摘要:

1. Although marine research has indicated that metabolic fractionations of13C due to differences in organismal trophic position and proximal composition can complicate the isotopic interpretation of energy flow pathways, such potentially confounding problems have never been examined in freshwater benthic food webs.2. The δ13C values of animals comprising a littoral benthic food web composited from four Canadian Shield lakes showed no relationship with either individual trophic position (δ15N) or lipid content (C/N ratios).3. Differences in the relative incorporation of autochthonous and allochthonous energy sources by freshwater benthic organisms will alter their δ13C and δ15N values, thereby masking any possibility of observing13C trophic enrichment.4. Removal of the possibly confounding influences of lipids through either empirical correction or by analytical extraction may be unnecessary in studies of freshwater benthic food webs. Likewise, a priori adjustments in δ13C for freshwater benthic organisms in order to accommodate trophic fractionations which are presumed to occur, based on data from marine offshore food webs, may also be inappropr

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00052.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. We assessed the patterns of amphibian species richness and distribution in relation to water chemistry over a large geographical area in 1992–94.2. Thirteen amphibian species were observed at 180 ponds, with mean species richness 3.5 ± 0.13 species per pond (range zero to nine). Water samples were collected from 143 ponds, analysed for fifteen chemical variables, and further analysed by multivariate statistical techniques.3. Water in the study area was hard, alkaline and well‐buffered against pH change, and most ponds were eutrophic. Amphibian species richness was negatively correlated with five chemical variables (chloride, conductivity, magnesium, total hardness, turbidity).4. Principle components analysis reduced the data set to four chemical components that explained 65.4% of the variance in the original variables. Principle component scores were retained for use in further multivariate tests. Multiple regression accounted for only 19.0% of the variance in amphibian species richness. Discriminant function analysis (DFA) was used to determine if water chemistry variables discriminated among species, but it was only able to classify 17.5% of cases correctly. DFA was also used to determine if water chemistry distinguished between used and unused sites for individual species. DFA was moderately successful, classifying 61–77% of cases correctly.5. General water chemistry appears to play only a minor part in affecting amphibian species richness in south‐western, Ontario. However, chemical variables may be helpful to distinguish between used and unused sites for some

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00054.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Clones ofDaphnia longispina(O.F.M.), collected from ponds with different levels of predation, were monitored using video techniques in order to test the effects of temperature and visual cues on vertical migration behaviour.2. Endogenous rhythms were found to have a part in the control of vertical migration in some clones but responses were highly variable.3. Low temperature caused a marked increase in the amplitude of vertical migration inD. longispina, consistent with field studies.4. Clones from ponds with fish predators had larger vertical migration amplitudes than clones from ponds with no fish, providing further evidence for the genetic basis of this mechanism.

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00055.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The occurrence of larvae ofLimnephiluscoenosusandL. vittatus(Trichoptera) was recorded in 103 rock pools both before and after the dry periods in spring–summer (April–May and July–early August), when a great number of the pools dried out. In early spring, 84% of the pools sampled contained larvae of at least one of the species.Limnephilus coenosuslarvae were present in a higher proportion of pools that later dried out than in the permanent ones, whileL. vittatuslarvae were predominantly found in permanent pools. Larvae of both species were found together in 31% of the inhabited pools.2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases ofL. coenosuslarvae held water more efficiently than did the mineralL. vittatuscases. Full‐grown (fifth instar)L. coenosuslarvae also survived dry conditions better than didL. vittatuslarvae. The higher survival ofL. coenosuswas due to a combination of drought‐resistant case material and a higher survival ability of the larvae themselves.3.Limnephilus vittatuslarvae were restricted by their low capability to withstand desiccation, although case material and food were available forL. vittatuslarvae in all pools. Absence of case material and high‐quality food in many pools, however, restricted the presence ofL. coenosuslarvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations ofL. coenosussurvived until pupation.4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival ofL. coenosuslarvae during drought, together with the water‐retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as te

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00057.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. A fertilization experiment was performed to identify the limiting nutrient for the growth of submerged vegetation in ditches of a peat‐grassland system in the Netherlands, in which restoration measures involved ceasing fertilization, exporting nutrients by removal of above‐ground plant mass and large‐scale introduction of calcium‐rich, nutrient‐poor artesian water.2. Growth ofElodeawas significantly enhanced by enrichment with nitrogen alone, and by fertilization with nitrogen in combination with phosphorus, and by nitrogen in combination with phosphorus and potassium.3. Plant tissue nutrient concentrations increased significantly, for nitrogen by enrichment with nitrogen alone, and with nitrogen in combination with phosphorus and potassium; for phosphorus by enrichment with phosphorus alone and with phosphorus in combination with nitrogen and potassium; tissue concentrations of potassium were not enhanced by any treatment.4. The elemental ratios of treated plants indicated that nitrogen, rather than phosphorus, was limiting in all treatments, except in those involving nitrogen and NK enrichment (when phosphorus was limiting).5. The efficiency with which plants used nutrients declined with increased supply of nitrogen and phosphorus, but was unchanged when potassium was increased. Efficiencies were similar to those of other aquatic ma

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.d01-474.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Lake Okeechobee is a large (1732 km2), shallow (mean depth 2.7 m), eutrophic, subtropical lake located in southern Florida. Approximately 25% of the lake surface area is occupied by an extensive littoral zone. From August 1988 to June 1992, ≈ 2000 zooplankton samples were collected throughout the lake.2. During the study period, a severe drought lowered lake levels more than 1 m. At low and normal lake stage, the average lake‐wide abundance of rotifers (c. 2000 l–1) was greater than during high water periods (c. 1600 l–1). The average abundance of adult crustaceans (cladocerans and copepods) (c. 30 l–1) varied little regardless of lake stage.3. Although only minor differences were apparent when lake‐wide means in rotifers and adult crustaceans for each lake stage were compared, pronounced differences were evident in the distribution of zooplankton communities within Lake Okeechobee. During high and normal lake stage, both rotifer and adult crustacean populations were more uniformly distributed throughout the lake. At low lake stage, the densest zooplankton populations were concentrated in the transition area between the central lake and the littoral fringe. The abundance of all zooplankton groups was inversely correlated with lake stage, but the relationship was much stronger for rotifers than crustaceans. Both rotifer and crustacean zooplankton population densities were positively related to increased phytoplankton biomass (as measured by chlorophylla) but the relationship was much stronger for rotifers than

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00071.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8‐year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status.2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir’s euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyllaconcentration was significant only for the MRR regression.3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow.4. Although the colour of catchment run‐off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log10transformed data for both reservoirs.5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turb

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00072.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Relatively undisturbed streams in continental U.S.A. were classified according to variation in ten ecologically relevant hydrological characteristics. Measures of flow variability and predictability for average conditions, as well as for low‐ and high‐flow extremes, were extracted from long‐term (15–58‐year) daily streamflow data for 806 streams.2. Two groups of sites were analysed: all 806 sites and a subset of 420 ‘best’ sites. For each group, cluster analysis identified ten distinctive stream types, seven permanent and three intermittent. The geographical clustering exhibited by the stream types indicated regional differences in climatic and geological features. A bootstrapping technique applied to the permanent stream classes showed the majority of them were statistically robust.3. The derived classification of U.S. streams based on ecologically relevant hydrological characteristics provides a comprehensive catalogue of small to mid‐size streams that, according to ecological theory, may differ in major aspects of their ecological organization. The classification provides a basis for hypothesis generation and affords an objective framework for matching streams for purposes of comparative ecological investigations.4. A subset of 118 streams from the ten classification groups was selected to determine whether certain hydrological variables often used by ecologists to make cross‐system comparisons are sensitive to the temporal coarseness of the hydrological time series used to derive the variables. The three hydrological variables considered were streamflow predictability, streamflow variability and flood timing.5. Streamflow predictability (using Colwell’s Index) was calculated at daily, weekly, monthly and seasonal time scales. Estimates of predictability showed either no change across time scales, a gradual and consistent increase across time scales, or a maximum value at the monthly time scale. Coefficient of variation of streamflow was calculated at daily, weekly, monthly, seasonal, and annual time steps. Daily values were always greatest for all streams. Some groups showed minimum variability at the monthly scale, others at the seasonal. Timing of daily peak flows could be detected with 50–90% accuracy across stream groups using coarser grain monthly and annual hydrographic data.6. Inferences about hydrological similarity among streams across broad geographical scales can be sensitive to choice of time scale used in the hydrolog

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00073.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Egg masses, oviposition site preferences, and abiotic and biotic factors causing mortality during embryonic, larval and adult life stages of Apatania fimbriata were studied. Laboratory investigations provided information on the temperature dependence of embryonic development, measured as an increase in egg volume.2.A. fimbriatalaid hemispherical egg masses, consisting of a transparent matrix containing a mean of 208 eggs. Egg masses were laid on stones situated just above the water surface in dark cavities in the stream bank.3. Two hundred egg masses were mapped and individually monitored during embryonic development. There was no significant correlation between mortality during embryonic development and any of the abiotic parameters measured. First‐instar larvae ofOsmylus fulvicephalusconsumed developing eggs, and chironomids preyed on newly hatched larvae.4. A mean of seventy‐two females emerged per metre of stream. Mortality during the 1993/94 life cycle was measured as a percentage of the potential number of eggs laid. Female mortality between emergence and oviposition was ≈ 80%. Eight per cent of individuals were lost during embryonic development. Larval mortality to emergence in 1994 was 11.3%. This indicates that the terrestrial life stage is probably decisive in the regulation ofA. fimbriatapopulations.5. Duration of embryogenesis at constant temperatures (4–20 °C) in the laboratory was described best by a negative exponential function. This species is cold stenothermal and there was no hatching success at 20 °C.6. Egg volumes during embryonic development increased sigmoidally

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00081.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Inputs of terrestrial arthropods (number and mass m–2d–1) from riparian corridors to three streams representing different orders were highly variable among seasons and sites, with significantly greater (P<0.05) inputs at the headwater stream during summer months, compared with other sites and seasons.2. No significant differences in estimates of stream retention of terrestrial arthropods (number and mass m–2d–1) were observed among sites; however, retention of terrestrial arthropods at all sites was significantly greater during summer months, compared with other periods.3. The gravimetric proportion of terrestrial arthropods present in the stomachs of redbreast sunfish (Lepomis auritus) and bluegill (L. macrochirus) was equivalent among sites. However, estimates of the dietary importance of terrestrial arthropods at all study sites were significantly greater in the summer, compared with other seasons.4. Estimates of the potential annual energetic contribution (kJ m–2d–1) of terrestrial arthropod inputs to the stream system were comparable with published rates of total annual production of aquatic macroinvertebrates in other Virginia headwater streams.5. Results of this study supported the hypothesis that terrestrial arthropods represented an important energetic subsidy to stream fish during periods of low aquatic macroinvertebrate availability, and suggest that this component of allochthonous input is a potentially significant, but poorly understood energetic linkage between riparian landscapes and stream

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00080.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY