摘要:

SUMMARY1 Hyalella azteca(Amphipoda) inhabiting macrophyte beds in eight Canadian Shield lakes were sampled during the ice‐free seasons of 1984 and 1985. These amphipods were found to be predominantly univoltine in contrast to suggestions from a previous study.2 Annual production determined by the size‐frequency method ranged from 1.21 to 2.77g dry wt m−2year−1, and are the highest rates recorded for this species in temperate waters.3 Turnover rates (P/B ratios) ranged from 2.27 to 3.48 and are among the lowest values that have been measured. A synthesis of these data indicates that H.aztecaturnover rates increase sigmoidally with degree

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00818.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Behavioural experiments were performed in artificial stream channels to determine if nymphs of the mayflyParaleptophlebia adoptiva(Ephemeroptera: Leptophlebiidae) respond to (i) chemical cues from stonefly nymphs, (ii) chemical cues from disturbed conspecific mayflies, and (iii) body fluids of injured conspecifics, and (iv) whether responses to these chemical cues are different when combined with contact by foragingAcroneuria carolinensisstonefly nymphs (Plecoptera: Perlidae).2 Although none of the chemical cues elicited changes in mayfly behaviour in the absence of predator contact, stonefly chemical cues significantly enhanced the avoidance response of mayflies to stonefly contact. Mayfly nymphs swam more frequently and crawled further in response to predator encounters when chemical cues were present than when chemical cues were absent. Thus, direct stonefly precontact chemical cues appear to sensitizeP. adoptivato the potential for an encounter withA. carolinensis, enabling stronger escape or avoidance responses upon contact.3 Mayfly chemical cues that provide indirect information about the proximity of a predator (disturbed or injured conspecifics) did not stimulate increased mayfly response to stonefly contact. Indirect cues may provide less reliable information about the proximity of a stonefly than chemicals emitted directly from an adjacent predator. Mayflies might use chemical cues only in the presence of predator contact because of the high cost of premature escape in a running water s

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00819.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The accrual of organic matter, chlorophyllaand bacteria, and the activities of various extracellular enzymes were studied during biofilm formation on River Red Gum (Eucalyptus camaldulensis) wood submerged in two temperate Australian billabongs for 24 weeks over summer and winter of 1989–90.2 Peak organic matter content of the biofilm ranged from 0.7 to 3.3mg AFDW cm−2, chlorophyllacontent from 1.3 to 4. 2μg cm−2and bacterial abundance from 18 × 106to 94 × 106cells cm−2. Most variation in organic matter content, chlorophyllacontent and bacterial abundance in the biofilms couid be attributed to the duration of immersion (28–48% of variation) and to the interaction between site and submergence period (11–12%). Differences between sites and between seasons were less important in explaining total variation.3 Alkaline phosphatase, aminopeptidase and [3‐D‐glucosidase activities, determined per unit substratum surface area, were up to 138 ± 26 nmol cm−2h−1, 113 ± 1 nmol cm−2h−1and 9.3 ± 2.2 nmol cm−2h−1, respectively. Activities of these three enzymes determined per unit organic biomass were up to 203 ± 25, 157 ± 13, and 16 ± 2.1 nmol mg1AFDW h−1respectively. Enzyme activities expressed on an area‐ or biomass‐specific basis responded differently to the effects of season, site and duration of substratum exposure.4 Few consistent relationships could be established between the activity of a given enzyme system and the activity of other enzymes, nor with the various biomass parameters, such as total organic matter content, chlorophyllacontent or bacterial abundance.5 We suggest that submerged wood of the River Red Gum is an important site for biofilm development in lentic systems in south‐eastern Australia, and thus as a food resource for grazing invertebrates and for t

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00820.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Seston elemental composition (C, N, P) and the orthophosphate uptake rate constant,k(upt), were measured in the epilimnion of the eutrophic Římov Reservoir in the period March‐August 1989.2 Seasonal series of log C/P, log N/P and log [k(upt)] values were highly correlated (r2in the range 0.84–0.93), but, based on literature‐derived criteria,k(upt) values indicated stronger P deficiency than did the C/P values.3 The results showed moderate to strong phosphorus deficiency in summer, moderate deficiency at the end of the spring peak of phytoplankton, and no deficiency early in the spring or during the spring clear

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00821.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The susceptibility of ciliates in a mesotrophic lake to predation byEpischura lacustris, Diaptomus minutusand D.pygmaeuswas assessed during summer. Oligotrichs, particularlyStrobilidium velox(c. 43 μm), were removed efficiently by adult copepods and contributed substantially to the diet of femaleD. minutus. The presence of approximately 1,6 adultEpischura1‐−1, or sixteen adult femaleDiaptomus1‐−1, could halt the growth of S.vechxpopulations in summer.2 Factors affecting the rate at which copepods prey on ciliates were examined in experiments with D.pygmaeusand cultured ciliates. Rate of predation on S.velox, the preferred species, became saturated at 5 S. veloxml−1(45ngCml−1) and did not change with a 10‐fold increase in alternative algal food.3 Behavioural differences among ciliates, and the presence of other ciliates, contributed to differences in ciliate susceptibility to predation and suggest reasons why rates of removal of ciliates are not related to ciliate size.4 By feeding selectively, at high rates, calanoids may suppress populations of some ciliates and thereby influence microzooplankt

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00822.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The spatial and temporal distributions of the most abundant bdelloid rotifer,Embata laticeps(Murray), inhabiting the sediment surface and the hyporheic interstitial of a gravel stream were investigated between October 1991 and October 1992. Three temporal peaks of population density occurred during the year at the sediment surface differing in their riming from the density peaks detected within the bed sediments.2 The depth distributions ofE. laticepsin pool and riffle areas differed significantly. Higher abundances were found between 10 and 20 cm depth in the pool and between 20 and 30 cm in the riffle area. In these two sites a significant effect of surface discharge (estimated 1 week before sampling) on rotifer densities was found. Discharge greater than 0.424 m3s−1significantly reduced the densities in the riffle, while only at values greater than 1.660m3s−1were abundances influenced in the pool area.3 The percentages of egg‐bearing females were higher within the bed sediment than in the surface layer, and in the pool area than in the riffle. Thus, overall mean values of population increase were higher in the pool habitat (x̄= 0.015 ± SE 0.029 day−1) than in the riffle and at the sediment surface (x̄= 0.004 ± 0.025 and 0.005 ± 0.026 day−1, respectively). In addition, population growth fluctuated more strongly at the sediment surface than within the hyporheic intersiritial. Comparison of the observed values of population increase with a randomization test, where observed densities were randomly permuted, revealed no significant differences between those observed and values from a random model. Thus, a clear trend in population growth ofE. laticepsover time could not be demonstrated i

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00823.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 In a study of five ponds sensitive to acid precipitation, we document seasonal acidification profiles and assess the impact of short‐term acid pulses on the reproductive success of resident sunfish (Lepomisspp.).2 Three years of water sampling at 2–3 week intervals showed substantial seasonal variation in pH and alkalinity consistent with a carbonate buffering system. Though all ponds shared a common seasonal pattern in pH, ponds with relatively low pH and alkalinity showed the greatest variation in these parameters. Spring minima may dispose some of the ponds towards episodes of extreme acidity during heavy spring rains.3 Otolith analysis of young‐of‐the‐year sunfish revealed recruitment failures for eggs laid early in spring in ponds with relatively low alkalinity and pH, and, in the most extreme case, missing day classes at subsequent irregular intervals even though average pH and alkalinity were well above those demonstrated to affect centrarchid fishes.4 Age‐class distributions of sunfishes revealed gaps in adult age distributions which could be traced through 3 years of the study, but there was no clear‐cut relationship between pond acidification and the age structure of adult fish.5 Seasonal profiles of acidity may enable researchers to predict the time during which a pond or lake may be highly sensitive to acid inputs. Comparative otolith analysis of young‐of‐the‐year fishes and short‐term continuous monitoring of water chemistry may provide an early warning of biological effects of acidificati

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The major components of the microbial food web (dissolved organic carbon, bacteria, protozoa, rotifers and algae) of Priest Pot, a small freshwater pond, were investigated over a period of 5 months. Water samples were collected from the epilimnion every 1–3 days.2 Time series analysis helped identify the trophic relationships within the planktonic community. There were strong predator—prey relationships between both ciliates and large rotifers and the total nanoplankton, between rotifers and small ciliates and between the total microzooplankton community and phytoplankton. Small rotifers and small ciliates probably share the same food resources. The major bacterivores in the system could not be identified with our methods. However, our previous results point to a dominating role of nanoplanktonic (2–20 μm) heterotrophic protists as the main grazers of bacteria.3 Rotifers are the major type of metazoan zooplankton in Priest Pot; crustacean zooplankton are absent from the community. Bacterial production probably reaches rotifers via a variety of pathways: there may be a three‐step link from bacteria to bacterivorous nanoplankton, to ciliates and then to rotifers. Furthermore, a strong correlation between the nanoplankton and rotifers suggests a direct link between these components, implying a much shorter pathway. Some of the rotifers in the pond can graze directly on bacteria, and many of the larger planktonic organisms (large ciliates and rotifers) are algivores. The latter two predator—prey relationships suggest an efficient transfer of bacterial and primary production to highe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Two methods for estimating the average body size at the onset of reproduction were applied to populations ofDaphnia hyalina. The first, ‘average maturation size’, assesses maturity by the relative length of abdominal processes ofDaphnia; the second, ‘size at first reproduction’ (SFR), calculates the size class in which 50% of the maximum proportion of egg‐bearing females is reached.2 The influence of environmental factors on the expression of the difference in length between the first and the second abdominal process was tested in the laboratory. Neither temperature nor chemical cues from predators affected the difference in length, but the processes were indistinguishable at very low food concentrations.3 During one season,D. hyalinaexhibited pronounced changes in fecundity, proportion of egg‐bearing adults and SFR. The pattern obtained by the two methods was similar in many cases, although maturation size estimated by the first method was slightly smaller than SFR obtained by the second method. Neither method gave reliable results during times of starvation (c

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00826.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The dispersal of adult Trichoptera at the small Danish forest brook, Stamperenden, was studied from 10 May to 6 October 1990 using Malaise traps placed across the brook, parallel to the brook at distances of 2, 20 and 40m, and perpendicular to it at a distance of 1–3m.2 Of the total of 4175 specimens caught, lotic species breeding in Stamperenden accounted for 95.6%. The dominant species wereAgapetus fuscipes, Lype reducta, Plectrocnemia conspersa, Potamophylax nigricornisandSilo pallipes.3 The sex ratios in the catches of most species were uneven.Agapetus fuscipesmales were in excess, probably because males fly more frequently than females.4 The dominant species flew predominantly above the surface of the brook. Whereas both sexes ofA. fuscipes, L. reductaand S.pallipeswere rarely found even as little as 20–40m from the brook, the dispersal range ofP. conspersawas much wider.5 The implications of low dispersal for the biological recovery of damaged but subsequently restored streams and stream catchments are discussed. It is concluded that complete biological recovery may be a process requiring decades unless the original aquatic fauna is re‐establish

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00827.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY