摘要:

SUMMARY.1. This study was designed to determine how catchment use affects stream phosphorus retention by comparing retention in streams draining three mixed hardwood catchments and three catchments that were planted in white pine in the 1950s.2. Catchments of similar area and stream discharge were chosen and phosphorus uptake was measured monthly in each catchment along with temperature, discharge, velocity, coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), and microbial respiration associated with FPOM.3. On an annual basis, average phosphorus retention was not different between streams draining pine and hardwood catchments nor were there significant differences between physical (temperature, velocity and discharge) or biological (CPOM, FPOM and respiration) parameters based on catchment type. However, discharge was more variable in streams draining pine catchments.4. Because phosphorus uptake was correlated with discharge, phosphorus retention was also more variable in streams draining pine catchments. Storms caused a greater increar.e in discharge and loss of phosphorus in pine streams than in mixed hardwood streams, but discharge returned to baseline more quickly in pine streams.5. We suggest that discharge regimes and phosphorus dynamics of streams draining pine catchments are less resistant to change but more resilient than streams draining mixed hardwood forests.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01401.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The effect of the water‐lily beetle,Galerucella(=Pyrrhalta)nymphaeae(L.), (Coleoptera, Chrysomelidae), on the leaf production and leaf longevity of the yellow water‐lily,Nuphar lutea(=N. luteum) (L.) Sibth.&Sm., was studied experimentally in southern Finland during one growth season.2. Twelve cages, each containing a single rosette of the water‐lily, were established in the lake during May. Two treatments were randomly applied to cages: (i) control (herbivory not allowed), and (ii) fifty beetles added at the beginning of the season. Leaves were marked individually and the production of new leaves was followed until October.3. In both treatments the production of floating leaves continued until the end of August but declined towards the end of summer. Herbivory did not affect the number of leaves produced, i.e. the plants did not compensate for the loss of leaves.4. Leaf longevity was reduced dramatically (up to —60%) when herbivores were present. Leaves that emerged during the most intense period of larval growth had a life‐span one‐third of that of the co

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01402.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The common pennate diatom (Bacillaryiophyta)Fragilaria crotonensisKitton showed strong periodicity in its photosynthesis ‐irradiance (P—I) relationship under summer conditions of high irradiance and temperature which damped progressively throughout the growth phase. Under winter conditions of low irradiance and temperature, weak periodicity was observed.2. The amplitude of diel oscillations in photosynthesis as a function of irradiance under winter conditions showed only slight variation throughout the growth phase. Under summer conditions, however, amplitudes for both α and Pmaxwere highest in the early exponential phase, declining progressively during growth.3. These results indicate that the occurrence of periodicity is dependent, in part, on the growth phase of the cells and, in part, on environmental parameters of irradiance and temperature variations under simulated summer and winter condit

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01403.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1, Microhabitats chosen by young grayling (Thymallus thymallusL.) were investigated by electrofishing. The first feeding habitat was marginal areas where water velocity did not exceed 15 cms−1. Fry fed on drift in the first 10 cm of the water column below the surface. This location was very stable during the first weeks of growth (mid‐April to mid‐May). When they were 3–3.5 cm long, fry began using benthic areas and gradually moved away from the banks towards the channel.2. A downstream migration was noted from the beginning of emergence (mid‐April) to the end of May. This mainly nocturnal movement involved all fish sizes and caused a complete removal of young‐of‐the‐year by June from the spa

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01404.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Three species of the superfamily Unionacea live in Bavarian trout streams: the freshwater pearl musselMargaritifera margaritiferawhich usually occurs alone, and the unionidsUnio crassusandAnodonta piscinaliswhich are frequently associated.2. We found no evidence for competition betweenM. margaritiferaand the unionids. Two types of habitat factors were analysed: (i) the occurrence of host fish, which does not explain the distributional relationships of mussels; and (ii) hydrochemical factors indicating a lower productivity in the rivers inhabited byM. margaritifera.3. With respect to physiological differences,M. margaritiferais separated from the other two species by low growth constants and low metabolic rates. We conclude, therefore, that the metabolic rate is an important factor governing distribution of the species:M. margaritiferais able to grow in rivers with low food availability, whereas the higher metabolic rates ofU. crassusandA. piscinalispresumably necessitate a richer food supply.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01405.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Although the bulk of litter input to stream ecosystems is in the form of fresh leaves, current understanding of organic matter processing is largely founded on experimental studies made with pre‐dried leaves. This paradox points to the critical need for evaluating to what extent those experiments with dried leaves reflect natural litter decomposition.2. The mass loss rates, patterns of mass loss, and chemical changes during processing of fresh leaf litter were compared with air‐dried leaf litter in a stream ecosystem.3. Although overall mass loss rates were similar between treatments (k= 0.0213 day−1and 0.0206 day−1), fresh leaves lost mass at a constant rate, whereas the decay of dried leaves proceeded in two distinct phases. Soluble organic carbon, phosphorus, and potassium were rapidly leached from dried litter, but were largely retained in fresh material for more than a week. Kinetics of concentrations of cellulose and changes in amounts of lignin remaining per leaf pack revealed further differences in decomposition dynamics between treatments, apparently related, either directly or indirectly, to differences in leaching behaviour.4. Dynamics of nitrogen and protein contents were similar between treatments, indicating that microbial colonization was not greatly delayed on fresh leaves.5. It is concluded that the retention of labile carbon and nutrients in fresh leaf litter facilitates their utilization by leaf‐associated micro‐organisms and invertebrates, resulting in an increased importance of biotic processes relative to physical processes such as leaching.6. At the ecosystem level, retention of carbon and nutrients in streams would be increased, allowing greater overall productivity. Conversely, the availability of labile organic carbon would be reduced in compartments such as the epilithon, fine sediments, and the w

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01406.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Quantitative samples of lotic benthic invertebrates and associated organic material were taken monthly for 18 months from bryophyte and gravel habitats in two New Zealand alpine streams in Arthur's Pass National Park, South Island; an unshaded site above the tree‐line and a shaded stream flowing through mountain beech forest. This was to assess the ecological role of bryophytes in these habitats and to determine the relative effects on the fauna of algal and detrital resources.2. Bryophytes were confined to stable bedrock substrata in shallow (mean depth of 4.5 and 10.5 cm), fast water (mean velocity of 0.21 ms−1and 0.30ms−1) at the unshaded and shaded sites. Mean ash‐free dry weight (AFDW) of organic material from bryophyte areas was similar at the unshaded and shaded sites (335.6 and 272.4 gm−2). Low stream‐bed stability of the gravel areas resulted in poor retention of organic matter, with average AFDW of 59.1 and 77.9 gm−2at the unshaded and shaded sites, respectively. Periphyton biomass, however, was much higher at the unshaded site.3. Within bryophytes, water velocity is reduced and large quantities of periphyton and detritus accumulate. This explains the greatly enhanced invertebrate densities within bryophytes (218400 and 53500 individuals m−2), compared with gravel areas (20900 and 7400 individuals m−2) in the unshaded and shaded sites, respectively. The higher invertebrate densities at the unshaded site reflect greater periphyton biomass there.4. Invertebrate densities followed clear seasonal patterns, attributable to changes in chironomid densities. These reflected larval chironomid hatching following adult oviposition. This illustrates the importance of these plants as oviposition sites, and as protective nurseries for small larvae where they can obtain shelter during floods and consume the abundant food sources available to them.5. DECORANA ordination revealed taxonomically distinct invertebrate communities in each stream, and in bryophytes and gravels. Several taxa appeared restricted to either the unshaded site (e.g.Acroperla spinigerandHydrobiosis silvicola) or the shaded sit

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01407.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1.Daphnia ambiguawas exposed to harmful concentrations of pesticides (six insecticides, two herbicides, one fungicide) for 10 h from the final embryonic stage to the first instar, and effects on morphology were investigated.2. The animals developed helmets at the second instar after exposure to the insecticides, but did not show the same response when exposed to the herbicides and the fungicide.3. Some stimuli due to the insecticides on the nervous system of the animals may switch on the formation of the helmet, an antipredator morphology, which originally evolved as a response to chemicals released by predators.4. It is suggested that a range of chemicals other than the predator/prey kairomone can induce the helmet formation inDaphnia.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01408.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Field experiments in a lake outlet stream were carried out on filter‐feeding larvae of the caddisflyHydropsyche siltalaiDöhler, to assess whether microhabitat quality, establishment and growth rate is affected by position (upstream—downstream) within a dense aggregation of larvae.2. Artificial substrates holding high‐density aggregations of hydropsychid larvae were used. Marked III‐instarH. siltalailarvae were implanted either in the upstream end or in the downstream end of an aggregation and recovered after 17 days.3. Larvae recovered from the downstream end of an aggregation were smaller than those that had been implanted in the upstream end.4. Fewer larvae had settled in the downstream end of aggregations compared to the exposed upstream part.5. Naturally colonizingH. sitalailarvae were, in contrast to implanted larvae, more numerous behind aggregations. Small (first and second instar)Hydropsyche angustipennis(Curtis) and/orH. pellucidula(Curtis) larvae were more numerous in front of aggregations.6. Current velocities, measured with a microcurrent velocity meter, and density of drifting prey, were significantly lower behind aggregations of hydropsychid larvae. Food availability decreased by about 50% behind aggr

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01409.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The protein content of individuals of four species of cladoceran and two species of rotifer in eight ponds was measured over several time periods. The protein content in coarsely filtered water, which includes particulate (less than 31 μm for cladoceran and less than 10μm for rotifers) and dissolved proteins, was also analysed to estimate the amount of food available to the animals.2. A positive relationship between protein content of individuals and protein in the food was found for all the species. The increase in protein content of the animals was less pronounced when food was more abundant.3. When food concentration was lower, a greater reduction in protein content was observed in two species of rotifers than in four cladoceran species. Moreover, when comparing among species of Cladocera, the reduction in protein content at low food concentrations was more marked in the small‐bodied than in the large‐bodied species. These results are consistent with the size‐efficiency hyp

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb01410.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY