摘要:

SUMMARY1. Food preference, consumption and growth ofTipula lateralisfeeding on leaves of one exotic (Eucalyptus globulus) and three native trees of central Portugal (Alnus glutinosa, Castanea salivaandQuercus faginea) were investigated.2. Larvae preferred and consumed more alder than the other three species. Larvae fed oak and eucalyptus did not grow, while those fed alder had a faster mean specific growth than those fed chestnut. Alder also provided a higher and earlier peak growth rate, which occurred at 35 days vs. 91 days for chestnut.3. High values of survivorship to 126 days were observed in larvae fed alder and chestnut. All larvae fed oak died within 63 days; those fed eucalyptus died within 91 days.4. Leaf utilization byTipula lateralisseems to be negatively correlated with cuticle thickness and polyphenolic content and positively correlated with microbial colonization and nutrient content of the leaves. We hypothesize that the replacement of the original deciduous forest by eucalyptus plantations may induce deleterious changes in the associated invertebrate communities and stream ecosystem processes.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00881.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. The influence of inorganic nitrogen and phosphorus enrichment on phytoplankton photosynthesis was investigated in Lakes Bonney (east and west lobes), Hoare, Fryxell and Vanda, which lie in the ablation valleys adjacent to McMurdo Sound, Antarctica. Bioassay experiments were conducted during the austral summer on phytoplankton populations just beneath the permanent ice cover in all lakes and on populations forming deep‐chlorophyll maxima in the east and west lobes of Lake Bonney.2. Phytoplankton photosynthesis in surface and mid‐depth (13 m) samples from both lobes of Lake Bonney were stimulated significantly (P<0.01) by phosphorus enrichment (2 μM) with further stimulation by simultaneous phosphorus plus NH4+(20 μM) enrichment. Similar trends were observed in deeper waters (18 m) from the east lobe of Lake Bonney, although they were not statistically significant at P<0.05. Photosynthesis in this lake was never enhanced by the addition of 20 μM NH4+alone. Simultaneous addition of phosphorus plus nitrogen stimulated photosynthesis significantly (P<0.01) in both Lake Hoare and Lake Fryxell. No nutrient response occurred in Lake Vanda, where activity in nutrient‐enriched samples was below unamended controls; results from Lake Vanda are suspect owing to excessively long sample storage in the field resulting from logistic constraints.3. Ambient dissolved inorganic nitrogen (DIN) (NH4++ NO2−+ NO3−): soluble reactive phosphorus (SRP) ratios partially support results from bioassay experiments indicating strong phosphorus deficiency in Lake Bonney and nitrogen deficiency in Lakes Hoare and Fryxell. DIN : SRP ratios also imply phosphorus deficiency in Lake Vanda, although not as strong as in Lake Bonney. Particulate carbon (PC): particulate nitrogen (PN) ratios all exceed published ratios for balanced phytoplankton growth, indicative of nitrogen deficiency.4. Vertical nutrient profiles in concert with low advective flux, indicate that new (sensuDugdale&Goering, 1967) phytoplankton production in these lakes is supported by upward diffusion of nutrients from deep nutrient pools. This contention was tested by computing upward DIN : SRP flux ratios across horizontal planes located immediately beneath each chlorophyll maximum and about 2 m beneath the ice (to examine flux to the phytoplankton immediately below the ice cover). These flux ratios further corroborated nutrient bioassay results and bulk DIN : SRP ratios indicating phosphorus deficiency in Lakes Bonney and Vanda and potential nitrogen deficiency in Lakes Hoare and Fryxell.5. Neither biochemical reactions nor physical processes appear to be responsible for differences in nutrient deficiency among the study lakes. The differences may instead be related to conditions which existed before or during the evolution

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00882.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. The effects of food level on the development of crests byDaphnia carinatain the presence ofAnisops grains(Notonectidae) were investigated in two laboratory experiments and in the field.2. In the laboratory experiments D.carinatawere grown at different food levels either in the presence ofA. gratusor in predator‐free water. In the field study the effects of six variables (temperature, food level, density ofDaphnia, density ofAnisops, brood size and maternal nutrition) on development of crests in the next generation ofDaphniawere investigated over a 12‐month period at a single field site.3. In the laboratory food level had a small but significant effect on relative crest height of D.carinata. In the presence of notonectid predators the rate of crest growth relative to body length was higher than for controlD. carinataonly during embryogenesis and/or the first two neonatal instars. Beyond this age the rate of crest growth was similar in both morphs.4. In the field study, crest height was negatively correlated with density ofDaphniaand positively correlated with density ofAnisopsand maternal nutrition (maternal nutrition was defined as the somatic weight of a female with a body length of 2.5 mm, calculated from the length‐dry weight regression based on a sample of the population). However, these data were biased by a short period when noAnisopswere present in the pond. When these data were excluded, the only factor which significantly correlated with crest height was maternal nutrition. This finding indicated that relative crest height of the next generation was determined primarily during embryogenesis on the basis of maternal feeding success and possibly on food availability during the first two in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00883.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Picophytoplankton (picocyanobacteria and picoeukaryotes) communities in Lake Kinneret were studied from 1988 to 1992. No prochlorophytes were observed in the lake.2. Picocyanobacteria were a prominent and ubiquitous component of the phytoplankton, being present at all depths throughout the year, with concentrations ranging from 2 ± 10–8 ± 105cells ml−1. Low cell numbers in winter and spring were followed at the end of the annual dinoflagellate bloom by maximal abundances in summer‐autumn in the epilimnion. High cell numbers (>104cells ml−1) were sometimes also found in the anaerobic hypolimnion. Net growth rates for picocyanobacteria ranged from 0.29 to 0.60 divisions day−1.3. Picoeukaryotes were a very minor constituent of the picoplankton, mostly present in winter and spring, and sometimes at the end of autumn, with concentrations ranging from 44 to 5700 cells ml−1. Higher cell numbers tended to occur in the near surface water layers. In August‐September, picoeukaryotes were found only in the hypolimnion. In December, the occurrence of picoeukaryotes in the deep water layers probably resulted from advection with cold water currents from the Jordan river. Net growth rates for picoeukaryotes ranged from 0.26 to 0.43 divisions day−1.4. Overall, the contribution of picophytoplankton to the phytoplankton standing crop in Lake Kinneret was limited; picocyanobacteria and picoeukaryotes accounted for no more than 7.0 and 0.1% of total algal biomass (semiannual average), respectively.5. Picophytoplankton cell numbers in pelagic waters were usually similar to those in shallower lake stations.6. Picocyanobacteria appear to be an autochthonous population, whereas picoeukaryotes are probably brought annually by the Jordan River and do not maintain thems

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00884.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Several models predict that elevated levels of zooplanktivory will promote increases in phytoplankton abundance and corresponding decreases in water clarity. Because estimates of zooplanktivorous fish abundance are logistically difficult, empirical testing of these models has been limited. Our goal was to examine whether the impact of mysids and larval chaoborids on their herbivorous zooplankton prey is either transmitted to, or becomes uncoupled at, the phytoplankton and water quality levels.2. A secondary analysis of ninety‐eight correlation coefficients from twenty‐five published and unpublished data sets indicated that on average 71% of all correlations agreed with the predictions of top‐down trophic interactions, although most did so with only marginal or weak support.3. Potential confounding by variable nutrient concentrations, alternative determinants of water clarity and omnivory may complicate simple interpretation of the influence of pelagic invertebrates on zooplankton in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00885.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. This study shows that females ofSynchaeta pectinataEhrenberg can produce two morphologically and physiologically distinct kinds of amictic eggs that develop parthenogenetically into females. One kind, until now the only one known in monogonont rotifers, is a thin‐shelled (about 1.4 μm) subitaneous egg that develops without arrest. The other kind is a thick‐shelled (about 9 μm) egg that enters obligatory diapause after 1–3 cleavage divisions before resuming development. The thicker shell of the diapausing egg is due to an expansion of the outer sublayer of the single‐layered shell.2. The mean duration of the diapause at 19 °C (L : D 16 : 8) is about 14 days. This diapause is not broken by low temperature (5 °C), and it is not greatly extended by storage at low temperature (5 °C).3. Diapausing eggs are induced immediately after a brief starvation period, and seem to be produced at no additional energetic cost. However, a population producing a high proportion of diapausing eggs has a much reduced reproductive potential.4. Production of diapausing amictic eggs may be a strategy to increase the ability of clones to survive food limitation.5. Diapausing amictic eggs differ markedly from fertilized resting eggs produced following bisexual reproduction during favourabl

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00886.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. A diatom‐phosphorus weighted averaging (WA) transfer function, derived from a training set of currently oligotrophic to mesotrophic European Alpine lakes, was applied to a high‐resolution sediment core with annual laminae from Mondsee, an Austrian pre‐alpine lake, in order to reconstruct the eurrophication history of the lake.2. The water chemistry records of total phosphorus (TP) available for Mondsee were compared with the diatom‐inferred TP from the model for the period 1975–93. The trend in TP values as inferred by the model paralleled the monitored trend in TP values closely, with matching peaks in 1979/80, a decrease in values from the early 1980s, a second smaller peak in 1986/7, and a further reduction in concentrations in the last 6 years.3. However, there was a clear mismatch between the actual timing of the major TP peak, with the water chemistry records reporting its occurrence in 1979, and the diatom model indicating a small peak in 1980 and the highest concentrations in 1982. This can be attributed to the uncertainty of the sediment chronology for this section of the core, and possibly to the inconsistency between the core resolution and the resolution of the diatom model.4. In terms of the actual concentrations of TP inferred by the model, they compared reasonably well with the measured data, although the model tends to underestimate for the lower core section owing largely to poor diatom assemblage analogues. In the upper part of the core, the diatom‐inferred TP values were in extremely close agreement with the monitored chemical data.5. This validation study indicates that diatom‐phosphorus transfer functions are robust and are able reliably to infer past‐TP concentrations from fossil diatom assemblages in sediment cores. Despite the natural intra‐ and interannual variability in diatom assemblages and epilimnetic water chemistry, the technique can provide accurate estimates of TP with an annual resolution. The model can be applied to selected sites with suitable sediment records to reconstruct lake TP histories, thus providing a pragmatic management tool for addressing lake eutrop

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00887.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. We studied how species richness of three hierarchical insect species groups, namely all benthic, lotic and filtering taxa, were related to a number of environmental variables in a data set from fifteen Swedish lake outlets.2. In partial least‐squares analyses, we found that size‐related factors (stream width, discharge) and velocity‐related factors (current velocity, substratum particle size) were positively associated, and productivity‐related factors (chlorophylla, seston energy, conductivity) negatively associated, with the species richness of the three groups.3. The weak and negative relationship of richness with productivity largely negated theoretical predictions, whereas the species‐environment results corroborated earlier findings from running water systems.4. The most important factors associated with the species composition of the lake outlets studied included pH, lake area, discharge, channel width and detritus.5. Of the filter feeders, most species of blackflies (Diptera: Simuliidae) showed a negative relationship with pH.6. A nested subset analysis demonstrated that species‐poor sites did not have a subset of species found at more species‐rich sites in any of the three hierar

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00888.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. The spatial niche shifts of the nymphs of two mayfly species(Rhithrogena semicolorataandEcdyonurussp, gr.venosus)in relation to their growth were investigated in two lowland springs of northern Italy where they are dominant species.2. Ordination of the different size classes of the two species revealed a canonical trend related to season and bottom roughness.3. Larger nymphs of both species colonized rougher substrata. Differences between species in the roughness of areas colonized by small nymphs, which were very numerous, may have been due to competition for space.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00889.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Biofilm development and activity on wood substrata(Nothofagus menziesii)were examined at four forested sites in a South Island, New Zealand, river catchment over a period of 6 months. Two of the sites had brown waters and mean pH of 3.7 and 4.5, whereas the other two had clear waters and mean pH of 6.3 and 6.8.2. Fungi and other filamentous heterotrophs were the dominant colonizers of wood at all sites; few algal cells were present. Incorporation of14C‐glucose by biofilms was greatest in all four streams after 3 months, whereas endocellulase activity fluctuated over time and temporal patterns differed among streams.3. No clear relationship was found between the incorporation of14C‐glucose or endocellulase activity of biofilms and pH, although at one near‐neutral pH site14C‐glucose uptake increased in response to nutrient (N + P) additions.4. After 6 months, incorporation of14C‐glucose and endocellulase activity of biofilms onPinus radiatadowels buried vertically in the stream beds did not differ at depths of 3–9 cm and 19–25 cm in each stream.5. Radiotracer experiments with a grazing amphipod (Paraleptamphopussp.) demonstrated that biofilms on wood from all four sites could be ingested and at least partially assimilated. Chironomid larvae and harpacricoid copepods were the most abundant invertebrates colonizing wood substrata at all sites. Different chironomid species dominated at acidic and near‐neutral pH sites.6. Overall, our findings provide little support for the hypothesis that microbial activity on organic substrata is necessarily lower in st

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00890.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY