摘要:

SUMMARY.This paper describes a day/night feeding rhythm in the copepodPseudodiaptomus hesseiin subtropical Lake Sibaya (27°20′ S, 32°40′ E) and examines the origin of this rhythmicity on the basis of field and laboratory observations.Under natural conditions, adult and late copepodite stages (CIV‐CV) of this copepod were predominantly benthic during daylight and migrated at dusk into pelagic waters in which they remained until dawn. Pronounced changes in feeding activity (based on the proportion of animals which contained food in the gut) were associated with this transition from a benthic to pelagic distribution; feeding activity was low by day and high at night. The younger copepodite stages (CI‐CIII) were less strongly benthic during daylight and showed correspondingly less pronounced diel changes in feeding activity.Laboratory experiments involving concurrent light/dark and continuous dark regimes showed that batches of adult and CIV—CVstages fed throughout 24 h, although faecal pellet production increased with time under both light regimes. The laboratory observations are interpreted as negating the possibility that diel differences observed in the field arose through an endogenous feeding rhythm. The possibility that food resources in near‐bottom waters was inadequate to support reasonable feeding activity is rejected on several counts. It is concluded that the feeding rhythm inP. hesseiarises from an inferred infaunal distribution during daylight which would preclude filter‐feeding activity. The circumstantial evidence supporting this suggestion is given and the suggesti

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01651.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Weekly skim‐net samples of chironomid pupal exuviae were collected at a single station on the River Chew, Avon, England, from September 1972 to September 1973. Eighty‐six types of exuviae were characterized in this study, of which sixty‐four made up only 4% of the year's catch. Thirty ‐eight percent of the year's catch was referable toMicropsectra atrofasciataKieffer.The samples showed the expected maxima of numbers and species in spring and early summer. The emergence periods for many of the more common species were very extended, with one or mor

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01652.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.An extensive limnological study of a tropical African montane lake (Little Connemara Dam No. 3) was undertaken in 1975 to explain the discrepancy between the high nutrient content of the bottom muds and the oligotrophic status of the water column. Little Connemara Dam (No. 3) lies in a small dolerite catchment. The dolerite is strongly jointed allowing considerable water movement and it weathers easily under high rainfall. A number of homes are built in the small catchment.The results of the study showed that the majority of the nutrients were being flushed into the lake from septic tanks via underground streams. As the dolerite weathers, large amounts of iron and manganese, but little calcium or carbonate, are released. The PO4‐P in the water column is complexed with the Fe and Mn allowing only small concentrations for use by algae. Nitrogen enters the lake mainly as particulate nitrogen but is not significantly converted to soluble combined forms of nitrogen at the low pH values (6.2—6.7) found in the lake. Bioassay experiments indicated that combined forms of nitrogen limited phytoplankton gro

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01653.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.The life cycle ofTrichocorixa verticalis interioreswas studied in six Saskatchewan saline lakes. A detailed study of the timing of the stages in the life cycle showed thatT. v. interioreshas a life cycle which differs from that of all other Corixidae. This species overwinters solely in the egg stage. Females oviposit in the late summer and all adults die in the fall. The eggs, which remain in a pre‐blastokinesis stage of embryonic development until the following spring, are prevented from developing in late summer by diapause which lasts approximately 2 months. Although diapause terminates in October, embryonic development does not occur in cold water during the winter months. Experimental results indicate that exposure to cold is not necessary to break diapaus

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01654.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Changes in the numbers and species composition of mormyrid fishes since the impoundment of the Niger (Lake Kainji) are analysed. An initial decline after impoundment appears to have been reversed and these fish are now increasing. The increase is, however, restricted to a few species only; many forms common in the river are still declining or have disappeared altogether. Marked seasonal variations in abundance are described and possible explanations discussed.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01655.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.An account is given of the distribution of macrophytes in the River Tees and its tributaries, north‐east England, together with a critical discussion of the problems involved in recording data in a form which can be used for monitoring long‐term changes of vegetation in rivers. Among the conventions and methods adopted in the present study are an attempt to define the vertical limits of the riversensu strictuas opposed to the bank, the extension of the term macrophyte to include as many visually obvious photosynthetic organisms as possible, the use of a check‐list prepared in advance which contains a wider range of species than are actually expected for the river, and the collection of two different types of standard record for each 0.5 km length of river. The Tees has been the subject of intermittent observations on its vegetation for some 45 years. The most obvious change has taken place since 1965, with a substantial upstream spread of four submerged angiosperm species.Potamogeton crispus, Zannichellia palustrisandMyriophyllum spicatumwere previously present only in the lower reaches of the Tees, and have spread 25, 9.5 and 4.5 km respectively upstream from their previously known most upstream localities.Ranunculus penicillatusvar.calcareusis an apparent invader to the river. It seems probable that these changes have taken place since 1971 as a result of regulation of the Tees by Cow Green Reservoir. Further changes are predicted with the advent of water transfer from the Tyne to Tees around 1980, because at least twenty‐six macrophytes are known to be present in the former river that are either absent or confined to the lowest stretches of the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01656.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Hynes&Coleman (1968) proposed a method for estimating benthic secondary production for use with populations in which cohorts cannot be distinguished and for use with unidentified benthos. Hamilton (1969) corrected and refined the method, emphasizing the concept of the average cohort. Zwick (1975) recently suggested the method should not be used since: (1) too many conditions need to be filled for use with unidentified material, and (2) it is strongly dependent on growth patterns. This paper shows that Zwick misinterpreted the concept of the average cohort, and his apparent invalidation of the method due to dependence on growth patterns is erroneous.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01657.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01658.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.The difference between the results of viable and total counting procedures for bacteria are exemplified by vertical profiles from a deep and a shallow lake and from seasonal changes in the epilimnion and hypolimnion of a shallow eutrophic lake. The viable count was, on average, 0.25% of the total count, the greatest difference being noted in the anoxic hypolimnion, probably due to the inadequacy of the viable counting procedure for the isolation of bacteria from such samples. There was a general trend for the more nutrient‐rich waters to support larger bacterial populations but such observations did not provide any further information on the factors responsible for the population changes observed. Seasonal fluctuations in the counts are studied and the qualitative and quantitative changes resulting from artificial enclosure of water are discussed. Not all the temporal changes could be explained and short‐term changes resulting from nutrient additions to the experimental enclosures were not always reproducible. Horizontal variability was examined, found to be significant and could play an important role where water movement and turbulence is considerable. Results from six sites sampled between 1969 and 1974, representing total and viable bacterial population estimates and a total of eighteen independent or regressor variables were then subjected to principal components analysis. Results taken from the whole water column showed the overwhelming effect of the process of stratification on the bacterial population accounting for 30%‐60% of its variability. Secondary components representing algal productivity could account for 10% to 20% of the variability. Many of the chosen regressor variables were acting as measures of the same phenomenon without providing significant information on what affected the bacterial population. To overcome this problem results from the hypolimnion and epilimnion were analysed separately. The analysis demonstrated the importance of seasonal changes in nutrient concentrations in the epilimnion and the development of anoxic conditions in the hypolimnion. Algal biomass, phosphate concentration and the interaction of pH and ammonia appeared to be important. It was concluded that most of the variability in the bacterial population estimates could have been explained by five of the regressor variables and that the factors most likely to provide more information would include some measure of predation and lake retention

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01659.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Certain larvae and pupae have been identified asNotidobia ciliaris(Linné) by rearing field‐collected larvae to the adult stage and by rearing larvae from eggs laid by a female in captivity. The larvae differ in many important respects from larvae of this species described by earlier workers. Characters are provided to distinguish these larvae and their associated pupae from those ofSericostoma personatum(Spence). The habitat and distribution of both species in Britain is outlin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01660.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY