摘要:

SUMMARY.Factors affecting invertebrate colonization of samplers consisting of twenty‐five 5‐cm diameter porcelain balls were studied in small northern California streams. Peaks in diversity, in number of individuals and in taxa, occurred after 2—4 weeks in each of four 10‐week colonization runs. Most variation in number of organisms was correlated with increases in organic detritus. Time was the second most important variable.The average coefficient of variation in total numbers collected from the artificial sampler was 0.40, slightly less than the average 0.56 for the Surber sampler. Published coefficients of variation for artificial substrates range from 0.109 to 0.849, which are similar to values reported from work with the Surber sampler. We had several practical difficulties with the artificial substrates. Samplers were lost, became clogged or buried, supported vertebrate predators and were costly. The samplers also collected some organisms in greater proportion than their occurrences in the natural substrate. In sampling small streams these disadvantages (compared to a Surber sampler) outweigh the slight reduction in sampling vari

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01420.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Llyn Padarn and Llyn Peris have distinct phytoplankton populations. During 1975–76, the standing crop measured as chlorophyll‐awas 5.5 times greater in Padarn than in Peris and the production rate, determined by the14CO2method, was faster by 3.4 times. These differences were attributed to the higher concentrations of phosphorus in the lower lake caused by treated sewage effluent. Incident light intensity, which was slightly lower in Peris due to mountain shading, and temperature, which was 1–4°C higher in Padarn, made little significant contribution to these differences during the summer. The reduced transparency of Padarn water, compared with that of Peris, resulted from denser phytopiankton crops in Padarn. During the summer, Padarn exhibited carbon dioxide depletion which correlated with the chlorophyll concentration. Light inhibition at the surfaces of both lakes correlated with solar radiation intensity. However, the relationship between pigment content and maximum photosynthetic rate was poor. Extracellular products accounted for about 16% of the total production in the lakes. Uptake of14C‐labelled acetate was low compared with that of14C

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01421.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Oligochaete worms dominate the macroinvertebrate fauna of the River Irwell, in north west England. The river is polluted by domestic and industrial wastes. Tubificids constituted 86.8% of the worm fauna, with three dominant species;Tubifex tubifex(Müller), representing 43.1% of the total oligochaetes,Limnodrilus hoffmeisteriClaparède, representing 26.8% andLimnodrilus udekcmianusClaparède, representing 16.7%. The Naididae were the next most abundant worms, representing 6.1% of the oligochaete fauna, withNais elinguisMüller comprising 5.0%.T. tubifex and L. hoffmeisteriwere abundant along the length of the river, but reached their greatest numbers in the organically polluted lower reaches at Agecroft and Salford. The density ofL. udekemianuswas low in the Irwell above the entry point of the heavily polluted River Roch, but high below this point.N. elinguiswas abundant above the Roch entry point and scarce below it.In the three dominant tubificids, the main population recruitment occurred during the summer months (April to September forT. tubifex, May to November forL. hoffmeisteriand June to October forL. udekemianus). InN. elinguis, there was massive recruitment in Ap

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01422.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Phytoplankton standing crop, primary production, light penetration, temperature, and various chemical concentrations were measured in a man‐made, deep‐discharge, reservoir and in a natural, surface‐discharge, lake in order to relate limnological conditions in the two bodies of water to their depth of outflow. The quantity and depth distribution of heat stored during the summer varied markedly. The reservoir functioned as a heat trap, whereas heat was readily dissipated from the lake. Salinity increased more in the lower layer of the lake. Throughout the summer, nutrient‐rich water was discharged from the reservoir whereas nutrient‐poor water was discharged from the lake. Phytoplankton standing crops were greater in the lake and were dominated by flagellates and diatoms. In the reservoir, blue‐green algae were predominant. Rates of primary production and respiration were higher in the lake, but estimated algal turnover times were faster in the reservoir. It was concluded that depth of outflow has a direct and predictable effect on certain physical and chemical conditions within these two bodies of water; but effects of discharge depth on phytoplankton were secondary and thus difficult t

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01423.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Campanulate females ofA. sieboldi(clone 12C1) attackAsplanchna brightwelliandA. girodimuch more readily than either the algaVolvox aureusor the rotiferBrachionus calyciflorus. Pre‐feeding campanulates onB. calyciflorusprior to testing does not appreciably affect their response to this prey. Discrimination during feeding occurs immediately after the campanulate's corona contacts a potential food organism and is probably mediated by chemoreceptors. Once a food organism is attacked, the probabilities of it being captured and subsequently swallowed are high and similar for each of the four organisms tested.Since food organisms other thanAsplanchna. such asV. aureusandB. calyciflorus, induce campanulates in this clone to produce cruciform, and thus frequently sexual, females in succeeding generations, a tendency of these campanulates to select congeneric prey would favour the maintenance of the campanulate morphotype and thus the continuation of parthenogenetic reproduction in the ensuing populatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01424.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Eggs ofEphemerella ignita(Poda) were kept at eight constant temperatures (range 5.9–19.8°C) in the laboratory. Over 85% of the eggs hatched in the temperature range 10.0–14.2°C but the percentage decreased markedly to 39% at 5.9°C and 42% at 19.8°C. Hatching time (days after oviposition) decreased with increasing water temperature over the range 5.9–14.2°C and the relationship between the two variables was well described by a hyperbola. Therefore, the time taken for development was expressed in units of degree‐days above a threshold temperature. Mean values (with 95%CL) were 552 (534–573) degree‐days above 4.25°C for 10% of the eggs hatched, 862 (725–1064) degree‐days above 3.57°C for 50% hatched and 1383 (1294–1486) degree‐days above 3.14°C for 90% hatched. These values can be used to predict hatching times at temperatures below 14.68°C for 10% hatched, 14.54°C for 50% hatched and 14.45°C for 90% hatched. At higher temperatures, the hatching time and the number of degree‐days required for development both increased with increasing temperature. Equations were developed to estimate the number of degree‐days required for development at these higher temperatures.Eggs were also placed in the Wilfin Beck, a small stony stream in the English Lake District. Maximum and minimum water temperatures were recorded in each week and the summation of degree‐days was used to predict the dates on which 10%, 50% and 90% of the eggs should have hatched. There was good agreement between these estimates and the actual hatching times. Only 10–15% of the eggs hatched between October and late February with most of the eggs hatching in March, April and May. Nymphs hatching in October and Novemb

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01425.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Perch were sampled for their stomach contents at regular intervals throughout 24 h from June until October in 1973 and from February 1975 until January 1976. They were found to feed on benthic organisms from November until April, on benthos and plankton during May and June and on perch fry and zooplankton from July until October. Perch over a wide size range feed on similar prey. Fish showed great variability in the weight of their stomach contents. A method based on a points system was developed to estimate the weight of food in the stomach for a given weight of fish at a known time. A diel feeding pattern which varied with the season was apparent from these data. Rates of gastric evacuation were assumed to be exponential and were calculated from the drop in night‐time stomach content weights when food intake was assumed to be zero. The rates ranged from 0.18 mg h−1at a mean water temperature of 11°C in May to 0.35 mg h−1at a mean water temperature of 17°C in July. Assuming that food consumption followed a linear rate of intake, the standard Bajkov method was considered an adequate model to calculate daily food consumption. Daily food consumption (mg dry weight) was calculated for 150 g perch for all months of the year (November to April and September and October being combined). A second series of values was calculated making corrections for the time spent in the fishing gears when food intake was zero but gastric evacuation continued. Daily food consumption figures for 150g male perch based on Winberg's hypotheses (1956) and growth data showed no significant differences from this second series of values, when both were expressed in energy terms. When certain assumptions have been tested, growth data and Winberg's equations together may be a suitable method for calculating an energy budget for the Windermere perch pop

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01426.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.A cheap messenger‐operated device for sampling water immediately above sediment is describe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01427.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.A quantitative funnel‐trap sampler for air‐breathing aquatic insects is described. Performance tests with special reference to adultGlaenocorisa propinquaare presented. Abundance was calculated from pilot surveys with the funnel‐trap sampler during 1976 and compared with results from a trial with the capture‐recapture method. The influence of temperature on the frequency with which adultGlaenocorisa propinquarenews the bubble gilt was m

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01428.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

SUMMARY.Daphnia cephalataKing is a major component of the zooplankton in freshwater ponds of eastern Australia. Phenotypic variation in head shape both within and between populations is striking. Some of this variation is ontogenetic, but among individuals of similar size head length still varies by a factor of two. The causes of this variation have been investigated by analysing head size in thirty‐four populations ofD. cephalataover a 17‐month period. An annual cycle in crest size, apparently related to seasonal changes in mean temperature, was evident when the data were pooled. Large differences in head size were commonly observed, however, among samples collected simultaneously. Some of this variation was correlated with local differences in resource availability, which were due, in part, to local variation inDaphniadensity. Other consistent interpopulation differences in head size were related to stable environmental differences among sites and probably also to genetic differences among populati

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1978.tb01429.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY