positive, they decreased markedly with increasing fish weight for small fish but decreased more slowly for larger fish. At the start of the experiments, weight–length relationships were similar for fish from all three populations and were well described by a power function. There was excellent agreement between growth rates estimated from the fitted growth model for fish from Great Oaks Wood Beck and values obtained for fish from Black and Ford Wood Becks. Data from all three populations were therefore pooled (n= 180) to obtain new estimates of the five parameters in the model.4. Comparisons between parameter estimates for trout and stone loach showed that the latter grew better in warmer waters (e.g. optimum value for growth was 19.0 °C for stone loach and 13.1 °C for trout, with ranges for growth of 5.0–25.0 °C and 3.6–19.5 °C

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00110.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The denitrifying capacity of epiphyton was used to evaluate differences in the function of epiphytic microbial communities on submersed macrophytes in nutrient‐rich freshwater ecosystems. The denitrifying capacity of epiphyton onPotamogeton perfoliatusshoots of different age and with different epiphytic abundances from a eutrophic lake was investigated in laboratory microcosms in the light and dark. Additionally, differences between epiphyton on shoots ofPotamogeton pectinatusgrown under differentin situnutrient and hydraulic conditions were investigated by examining their denitrifying capacity.2. Denitrification was registered in well‐developed epiphytic layers on both mature and senescent shoots in the dark, with activities 3‐ to 10‐fold higher in the epiphytic communities of senescent shoots. No activity was detected on young shoots with sparse epiphyton or on shoots from which loosely attached epiphyton had been removed. Denitrification never occurred during illumination.3. Even though the epiphytic abundance was similar in magnitude, the denitrifying capacity of epiphyton adapted to high nutrient loadings was about a hundred times higher than that of epiphyton adapted to lower nutrient levels. Additionally, epiphytic abundance and denitrifying capacity were higher at sites less exposed to wave turbulence or water currents, than at sites with more water turbulence.4. The results illustrate how the hydraulic and nutrient conditions of the surrounding water affect both the quantity and function of epiphytic microbial communities in nutrient‐rich freshwater e

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00120.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The feeding frequency, the size of meals, the number of meals required to attain reproductive maturity and the number of meals taken between iteroparous reproductive bouts were determined in the laboratory under optimal conditions for the medicinal leechHirudo medicinalisfed exclusively on mammalian (bovine) blood. In addition the number of bouts of reproduction and the numbers of cocoons and hatchlings per cocoon produced were determined.2. The average time forH. medicinalisto reach reproductive maturity at 20°C was 289 days, at an average wet biomass of 8143 mg with two–nine separate bouts of cocoon production. The number of meals to first reproduction was 8.9 (mean meal size of 3066.7 mg), with a significant correlation between total mass of blood ingested and the numbers of reproductive bouts and number of cocoons produced. Mean lifetime cocoon production per individual was 12.43, with 3.9 hatchlings per cocoon.3. The significant positive relationships between ingestion, fecundity and developmental rate observed support the hypothesis that declining abundances of field populations ofH. medicinalisare the result of lower available energy for growth, reflecting leeches now feeding predominantly on amphibian blood of lower energetic value than mammalian blo

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00121.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. We conducted experiments in a Colorado Rocky Mountain stream to measure the effect of foraging by predatory stoneflies (Megarcys signata) on fine sediment deposition and removal.2. Cages containing one of four treatments were placed in the stream substratum and removed 3 days after fine sediment load to the stream was experimentally increased. Cages containing a stonefly but no prey accumulated less sediment than cages initially with no benthic invertebrates. Although cages withMegarcysplus prey also tended to have less sediment than controls, sediments were not reduced in cages with prey only.3. Distance from sediment source, depth and current velocity at cages, final prey density and numbers of prey per predator gut at the end of the experiment had no effects on sediment accumulation in cages.4. To determine the mechanisms underlying this effect, behavioural tests were conducted in a stream‐side artificial stream system. To simulate the different hunger levels of stoneflies in cages,Megarcyswere fed or starved for 3 days before behavioural trials that were repeated during high (night) and low (day) stonefly feeding periods. During night trials, foraging movements by starvedMegarcyswere more prolonged and active than those of fed stoneflies, regardless of the presence of prey. However, neither hunger level nor prey presence affected stonefly foraging behaviour during day trials.5. Results of field experiments suggest that the presence of stoneflies enhances sediment removal from interstitial spaces. Behavioural observations indicate that nocturnal searching for prey by hungryMegarcysdislodges fine sediments from interstitial spaces.6. Future studies should explore beyond the direct impacts of predators on stream invertebrate communities, and investigate the potential impact of predators on benthic microhabitat qualit

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00132.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Over a 1‐year period, twenty controlled experiments were performed using small mesocosms (20‐l clear plastic carboys) and plankton communities collected from four sites in shallow, subtropical Lake Okeechobee, Florida. In replicated treatments, macrozooplankton grazers were excluded by size fractionation (115 μm), and/or nutrients (N and P) were added, and impacts on phytoplankton biomass and productivity were measured after 3‐day incubations.2. In most experiments (fifteen out of twenty), there was no significant effect of zooplankton exclusion on phytoplankton biomass or productivity, but there were significant increases in those attributes due to nutrient additions. The magnitude of the responses was a function of light availability at the collection sites.3. In three experiments, zooplankton exclusion led to declines in phytoplankton biomass and productivity, suggesting that animals may sometimes have net positive effects on the phytoplankton, perhaps via nutrient recycling.4. In only two experiments was there evidence of net negative impacts of grazers on the phytoplankton. In both instances, cladocerans (Daphnia ambiguaandEubosmina tubicen) were dominant in the zooplankton. However, the increases in chlorophylladue to zooplankton exclusion were small (5–20%), probably because of the small size and relatively low grazing rates of the cladocerans.5. The results support the hypothesis that phytoplankton biomass in Lake Okeechobee is little affected by herbivorous macrozooplankton. This may be a common feature of lowland tropical and subtropic

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00122.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY