摘要:

SUMMARY1. In Lake Geneva (Switzerland), total phosphorus concentrations have decreased from 90 mg m−3in 1979 to 55 mg m−3in 1990.2. To assess the effects of this improvement, tubificid and lumbriculid communities were sampled in 1982 and in 1991 in the same areas, at a depth of 40 m.3. Abundance of mesotrophic species (mostlyPotamothrix vejdovskyi) and of eutrophic species (mostlyPotamothrix hammoniensis) was lower in 1991 than in 1982; in contrast, oligotrophic species (mostlyPeloscolex velutinus) were more abundant in 1991 than in 1982.4. The changes recorded in 1991 were the same as those associated with a decrease of organic sedimentation.5. Mean relative abundance of oligotrophic species increased from 17% in 1982 to 41% in 1991. According to these values, Lake Geneva was mesoeutrophic in 1982, but mesotrophic in 1

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00571.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. A survey of thirty‐two rheocrene springs in central Pennsylvania revealed that, LikeGammarusin lakes and streams,Gammarus minusis absent from springs with pH<6.0 and conductivity<25μS cm−1(total range in pH = 4.6–7.7, and in conductivity = 14–411 μS cm−1).2. In ten springsG. minusdensity was positively correlated with Ca2+and Mg2+hardness, but not with pH, unless three springs with either an exceptionally high velocity or extremely high densities of the potentially competing snailFontigens nicklinianawere omitted.3. Adults were larger in the springs with few or no large predators than in those with more predators. In all ten springs, adult dry mass was unrelated to spring pH and ionic content, but brooding female dry mass covaried positively with Ca2+and Mg2+hardness in the five predator‐poor springs.4. Body water, Na and Ca contents and body mass/length ratios varied independently of spring pH and ionic content. Water content was inversely correlated with fat content, but even when expressed as a percentage of fat‐free wet mass, it was unrelated to water chemistry.5. In juveniles, males and non‐brooding females, fat content varied independently of spring pH and ionic content, but in brooding females it was correlated with alkalinity and Ca2+and Mg2+hardness. The cost of reproduction in brooding females may have been a factor here; they had significantly lower per cent fat than did non‐brooding females. Juvenile fat content did not differ significantly among spring populations, whereas adult fat content did. The per cent fat of brooding females covaried positively with body size among springs, and this was marginally true for non‐brooding females, as well. The residuals of brooding female per cent fat against dry mass were not related to water chemistry.6. Brood size (number of embryos in a brood) and brood mass varied significantly among populations, but independently of spring pH and ionic content. Both covaried positively with maternal body size among springs. The residuals of these relationships were unrelated to water chemistry, as was the percentage of females brooding.7.G. minusfrom a pH 6 spring survived better and lost less body mass in acidic soft water than did those from a pH 7.6 spring. However, althoughG. minushas apparently been able to adapt (or acclimate) to pH 6 water it has failed to adapt to more acidic waters. A physiological or structural constraint may be involved because this species has probably had ample opportunity to evolve resistance to dilute acidic water. This hypothesis is consistent with the threshold effect observed: above pH 6 G. minus shows very little evidence of osmotic or metabolic stress, but beiow pH 6 viable populations apparently cannot survive at all. However, the gradual linear decrease in population density of G. minus with decreasing alkalinity and Ca2+and Mg2+hardness suggests that other factors may also be involved (e.g. a decr

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00572.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The elimination rate of radiocaesium in brown troutSalmo truttaL. was determined in the laboratory at four water temperatures (range 4.4–15.6°C). In the experiments three or four homogenous size‐groups of fish (mean weights 23–496 g) were studied at each temperature.2. The brown trout received acute oral doses of134Cs and were killed at intervals for radioactivity counting. The retention versus time curves were composed of two distinct exponential components. The long‐lived component was quantitatively the most important for retention of radiocaesium. Elimination rate increased with increasing water temperature and decreased with increasing body weight.3. The biological half‐life of134Cs (Tb, days) was related to fresh body weight (W, g) and water temperature (t, °C) by the equation:Tb= 290 ×W°.176× e‐°.106×t. The elimination rate of Cs could be predicted from weight‐specific metabolic rate as given by Elliott's equat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00573.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The relationship between algal biomass accumulation, invertebrate colonization, and stream‐water pH was investigated in seven streams in three regions of England and Wales. Possible nutrient limitation of algal production at all sites was examined with diffusion substrata.2. Periphyton assemblages on experimental substrata after 30 days were dominated by diatoms, notablyEunotiaspp., at all sites. Algal pigment concentration (chlorophyllaand phaeopigments) was not correlated with stream‐water pH, and mean concentrations on control (unenriched) substrata ranged from 0.08 to 1.94 μg cm−2.3. The growth response of periphyton to nutrient additions was site specific. Algal production was stimulated by nutrient additions at sites in the English Lake District and Llyn Brianne (south‐west Wales), but not in the Ashdown Forest (southern England).4. Larval Chironomidae were the main invertebrates retrieved from substrata at all sites. Within all three regions, larval abundance was positively related to algal pigment concentration (biomass). Abundance of the stoneflyNemurella pictetiiwas also positively correlated with algal biomass at the one site where it occurred.5. Our results indicate that epilithic algal production in small, oligotrophic streams is unlikely to be determined primarily by pH. Neither do they support the view that an absence of grazers from acid streams is necessarily due to an inadequate foo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The seasonal cycle of cyclopoid copepods during and following an approximately 50% reduction in planktivorous fish biomass was studied in shallow, eutrophic Lake Vaeng, Denmark, from 1986 to 1990.2. The dominant cyclopoid copepods changed fromCyclops vicinusandMesacyclops leuckartiduring 1986–1989 toM. leuckartiandMegacyclops viridisin 1990. The abundance of cyclopoid copepods gradually increased from 1986 to 1988–89, decreased in autumn 1989 and markedly decreased in 1990.3. The increase in the abundance of cyclopoid copepods from 1986 to 1988 is attributed mainly to the reduction in fish predation pressure, there being no concomitant increase in edible phytoplankton. The appearance ofM. viridisin 1990, and the general decrease in cyclopoid copepod density in autumn 1989 and in 1990, are attributed to the appearance of submerged macrophytes.4. Temperature, predation and availability of edible phytoplankton appear to determine whether C.vicinusorM. leuckartidominates the cyclopoid copepod population of eutrophic Lake V

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The breeding success of dippersCinclus cincluswas assessed in south‐west Scotland over 3 years and related to the acidity of the streams along which they bred.2. At sites of high acidity, clutch and brood sizes were significantly smaller than those at sites of lower acidity.3. Egg weight and the incidence of second clutches increased significantly with pH, but there was no evidence to suggest an effect of acidity on hatching success.4. The rate at which food was delivered to individual nestlings was significantly lower at acidic than non‐acidic sites. Nestling weights and survival were lower at more acidic sites.5. Reduced brood sizes, low nestling survival and the low incidence of second brooding attempts resulted in a significant reduction in total productivity (number of fledglings produced, per pair, per year) at acidic compared with non‐acidic streams.6. It is suggested that pH‐related differences in the invertebrate fauna of streams result in low prey availability for dippers on acidic streams, leading to reduced produ

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Larvae ofChironomus tentansFab, decreased the amount of time they spent outside their tubes as the presence of predatory pumpkinseed sunfish (Lepomis gibbosusL.) increased. Greatest reductions in activity occurred at low levels of fish presence; above a certain level further increases in fish presence had little effect on activity.2. Whether the pattern of predator presence was ordered or random had no effect on larval behaviour. Larvae did not habituate to short‐ or long‐term predator presence.3. Larvae were less active when more food was available and predator‐induced reductions in activity were negatively related to food availability. Larval activity was much higher in the dark than it was in the light.4. Over 7 days, presence of fish reduced the proportion of third‐instar larvae that moulted but did not affect head width or dry mass; low food availability reduced the number of larvae that moulted as well as head width and dry mass of larvae in the fourth instar.5. Results indicate that the behavioural response of larval chironomids to predator presence depends strongly on environmental conditions and that estimating the developmental costs of these behavioural responses under field conditions will be comp

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00577.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. Flow‐chamber experiments were conducted to evaluate the ability of microcrustacea to maintain position in moving water. These results were compared to distributions of zooplankton and water velocity in a stream pool to determine the relationship of animal density to water movement and swimming ability.2. Cladocerans exhibited negative rheotaxis (directed behaviour against a current) but poor ability to maintain position at velocities>2.5cm s−1.DaphniaandScapholeberiswere better at avoiding washout thanMoinaandDiaphanosoma. At velocities7.75 cm s−1. Washout time ofDaphniaandScapholeberiswas positively related to body size and negatively to water velocity and possession of eggs. Washout was inversely related to water velocity forEucyclops.4. Highest densities of microcrustacea in a stream pool were found in non‐flowing or downstream zones of the pool. Benthic (Hydracarina, harpacticoid copepods, ostracods) and fast‐swimming (cyclopoids) forms were most common in flowing zones. Facultatively benthic Cladocera were abundant in regions of no flow. Rotifers and immature copepods were most abundant at the downstream end of the pool.5. Behavioural mechanisms for remaining in stream pools at times of high flow appear to include: (i) flow avoidance (Simocephalus, Chydorus, Scapholeberisand cyclopoids), (ii) use of benthic habitat (ostracods, harpacticoids, Hydracarina), (iii) strong swimming abili

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00578.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1. The distribution of individuals, prey capture success and prey choice were studied in a water cricket (Velia caprai) population in southern Ireland. Groups of different sizes were observed in the field during the summer and all potential prey animals entering the groups were counted. Surface drift samples were collected to assess the proportion of profitable prey items.2. Two types ofVeliagroups were observed: mixed groups (adults and juvenile instars 4 and 5) and juvenile groups (instars 1–3), A greater proportion of the available prey was captured by the mixed groups.3. Individuals in large groups had a lower capture rate than individuals in small groups.4. No differences in capture rates could be found between males, females and juveniles, but differences in prey choice were apparent. Females captured more large prey than expected.5. Water cricket distribution in the stream did not follow the ‘ideal free’ model; too few individuals were found at the most profitable sites. Food might not be the limiting factor during summer, and other factors such as intraspecific interference and predator avoidance could be more impo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00579.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARY1 The accuracy of death‐rate estimates provided by the egg‐ratio method was assessed by directly measuring the real death rates of six large laboratoryDaphniapopulations for 40 days.2. Of six models tested the Kawecki iterative model gave the best relationship to real death rates in terms of variance explained, bias, and fit at both 4‐ and 8‐day sampling intervals. Although considered theoretically correct by persons familiar with the mathematics of egg‐ratio models, the Edmondson—Paloheimo model gave slightly worse results in terms of bias and fit.3. Using raw data, as opposed to smoothed data, gave the best fit between estimated and observed rates for both the Kawecki iterative and Edmondson‐Paloheimo models.4. Size‐selective predation did not increase error in estimates of the death rate; however, non‐steady‐state dynamics were correlated with error in model estimates.5. In general, the models gave a relatively good description of real dynamics, but they regularly produced negative death rates, and were grossly wrong for some individual estimates. The present study also gives practical suggestions on application of this technique t

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1992.tb00580.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY