摘要:

SUMMARY1. The predatory caddisflyRhyacophila vaoMilne (Rhyacophilidae) displayed a 2‐year, semivoltine life cycle in a small, spring‐fed stream in southern Alberta, Canada. Three overlapping cohorts were identified throughout the 2‐year sampling program, with five larval instars recognized. Larvae overwintered in instars I —ELI, developed to instar IV by summer and instar V by autumn. The second winter was spent in instar V, Pupation occurred from late May to August and did not commence until stream temperature exceeded 3°C. Adults were collected from mid‐June to early September.2. Larvae displayed a diphasic growth pattern: Phase I, a positive, non‐linear growth rate for instars I‐IV; Phase II, a constant growth rate during instar V. Phase I coincided with increasing stream temperatures in late winter and spring, where mean instantaneous growth rates (maximum of 2.78% dry wt day−1) were significantly correlated with stream temperatures. Although the duration of Phase II spanned a temperature range similar to that in Phase I, the instantaneous growth rate remained temperature‐independent at 0.87% dry wt day−1.3. Larvae exhibited a type III survivorship curve (i.e. an exponential decrease on an arithmetic scale), with the finite rate of mortality averaging 0.80% larvae day−1.4. Cohort 1 (later part of 1983 year class) displayed lower total production compared with the equivalent growth phase in the 1984 year class (Cohort 2). In contrast, production of the non‐linear and linear growth phases of Cohort 2 was similar. Periods of similar growth characteristics for Cohorts 1 and 2 had comparable P/B ratios for both the unadjusted and time‐adjusted annual estimates, although higher ratios were observed for the non‐linear growth phase of Cohort 2. Total cohort production (linear + non‐linear growth phases) could only be calculated for Cohort 2, and was 870.2 ± 1011.4 mg dry wt m−2. The corresponding cohortP/Bratio was 5.01 and the adjusted annualP/B, 3.01.5. Annual larval production (±SE) for the first and second years of the study was similar (Year 1, 480.0 ± 387.5mg dry wt m−2; Year 2, 526.9 ± 967.5mg dry wt m−2)

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00518.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Temporal fluctuations were measured in the concentrations of the trace metals cadmium (Cd), copper (Cu) and zinc (Zn) in six insect taxa collected from the same sites in a temperate zone lake over a 14‐month period. The consequences of temporal changes in insect contaminant concentrations for biomonitoring studies are assessed.2. Significant temporal fluctuations in the concentrations of the three metals were measured in almost all of the insect taxa studied. In no case was there a greater than sixfold change in the concentration of a trace metal over the course of the year. The extent of the fluctuations was generally greater for CD, a non‐essential metal, than for the essential micronutrients Cu or Zn.3. Temporal fluctuations in CD concentrations appeared to follow a seasonal periodicity for most taxa. Minima were measured during the winter period in the megalopteranSialisspp. and in the dipteran taxaChaoborus punctipennis, Glyptotendipessp., andProcladiusspp., whereas a maximum was measured in the mayflyHexagenia Hmbataduring the same season. In general, temporal fluctuations in Cu and Zn concentrations were less seasonal in character than were those of Cd.4. For some of the taxon—metal combinations studied, temporal fluctuations in metal concentrations could be ignored in biomonitoring studies, whereas in other cases a temporal window of minimum variability should be chosen for the collection of organisms from different

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00519.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Allozyme electrophoresis was used to describe the genetic structure ofHelicopsyche borealiscaddisflies collected from three sites in each of three streams in northern California, U.S.A.: the Rice Fork of the Eel River; Big Sulphur Creek; and Alameda Creek. Between 7 and 11km separated adjacent sites within these three streams.Helicopsyche borealisfrom three additional streams in eastern North America (Christiana Creek, Indiana; Byrd's Mill Creek, Oklahoma; Susquehanna River, Pennsylvania) were also analysed electrophoretically to address taxonomic questions that arose during the study.2. Four genetically distinct groups of individuals were identified (i.e.Helicopsychetypes A, B, C, and D). Lack of interbreeding between sympatric groups (as evidenced by fixed allelic differences) and large genetic differences (mean Nei's genetic distances = 0.396–0.693) indicate that these four groups ofHelicopsychewere actually reproductively isolated species rather than genetic variants of a single species.3. Occurrence ofHelicopsychetype A at multiple sites permitted an analysis of spatial variation in genetic structure. Within a drainage basin, small differences in allele frequencies were observed among sites in the Rice Fork and Big Sulphur Creek, but not in Alameda Creek. Larger genetic differences were found among sites in separate drainage basins. Genetic distances (Nei's) betweenHelicopsychetype A from California and from eastern North America sites (mean = 0.236) were greater than interpopulation differences commonly observed for insects, which suggests thatHelicopsychetype A from California may represent a different species thanHelicopsychetype A from eastern North America.4. Geographical and taxonomic differences observed in this study underscore the importance of understanding both population structure and genetic relationships among populations in the design and interpretation of stream faunal studie

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00520.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Comparisons of chlorophyll a, bacterial density, frequencies of dividing cells, ash‐free dry mass (AFDM) and extracellular polysaccharide content were made for biofilm developing on wood (Salix) submerged in replicated stream‐side flumes exposed to either ambient light (light treatment) or covered to exclude light (dark treatment). Biofilm was sampled on days 3, 6, 9 and 14 during experimental periods occurring irrMay, September, November and December.2. There were no significant differences in bacterial cell densities, frequencies of dividing cells, AFDM or extracellular poiysaccharide content between light and dark treatments. Ash content and bacterial biomass was similar to seston, suggesting the importance of seston as a source of material accumulating in the biofilm.3. Of total epixylic organic carbon 7.2% was estimated to be extracellular polysaccharide, and 0.8% was bacterial carbon. At least nine times more carbon was contained in extracellular polysaccharide than in bacterial biomass.4. In the epixylon of the Ogeechee River, bacterial dynamics appear to be controlled by factors other than the availability of algal substra

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00521.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Small cages (294cm2) containing unglazed clay quarry tiles were used to investigate the influence of periphytic algae on macroinvertebrate abundance in a Hong Kong stream. Algal biomass was manipulated by shading cages with plastic sheets. Individual cages were assigned to one of three treatment groups: unshaded, shaded and deeply shaded. Invertebrate densities and algal biomass within cages were monitored after 23, 37 and 65 days.2. Multiple‐regression analysis revealed that algal biomass, invertebrate morphospecies richness and total abundance declined with greater shading intensity. The responses of individual invertebrate taxa varied: some (especially Trichoptera) were unaffected by shading, whereas grazers (Baetidae, Psephenidae and Elmidae) declined as shading increased.3. Significant regressions of the densities of individual taxa upon algal and detrital standing stocks in cages had positive slopes, but algal biomass increased during the study while detrital standing stocks declined. Abundance of invertebrates declined or remained rather stable over time. Density increases resulting from a positive association with algae were apparently offset by declines in abundance correlated with reductions in detritus.4. Declines in algal biomass were associated with greater shading to which animals may respond directly. To uncouple the link between scarcity of algae and reduction of light intensity, the plastic covers on two groups of cages (deeply shaded and unshaded) which had been placed in the stream for 28 days were reversed so that cages which had been shaded became unshaded and vice versa. The cages were recovered on day 33, Only Coleoptera demonstrated a positive association with atgae inside cages; no relationship between population densities and algal biomass or light intensity was apparent for other taxa. However, the design may have been confounded by deposition of sediment in the cages (due to declining stream discharge) which reduced population densities of colonizers.5. This study documents changes in invertebrate abundance and morphospecies richness in response periphyton and detritus standing stocks within patches. Summation of such responses may account for observed variations in benthic communities among Hong Kong streams which differ in the extent of shading by riparian vegetatio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00522.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Two broad‐scale environmental influences affecting species of Ephemeroptera, Trichoptera and Plecoptera inhabiting riffle habitat of three study catchments in New Brunswick and Nova Scotia were stream size‐temperature‐related variables and acidity‐related variables.2. Species richness was most affected by acidity in tributaries of intermediate size<0.001<0.1m3s−1).3. Of the three insect orders investigated, mayfly species richness was affected most by acidity, and stonefly species richness affected least by this factor.4. Zoogeographical isolation of the Nova Scotian catchments resulted in absence of some species of low general abundance, but these species had little influence on the site classification by TWINSPAN analysis.5. Predaceous stoneflies were collected in greater numbers from circumneutral sites and predaceous caddisflies in greater numbers from the Nova Scotian sites.6. Although the Nova Scotian catchments have probably been historically acidic, due to high concentrations of organic acids, pH currently limits the distributions of many indigenous invertebrate species. These species may be vulnerable to the more recent, additional, anthropogenic acidification of these c

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00523.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The objective of this paper was to reveal the toxicity of Fe3+and Fe24at pH 4.5 and 7 on larvae of the mayflyLeptophlebia marginata, by examining survival, motility, gill ventilation, moulting and feeding in experiments.2. Fe2+was the dominant metal species at pH 4.5, and Fe3+at pH 7. Precipitation of Fe occurred only at pH 4.5, where Fe‐precipitarions were observed on the thorax and the gills of the larvae.3. Both feeding activity and motility of the animals decreased at pH 4.5 and 10, 20 or 50mg1‐−1Fetot. After a short period of normal feeding, the animals stopped feeding for approximately 2 weeks and did not start to feed again until the end of the experiment. They were constipated. Survival was>95% in all treatments, except at pH 4.5 and 50 mg Fetot. In this group, about 20% of the animals died after having been constipated for 2

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00524.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. A clear seasonal alternation ofEndochiranomus albipennislarvae between submerged plants and the bottom sediment was observed in the littoral of a deep mesotrophic and a shallow eutrophic lake. The analysis of change in larval density and of occurrence of pupae suggests that larvae migrated from plants to the bottom sediment in early autumn and back to the plants, where they pupate, in spring.2. Up to 95% of the third and fourth instar larvae overwintered in the bottom sediment in special cocoons. Larvae staying in the sediment without cocoons were also dormant. The timing of cocoon formation was different in the two lakes.3. Migration may have a significant influence on the seasonal changes in dominance structure and density of epiphytic and benthic faunas.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00525.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. We examined whether the isopod,Lirceus fontinalis, an important facultative shredder in low‐order streams in the eastern United States, responded to chemical cues of the skin mucus of five fish species varying in relatedness and feeding habits, and if fish‐induced alterations in the foraging activity of isopods indirectly affected leaf processing.2. In the laboratory, isopods generally responded to the presence of fish mucus by reducing their activity. Isopods were most responsive in water containing the skin mucus of predatory sunfish (Lepomis) and least responsive in water treated with mucus from algivorous stonerollers (Campostoma anomalum).3. Rates of leaf disc breakdown by isopods in the laboratory were significantly reduced when isopods were exposed to chemical cues of confined green sunfish (L.cyanellus).4. The rate of leaf processing in a fishless reach of a headwater stream was four to five times greater by isopods 7—10mmTL (total length) than those ≤ 5mm TL. Rates of leaf processing by isopods in low‐order streams may be affected directly by the size structure of the isopod population and indirectly by the presenc

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00526.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. We compared aquatic macroinvertebrate assemblage composition within and between habitats (pools and riffles) at four sites on two intermittent streams in Victoria, Australia during a drought year followed by a wetter year to see how different spatial and temporal scales influenced patterns of community structure detected by multivariate techniques of ordination and classification. We also examined the fit between faunal groups and ‘flow phases’ characterized by multivariate analyses of physicochemical variables in an earlier paper.2. Pools contained more taxa and individuals than riffles. At the more temporary site, there was considerable overlap between the faunal composition of pools and riffles, whereas habitat‐specific assemblages consistently occurred at the more permanent sites. Most taxa were either tolerant, permanent stream forms able to persist in streams that dry briefly, or facultative species that occur in lotic or lentic habitats. Few species appeared specifically adapted to temporary waters.3. Within habitats, there were some matches between faunal groups and flow phases, especially with the onset of the ‘diminishing flow’ phase, characterized by rising water temperature and conductivity, and declining pH and dissolved oxygen. However, disjunctions among faunal groups were less marked than those between flow phases, and were absent at an intermediate scale when habitats were pooled within sites. At the broadest scale of analysis (within habitats between sites and years), historical events (e.g. whether pools upstream dried completely during the previous summer) apparently influenced community composition as much as site‐specific abiotic

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00527.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY