摘要:

SUMMARY.1. The inherent optical properties (scattering coefficients and absorption coefficients across the photosynthetic waveband) are presented from diverse tropical water bodies (billabongs) in the Alligator Rivers Region of northern Australia.2. The data are used to interpret observed characteristics of the underwater light field as exemplified by the spectral distribution, and overall rate of attenuation, of photosynthetically available radiation (PAR).3. Attenuation of PAR, especially in the blue waveband, is caused primarily by intense light absorption by the yellow‐brown humic pigments, both soluble and particulate, in the water.4. It was estimated that in six moderately turbid billabongs, light scattering increased attenuation by an average of 58% above that attributable to absorption alone, whereas in a highly turbid billabong the increase was 111%.5. A distinguishing feature of the optical character of these billabongs, compared with previously studied water bodies in southern Australia, is the great contribution to light absorption made by the particulate humic materia

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01001.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The results of 5 years of continuous monitoring of river water temperatures at seventeen stations within the Exe basin, Devon, U.K., are presented and discussed.2. Systematic spatial variation in mean annual water temperature was evident and was strongly related to the topographic variable of elevation. Deviations from this relationship reflect local influences of vegetation shading, runoff source and channel character.3. Considerable spatial variation in temperature extremes was also apparent, and the Exe basin differs from several other British river systems in exhibiting highest peak temperatures at downstream sites on the mainstream. Discharge from Wimbleball Reservoir exerted a significant influence on annual maxima and minima.4. A clear seasonal cycle characterized all stations and was objectively defined by second‐order harmonic functions which varied in amplitude and phase across the study area. Marked spatial variability in the magnitude and timing of diurnal temperature fluctuations, in temperature duration curves and in accumulated temperatures was also recorded.5. The implications of the spatial variation in thermal regime for the growth of brown trout was also investigate

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01002.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The leeches,Erpobdella octoculata, Glossiphonia complanataandHelobdella stagnalis, were collected at monthly intervals over a 2‐year period from a eutrophic English lake, and examined for the presence of metacercariae of the trematode.Cyathocotyle opaca.2. Only one specimen of each ofH. stagnalisandG. complanatawas recorded with the parasite. Seasonal changes in prevalence levels inE. octoculatawere similar for each of the three cohorts identified during the study period. Values, low in young leeches recruited in the autumn, rose slowly until the following spring, and then increased more rapidly till the autumn, when the cohort died out. Mean intensity and relative density showed similar patterns of seasonal change to that of prevalence.There was no evidence of parasite induced mortality inE. octoculata.Attainment of sexual maturity did not differ between infected and uninfected leeche

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01003.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The life history responses of two common and three rareDaphnia magnaclones to constant conditions of temperature and photoperiod were investigated, and intraspecific variation in the genes controlling growth, survivorship and reproduction was observed.2. Rearing temperature had a significant effect on growth, survivorship and on all reproductive parameters measured (generation time, intrinsic rate of increase and male production), while photoperiod influenced significantly only survivorship and male production.3. The maximum proportion of male offspring was produced at a low temperature (14°C) and at a mid‐range photoperiod (L:D16:8).4. The likely mechanism whereby clones with different life histories are maintained in the population is discuss

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01004.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Spatial and temporal changes in functional organization of the invertebrate community of streams of the northern jarrah forest, Western Australia, were examined in the light of predictions of the river continuum concept (Vannoteet al., 1980).2. The composition of the fauna was largely as predicted for forested headwater streams with detritivores, principally collectors, dominating the fauna. Although shredders are generally considered to be codominant in such streams, they were not abundant in the riffle areas sampled in this study.3. Some of the observed temporal changes in the composition of functional feeding groups were in agreement with those predicted by the generalized model. The abundance and richness of collectors were higher during the summer than winter, whereas the converse was true for filterers. This corresponded to the presumed availability of deposit and suspended fine‐particulate organic matter during summer and winter respectively. Scrapers and predators showed no consistent temporal pattern among sites. However, the density of the latter was highly correlated with the density of other invertebrates, particularly collectors.4. Temporal changes in the abundance and richness of shredders were not synchronized with the marked summer input of coarseparticulate organic matter. The possible reasons for this, and the role of shredders in Australian stream systems, are discusse

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01005.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Concentration of total suspended bacteria and heterotrophic activity (as turnover rate and turnover rate per bacterium for glucose assimilation by a trace‐addition approach) were determined at distance intervals along four high‐trophic‐status calcareous headstreams in the Yorkshire Worlds and along four low‐tropic‐status acid headstreams in the Galloway Hills.2. Mean concentration of suspended bacteria was marginally greater in the calcareous streams while turnover rate and turnover rate per bacterium were substantially greater.3. Further determinations of heterotrophic activity (as turnover rate, turnover rate per bacterium,VmaxandVmaxper bacterium for glucose mineralization by a kinetic approach) supported the conclusion that heterotrophic activity was greater in the calcareous streams.4. Mean cell volume of suspended bacteria, measured by electron microscopy, was found to be greater in the calcareous streams.5. In the calcareous streams the concentration of total bacteria and turnover rate usually increased substantially, in a straight‐line relationship, with distance downstream from the source. In the acid streams such downstream increase was less usual, the rate of increase per unit length of stream was less, curvilinear relationships were more frequent and on some occasions downstream decrease was observed.6. The calcareous and acid streams thus formed two distinct groups on the basis of heterotrophic activity, cell volume and rate of downstream increase of suspended bacteria. This division was not necessarily caused solely by difference in pH but might be due to the combined effects of the many environmental variables which change in paral

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01006.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. When a predator attacks a mixed‐species group, individual prey arc faced with a conflict between retaining the advantages of large group size and the disadvantages of remaining among aliens. Experiments were designed to show how this conflict is resolved in fish shoals.2. Simulated attacks with a model predator were made upon mixed and single species shoals of three cyprinid species under semi‐natural conditions in a fluvarium.3. Measurements of elective group size, neighbour identity and distance, and encounters within and between species revealed behaviour which sorted fish into species at the onset of predator attack.4. A control experiment demonstrated the same effect for fish of matched size.5. The value to the individual of segregative behaviour in response to predator threat is discus

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01007.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The main source of P, Fe and DOC in the humic Lake Tjeukemeer is superfluous water pumped from surrounding peaty polders. Most particulate P is intracellular but almost all particulate Fe is abiotic.2. The size and molecular weight of the P, Fe and DOC (mainly fulvic acids (FA)) were determined by ultrafiltration and Sephadex G‐100 gel filtration. Throughout the year most dissolved P and Fe was in colloids>35 nm with apparent molecular weight between 30,000 and 150.000. The bulk of FA occurred in particles<35nm.3. Calculating the atomic ratios of P, Fe and organic C in the different size classes revealed that Fe‐FA chelates are a minor species of the Fe pool. Less than 10% of the fulvic acids occurred as Fe‐FA chelates.4. Based on their apparent size and molecular weight, the Fe‐FA chelates are colloidal aggregates, probably with the formula Fen‐1(FA)n.5. About 50% of the dissolved P had the same size as the Fe‐FA aggregates. These aggregates were only noticeable in winter when humus‐rich polder water was flushed through the lake. During the rest of the year the dissolved Fe and P consisted mainly of acid‐labile inorganic colloids which might have been org

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01008.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The midsummer succession of cladoceran zooplankton in Lake Texoma was examined by demographic characterization of lake populations and a parallel set of life table experiments in which the dominant cladoceran species were raised on naturally occurring lake phytoplankton at lake temperatures.Diaphanosoma leuchtenbergianumoccurred throughout the study period (mid June‐mid August 1981) butDaphnia parvula, D. galeata mendotaeandCeriodaphnia lacustriswere rarely detected after 15 July.2. Analyses of size structure and size‐specific fecundity of the cladoceran populations showed that (1) size structure shifted to smaller individuals in mid July, (2) size‐specific fecundity was relatively constant in the smaller size classes and was constant or declined in larger females of each species, and (3) size at maturation did not vary significantly during the study of any population.3. Individual growth rates of the twoDaphniaspecies andCeriodaphniain the life table experiments were significantly lower in mid July when populations were declining and when size structure of each population was more dominated by smaller Individuals. The reduction in individual growth rates was short‐lived in the life table experiments; growth rates returned to pre‐decline levels by the end of July.4. Two effects of temporary reductions in individual growth rates when size‐specific fecundity and size at maturation are constant are (1) that size structure is temporarily shifted to smaller individuals, and (2) the potential rate of population growth is reduced because of delays in reproduction. Because data on size structure and size‐specific fecundity are commonly used to evaluate the relative effects of predators and resource changes on populations it is noteworthy that erroneous conclusions about the mechanism of population decline may be reached when individual grow

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01009.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The initial colonization of periphyton on natural and artificial apices ofMyriophyllum heterophyllumMichx was compared at three depths in the littoral zone of Lake Winnipesaukee, a soft‐water New England lake. After a 1 week incubation period, the apices were sampled and the periphyton was removed and counted as numbers of periphyton organisms per centimetre of stem.2. Initial colonization on both substrates was characterized by diatoms, particularly small single‐celled species, throughout the spring and summer. Blue‐green and green algae occurred in low numbers on both substrates during mid‐summer, usually forming a greater percentage of the population of the natural apices. Blooms of the green algaZygnemasp. dominated both substrates in late August.3. Community composition generally did not differ significantly by depth or substrate on the natural and artificial apices: however, total abundance was significantly greater on the natural apices.M. heterophyllumappeared to serve as a neutral substrate in terms of community composition but had a positive effect on the total numbers o

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb01010.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY