摘要:

SUMMARY.Microcystis, an important bloom‐forming blue‐green alga in Lake Mendota, Wisconsin, was found to accumulate at the lake bottom and overwinter there.Microcystiscollected from winter sediments were photosynthetically active, showing temperature and light optima similar to summer and autumn populations. Sediments incubated underin situconditions in the laboratory maintained photosynthetic activity for at least four months. Such a maintenance ability may be part of an overall strategy byMicrocystispopulations to ensure a suitable inoculum for the following growth sea

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01255.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.The estimated average number of bacteria in the gut of laboratory‐culturedNais variabiliswas 100.4 × 104. This compares with values of 6.7 × 104and 32.8 × 104, respectively, forN. variabilisandN. barbataobtained from a river.Comparison of the viability of heterotrophic bacteria in the food and gut ofN. variabilisindicated a decline in viability of up to 99.6% during the passage of bacteria through the gut. The estimated gut retention time was 39 ± 8 min at 18°C and therefore loss of viability is unlikely to be due to long retention in the gut. Loss of viability is, however, a prerequisite of bacterial digestion by the worm and provides circumstantial evidence that ingested bacteria are used as food.No conclusive evidence was obtained indicating (a) preferential ingestion of certain kinds of bacteria, (b) that the gut environment was selectively hostile to the particular kinds of bacteria studied or (c) that worms had a specialized gut micro

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01256.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Comparison is made of resistance to anoxia at 0°C of an English and a Swedish winter larval population of two closely related forms ofCloeon (dipterum?). The English population was not very resistant but contained a few slightly resistant larvae; the Swedish population was very resistant. Swedish larvae initiated hibernation more rapidly than English larvae and were also more resistant to starvation. The different properties of the populations are seen as an adaptation to different winter conditions in ponds in England and Sweden. Evidence is presented that low temperatures but not decreasing photoperiod are decisive for the final induction of hibernation in the larvae. In Swedish larvae this induction starts at between 4 and 5°

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01257.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.After considering the large number of dredges described in the literature, four light‐weight dredges were chosen for manual operation from a small boat or the bank: Irish triangular dredge, small Fast dredge, medium‐sized and large Naturalist's dredges. The dredges were tested in a series of trials at three sites in two rivers. A stratified random sample (number of sampling units, n = 5) was taken at each site and the modal particle sizes at sites 1–3 were 1–2 mm (fine gravel), 64–128 mm (larger stones) and 128–256 mm, respectively.The dredges usually took a similar range of stone sizes at each site but the design of the Fast dredge excluded larger stones (>16 mm). The Irish dredge sometimes failed to operate correctly. Variations in the volume of substrata taken with each dredge were large, both between sampling units in the same sample and between samples. The latter differences were partially due to the increase in the modal size of the stones, especially between sites 1 and 2, the different sampling areas of the dredges and the depth of penetration into the substratum. Penetration depth was probably greatest for the two Naturalist's dredges, smaller for the Fast dredge and smallest for the Irish dredge.In field trials, the relative abundances of major taxa were similar for most dredges at each site; major exceptions were the Fast dredge at site 2 and the Irish dredge at site 3. There was a high variability between sampling units in the same sample and therefore a lack of precision in the estimates of the mean number of invertebrates per sample. Therefore, the dredges cannot be used as quantitative samplers for the estimation of population density. Their adequacy as qualitative samplers for the estimation of total number of taxa per sample varied considerably and maximum estimates of their efficiencies for a small sample (n= 5) were76% for the large Naturalist's dredge.There was a clear relationship between the number of taxa and the number of invertebrates taken at each site and this relationship was well described by a power law with an exponent within the range 0.18–0.53. The number of sampling units in the sample had no significant effect on the power‐law equations for each site. The power‐law equation was very similar for most of the dredges at each site, the only major exception being the Fast dredge at site 1. The implications of this relatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01258.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.Replicated benthic samples were collected from a wet gravel‐pit in the English Midlands at fortnightly intervals during 1978. The aggregation patterns of the four most numerous genera,Chironomus, Polypedilum, ProcladiusandTanypus, were analysed by fitting the means and variances of replicated sampling units to Taylor's power law and Iwao's plot of mean crowding against mean density.Chironomuslarvae were not aggregated; all other genera showed an increased aggregation with density. The Iwao plots indicated thatTanypuslarvae tended to be aggregated at low as well as high densities. Gut contents were analysed in larvae of the above genera and also inCryptochironomuslarvae, to investigate the relationship between dispersion pattern and feeding.ChironomusandPolypedilumlarvae fed mainly on detritus,Tanypuson algae,Procladiuson algae and crustacea andCryptochironomuson oligochaetes. The extent of overlap in feeding niche was measured by Levins’ index and shown to be low in all except the pair feeding upon detritus. Differences in the feeding niche may partly account for the dispersion patterns of the genera investiga

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01259.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARY.There are thirty‐one British leptocerid species in nine genera. A key is provided to identify larvae of all species at the final (fifth) instar and many species are also separated at earlier instars. The work is based on British material for all but one specie

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01260.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Moss, Brian (1980)Ecology of Fresh Waters.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1981.tb01261.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.tb01262.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY