摘要:

SUMMARY.1. Body growth, reproduction and survivorship ofBosmina longirostriswere monitored at four food concentrations (0.05, 0.10, 0,25 and 2.50 ing Cl−1) to examine the extent to which food concentration affects these life‐history parameters.2. Food concentration had a significant effect on growth, and most of the reproductive parameters (size and age at maturation, brood size, instar duration and egg development time). More than 60% of animals died before maturation at the lowest food concentration, although most animals survived until maturation at other food concentrations.3. Change in life‐history parameters resulted in a decrease in rate of population growth (r) from 0.310 to 0.020 day−1with decreasing food concentration, showing that this cladoceran is highly food‐limited in many lakes.4. Importance of the effect of food concentration on egg development time was emphasized in relation to analysis of natural po

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00467.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Food web manipulation, by removal of planktivorous or benthivorous fish, is a promising method for reducing phytoplankton concentrations in shallow lakes. The part that nutrients may play in the success of such a measure is not well documented.2. In this study, we analysed the flow of phosphorus through the food web of the shallow, eutrophic Lake Wolderwijd/Nuldernauw. Our studies occurred in the years 1981 (when a bloom of cyanobacteria occurred) and 1987 (no bloom); a hypothetical situation was also examined in which most of the bream are assumed to be removed.3. The analysis shows that the success of biomanipulation is probably due not only to an increased grazing pressure on the phytoplankton, but also to a decreased availability of phosphorus. The reason for this is the removal of detrital phosphorus by increased sedimentation as a result of a predicted increase in growth of macrophytes after biomanipulation.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00468.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. A flow tank was constructed which generates homogeneous and stable flow of water up lo velocities of 1.2 m s−1.2 A sensitive, two‐component balance with its platform inserted in the bottom of the flume allowed the measurement of drag and lift forces in the mN range.3 The drag forces experienced by several benthic arthropods, which cling to the roughened surface of the platform, are proportional to the square of the flow velocity.4 Large biological variations in lift forces, leading even to negative lifts in some cases, are indications of special adaptations of the animals to counter the danger of being swept away from their supp

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00469.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Weight‐specific respiration and feeding rates ofGammarus pseudolimnaeuswere inversely related to body weight at 12°C, the temperature of the stream from which they were collected.2. At this temperature animals could digest about a third of ingested, purified14C‐cellulose. In animals greater than 20 mg live weight, about 38% of ingested cellulose was metabolized; animals smaller than 20 mg metabolized about 28%.3. Respired CO2from cellulose metabolism was 33–47% of measured uptake of C2in animals greater than 20 mg live weight and approximately 25% in smaller animals.4. Ability to digest cellulose would be of nutritional benefit toGammarusfeeding on any plant material, but would be of particular advantage in the spring/summer period when fine detritus is the main foo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00470.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Five populations of the cladoceranSimocephalus vetulus(O. F. Muller) examined by enzyme electrophoresis at four to five loci revealed high levels of genetic variation.2. The one intermittent population had genotype frequencies in Hardy Weinberg equilibrium, the three permanent populations showed deviations from equilibrium of varying magnitude. The fifth population was fixed for a single clone, and was possibly recently derived from a single ephippial hatchling.3. Laboratory breeding experiments confirmed that this species is a cyclic parthenogen.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00471.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Tadpoles ofAcris crepitanswere collected from two ponds in central Illinois, Depth, water temperature, distance from shore and water samples were taken at each sample site. The potential for food limitation and non‐random habitat selection were examined.2. Algal densities from water samples averaged over 1.0× 106cells ml−1in Scott's pond hut only 4.6×103cells ml−1in Vic's pond.3. Guts of tadpoles from Scott's pond contained more algal cells than did guts of tadpoles from Vic's pond. Tadpoles from Scott's pond were consistently larger and more advanced in development than tadpoles collected from Vic's pond at the same lime. Therefore, tadpoles of Scott's pond were able to utilize the higher algal densities whereas tadpoles of Vic's pond may be food‐limited, causing reduced growth and development.4. Canonical discriminant analysis was used to test whether sites with different numbers of tadpoles could be distinguished based on environmental variables. Canonical function I was primarily a measure of water depth at a sample site. This function was significant in Scott's pond only. Sites containing one or more tadpoles were not easily distinguished from each other, but were found in consistently shallower water than sites where no tadpoles w

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00472.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The chief objective was to construct a thermal tolerance polygon for juvenile Atlantic salmon,Salmo salarL., using fish from four groups and two populations: two age groups from one population (0+, 1+ parr from River Leven), two size groups from the other population (slow and Fast growing 1+ parr from River Lune).2. Fish were acclimated to constant temperatures of 5, 10, 15, 20, 25 and 27°C; then the temperature was raised or lowered at 1°C h−1to determine the upper and lower limits for feeding and survival over 10 min, 100 min, 1000 min and 7 days. As they were not significantly different between the four groups of fish, values at each acclimation temperature were pooled to provide arithmetic means (with SE) for the thermal tolerance polygon.3. Incipient lethal levels (survival over 7 days) defined a tolerance zone within which salmon lived for a considerable time; upper mean incipient values increased with increasing acclimation temperature to reach a maximum of 27.8±0.2°C, lower mean incipient values were below 0°C and were therefore undetermined at acclimation temperatures<20°C but increased at higher acclimation temperatures to 2.2±0.4°C. Resistance to thermal stress outside the tolerance zone was a function of time; the ultimate lethal level (survival for 10 min) increased with acclimation temperature to a maximum of 33°C whilst the minimum value remained close to 0°C. Temperature limits for feeding increased slightly with acclimation temperature to upper and lower mean values of 22.5±0.3°C and 7.0±0.3°C.4. In spite of different methodologies, values in the present investigation are similar to those obtained in previous, less comprehensive studies in the laboratory. They also agree with field observations on the temperature limits for feeding and survival. Thermal tolerance polygons are now available for eight species of salmonids and show that the highest temperature limits for feeding and survival are those recorded for juvenile

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00473.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. In regional studies of surface‐water acidification, annual means of chemical variables are often used to describe differences and change. Outputs from hydrochemical models are often in the form of mean values, which are used in biological models, and these, in turn, are usually derived from responses to mean conditions. Thus, biological forecasts are constrained to ignore the possible effects of the short‐term variations in water chemistry which characterize acid streams. This approach requires appraisal.2. Here, regional Welsh data and daily records from a smaller number of streams were used to investigate the estimation of pH parameters. Variations in aluminium concentration in relation to pH were also assessed. Empirical relationships between invertebrate assemblages, fish populations, mean stream chemistry and measures of fluctuation in pH and aluminium concentration were explored.3. In general, pH or Al variability and mean pH or Al in Welsh streams were closely related, so that the biological influences of episodes could not easily be separated from those of chronic conditions. Mean pH and mean aluminium concentration were the most effective pH and aluminium statistics used in multivariate models of trout density, which were not improved by including other pH or aluminium variables. For models of invertebrate assemblages based on mean pH or mean aluminium, the inclusion of variables related to episodicity (e.g. pH minimum, aluminium maximum) gave moderate increases in precision.4. This analysis indicates that it is reasonable to use means of stream chemical variables in biological models of acidification. Consideration of chemical variability could give improvements in some cases, but at the expense of increased model complexity and effort in parameter selection. Nevertheless, we emphasize the need for accurate calibration of both biological and hydrochemical mod

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00474.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. We investigate the importance of a refuge from fish predation to the abundance, species composition and seasonal succession of zooplankton. Thirty lakes representing a range of depths were sampled twice in summer for physical/chemical parameters and zooplankton community structure.2. We define the refuge from centrarchid predators to be that space between the thermocline and the zone of anoxia. As lakes vary in rate of oxygen depletion from the hypolimnion. the refuge size and lake depth are independent: refuge size decreases during the summer period.3. Lake depth and refuge size independently explain variation among lakes in zooplankton species composition, but seasonal community change within lakes is best predicted by loss of refuge size.4. Refuge size also explains the substantial variation in the relative dominance of the two major daphnid species. Lakes possessing a large refuge are dominated byD. pulicaria; those with a small refuge are dominated by the smaller,D. galeata mendotae. We suggest that lakes of intermediate refuge size, which are characterized by high species diversity, represent a more equitable balance of predation and competition.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00475.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. A taxonomic analysis of 171 phytoplankton samples obtained from Crater Luke, Oregon, between 1985 and 1987 revealed 132 taxa in the upper 250 m of the water column. The greatest temporal variation in taxonomic structure occurred between 40 and 80 m below the water surface, a depth range which corresponded to the zone of maximum primary production.2. Phytoplankton cell biovolume in the upper 20 m of the water column was relatively high during the summer months, a period whenNitzschia graciliswas dominant in the epilimnion. However, 72% or more of the cell biovolume between 0 and 200 m was distributed below 20 m and, during the winter and spring months, 61% was found below 80 m.3. Cluster analysis identified a sparse, temporally ubiquitous flora which was modified to various degrees when environmental conditions became favourable for the growth of a few dominant taxa. These surges ot dominance by individual taxa accounted for 2 to 5‐fold increases in cell biovolume and generated a pronounced taxonomic discontinuity between the floras in the epilimnion and hypolimnion.4. While the taxonomic structure of the phytoplankton in the epilimnion corresponded closely with the structure found in a 1978–80 study, the flora below the metalimnion was more diverse and less predictable in species composition than the pattern reported in the earlier st

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00476.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY