摘要:

SUMMARY.Cohort production of the crayfish.Orconectes virilis, ranged from 148.8 to 70.2 kg in North Twin Lake (surface area 1.9 ha) and from 151.9 to 84.9 kg in West Lost Lake (surface area 1.4 ha). Both cohort production (P) and cohort mean biomass (B) showed a long‐term decrease with time. The cohort P/B ratios did not show such a trend but remained steady. The P/B ratio approximated the life cycle instantaneous rate of growth (G) which could then be used for estimating cohort production from mean biomass.Production remained consistently higher in West Lost Lake. Analysis of horizontal life table data revealed no inherent difference between survival and fecundity rates of the crayfish population in each lake. Slight differences in basin morphometry between the two lakes determined nursery habitat availability and this affected recruitment of young from each female brood stock. Small differences in carrying capacity between two similar sized nearby lakes, along with a decrease in carrying capacity over time, were sufficient to nullify attempts to manage these populations using a maximum sustainable yield mode

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00653.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.The results of a survey of the macro‐invertebrates of the polluted River Ely, South Wales, are used as a basis for comparing several classification methods which have been used previously in river survey work to determine species groupings. The methods compared are product‐moment correlation (clustered by the nearest neighbour technique), Kendall'staucoefficient (clustered by the nearest neighbour and average linkage techniques), and Squared Euclidean‐Distance coefficient (clustered by nearest neighbour and Ward's techniques). The species groupings determined by these methods were influenced both by the association coefficient and the technique used to cluster it. Some species were grouped together by all or most of the methods. The ecological validity of these robust groups is examined. A clear recommendation regarding the most appropriate method is frustrated by incomplete knowledge of the ecological requirements of most of the aquatic macro‐invertebrates used in the data‐set. However, Kendall'staucoefficient clustered by the average linkage technique appeared to produce ecologically meaningful species groups. Product‐moment correlation was also reasonably successful and since it is based on absolute abundance data whereas Kendall'staucoefficient is based on relative abundance data, the use of the two together is recommended for determining ro

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00654.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.A method is described whereby ephippia (sexual eggs plus protective membranes) are experimentally induced at low food levels (≤ 0.05 mg spinachD. magna‐1), high female culture‐densities (≤ 0.4D. magnaml‐1) and in short‐day photoperiods (L:D<12:12, 12°C). The density‐dependent ephippial response was related to an increased encounter rate between females at the higher densities. External metabolites had no significant effect on ephippia production. Ephippia were formed in the second generation after exposure to short day‐lengths. Five clones from the same population exhibited genetic variation in their critical photoperiods for induction of sexual reproduction (≥= 10% ephippia). There was evidence of a genetic difference in photoresponse between two populations ofD. magna.The evolution of timing mechanisms for ephippia production are discussed in relation to the predictability of en

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00655.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.Diatoms from surface sediment samples from lakes on both sides of a glacial drift border in eastern Minnesota show that Araphidinate diatom genera likeFragilaria, AsterionellaandSynedraare more common in lakes in drift with lower CaCO3whereasStephanodiscusandMelosiraspecies are more abundant in those with high CaCo3. In a lake sediment core from low carbonate driftFragilaria crotonensisandAsterionella formosaincreased when pioneer farmers arrived. These results confirm speculation that high A/C ratios are associated with low‐alkalinity eutrophic lake

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00656.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.1 The development of stone surface organic layers was investigated in dark and light experimental channels at two field sites. Layer formation was monitored by measuring organic carbon, chlorophyll‐a, ATP and rates of oxygen consumption, and using scanning electron microscopy.2 In the darkened forest stream channel an organic layer consisting of slime, fine particles, bacteria and fungi developed and attained maximum biomass (=0.08 mg cm‐2) in about 2 months. At the second site, channels were fed by spring water low in dissolved and particulate organic matter (DOC<0.5 g m‐3) and no organic layer developed on stones in the dark. Organic layers grown in channels subject to natural light intensities and photoperiods were dominated by diatoms and/or filamentous algae at both sites.3 Laboratory experiments carried out in enclosed, recirculating stream channels demonstrated the importance of dissolved organic matter (DOM) as a prerequisite for layer formation. Also. DOM additions in the form of leaf leachates stimulated oxygen consumption by preformed layers. Uptake by microorganisms accounted for most of the reduction in water‐column DOM.4 Radiotracer experiments (14C and144Ce) showed that several common stream invertebrates could feed on ‘heterotrophic’ layers. Calculated assimilation efficiencies ranged from 18% to 74% and imply that nonautotrophic components of stone surface organic layers are likely to play a significant role in carbon transfer to the benthos, particularly in sm

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00657.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.Methods for determination of low levels of biogenic silica (0.2–0.4 mg SiO2) in aqueous samples after digestion with three wetalkaline extraction procedures compared favourably in both precision of replicates and recovery of silica utilized by diatoms in budgeted cultures. Leaching samples with 0.2 M NaOH for 10–15 min at 100°C was the least time consuming procedure. Also interference from silicate minerals was lower for this method than leaching with either 0.5 or 5% Na2CO3for 2 h at 85°C. The use of filters to concentrate samples enables detection of low levels of biogenic silica with colorimetric procedures. Polycarbonate filters are recommended in preference to cellulose acetate or polyvinyl chloride filters for sample collection. Time‐course experiments are recommended for establishing digestion times and determining the presence of mineral silicate interference. Wet‐alkaline digestion methods are recommended for routine analysis of biogenic silica in suspended matter in preference to infra‐red analysis, alkaline fusion and hydrofluoric acid/nitric a

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00658.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.The key distinguishes the previously unknown larva ofPlectrocnemia brevisMcLachlan from larvae of the other two BritishPlectrocnemiaspecies,P. conspersa(Curtis) andP. geniculataMcLachlan. Notes are given on the larval habitat, life cycle and identification of the adult ofP. brevis.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00659.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SUMMARY.The did response of the thermal structure of Esthwaite Water to prevailing meteorological conditions was analysed for seven selected days, covering different phases of stratification. Meteorological measurements were combined with published empirical relations to compute 24‐h thermal energy budgets for 2 days. Amplitudes of diel changes were controlled by the seasonal phase of stratification and the magnitude of incident solar radiation. Heat storage usually followed a sinusoidal curve with a minimum during the night and early morning and a maximum during the late afternoon. Wind‐induced turbulent mixing, and vertical circulation induced by nocturnal cooling of the surface water through evaporative and conductive processes, also modified depth‐time trends in thermal structure.The budget accounted for almost all the thermal energy exchanges of the lake. Possible sources of a slight imbalance are considered. Although there was a positive daily surplus of net radiation, it may not always imply heat gain by the lake as it may be counter‐balanced by heat losses through fluxes of latent and sensible heat, Net back‐radiation was a major component of daily heat loss. The combined latent and sensible heat fluxes also accounted fora high proportion of heat loss to the atmosphere. Net flow of sensible heat to the lake was small but not always inappreciable. Net daily heat storage represented 26% (9 May) and 13% (17 June) of solar radiation Input. Advected energy due to lake inflow and outflow was negligible. Qualitative comparisons are made with long‐term (seasonal and annual) energy budgets and

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00660.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Book reviewed in this article:Beadle, L.C. (ed.) (1981)The Inland Waters of Tropical Africa: An Introduction to Tropical Limnology.Shang, Y.C. (1981)Aquaculture Economics: Basic Concepts and Methods of Analysis.Say, P.J. and Whitton, B.A. (eds) (1981)Heavy Metals in Northern England: Environmental and Biological Aspects.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00661.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1983.tb00662.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY