摘要:

SUMMARY.1. Based onin situgutter trials we related the drift of caddis flies to their benthic densities and to various abiotic factors in streams in the Ivory Coast (West Africa). Members of the families Hydropsychidae, Philopotamidae. Hydroptilidae and Leptoceridae were considered in detail.2. The drift of larvae peaked at night in both early and late larval instars.3. Drift of a larval group (a certain instar, species or higher taxon) was more often related to the benthic density of other larval groups than to its own benthic density.4. Self‐regulation of an upper benthic density of a larval group by emigration through drift was not statistically evident.5. There was no straightforward relationship between drift and abiotic factors.6. Drift rates differed between taxa as well as between larval instars (size groups) within a taxon. Newly hatched larvae had very high drift rates, whereas the last larval instar usually had the lowest drift rate.7. We related these results to the violently fluctuating discharge of the streams in the study area and the consequent variability of space for lotic insects.8. Drift estimates, made at the same time as a monitoring programme on possible side‐effects of insecticides (Onchocerciasis Control Programme), failed to reflect benthic densities except in the night drift of Hydropsychi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01061.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Coidingham Loch (Berwickshire. Scotland) (area. 8.4 ha, mean depth 2.9 m, max. depth 12.3 m) belongs to Hakansson's convex shape category. It lies in a basin of Silurian Greywackes rock within 0.25 km of coastal sea cliffs (c. 133 m a.s.l.). The theoretical hydraulic replacement time is 3.17 years.2. The loch stratifies intermittently in summer. Fluctuations in oxygen concentration generally correspond to spells of mixing and stratification; low values of 10% saturation occur at the bottom.3. The sum of the concentrations of major cations (Na+, K+, Ca2+, Mg2+) is in accordance with measured conductivities ranging between 380 μS cm−1and 420 μS cm−1(k.25). The ratios (by equivalents) of Na+/Cl−(0.04) are similar to those in sea‐water, whilst values for Ca+2+/Cl−(0.85–1.01) and Mg2+/Cl−(0.79–0.88) reflect the bedrock.4. Nitrate concentrations were lowest (<0.05 mg N1−1) in summer following losses from the column of 107 mg N m−21−1, a rate corresponding well with published figures on microbial nitrate reduction. Nitrate increased at a rate of 8μg N I−1d−1to a winter maximum of 1.55 mg N I−1. Mass balance calculations show that if this rise is attributed to run‐off from surrounding land, a loss rate of 11.1 kg N ha−1yr−1would be required; this value is also commensurate with published figures.5. Changes in phosphorus and factors controlling them contrast markedly with those of nitrate. The minimum concentration of 55 μg total P l−1(mainly in soluble reactive form) occurs in spring. An increase to the maximum ofc.300 μg l−1in summer is sustained mainly by release from the sediments at a regular rate of 3 μg P l−1d−1(8.7 mg m−2d−1). Adsorption by the sediments is considered to be the major process accounting for autumnal losses of phosphorus of 2.6 mg P M−2d−1.6. Silica showed a less regular seasonal pattern, but varied so

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01062.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Total phytoplankton biomass in the small (8 ha), intermittently stratifying, eutrophic Coldingham Loch exhibited spring and autumn maxima of about 35 μg chlorophyll a l1. Late winter and early spring assemblages included Chlorococcales (dominated byCoetxochloris pyrenoidosaKorsch. andDichotomococcus curvatusKorsch.), diatoms (unicellular Centrales andAsterionella formosaHass.) and desmids (Closterium acutumBrèb. andStaurastrum chaetoceras(Schrod.) G. M. Smith). Small populations ofCoetastrumandOocystischaracterized the summer period. The commonest “blue‐green alga”,Aphanizomenon flos‐aquaeMorr.exBorn,etFlah. (Cyanobacteria) attained its maximum population density in September just after the loch had permanently de‐stratified. It was replaced by another growth ofClosterium acutumwhich reached its annual peak density of 900 cells ml−1in October.2. It is likely that nitrogen in summer and silica at various times of the year limited the growth of certain species; it is also possible that phosphorus limited growth in spring.3. When physical conditions and nutrient concentrations are resolved into their basic, simple, seasonal patterns, a number of species preferences for particular environmental requirements become apparent. Of special significance is the competitive advantage over other plankters ofAphanizomenonin being able to resist sinking losses under stratified conditions and thrive at low ambient nitrate levels. Equally, there are some species exhibiting adaptability to a wide range of conditions.4. The observed periodicity is examined in relation to recently published schemes that summarize phytoplankton‐environme

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01063.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. A 23.1 m sediment core from Lake Rukwa, southwest Tanzania, records 13,000 years of climatic change in five diatom assemblage zones. Zone E (13,000–12,7000bp) reflects the transition from the waning late glacial arid phase to pluvial conditions, as indicated by the co‐occurrence of diatoms associated with fresh and relatively saline conditions. Zone D (12,700–4400bp) represents a moist period with frequent stratification, indicated by the halophobic generaMelosira and Stephanodiscus, whieh also represent alternating silica‐rich and silica‐dcpleled waters. Beginning with Zone C (4400–3900bp) the lake became much more saline withThalassiosirapredominating. This drying trend was reversed slightly in Zone B (3900–3300bp). During the last three millennia (Zone A), lake salinity was further reduced, while transitory moist phases were occurring in more northerly lakes such as Victoria and Kivu.2. Lake Rukwa was relatively stable over a time scale of centuries, but on an annual basis is quite variable in salinity depending on the local rainy season.3. These results agree well with the generalized paleoclimatie chronology of East Africa and suggest that the Holocene climatic regime of East Africa extended at

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01064.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The immature stages of the cranefliesLipsothrix nigrilineaandL. fenderiare spent in galleries within decayed red alder (Atntts rtibra), in low order streams of the Pacific Northwest.L. fenderialso occurs in some coniferous wood and wood in semi‐terrestrial sites at stream margins. Larvae of both species feed on the wood and are important degraders of this material.2. The immature stages are briefly described and behaviour of the two species is compared.3.L. nigrilineahas a predominantly biennial life cycle. It emerges from April to August in response to receding water level. The absence of this cue results in an extension of the life span to 3 or more years. The non‐deterministic life cycle results in high variability of juvenile and adult weights.4.L. fenderiis basically a biennial species, with a more synchronized autumn emergence. A portion of the population may emerge after 1 year if oviposition occurs early enough to allow autumnal growth of larvae or if growth is relatively rapid.5. The extended life cycle ofLipsothrixspp. and the broad emergence ofL. nigrilineaare concluded to be adaptations to a habitat/resource which is relatively stable and allows long‐term associ

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01065.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The effect of ionic strength on the configuration of aquatic humic substances was studied by gel filtration and dialysis of water from small. Finnish forest lakes of varying colour.2. Sephadex gel filtration of water from the most humic lake gave similar elution profiles of UV absorbance and dissolved organic carbon (DOC). Gel filtration of unconcentrated samples from all three lakes under natural conditions of ionic strength (I = 1.7 × 10−4) and pH (5.5–6.0) gave similar fractionation of humic substances, despite their widely differing colour (30–350 mg Pt l−1) and DOC (5–25mg C l−1).3. Increasing the ionic strength by two orders of magnitude caused considerable retardation on the Sephadex columns of the humic substances, suggesting a decrease in their molecular size and/or shape.4. Dialysis experiments strongly indicated that ionic strength‐induced changes in the configuration of the aquatic humic substances are indeed real. Hence it is probable that the elution behaviour of aquatic humic substances on Sephadex gels has previously been wrongly attributed to ionic strength‐dependent interactions between the gel and the

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01066.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Populations ofStalls lutariaL. were sampled quantitatively at about monthly intervals during 3 years at two localities in the macrophyte rich River Suså, Denmark.2. The life cycle was univoltine. The larvae hatched in June‐July, and the initialS. lutariapopulation densities varied between 10 and 370 ind. m−2. These differences were probably due to extreme variations in stream discharge during the period of recruitment, high velocities preventing the small swimming larvae from reaching the sediment.3. TheS. lutariarate of elimination varied between 0.11 and 1.47% d−1at the two localities. The high rate of elimination was possibly due to fish predation.4. The growth rates varied between 0.54 and 15% d−1. Growth rates differed between localities and years.5. Numbers of potential prey organisms were not higher in sample units withS. lutariathan in sample units withoutS. lutaria. Numbers of leeches, which were potential competitors, did not differ significantly in sample units with and withoutS. lutaria.6. Production ofS. lutariavaried between 0.16 and 2.49 g ash free dry weight m−2y−1, and the P/B̄ ratios varied between 3.0 and 7.3 y−1. The P/B̄ ratios increased significantly with increasing rat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01067.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Reactions of individual predatory stoneflies to contact by individual mayfly prey, and vice versa, were studied in the laboratory using two sets of species, one from a stream in southern Ontario. Canada, and the other from a stream in North Wales.2. Based largely on information received via their antennae, the stoneflies were capable of distinguishing between conspecifics and mayfly prey and between prey species. A clear preference for certain prey species was evident but less preferred species were made more attractive when damaged or when the stoneflies were very hungry. Detection of conspecifics by stoneflies was confused in the presence of prey or the local smell of prey body fluids and this led to interference during hunting and feeding at high predator densities.3. Some mayfly species were capable of distinguishing between conspecifics. other mayflies and predators. The cerci were important in intra‐ and interspecific contact encounters between mayflies and were used in a fencing fashion to establish a minimum distance between nymphs. However, the cerci did not appear to play an anti‐predation role as stoneflies captured and ate mayflies with and without cerci in equal numbers.4. Reactions to conspecifics by the Palaearetie mayfliesRhithrogena semicolorata(Curt.) andBaetis rhodani(Pictet) were similar to those of the ecologically‐equivalent Nearctic speciesStenonema vicarium(Walker) andBaetis vagansMcDunnough.5. In encounters between mayflies, intra‐ and interspecific responses were similar. However, the responses of some mayfly species to conspeeifics were modified in the physical presence of a predator or the water from its holding tank. Different mayfly species made specific responses to predaeeous stoneflies. Responses to a herbivorous stonefly were either similar to conspeeific encounters or were intermediate between them and encounters with predators.6. Experiments to reveal the exact nature of the stonefly stimulus detected by the mayfly nymphs strongly suggested that there were two components to the stimulus. One was physical contact by the predator's antennae, the other was chemical in nature and could be detected only over short distances (up to a few mm). Independently each could elicit a response, but combined their effect appeared to be synergistic.7. Different mayfly species responded differently to the stoneflyPhasganophora capitata(Pictet) and this sequence of sensitivity was mirrored by the predator's choice of prey species—the most sensitive to the predator being the favoured prey and the less sensitive the least favoured. The significance of these findings to optimal foraging theory, as applied to tactile predators, is

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01068.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. Field experiments were performed in the day and night at six modal water velocities (range 10–52cm s−1), using: (i) newly‐ emerged fry without neutral buoyancy; (ii) older fry in poor condition (weight well below that expected for resident fry); (iii) older fry in good condition (weight similar to that of resident fry); (iv) dead fry.2. An exponential model described the return rate of fry to the stream bottom; the mean distance travelled downstream varied considerably between the four fry categories, but always increased linearly with increasing water velocity.3. Results were similar for dead fry and newly‐emerged fry released at night; 50% of the fry returned to the bottom in 10–11 s and nearly all returned inc. 70s, the maximum distance travelled ranging fromc. 7 m at 10 cm s−1toc. 37m at 52cm s−1, Newly‐emerged fry released in the day returned slightly faster (54s for 99% return to bottom).4. Older fry in poor condition returned to the bottom slightly faster in the day than at night, but took about 2 min and travelled about twice the distance covered by dead fry. Older fry in good condition returned to the bottom at the fastest rate (3–6s for 50% andc. 30s for the rest), and travelled only about half (at night) or a third (in day) of the distance covered by dead fry.5. The implications of this investigation are discussed and it is concluded that, apart from water velocity, the age and condition of the fry were the two most important factors affecting their do

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01069.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY.1. The horizontal distributions of Daphnia longispina and Bosmina tongispina in Lake Kvernavatn (Norway) were investigated twice in 1982. In late spring, when populations were small, the two species inhabited the same areas, and they were evenly distributed from the littoral to the pelagic. At high population densities, during midsummer, the species were spatially segregated, D. longispina being pelagic and B. longispina littoral in distribution.2. The distribution and feeding of three‐spined sticklebacks (Gasteros‐teus aculeatus) were also studied. The sticklebacks were apparently forced into littoral areas by larger piscivorous predators in the pelagic and they were consequently restricted to foraging primarily on B. longispina, which formed dense swarms during daytime in summer.3. We suggest that predation and competition influence the spatial distribution of zooplankton species. The feeding efficiency of fish foraging on high‐density zooplankton populations can be reduced by spatial segregation of zooplankton species. Where high local densities occur, due to swarm formation, predation is changed from size‐selective feeding to consumption of spatially isolated indi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1987.tb01070.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY