摘要:

SUMMARY1. The larval chironomid community was studied quantitatively in three cross‐sections of an impounded area of the River Danube between July 1985 and July 1986.2. Sixty‐six species were identified, most of which belonged to the subfamily Orthocladiinae, but species of the tribe Chironomini were numerically dominant.3. The sections differed distinctly in terms of species number and diversity; a tendency towards increasing species richness and diversity was observed in the upstream sections of the impoundment. Marked fluctuations in these two parameters characterized the area close to the dam; the temporal oscillations in diversity values differed significantly between the sections (ANOVA:P<0.05).4. Clear differences were found between sampling sites in terms of community resilience, the minimum eigenvalue of the community matrix defined as the rate of return of a disturbed system. Longer return times after ‘disturbances’ could be expected at sites further upstream from the dam.5. Temporal persistence of species composition was estimated for each section with Kendal's correlation coefficient from 1985 to 1986. Sites further upstream of the dam illustrated a significantly greater temporal species persistence over time and a smaller degree of fluctuation, compared to the dam area (ANOVA:P<0.05). A significant negative relationship was found between overall persistence and cumulative monthly water discharge, at the dam site (P<0.01).6. Classification of the larval chironomid community gave evidence of generally low spatio‐temporal overlap between species in the impound

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00530.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Leaf packs in streams may serve as food and substrate to many macroinvertebrates, but the relative importance of these two functions has not been disentangled. To test the hypothesis that leaf packs are colonized primarily for their food value rather than as microhabitat, the colonization of leaf packs of red alder and of polyester cloth in a natural stream was compared.2. Species of shredders showed large differences in the colonization of the two types of leaf pack with almost no use of artificial leaf packs. Non‐shredders were also more abundant on natural leaf packs, however, they colonized artificial leaf packs six to eighty times proportionally more than shredders.3. The effect of different leaf types was virtually eliminated for non‐shredders when the amount of fine parriculate detritus (food for many non‐shredders) trapped in the leaf pack was added to the analysis as a covariate. Therefore, to non‐shredders, leaf types differed only in the retention of fine particulate organic matter.4. Comparisons of the use of both kinds of leaf packs in riffles versus pools revealed that significantly fewer animals colonized pool leaf packs.5. These results suggest that food value, and not microhabitat, is the primary determinant of leaf pack use for most shredders and non‐

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00531.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Community structure of interstitial invertebrates was studied in the sediments of two gravel bars in a bypass section of the Rhone River (France), in relation to hydrological patchiness and to major geomorphological characteristics of the sampling areas. Hydrological patchiness was characterized by upweiling or downwelling zones while geomorphological characteristics were concerned mainly with position towards the head or tail of each bar, which presented different environmental conditions.2. Longitudinal profiles of the two bars, at 0.5 and 1.0m below the substrate surface, were compared. At each station 10‐l samples were taken using mobile standpipes and a Bou—Rouch pump. During low‐water conditions, replicate samples were taken in both the head‐bar and tail‐bar regions to confirm the results. Physicochemical parameters were used to differentiate surface water from ground water (conductivity, alkalinity, silica, nitrates, sulphates and temperature) and to detect hydrological patterns.3. Two different situations were observed within the gravel bars. In the first one, the upweiling zone was situated in the tail bar and downwelling zone in the head bar. The reverse was observed in gravel bar 2 where the head‐bar region formed the upweiling zone and the tail‐bar region formed the downwelling zone.4. In the first situation, the distribution of interstitial assemblages corresponded with the observed hydrological patterns: epigean fauna characterized the downwelling zone and stygofauna characterized the upweiling zone. The interstitial fauna seemed to be strictly linked to the mode of water movement within the sediments. Hydrological patchiness therefore appeared to be an important factor for the structure of interstitial assemblages.5. In the second case there was no relationship between the hydrological and the biological pattern. Epigean fauna and hypogean fauna were scattered all along the gravel bar. These results suggest that geomorphology is a second important factor governing the composition and structure of interstitial assemblages. A precise structure was obtained when hydrological and geomorphological characteristics were superimposed (case 1). When they were opposed (case 2) all the species responded according to their individual ecological

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00532.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Patterns in invertebrate community structure were determined from analysis of benthic samples taken quarterly for 1 year from four sites in the Great Smoky Mountains National Park (GSMNP). Sites ranged in baseflow pH from 4.5 to 6.8, with a corresponding range in inorganic monomeric aluminium concentrations from 3 to 197 μgl−1.2. Total invertebrate density (excluding Chironomidae) was correlated with pH (R2= 0.90,P<0.05). Density of Ephemeroptera was more highly correlated with pH than density of invertebrates in other taxonomic orders. Invertebrate density (total and density of different orders) was generally more strongly correlated with pH than to inorganic monomeric aluminium concentrations.3. Species richness declined from sixty‐nine species at the highest pH site to thirty‐three species at the lowest pH site. Richness of Ephemeroptera and Trichoptera was positively correlated with pH (R2= 0.96 in both cases). Trichopteran richness was also negatively correlated with inorganic monomeric Al concentrations (R2= 0.96,P<0.05). Plecopteran richness was not related to stream acidity.4. Not all species of Ephemeroptera were negatively affected by low stream water pH. At low pH sites,Ameletus lineatusTraver (Family: Siphonoluridae) was relatively more abundant compared to other species of Ephemeroptera, and had greater biomass and greater weight per individual length than at higher pH sites.5. Differences in invertebrate community parameters among sites were not based on changes in food abundance. Although grazer densities were positively correlated with pH (R2= 0.93,P<0.05), differences in density were not related to differences in food. To the contrary, lower grazer densities occurred at the lowest pH site where measured food abundance (algae) was highest. Likewise, shredder density increased with increasing pH but was correlated with standing stocks of benthic organic matter (BOM), which had generally higher standing stocks at lower pH sites.6. Transplants of two species of Ephemeroptera between sites differing in pH (6.4v5.0) resulted in increased mortality of organisms placed at lower pH sites. In another transplant experiment, differences in mortality were not observed, although surviving invertebrates at low pH sites had ×10 higher body burdens of aluminium following the transplant than invertebrates from the reference site.7. These results indicate that direct effects of pH and Al (affecting survival) were more important than indirect effects of food availability in determining changes in invertebrate community structure between the stud

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00533.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The total body length, cephalic length, wet weight and dry weight was measured in juveniles, males and females ofGammarus fossarumandG. roeselikept in the laboratory. Numbers of flagellar segments on the first and second pairs of antennae ofG. fossarumandG. roeseliwere quantitatively related to body size and in stars. The addition of segments cannot be used to identify particular instars of individuals or to determine their ages in natural populations.2. At experimental temperatures ranging from 3.8 to 20.2°C, the number of moults, duration of intermoults, maturation times and specific growth rates were studied from birth in isolated specimens. Sexual maturity was reached after 9 or 10 moults, at a mean wet weight ofc. 5mg for females andc. 7mg for males ofG. fossarum, and atc. 10 mg for females andc. 13 mg for males ofG. roeseli. At 3.8°C neither species reached sexual maturity within 550 days.3. The mean interval between moults was observed from birth to sexual maturity and was linearly related to moult number and exponentially related to age. The relationship between each intermoult interval, or the maturation time, and the experimental water temperature was described by a power function. Maturation times increased from 96 days at 20.2°C to 355 days at 7.9°C inG. fossarum, and 85 days to 403 days inG. roeseli.4. Over the range 3.8–20.2°C there was a log—log relationship between temperature and specific growth rates. Growth was maximal at 20.2°C in newborn animals as well as in small sexually mature animals; interspecific differences were highly significant.5. Increase in body wet weight ofG. fossarumandG. roeselifedad libitumon a constant mixture of autumn‐shed, naturally decaying, tree leaves and aquatic macrophytes was followed to senescence and death. The instantaneous or specific growth rate was maximal near birth, atc. 7.98% wet weight day−1inG. fossarumand 9.03% inG. roeseli. At ≥12°C, growth conformed to a logistic curve; maximum absolute increments in weight occurred about half‐way through a life span of 280–300 days at 20°C, 380–420 days at 16°C and 550–600 days at 12°C. Some individuals lived longer than 850 days at ≤12°C. The wet weight at birth was 0.112mg forG. fossarumand 0.123mg forG. roeseli. Asymptotic mean body weights of males and females were, respectively, 61 and 41 mg forG. fossarumand 87 and 58 mg forG. roeseli. However,G. roeselireached the inflection point of the logistic curve significantly faster thanG. fossarum. In the latter species, growth and maturation were relatively faster at temperatures below 12°C, whereas they were faster inG. roeseliat 16–20°C. ThusG. fossarumis adapted to summer‐cool streams andG. roes

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00534.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The physiological characteristics of nitrogen uptake by sublittoral and eulittoral (splash zone) epilithic periphyton as well as epipelic periphyton in N‐deficient Castle Lake, California were determined by evaluating the half‐saturation constants (Kt) and initial slopes (Vmax/Kt) of uptake kinetics curves. These results were compared to similar studies of phytoplankton nitrogen uptake in this lake.2. The strategies of nitrogen uptake differed among the various communities and were largely determined by the proximity of each to pools of available dissolved inorganic N (DIN).3. The sublittoral algae did not have a high biological affinity for either NH4or NO3and depended on nitrogen fixation for their N supply. The eulittoral community showed an increased capacity for DIN uptake at low substrate concentration, but not as high as measured for the phytoplankton community. Epipelic algae live immediately adjacent to a large pool of interstitial sediment NH4and showed no physiological adaptations for surviving in a N‐deficient environment.4.Ktvalues for all benthic communities were approximately two orders of magnitude greater than ambient substrate levels. In contrast, the half‐saturation constants for NH4+ NO3uptake by phytoplankton were very similar toin situlevels of these nu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00535.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. In four separate field experiments near Mount St Helens (Washington, U.S.A.) during 1986, the grazing effects of two large benthic herbivores, tadpoles of the tailed frogAscaphus trueiand larvae of the caddisflyDicosmoecus gilvipes, were investigated using streamside channels and in‐stream manipulations. In the experimental channels, abundances of periphyton and small benthic invertebrates declined significantly with increasing density of these larger herbivores.2. In eleven small, high‐gradient streams affected to varying degrees by the May 1980 eruption, in‐stream platforms were used to reduce grazing byA, trueitadpoles on tile substrates. Single platforms erected in each tributary and compared to grazed controls revealed only minor grazing effects, and no significant differences among streams varying in disturbance intensity (and, consequently, tadpole density). However, results probably were confounded by high variability among streams in factors other than tadpole abundance.3. Grazing effects were further examined in two unshaded streams with different tadpole densities, using five platforms per stream. In the stream with five tadpoles m−2, grazing reduced periphyton biomass by 98% and chlorophyllaby 82%. In the stream lacking tadpoles, no significant grazing effects were revealed. Low algal abundance on both platforms and controls, and high invertebrate density in that stream (c. 30000m−2) suggests that grazing by small, vagile invertebrates was approximately equivalent to that of tadpoles.4. The influence of large benthic herbivores on algal and invertebrate communities in streams of Mount St Helens can be important, but reponses vary spatially in relation to stream disturbance history, local environmental factors, and herbivore distributional patterns and

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00536.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. A two‐season investigation was undertaken to determine the contribution of benthic recruitment to the population development of several species of blue‐green algae.2.Gloevtrichia echinulatapopulations were shown to be heavily subsidized by benthic recruitment, deriving on average 40% of their planktonic colonies from the benthos.3. Benthic recruitment ofAphanizomenon flos‐aquae, Anabaena flos‐aquaeand a secondAnabaenaspecies contributed less than 2% to planktonic increases, whileMicrocystis aeruginosarecruitment was negligible.4. Phosphorus translocation via migratingG. echinulataaccounted for most of the phosphorus (P) in the planktonic colonies, and constituted a significant portion of the internal loading of the lake.5. Estimated P translocation viaAph. flos‐aquaewas relatively minor, although there was evidence of luxury uptake in th

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00537.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. A replicated natural experiment was used to assess the influence of pH and low alkalinity on abundance and richness of invertebrate families in streams draining catchments that receive acid deposition. Individual streams were used as the unit of replication, allowing conclusions to refer to a class of streams rather than to particular streams.2. We also controlled for several factors other than pH and alkalinity, including flow and temperature, that are recognized as determinants of invertebrate distribution. Samples were from indigenous rocks, standardized for size, surface area, and geology.3. Repeated measures analyses of variance (ANOVA) revealed that invertebrate abundance and richness were significantly lower at pH 5.8 than at pH 7.1 for the total community. Thirty per cent of the forty‐seven families exhibited significantly lower abundance at pH 5.8; thirteen families were absent at pH 5.8. Differences were greatest for Ephemeroptera: species richness was significantly lower at pH 5.8, and 71% of the twenty‐four species were either absent (seven) or found in reduced abundance (ten) in the acidic streams.4. Stream alkalinity is projected to continue to decrease with continued acid deposition in the Shenandoah National Park. Concurrent decreases in pH may lead to the absence or continued numerical decline of certain Ephemeroptera species in streams that acidify to less than pH 6.0 and/or 50μEql−1alka

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00538.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. We examined changes in position and growth ofCallitriche cophocarpapatches in a shallow section of a small Danish stream during the main expansion of plant cover between April and June. Mean upstream growth of patches was only 7.5% of downstream growth. The mean growth rate was 1,02cm day−1in length and 0.55 cm day−1in width and the growth rates were not significantly dependent on patch size. For patches with an area (A) above 100cm2, the growth rates in patch area (dA/dt) was proportional to patch circumference and thus √Aandthe relative growth rate (dA/dt A−1) was inversely proportional to √A.The smallest patches (<100cm2), however, expanded less than expected because of their combined tendency to grow more slowly in patch length and width than larger patches.2. The expansion of plant cover will be much more rapid in many medium‐sized patches compared to few large patches of a similar combined area, because internal selflimitation by light and space is partially relieved in smaller patches. We anticipate that recruitment and mortality of new‐formed patches are critical steps preceding areal expansion. Quantification of these processes are needed fully to evaluate patch dynamics and spa

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00539.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY