摘要:

SUMMARY1. We analysed the effect of several variables on the morphology of the rotiferKeratella tropicawith the aim of accounting for its morphological variability in nature. We used field data from (i) an extensive survey of Argentine lakes, (ii) a 1.5 yr, monthly sampling of Salto Grande Reservoir, and (iii) a 3‐month, outdoor experiment in fish culture tanks. In addition, we performed a series of laboratory experiments aimed at isolating the effects of different variables.2. The increase in crustacean biomass and the amelioration of their nutritional status (measured as the reciprocal of the starvation time) caused spine enlargement. In contrast, the presence of decomposers caused reduction of the spines. These results support the idea that a major proportion of the phenotypic expression ofK. tropicadepends on the concentration of an inducing factor, which in turn depends on the balance between release and decomposition rates of the chemical.3. Food concentration was identified as a secondary factor affecting morphology. In agreement with records for other rotifers, food concentration and spine length were inversely related. Both factors, crustacean chemicals and food availability, seemed to act independently, at different developmental stages. Our experiments suggest, however, that the most exuberant individuals can only be induced through chemicals released by predators and competitors.4. The presence of backswimmers (Notonectidae) resulted in individuals with very short or non‐existing posterior spines. Filtrates of backswimmer‐conditioned medium also produced a significant, although less striking, spine inhibition. Thus, different chemical factors seem to have opposite effects onK. tropicamorphology. Those released by crustaceans induce spine elongation, while those released by backswimmers inhibit spine development.5. Genetic differences were also identified as a source of morphological variability. Under identical laboratory conditions, different clones had spines of different length. Our experiments also suggest an inverse relationship between spine length and growth rate. The latter result, however, is based upon only three clones ofK. tropicaand is thus prelim

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00587.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Invertebrate herbivory on submerged freshwater macrophytes, measured as per cent leaf area lost, was determined for sixteen species and forty‐two populations of macrophytes during peak summer biomass in Danish streams and lakes.2. All seventeenPotamogetonpopulations and seventeen of the remaining twenty‐fivenon‐Potamogetonpopulations were grazed. Species ofPotamogetonwere significantly more heavily grazed (mean 4.2%) thannon‐Potamogetonspecies (mean 0.8%). Herbivory losses were not significantly different between stream (mean 2.4%) and lake populations (mean 1.9%). Wide ranges in herbivory loss were observed between species from the same locality and within species from different localities. The location of main damage to either old or young leaves was not species specific but varied among localities. Additional data for four macrophyte populations showed that herbivory loss had a strong seasonal variation (e.g. 1.0–26.3% forPotamogeton perfoliatus), with maximum losses during May‐June.3. Although the mean defoliation percentages were low during the period of maximum macrophyte biomass, they were not systematically lower than encountered for terrest

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00588.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Two species of freshwater mussels,Lampsilis radiata siliquoideaandAnodonta grandis grandiswere measured and permanently marked with pointed, plastic tape positioned at the postero‐lateral edge of the shell. Mussels were returned to original conditions at two sites in an oligotrophic lake, retrieved at yearly intervals, re‐measured, and external annuli that had been added since marking were counted.2. External annuli were formed much less frequently than annually; the overall median number of annuli formed each year was 0.5. In one of the four populations studied, the rate of annulus formation was>1 in small animals and<1 in large ones. Many mussels showed no new external annuli at all, even several years after marking.3. Ford‐Walford plots of shell annuli did not yield consistent indices of shell growth. Repeated measurement of mussels in successive years showed that estimates of growth based on shell annuli consistently overestimated real shell g

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00589.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand‐bottomed, headwater stream in Virginia, U.S.A.2. Annual mean density and biomass of predators in debris dams were 3897 individuals m−2and 2.5 g dry mass m−2, respectively, but only 711 individuals m−2and 0.2 gm−2on the sediment. Predator production was 8.36 gm−2yr−1in debris dams compared to 1.52 gm−2yr−1on the sediment. Annual predator production, weighted by habitat availability, was 1.73gm−2yr−1.3. The predominant taxa in terms of production were the chironomidsThienemannimyiaspp, complex,Ablabesmyia parajanta, Zavrelimyiasp., and the odonateCordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild.4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 gm−2yr−1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the chan

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00590.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Visual sensitivity of the mayfliesStenacron interpunctatum(Say) andStenonema vicarium(Walker) to red (650 nm) and infra‐red (950 nm) light was tested using a behavioural assay. Nymphs were placed in a runway and sequentially exposed to green light, red light, infra‐red light and no light (control) at one end of the runway. The distance run away from the light, and the number of alarm reactions to the light were recorded.2. Both species reacted strongly to both red and green light, running significantly greater distances and reacting more frequently to these wavelengths of light than to either infrared light or the control.3. These results show that unobtrusive observations of mayfly nocturnal behaviour should be made using infra‐red, and not red light, for illumination. Previous studies of aquatic insect nocturnal behaviour may have produced biased results if red light was

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00591.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Temperature, oxygen concentration and zooplankton density were measured simultaneously on 25 December 1990 at twenty‐six stations during an acoustic survey of the fish population of Lake Kinneret, Israel. Data from a preliminary acoustic survey were used to establish the optimal distance between transects (4km).2. The distribution of temperature and oxygen concentration (and their gradients), and zooplankton and fish densities were compared using three‐dimensional plots and correlation analysis. Both fish and zooplankton were concentrated in frontal zones where temperature and oxygen gradients were highest.3. In the south‐eastern part of the lake, where fish abundance was highest, a minimum of zooplankton density was observed, suggesting that predation by fish reduced zooplankton concentra

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00592.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Nutrient‐diffusing artificial substrata were used in summer and autumn to assess limiting nutrients for periphytic algal growth in streams draining sub‐alpine, forested, agricultural and urban catchments in eastern Victoria, Australia.2. Chlorophylladensity was primarily limited by nitrogen in most cases; often phosphorus was secondarily limiting. One sub‐alpine, one forest and one agricultural stream were primarily phosphorus limited in at least one season. Added trace elements and vitamins did not increase chlorophyll density.3. The dominant filamentous algal genera did not differ greatly between various nutrient enrichments. However, the relative abundance ofStigeodaniumspp. was sometimes increased on substrata containing the limiting nutrient.4. The results suggest that nutrient limitation is a widespread phenomenon in Victorian streams, and that limiting nutrients can be inferred from stream‐water nitrogen to phosphorus ratios in many in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00593.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The vertical migration behaviour in electrophoretically distinguishable clones ofDaphnia magnaStraus was investigated.2. Clones differed significantly in their tendency to stay near the surface of the tank during the light phase of the daily light/dark cycle, indicating that vertical migration has a genetic component.3. There was a significant difference in behaviour between juvenile and adultDaphnia: overall the juveniles stayed closer to the water surface than the adults, but the characteristic pattern of clonal differences persisted in the juveniles.4. When an adult population of each clone was exposed to a fish predator in an experimental tank, the position a clone maintained in the tank at the start of the day had a direct effect on its survival. Clones remaining near to the surface of the water suffered greatest predarion.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00594.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. This paper presents geological, climatic, morphometric and hydrological data, collected from 1941 to 1991, on a lowland kataglacial lake and its catchment, as a basis for the development of a descriptive hydrological model.2. The catchment occupies an area of 2.56 km2, at altitudes of 73–130 m above sea level, and receives an average annual net precipitation of 558 000 m3. The surface geology consists principally of sandy glacial drift and peat overlying Triassic strata which are exposed at the western extremity of the catchment.3. The mere (lake) has an asymmetrical basin lying in sandy glacial drift and peat. The area (18.4–22.9 ha), depth (7–8 m) and volume (320000–453000m3) fluctuate in relation to net precipitation in at least two ways: an immediate response and a response with a rime lag of approximately 2 years.4. The pH, normally<5.5 but varying from 4.0 to 7,8, and ionic composition of the mere fluctuate. The evidence suggests that the fluctuation is a response to at least two essentially separate types of water supply: a base‐poor surface supply and a base‐richer supply entering at a depth of 4m.5. Essentially, the descriptive model postulates that the mere waters are controlled by a water‐table of varying level, in relation to net precipitation, which is base poor at the surface but becomes increasingly base ri

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00595.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Extensive measurements of near‐bed flow velocity were made over a reconstructed section of a cobble‐bed stream using a laser‐Doppler velocimeter. Based on these measurements descriptions of the near‐bed flow structure and flow conditions within benthic habitats are made.2. The near‐bed flow classification system of Davis&Barmuta (1989) is discussed, and the threshold criteria of the system are shown to be incorrect. The correct criteria are stated and discussed in the context of two‐dimensional uniform bed roughness.3. The improved classification system is used to classify the laboratory near‐bed flow regime, and this classification is compared to the flow types depicted in near‐bed flow structure diagrams. This comparison highlights the importance of accurately assessing stream‐bed roughness parameters to obtain accurate and useful near‐bed flow classifications.4. The potential limnological applications of near‐bed flow regime classifications are discussed, with improved benthic invertebrate sampling procedures being given as the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00596.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY