摘要:

SummaryFood consumption of newt tadpoles caught during July and August was estimated as C=34W1·11±0·12where C is food consumption in milligrams wet weight/day andWis the live weight in grams.Well‐fed tadpoles assimilated the food with an efficiency of 90–6%, but at low rates of feeding, the efficiency fell. Gross growth efficiency was about 35 % at maximum r

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01551.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Summary(1) The pattern of absolute atid relative gonad growth during the life‐span and the seasonal gotiad cycle were determined from monthly samples of chub taken from two tributaries of the Herefordshire Wye.(2) A marked change in the pattern of absolute gonad growth was thought to indicate the attainment of sexual maturity. This was found to occur synchronously with corresponding changes in the pattern of body growth described previously and was in agreement with the age at which a seasonal gonad cycle was detectable.(3) Sexual maturity was attained during the eighth year of life (7+) in female chub and in males from the Afon Llynfi, but most males from the River Lugg matured a year earlier.(4) The chub gonads continued to increase in relative size after the attainment of sexual maturity. This was more evident in female chub.(5) Seasonal changes in the gonad condition and weight were followed. Gonad maturation occurred during spring and the gonad mass increased rapidly just prior to spawning.(6) Spawning occurred during Jun

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01552.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryThis paper describes a distribution problem involvingAgrypnetes crassicornisandPhryganea obsoleta(Trichoptera : Phryganeidae) in Malham Tarn, Yorkshire. The only suitable habitat for their larvae is the offshore vegetation, chieflyChara delicatula, but owing to the specialized egglaying behaviour of this family and the absence of other sites, the eggs ofAgrypnetescrassicornis are laid on the exposed rocky shoreline. The situation withPhryganeaobsoleta differs in that the emergence ofPotamogetonspp. provides new oviposition sites away from the shore. Investigations on both species however have provided further support for an hypothesis which postulates the importance of wind‐induced water movements in rapidly dispersing newly hatched insect larvae to the favourable habitats in deep wate

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01553.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01554.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Summary(1) Total copepod numbers per litre in Lake George, Uganda, vary slightly during the course of a year. Numbers increase during the dry seasons June‐August and January‐February, and decrease during the rains. This variation is more marked in the mid‐lake area, where copepod numbers are higher, but the change in numbers is not more than two‐fold. By comparison with populations in temperate regions the population in Lake George is stable in size and shows little seasonal variation.(2) The carnivorous cyclopoid Mesocyclops leuckarti forms only 4–21 %, by num‐bers, of the total copepod population and does not occur in numbers large enough to be analysed profitably.(3) The bulk of the population is the much smaller Thermoeyclops hyalinus and analysis of this population into the main development stages of its life history shows an almost constant age structure over the lake as a whole, throughout the year.(4) The development time of the eggs, as determined previously (Burgis, 1970), is 1–5 days. This, plus mean development‐times of 6 and 11 days for nauplii and copepodites respectively, has been used to determine the daily rate of recruitment from each stage of the life history to the next. The recruitment from nauplii to copepodites and from copepodites to adults are very similar and almost constant. Recruitment from eggs to nauplii is. however, mueh greater, and it thus appears that the major loss to the population is at this eariy stage in the life history. This may well be due to predation by the larvae of Chaohorus.(5) Using this recruitment rate from eggs to nauplii, the potential turnover time of population numbers was calculated to have a mean value of 4–2 days for the lake as a whole. This is similar to maximum summer turnover times found by authors such as Hall (1964) for Daphnia populations in temperate waters.(6) The biomass of individuals at various stages in their life history was deter‐mined as carbon, and application of these determinations to the numerical counts was used to calculate the standing‐crop biomass in the lake. With a constant population of stable age‐structure it is possible to estimate the daily biomass production from the turnover time of numbers. For the population of Thermocyelops hyalinus in Lake George this gives a mean figure of 211 μg C/I/day during 1969–70.(7) Instantaneous birth rates and instantaneous rates of change in population numbers (bandr) have also been calculated for the population of Thermocyclops. The values of r show some variation at one centre site, fluctuating around zero, but when calculated for lake mean figures r is hardly different from zero throughout the year. The values ofbalso show fluctuations when calculated for one site but when calculated for lake mean figures show no more than two‐fold variations, being higher at the beginning of the two rainy seasons. The values ofbare not as high as those attained during the summer in some temperate Daplmia populations such as those described by Wright (1965). The values of ZJ tend to be higher inshore than in mid‐lake areas of the lake.(8) The instantaneous mortality rate r/has been calculated fromb‐r. With such very small values ofr, dis always very similar tob. Most, if not all, recruitment to the population is counterbalanced by loss, probably predation.(9) At one inshore site the population was analysed and counted in detailed cate‐gories, over a period of 10 days. This allowed a more accurate estimation of the standing‐crop biomass and thus of production. A mean value of 103 μg C/l/day was obtained for these samples.(10) The mean daily level of production, c. 211 μg C/l/day, o(Thermocyclops hyalinus in Lake George, is among the higher values of zooplankton production available for comparison most of which are from temperate regions of the world. The fact that it is applicable throughout the year gives an annual value o

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01555.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01556.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryDuring the period April 1967‐ApriI 1968 the phytoplankton production and respiration of the River Thames and its tributary, the River Kennet, were measured at approxi‐mately 2‐week intervals using the light and dark bottle technique. Concentrations of chlorophyll and pheopigment were determined weekly. On fourteen occasions sets of light and dark bottles were rotated in a specially designed apparatus, and production and respiration values obtained were found to be 1·38 ± 0·31 times higher than in stationary bottles at identical depths over the same period. There was little horizontal, vertical or diurnal variation in chlorophyll concentration showing that the water was well mixed. Peaks of chlorophyll were found in spring, summer and autumn in the Thames (max. 219 mg/m3) but there was very little variation in the Kennet (max. 38·2 mg/m3). In both rivers lowest concentrations were found during winter. Pheo‐pigment concentration was low in both rivers for most of the period although in the Kennet this represented on average 50% of the pigments present. In the Thames a peak of pheopigments(1·33–5 mg/m3) was associated with the autumnal bloom and repre‐sented 61 % of the total pigments. No pheopigments were detected during the spring bloom. The average concentration of suspended organic matter was identical in both rivers but in the Thames over 25 % was due to phytoplankton and in the Kennet almost 95 % was non‐algal.In the Thames, net oxygen production reached a peak in May (10·81 gO2/m2/day) and was negative from November to February (min. −0·45 gO2/m2/day). In the Kennet, maximum production also occurred in May (0·85 gO2/m2) but was negative from the middle of May until the following March. The average annual net production was 1250 and −78 g O2/m2in the Thames and Kennet respectively.Respiration rates showed similar fluctuations being 4·59 g O2/m2/day in spring in the Thames to 0·09 g O2/m2/day in November. The Kennet was almost always lower (1·05–0·34 g O2/m2/day. The average annual respiration was almost three times higher in the Thames than in the Kennet (641–228 g O2/m2).Various factors which might influence production are discussed. The average net efficiency ofthe Thames phytoplankton fell within ranges described from other rivers. Net efficiencies ofthe Kennet were almost always negative.In the Thames it appeared that net production could be explained as a function of solar radiation, chlorophyll

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01557.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

SummaryThe phytoplankton of the River Thames and its tributary the River Kennet was studied weekly from May 1966 to May 1968. Samples were concentrated by sedimen‐tation and counted in a haemocytometer.Data on discharge, temperature and silica concentration are followed by descriptions of the variations in the number and composition of the phytoplankton. In both rivers there were spring and autumn peaks of the centric diatom. Stephanodiscus hantzschii. Chlorophyceae were most abundant during summer. Two cryptophyceans,CryptomonasandRhodomonaswere sometimes numerous.In the Thames, the size of the population was closely correlated with the discharge, highest numbers always occurring during periods of low discharge. In the Kennet, increases in discharge often brought about increases in cell number due to the infiux of benthic forms.It appeared that nutrients were always present in sufficient quantity and did not limit algal growth.Comparisons were made with earlier studies on the Thames and differences were noted in the composition of the phytoplankton which were almost certainly due to the process of eutrophicatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01558.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Hynes, H. B. N. (1970).The Ecology of Running Waters.Schwoerbel, J. (1970)Methods of Hydrobiology (Freshwater Biology).

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1971.tb01559.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY