摘要:

SUMMARY.1. Growth rate ofParameletus minorwas greatest between 10.8 and 19.8°C, survival rate peaked at 5.9°C, developmental time was shortest at 14.6°C, and adult size and fecundity reached maximum values between 5.9 and 10.8°C. Growth rate ofP. cheliferwas greatest between 14.6 and 19.8°C, survival rate peaked at 5.9°C, and developmental time was shortest at 14.6°C. A large adult size was found at 10.8°C, and highest fecundity between 10.8 and 14.6°C.2. Food quality significantly affected growth rate, developmental time, adult size and fecundity of both species. BothP. cheliferandP minorattained highest growth rate, largest adult size and highest fecundity when the C/N ratio of food was 5.95. Developmental time was shortest at a C/N ratio between 5.95 and 12.8.3. Nymphs of P.cheliferhad a higher temperature ‘optimum’ for growth than nymphs ofP. minor. Growth rate of nymphs ofP. cheliferreared on detritus from a seasonal stream (C/N ratio 12.8) was about 3 times that of nymphs reared on detritus from a river margin (C/N ratio 20.9). The corresponding growth rate difference for nymphs ofP. minorwas only about 1.5.4. When all life‐history parameters are taken into consideration,P. cheliferhad a higher temperature ‘optim

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00455.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1 Ingestion rate, assimilation efficiency and digestive enzyme activity were investigated in the New Zealand freshwater crayfish,Paranephrops zealandicus(White). Rates of ingestion of fresh and decayingElodea canadensisMichx. were highly variable at 15°C and assimilation efficiency averaged 21%.2.Hepatopancreas extracts showed enzyme activity towards each of nine substrates tested; microcrystalline cellulose (MCC), carboxymethyl cellulose (CMC), cellobiose, amylose, pectin, mannan, laminarin, chitin and‘Azocoll’ (a dye‐collagen complex).3. Three genera of Enterobacteriacae were isolated from digestive juices and hepatopancreas samples and microbial activity was implicated in the breakdown of MCC, laminarin and protein. Host‐specific activity was not detected in the assays with MCC suggesting a solely microbial source for this enzyme.4. Although cellulose cannot be broken down without some degree of prior conditioning, the polytrophic feeding strategy ofP. zealandicusis indicated by the presence of host‐specific enzymes that hydrolyse storage and structural sugars of algae, fungi and higher plants as well as anim

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00456.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Limiting nutrients for phytoplankton were studied experimentally in eight mountain lakes of central Colorado between May and November of 1984.2. Five categories of phytoplankton limitation were identified: no limitation, N limitation, P limitation, concurrent limitation (stimulation only by simultaneous additions of N and P), and reciprocal limitation (stimulation by addition of either N or P). The phytoplankton communities of three lakes were primarily N‐limited, one was primarily phosphorus‐limited, and four showed primarily combined limitation (concurrent or reciprocal). Switching between categories of limitation was also observed within lakes. Nitrogen was the most frequently limiting nutrient; N, either alone or in combination with P, accounted for 79% of all observed instances of limitation.3. Nine indices were tested for effectiveness in predicting phytoplankton limitation by N and P. The best indices for discriminating all limitations were ratios of dissolved inorganic N: total P (84% accuracy) and dissolved inorganic N:total dissolved P (80% accuracy). The effectiveness of these indices may be explained by the degree to which they represent N and P fractions actually available to the phytoplank

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00457.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Spatial and temporal changes in larval densities were used to infer patterns of habitat use and survivorship in a fourteen‐species assemblage of dragonflies (Odonata: Anisoptera) in a small fishless pond. The density of all species combined peaked at>1000 m−2in late summer, Most species (e.g.Libellulaspp.) were restricted to shallow, nearshore habitats (<1.0m in depth), but a few (e.g.Epithecaspp.) also used deeper areas of the pond. OnlyPerithemis tenerawas most abundant in deep habitats.2. Because many species exhibited temporal shifts in their use of habitats, it was necessary to estimate survival from changes in population size, calculated as the product of density and habitat area, summed across habitats. In most species, periods of high mortality in autumn and spring were separated by 3–4 months of negligible mortality in winter. Survivorship was linear only in the two species that completed all of larval development in summer (Sympetrum vicinumandPantala flavescens). Average survival rates for these two species (−0.0049 and −0.0079 log density d−1) were similar to those in previous studies (Lawton, 1970; Benke&Benke, 1975).3. Survivorship in many species was confounded by other life history phenomena such as (i) mixed voltinism, (ii) overlapping migrant and resident cohorts, and (iii) asynchronous development within species. Asynchrony made it difficult to estimate initial and final population sizes, hence total larval survivorship. However, based on emergence data, only 0.4–3% of larvae survived after peak abundance. None of this mortality can be ascribed to vertebrate predation, and only a little to overwintering stress and starvation. Thus, predation by invertebrates might play a major role in the regulation of thes

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00458.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Larvae and pupae ofSimulium noelleriFried, coated the concrete of parts of an artificial lake outlet in southern England.2. In the first two (of three) summer generations, development was synchronous and this allowed the calculation of their secondary production by the instantaneous growth method. The production of the two summer generations was, respectively, 229.1 g C m−2(7.4 g C m−2day−1) and 185.5 g C m−2(8.8 g C m−2day−1) The contribution of the third summer generation, and the overwintering generation, to annual production would be less than that of the first two summer generations. Nevertheless, annual production will have exceeded 500 g C m−2at this site.3. Larvae are suspension feeders and they captured the rich supply of particulate and dissolved organic material which passed over them after export from the lake. As food is brought to the larvae they only require space for attachment and can thus build up very high population densities (which exceeded 1 × 106m−2on some occasions during the summer). The high population densities result in a high biomass and hence in the high leve

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00459.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The aim of this study was to evaluate the impact of different amounts of water and organic material on the extraction of periphytic algal chlorophyll from lake sediments.2. Methanol extracted less chlorophyll than acetone from fresh sediment samples. The ratio between the amount of chlorophyll extracted with methanol and acetone increased with decreasing water content of the sample.3. When sediments were freeze‐dried prior to extraction of chlorophyll, the extraction efficiency increased between 3.4 and 10.0 times compared with fresh samples. It is suggested that the higher extraction efficiency for freeze‐dried samples is due to reduction in water content and pulverization of the sediment, allowing improved exposure to the solvent.4. As a result of these studies freeze‐drying, prior to extraction in acetone (90%) or ethanol (96%), is recommended as the best available method for quantification of chlorophyll a in sedi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00460.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. We present a broad description of the plankton community of a polymictic freshwater lake in the Ethiopian part of the rift valley of east Africa.2. Despite intermittent stratification, there is little vertical heterogeneity in pico‐, nano‐ or microplankton biomass. Some chemical constituents (O2NH4, NO3) showed strong vertical differences, as the hypolimnion quickly became anoxic following stratification.3. Phytoplankton biomass and activity is dominated by small Cyanobacteria, although the colonial green algaBotryococcusis also important. Primary productivity probably was limited only by the relationship of light penetration to mixing depth during our experiments, although neither phosphate nor inorganic nitrogen are so abundant that their exhaustion during prolonged stratification is precluded.4. Zooplankton biomass was dominated by small cyclopoid Crustacea, which were mostly absent from surface waters. Cladocera were small and in very low abundance; ciliates and rotifers were more abundant, and probably were the important grazers.5. We speculate that the present plankton community is sustained by strong vertebrate planktivory in the absence of effective piscivo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00461.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. We tested Krecker's model (1939) which states that the abundance of invertebrates per unit macrophyte biomass varies with plant species and is higher on plants with finely dissected leaves than on plants with broad leaves. The abundance of invertebrates was measured in thirteen lacustrine macrophyte beds in southern Québec, Canada. The model was tested for the total abundance of invertebrates and for the abundances of Chironomidae, Cladocera, Cyclopoida, Gastropoda, Hydracarina, Ostracoda and Trichoptera.2. More epiphytic invertebrates were found on the dissectedMyriophyllumspp. than on the broad‐leavedPotamogeton amplifoliusTuckerm,P. robbinsiiOakes andVallisneria americanaMichx. (P<0.01). More invertebrates were also found onP. amplifoliusthan onP. robbinsiiorV. americana(P<0.01). The total abundance of invertebrates was not systematically related to the degree of plant dissection.3. The abundances of Chironomidae, Cladocera, Cyclopoida, Gastropoda, Hydracarina, Ostracoda and Trichoptera varied on different plant species(P<0.01).Contrary to Krecker's hypothesis, however, macrophytes with finely dissected leaves(Ceratophyllum demersumandMyriophyllumspp.) did not in general support more invertebrates per unit plant biomass than plants with large leaves(Potamogeton amplifolius, P. robbinsiiandVallisneria american

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00462.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1 Total fluorescence spectra of thirty‐two freshwater algae show that the majority of the information is contained in the excitation spectrum of emission at 680 nm.2. Previously suggested characteristics for the automatic identification of blue‐green algae from their fluorescence properties, i.e. the presence of high phycoerythrin fluorescence and low chlorophyll fluorescence, are shown to be inapplicable to the freshwater blue‐green algae studied

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00463.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. A series of small seasonal pools on a freshwater marsh was used to estimate the element of chance in animal community patterns.2. The pools were artificially created in 1963. They were all the same age, size, shape, depth and had the same substrate. Other physico‐chemical parameters, and the faunas, were sampled. Community assemblages were analysed using multivariate classification and ordination (TWINSPAN and DECORANA). and related to physico‐chemical characteristics. Communities correlated with distance of pools from permanent water and annual drying/flooding regimes.3. TWINSPAN analysis in 1987 was used to identify co‐occurring groups of animals and the sets of ponds with which each group was associated. The presence or absence of a taxon from a pool within a set in which it otherwise commonly occurred was used as a measure of the element of chance.4. The mean occurrence of taxa in pools in which they were expected was 79.6.16.2%. The mean occurrence in pools in which they were not expected was 10.9.10.5% (

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00464.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY