摘要:

SUMMARY.After considering the large number of grabs described in the literature, seven grabs of weight<25 kg were chosen for manual operation from a small boat: Van‐Veen grab, weighted and unweighted Ponar grabs, Friedinger version of the Petersen grab, Dietz‐La Fond mud‐snapper, pole‐operated Birge‐Ekman grab and pole‐operated Allan grab.Random samples (number of sampling unitsn= 10) were taken in a large tank with a known number of 2‐mm cylindrical plastic pellets amongst stones of uniform size. Separate experiments were performed with four sizes of stones (model ranges: 2–4 mm, 8–16 mm, 16–32 mm, 32–64 mm). Stratified random samples (n= 10) were taken in rivers and the modal particle sizes at four sites were 0.004–0.06 mm, 0.5–2 mm, 16–64 mm and 64–128 mm. All grabs usually took a representative sample of the substratum at each site with no strong bias towards a particular particle size. The general performance of the Friedinger, Dietz‐La Fond and Allan grabs was poor, except on a muddy bottom, with frequent failure to operate, small samples of substratum and a mean depth of penetration<3 cm in all substrata except mud for the Dietz‐La Fond and Allan grabs. The Van‐Veen and Birge‐Ekman grabs sampled to a mean depth16 mm) were present in a gravel bottom. The mean depth was16 mm) were predominant on the bottom.In the tank experiments with pellets, the efficiencies for the total catches of the Friedinger, Dietz‐La Fond and Allan grabs were low with values<45% for fine gravel (2–4 mm),<22% for small stones (8–16 mm) and16 mm) were predominant on the bottom (sites 3, 4).The relationship between the variances and means of the samples taken with each grab followed a power law for the catches of pellets in tank experiments, and for major taxa and total numbers at each site in field trials. Values of exponents in the power law lay within the range 1.14–2.34. The coefficient of variation was also frequently related to the sample mean and w

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01247.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The distribution ofAustropotamobius pallipes, the only freshwater crayfish indigenous to the British Isles, is examined using over 300 records collected since 1970. The majority of records are for England where crayfish are found in areas associated with base‐rich easily weathered substrata. Waters containing crayfish tend to be in the pH range 7–9, with calcium levels above 5 mg l−1. Crayfish are found in a wide variety of habitats ranging from deep water‐filled quarries with a soft substratum to shallow fast‐flowin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01248.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The rate of gastric evacuation in perch (Perca fluviatilis) (89–170 mm length) fed on fish larvae was studied at temperatures between 12.0 and 21.7°C. Gastric evacuation rates were usually described by an exponential function. The instantaneous rate of gastric evacuation (R) was constant for a large number of different meal sizes. At higher food rations, a lag phase in digestion was found during the first part of digestion, and this ration size was smaller for smaller perch (89–110 mm) than for bigger perch (120–170 mm). Below these larger meal sizes, gastric evacuation was similar for the different size classes studied. The relation betweenRand temperature was described by an exponential function. The effects of meal size, number of food items, fish size and temperature on the rate of gastric evacuation are dis

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01249.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.A standard method is given for describing plant communities in fast‐flowing streams and rivers. This involves the selection of a representative 10‐m length of stream (termed a reach) which can be re‐located exactly. Various estimates of the relative areas covered by different physiognomic forms and the relative proportions of species present are then combined to give a ‘semi‐quantitative’ account, which can be compared with data collected at other sites or times. The method has been applied to six sites on the River Tees system. A site below Cow Green reservoir with markedly regulated flows, differs from the others in various ways. Bryophytes show a greater cover here than elsewhere throughout the year and a conspicuous cover ofPhormidiumoccurs in autumn. Filamentous green algae of many different species are abundant at this site in late summer and early autumn. At the most downstream site where such seasonal growths also occur, a single species,Cladophora glomerata, is dominant. Conspicuous spring diatom ‘bursts’ occurred at the two upstream sites and a month later at the two d

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01250.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The population density of the univoltine amphipodGammarus pseudolimnaeuswas estimated monthly from April 1977 to June 1978 along a 600‐m reach using a form of removal sampling at 0.5, 1.5 and 2.5 m from the bank. The probability of catching an amphipod with three sweeps over an area of 0.15 m2was 0.95. Drift and upstream migration were measured for 24 h, also monthly. Population density varied from 1600 m−2(newly‐hatched young in July) to 26 m−2(adults) within 3 m of the bank with 95% confidence limits of 40–60% of the mean; density was highest<1 m from the bank and beyond 3 m it declined to insignificant levels. No significant difference could be shown between the total catches in the drift and upstream nets over a year and there appeared to be no net migration of amphipods. Mean drift was 2 amphipods day−1.Growth was estimated from the length composition of monthly samples. Annual production (P) was 29.4 kg ha−1for one generation of the amphipod with aP/Bratio of 4.65. Egg production accounted for only 2% of this estimate. Recruitment was calculated from regressions relating female length to clutch size and egg development time to temperature in the laboratory; mean temperature was measured in the field.Mortality was greatest in July at the beginning of the generation. It was high again in September and during winter; at these later times it was suggested that starvation occurred in addition to predation. Annual consumption (C) of organic matter for the generation calculated from published data on feeding rate was 1547 kg ha−1which results in aP

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01251.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Increase in body wet weight ofGammarus pulexfed on decaying elm leaves was followed to senescence and death. Growth in juveniles was approximately exponential; from birth to death it conformed to a logistic growth curve, with maximum absolute increments in weight about half‐way through a life span of 350–450 days at 15°C. Some individuals lived longer, for up to 640–700 days. The instantaneous or specific growth rate was maximal near birth, at c. 5–6% wet wt day−1, and declined exponentially with increasing size and age. Over the range 4.7–14.8°C there was a log‐log relationship between temperature and specific growth rate. Growth was maximal at 20°C in newborn animals and at 15°C in 6–9‐mg animals.The specific growth rate of young individuals was fastest on decaying leaves of elm with a well developed flora of fungi and other microorganisms. Leached elm leaves without this flora supported growth at a lower rate. The latter diet was sufficient for survival and growth of newborn individuals; detritus, faeces or other food items were not needed. Isolated specimens grew as fast as those kept in groups. Growth was generally slower on leached leaves of oak and sycamore. In newborn animals fed on the fine roots of aquatic plants (Veronica, Rorippa and Glyceria), growth was as fast as on decaying elm leaves; growth on the green living leaves of the plants was slower, as on detritus from two streams and on a pure culture of an aquatic fungus.Consumption of leached elm leaves was related to leaf thickness. In a full gut the wet weight (1.34–1.37 mg) and volume (3.8–4.1 mm3) (for 20‐mg animals) was independent of leaf thickness but dependent on animal size, increasing 4‐fold over the range 2–50 mg body wt. Daily consumption (dry wt) was approximately equivalent to 50% body dry wt at 5 mg and 20% at 50 mg body wet wt. Individuals fed on thick leaves ingested 50% more dry weight per day and absorbed more in the gut than when fed on thin leaves, but the relative efficiency of absorption was the same at 36–59% for 10–20‐mg animals. Weight‐specific absorption in the gut was highest in juveniles and decreased with increasing body weight; relative efficiency of absorption was generally lower in the larger individuals. Assuming an energy value of 5 cal mg−1dry wt for elm leaves, daily mean energy intake by absorption in thegutof G. pu/ex was2.2 cal mg−1animaldry wt (9.2 J mg−1) in individuals of 0.4 mgdry wt (2 mg wet wt), decreasing to 0.3 cal mg−1(1.3 J mg−1) at 10 mg dry wt (50 mg wet wt).Growth inGammarusis briefly reviewed in the hght of work on other animals and it is emphasized that all aspects of feeding, growth and metabol‐ism should be specifically related to size a

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01252.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01254.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY