摘要:

Growth and reproduction of three different-sizedDahniaspecies were measured under increasing competitive conditions. Only when food was not limiting, the largest speciesD. magnawas superior to both smaller species with respect to total production and production of offspring. This advantage disappeared when the availability of food decreased. Under limiting conditions all three species had similar rates of production; thus, they utilized the available food resources with the same efficiency. Finally, at the lowest food concentrationD. magnawas no longer able to reproduce, but the smallest species,D. longispina, still produced eggs. Therefore, contrary to the “Size Efficiency Hypothesis.” the smallest species was the best competitor.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664609

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Bluegills (Leomis macrochirus) collected from discharge (heated) and intake (unheated) areas of a power plant cooling reservoir in South Dakota in 1979 were opportunistic feeders. The number of taxa ingested, evenness values, and meal sizes were generally similar between areas. However, several major differences between areas with respect to the relative contributions of ingested food categories to the diets were observed. Differences in diet composition between areas were explained by the relative abundances of food items as influenced by temperature and substrate for food organisms occurring in the reservoir.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664610

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Data collected during a limnological survey of 165 Florida lakes were used to examine statistical relations between chlorophyllaconcentrations and the abundance of total zooplankton, cladocerans, copepods, crustaceans, and rotifers. Abundances of the different groupings of zooplankton were positively correlated with chlorophyllaconcentrations, but all correlation coefficients were less than 0.72. Rotifers were most strongly correlated with chlorophyllaconcentrations during the summer (r=0.71). No major changes in community composition could be demonstrated with increasing chlorophyll levels. Empirical models derived from regression analyses were developed to predict zooplankton abundance from measures of chlorophyllaconcentrations.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664611

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Movements and densities of three species of darters were studied in a pool-riffle system during the spring spawning period. A total of 677Etheostoma flabellare, 212E. spectabile, and 200E. niqrumwere marked and released during the study. Fifty-one (19%) of 268 marked, recapturedE. flabellaremoved from their area of initial capture; values forE. spectabileandE. niqrumwere 27 (35%) of 78 and 8(24%) of 33, respectively. Most (70%) movements byE. spectabilewere in an upstream direction; movements byE. flabellareandE. niqrumwere equally distributed up- and downstream. Density estimates forE. flabellareandE. spectabilein riffles were 4.05 and 1.35/m2, respectively, and forE. niqrumin pools, 2.06/m2.E. spectabilemay make upstream spring spawning migrations, whileE. flabellareandE. niqrumremain comparatively sedentary. Competitive interactions between migratory and non-migratory darters may act to regulate darter densities in spawning areas.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664612

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

No detailed accounts of the microhabitat ofKrenosmittialarvae are available for North American species, although in Europe two species are known to be common in springs and moss filled seep areas. Recent speculation that larvae of the North American species occur in similar hygropetric or riparian microhabitats is contrasted with published and unpublished data that suggest the hyporheic zone of streams as an alternate hypothesis for the microhabitat of these larvae.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664613

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Submergent vegetation was removed from four locations in a shallow wetland lake containing a dense concentration of aquatic macrophytes. The distributions of selected species of zooplankton and macroinvertebrates were compared over a two month period between the vegetated sites and locations in which vegetation was removed.Chydorus, Al onella, GraptoleborisandScapholebrusshowed a preference for vegetated stations.Daphnia schodleriwas collected mostly in the open water. Three macro invertebrate predators,Enallagma boreale, Notonecta unifasciata, andHesperocorixa leavigatashowed a significant attraction to submergent plants over sites where vegetation had been removed as was also the case withHyallela aztecaandCallibaetis. Chaoborusan open water predator did not occur in significant numbers at vegetated stations but was most commonly observed in the deep water stations over the shallow sites. It is thought that predation ofD. schodleribyE. borealeis an important mechanism in reducing the number of this prey population especially during that time of year when dense concentrations of submergent plants are present in the lake.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664614

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Late instarBrachvcentrus americanuslarvae were collected just prior to and during normally high spring runoff; adults were collected immediately following runoff; and early instar larvae appeared during the late summer low flow period of September and October.Brachvcentrus occidentalisadults were collected prior to normal spring runoff and early instar were first collected following runoff during moderate flows of July and August. Both strategies helped these species avoid stresses of high water velocities and sediment scouring often associated with spring runoff. During the study period, yearly high stream flows and maximum sediment movement occurred during summer flushing releases from Electric Lake, rather than the normal spring runoff period. Increased stream discharges with associated sediment movement that occurred when early instarBrachvcentruslarvae were present, appear to have had noticeable negative affects. Whatever the cause, following these occurrences, either species having early instar larvae present during the occurrence, showed noticeable reductions in numbers of larvae. Inorganic suspended sediments associated with these flows could have interfered with feeding, scoured larvae off substrates, hindered respiration, triggered a drift behavior or possibly a combination of these and other factors. Whatever the cause,B. occidentalisnumbers were depressed and the distribution of numbers over the various larval body lengths was disrupted following flushes of 1975, 1979 and 1982.Brachvcentrus americanuslarvae did not show the same negative responses following these occurrences.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664615

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A new field washing technique for removal of invertebrates from aquatic vegetation was investigated. This technique, which involved field washing samples in alchohol (ETOH), was developed and tested with aquatic vegetation samples from two undisturbed lotic systems in Southern Nevada. Results indicated that approximately 60% of the animals were removed from watercress and algal mat samples by vigorous water washing in a bucket. Field washing of algal and watercress samples using ETOH removed an additional 20–40% of the total macroinvertebrates, with ETOH wash efficiency being higher in the watercress samples. Generally, tightly clinging organisms such as hydroptilid caddisfly pupae or case building midges were the only invertebrates not effectively removed from aquatic vegetation samples by a cambination of alchohol and water-washing in the field.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664616

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Zooplankton populations of Liberty Lake, Washington were investigated over a span of four years to determine the short-term effects of a series of multiphase lake restoration measures on lake zooplankton. The effects of the treatments, particularly of suction dredging of lake bottom sediments and of a two stage whole-lake aluminum sulfate application, were assessed by analyzing population density and biomass fluctuations of Rotifera, Cladocera, and Eucopepoda for several years before and after the treatments were completed. Suction dredging had no apparent effect upon the zooplankton in Liberty Lake. The gross effects of aluminum sulfate applications on the zooplankton population were also minimal. A sharp decline in numbers was observed in all major groups immediately following each alum application, but recovery was evident in the maintenance of typical seasonal growth patterns. The Eucopepoda exhibited rapid recovery following both alum treatments, responding most favorably to the short term oligotrophic-like conditions apparently created by the treatments. Similarities in zooplankton response to the alum application and to the May 1980 Mt. St. Helens ashfall are briefly discussed.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664617

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A laboratory study was conducted to determine (1) the effects of inorganic nitrogen and phosphorus enrichment on microbial leaf processing, and (2) whether inorganic nutrient enrichment would mitigate the effects of chemical perturbation of microbial leaf processing. Pre-leached disks from leaves ofAcer saccharumwere incubated in flasks of unfiltered stream water at 20°C for 56 days. Treatments consisted of a control, killed control (100.0 mg/1 HgCl2), nitrogen (3.0 mg/1 NO3-N), phosphorus (0.1 mg/1 PO4-P), nitrogen + phosphorus (3.0 mg/1 NO3-N + 0.1 mg/1 PO4-P), pentachlorophenol (10.0 mg/1 Na-salt of pentachlorophenol), and pentachlorophenol + nitrogen + phosphorus (10.0 mg/1 Na-salt of pentachlorophenol t 3.0 mg/1 NO3-N + 0.1 mg/1 PO4-P). Leaf disks in the control treatment lost 31% of ash-free dry weight in 56 days. Leaf decomposition, microbial biomass, and microbial activity increased in all treatments enriched with nitrogen. However, there were no increases in the treatment receiving only phosphorus. This implied that microbial leaf processing in certain aquatic systems may be nitrogen limited. Chemical perturbation by pentachlorophenol significantly reduced biomass and activity of microbes associated with leaves. However, nitrogen + phosphorus enrichment mitigated the effects of chemical perturbation.

ISSN:0270-5060    

DOI:10.1080/02705060.1984.9664618

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor