摘要:

SummaryA laboratory stream is described which has simulated steep‐ and shallow‐gradient bottoms whose gradients can be varied. It was found thatPolycelis felina, the principal triclad of shallow‐gradient streams had a much reduced ability to colonize the simulated steep‐gradient bottoms when compared toCrenobia alpina, which is the principal triclad of the steep‐gradient bottoms in the field.P. felinais unable to move in the steep‐gradient bottoms to any great extent, whileC. alpinashowed considerable ability to do this. When a reduction in flow was made this did not increase the proportion ofP. felinato be found in the steep‐gradient regions. The triclads were also tested for possible acclimatory responses and it was found that their responses were more fundamentally based. On the basis of the above evidence it is suggested that the absence ofP. felinafrom the steep‐gradient regions of streams in North Wales is due to a behavioural inability to tolerate the current regimes present in the steep

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00135.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryIn Frains Lake, individuals of the speciesBosmina longirostrisdecrease relative mucro and antennule lengths during the spring and summer, and increase them again during the fall. The cyclomorphosis involves both embryonic and post‐embryonic events, since the relative sizes of parts in neonates and the relative growth rates of parts in later instars change seasonally. Antennules grow during winter, but may even regress during summer. Mucrones show an opposite pattern, growing maximally during late summer and fall.The kinds of cyclomorphotic changes inBosminasuggest evolutionary adjustments to two principle types of predators: visual vertebrates and blindly grasping invertebrates. While laboratory experiments implicate temperature and turbulence as proximate factors in the cyclomorphotic changes, some unknown factor (or factors) also appears necessary to stimulate the magnitude of responses observed in natur

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00136.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryLaboratory observations on the egg production, development and growth in the CladoceranMoina micrurashow that this species has a life span of 13 days during which it produces 6M 8 eggs. Two preadult and eleven adult instars were recorded at a temperature range of 28°–30°C. The rate of egg production calculated on a cumulative basis was found to be lower (a= 1.0368) than that of other tropical species. The embryonic stages inMoina micruraclosely resembled other cladoceran species, although with a short development period of 24 h. The total life span, growth rate and the total number of eggs produced inMoina micrurahave been compared with those of allied tropical, temperate and arctic daphnids. The significance of this relationship to secondary productivity in tropical ecosystems has been discus

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00137.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryCasual observations had shown that, in laboratory cultures, populations ofCeriodaphnia quadrangula(O. F. Muller) rarely persisted for more than a month at most. It is shown here that populations ofC. quadrangulacan be maintained in static water on a diet of mixed algae (mainlyScenedesmus quadricauda(Turp.) Brev., but if the water is disturbed by a slow current of ascending air bubbles, the numbers ofC. quadranguladecline. Death is not, however, immediate, and at high densities populations may persist in disturbed water for several weeks before numbers start to decline.Numbers ofC. quadranguladid not decline in disturbed water when the food was changed from the algaScenedesmusto the animalArtemia salina(L.). Individuals ofC. quadrangulain the presence of decomposing naupliar larvae ofA. salinagrew as well in disturbed as in static water and in static water their numbers increased at a greater rate on this animal diet than on an algal diet ofScenedesmus. When the bacterial populations associated withScenedesmuswere greatly reduced, there was no increase in the numbers ofC. quandrangula. Microbes associated withScenedesmus, and not the algaper se, seem to be used as food byC. quandrangula.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00138.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe Norfolk Broads have recently shown a marked loss of both floral and faunal diversity. To detect any recent changes and to provide a baseline for future research, twenty‐eight broads were visited in 1972–73. Samples of aquatic flora and benthic fauna were taken and a number of physical parameters were measured.In the private broads a good inverse correlation between chlorophyll‐aconcentration and Secchi disc readings was found, suggesting that phytoplankton was largely responsible for the turbidity of the water. The relationship did not hold for the public broads where erosion and the stirring of sediments by motor launches is intense.Eleven broads were completely devoid of macrophytes. A macrophyte flora was well developed only in Upton and in the five Thurne broads and in these latter there was evidence of a recent loss in diversity. The sudden loss of formerly abundant species of macrophyte has been recorded frequently from the broads. The benthic fauna was poorly developed in most broads and was dominated byLimnodrilus hoffmeisteriand/orPotamothrix hammoniensis. Valvata piscinaliswas the only regularly occurring gastropod in the benthos. Most of those broads with a diverse benthic fauna also had an abundant growth of macrophytes.Possible reasons for the recent changes in the ecology of the broads are disc

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00139.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe standing crops of periphyton were measured on deadTyphastems and glass rods in a small, eutrophic lake from February to November. Chironomid larvae were also counted on theTyphastems; very few were present on the glass rods. The standing crop of periphyton on theTyphastems fell from 1.8 mg cm−2in early April to nearly zero in November. On the glass rods the periphyton reached a peak of 1.93 mg cm−2in late May and 1.94 mg cm−2in July, thereafter falling to a steady level of 1.6 mg cm−2. The population of chironomids showed a peak in late May and then declined. The alimentary canals of chironomids collected fromTyphastems contained diatoms and filamentous algae so it appeared that chironomids were grazing down the periphyton. Chironomids moved on to theTyphastems in spring and returned to the mud in autumn. The periphyton is a richer source of essential amino acids than the mud, so that a movement from mud to reedstems in spring may increase the rates of growth and metamorphosis of the larvae.A crude production estimate gave a net primary production of periphyton of 170 mg dry wt m−2day−1; the periphyton, however, would have contained bacteria and many small animals as we

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00140.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryEvidence is presented of a regular seasonal variation in the filament length ofOscillatoria redekeiVan Goor in Lough Neagh. This cycle is not in phase with the seasonal changes of the biomass of the species, but seems to occur in step with the nutrient concentrations. Some possible mechanisms of filament replication are discussed and evidence is presented that mechanical forces are not effective in breaking filaments. The ecological significance of cyclomorphosis in this species is difficult to establish.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00141.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryBrown trout (live weight 9–302 g) were fed to satiation in each of four meals at seven different water temperatures (range 3.8–18.1°C). The period (Ih) from the start of one meal to the start of the following meal was not significantly affected by the weight (Wg) of the trout, but was negatively correlated with water temperature (T°C). A regression equation described the exponential relationship betweenIandT, and also estimated the number of meals {N) in a day. Values ranged from one meal at about 4°C t o three meals at about 18°C, The greatest increase in appetite occurred at the end of the periodI.The maximum weight offood (Drng) eaten in a day was positively correlated with bothWandT, a relationship which was well described by a multiple regression equation. The maximum rate of feeding (Fmg h−1) was not significantly affected by W, but increased from 3.8 to 6.8°C, was fairly constant from 6.8 to 19.3°C, and decreased markedly above 19.3°C. Estimates ofDandF(with 95% confidence limits) were applicable to a wide variety offood organisms with the exception of mealworms. From comparisons with the results of other workers, it was concluded that the upper limit ofthe daily energy intake determines the optimum temperatur

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1975.tb00142.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY