摘要:

SUMMARY1. The functional response of the filter‐feeding blackfly larvaFrosimulium mixtum/fuscumwas examined in laboratory experiments. We focused on the relationship between a component of the particle handling process (the cephalic fan flick rate) and ingestion rate, to determine whether ingestion rate is limited by handling‐time. The influence of food deprivation on ingestion rate and feeding efficiency also was assessed.2. Ingestion rate rose asymptotically with increasing food availability, leveling off at a concentration of about 100 mg1−1. Satiation did not account for this plateau. Flick rate (the frequency with which larvae open and close their cephalic fans) increased in a similar fashion, though flick rate only accounted for about two‐thirds of the variation in ingestion rate.3. A simple equation describing the components of the feeding process in blackfly larvae was developed to investigate alternate flick rate ‘decision rules’ capable of predicting relationships between food concentration, flick rate and ingestion rate. The flick rate did not follow a fixed time rule, in which larvae allow particles to accumulate in the fan for a fixed amount of time prior to retraction. For most food densities, flick rate patterns more closely approximated a fixed number rule, in which fans are retracted after a fixed number of particles accumulate.4. Flick rate rose with increasing food concentration even after the ingestion rate had levelled off, whereas several optimal filter‐feeding models predict that filtering rate should decline as food concentration increases above this level. This predicted behavior was not observed because the number of particles ingested per flick failed to increase with increasing food concentration.5. The efficiency of particle ingestion (number ingested × number available−1× 100) was very low (<0.1%), and declined with increasing food concentration.6. An increase in food deprivation time prior to a feeding trial produced a significant increase in flick rate, ingestion rate and feeding efficiency. This adjustment of feeding behaviour allowed animals to replace their gut contents more quickly following longer periods of food deprivation, which agrees with the qualitative predictions of optimal dige

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00943.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Microfossil and X‐ray analyses of sediment cores from Lake Victoria. East Africa, reveal a history of dramatically shifting environmental conditions over the last 25,000 years.2. The diatom record of a 10 m core collected from beneath 66 m of water at an offshore station extends the known history of the lake 10,000 years beyond the published records from Pilkington Bay and Damba Channel, and shows that maximal late Pleistocene aridity occurred between 15,000 and 13,000bp. Lack of precipitated carbonates in the offshore sediments suggests that the lake remained relatively dilute throughout the period of record.3. There is no evidence that the lake level fell low enough to confine fishes to refugia in small isolated ponds or around river mouth

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00944.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Water samples were collected over two years from the Yorkshire Ouse and Yorkshire Derwent and the following were measured: (i) concentration of directly‐counted bacteria (free‐living and particle‐bound), (ii) concentration of colony‐forming units, (iii) bacterial heterotrophic activity (turnover rate for glucose assimilation), (iv) specific activity (turnover rate per bacterium), (v) a range of environmental variables.2. The abundance and activity of suspended bacteria showed similar seasonal periodicities in both rivers.3. Free‐living bacteria were usually more numerous than particle‐bound bacteria; low concentration of free‐living bacteria and maxima of particle‐bound bacteria usually occurred in winter.4. Concentration of colony‐forming units varied irregularly, but lowest levels were found in summer.5. Turnover rate and turnover rate per bacterium showed distinct summer maxima.6. Multiple‐regression analysis was used to relate bacterial variables to subsets (chosen by factor analysis) of environmental variables; up to 89% of variation in bacterial variables was related to the combined effects of variation by variables in

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00945.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1.Soyedina carolinensisClaassen, a leaf shredding stonefly, was reared in a series of three laboratory experiments from early instar to adult on different species of deciduous leaves and at various constant and fluctuating temperature regimes.2. Experiment 1, which involved rearing larvae on fourteen different leaf diets at ambient stream temperatures, showed that diet significantly affected larval growth and adult size but did not affect overall developmental time.3. Experiment 2, which involved rearing larvae on five different leaf diets at each of three fluctuating temperature regimes (viz ambient White Clay Creek (WCC), ambient WCC+3°C, and ambient WCC+6°C), showed that: (i) adding 6°C to the normal temperature regime of WCC was lethal to 99% of the larvae regardless of diet; and (ii) warming WCC by 3°C did not affect developmental time but did significantly reduce adult size relative to adults reared at WCC temperatures on certain diets.4. Experiment 3, which involved rearing larvae on five different leaf diets at each of five constant temperatures (viz 5, 10, 15, 20, 25°C), showed that: (i) temperature significantly affected the mortality, growth, and development time of larvae whereas diet only affected larval growth and mortality; (ii) temperatures at or near 10°C yielded maximum larval growth and survival for most diets; (iii) at 5°C, larval mortality was high and growth was low resulting in a few small adults for most diets; (iv) larval mortality was at or near 100% at 15°C regardless of diet; and (v) no larvae survived at 20 a

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00946.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Adult Trichoptera were caught during 3 years (1980–82) in the ‘Ritrodat’ research area of the Upper Lunzer Seebach. a mountain brook near Lunz. Lower Austria, using a set of thirty pyramid type emergence traps. During the three collecting periods (112 collecting days) a total of 1810 specimens were caught. The most abundant species wereMicrasema minimumMcL. (Brachycentridae).Rhyacophila vulgarisPictet (Rhyacophilidae), and the three Iimnephilid speciesPotamophylax cingulatusSteph.,Allogamus auricollisPictet andEcclisopteryx guttulataPictet.2. In six species (Micrasema minimum, Rhyacophila vulgaris, Atlogamus auricollis, Ecclisopteryx guttulata, Drusus biguttatusPictet,Chaetopteryx fuscaBrauer) the sex ratio was significantly different from 1:1. InMicrasema minimum422 females were caught but only three males.3. In each year there were peaks in total emergence in early summer and early autumn.4. The length of the emergence period of the most abundant species ranged from 38 days inMicrasema minimumto 210 days inRhyacophila vulgaris(mean values 1980–82); there was also a difference in the intensity of emergence in these species: the percentage of time required for 50% of the animals to emerge (0%=onset of emergence, 100%= emergence completed) was 16% inAllogamus auricollisbut 71% inRhyacophila vulgaris(mean percentages 1980–82).5. The distribution pattern of individuals per trap was tested against a Poisson distribution; in all three years the distribution was contagious.6. The dry weight of specimens ofDrusus biguttatus, Micrasema minimum. Ecclisopteryx guttulataandWormaldia copiosaMcL. was measured and. together with published dry weight values of other species (Malicky, 1976), these data were used to estimate the biomass emerging annually of twenty‐three species of Trichoptera (99.2% of emergence, 1980–82). This was equivalent to 35.3 kJ m−2in 1981 and 32.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00947.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Microcosms of Lake Balaton mud and sterilized sand and aerated water were used to evaluate ammonia increments in the overlying water as influenced by chironomid density and temperature. In the two approaches, the effects of sediment disturbance and metabolic excretion of chironomids were measured.2. The activity of larvae increased the ammonia content of the overlying water at temperatures above 10°C. A rise of temperature to 20°C resulted in a 5–20‐fold increase in ammonia release in both systems with chironomids.3. At 10°C combined effects of sediment disturbance and of excretion produced lower release rates than did excretion rates alone (mud‐water v. sand‐water treatments). At higher temperatures (15 and 20°C) release rates of ammonia by sediment disturbance plus excretion were higher than excretion rates alone. Ammonia excretion contributed significantly to the total release at each temperature.4. Metabolic mineralization of nitrogen compounds appears to be an important mechanism contributing to nitrogen regeneration from aerobic lake sediments. High N:P ratio (14:1) of chironomid excretion materials supports this int

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00948.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Streams of the northern jarrah forest, Western Australia, were sampled at twelve sites from December 1981 to December 1982 to examine spatial and temporal changes in the structure of the macroinvertebrate community.2. The climate of this region is quite predictable by Australian standards and each year a hot, dry summer is followed by a mild, wet winter. Highest stream discharge occurs during winter (June‐November) reducing to negligible flow over late summer and autumn (January‐May). The low flows in summer were associated with warm water, lower dissolved oxygen, increased concentrations of cations and, in many cases, lower pH.3. Temporal changes in abundance, diversity and evenness indicated that the invertebrate fauna became dominated by a few taxa during the summer months. Major spatial and temporal changes in the composition of the fauna were detected by classification and ordination. Summer and winter faunas were identified at most sites and were clearly associated with the seasonal changes in the physical and chemical environment. This seasonality is not typical of stream systems previously studied in Australia. Large spatial differences also occurred over small distances among sites in two similar‐sized forested catchments.4. Multiple discriminant analysis and stepwise multiple regression analysis showed that velocity and depth were highly associated with the observed temporal changes in the fauna, though other variables, including concentrations of cations and water temperature, were also important. Spatial differences were correlated with concentrations of cations which may simply reflect differences in the geologies of the catch

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00949.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. From forty‐five values reported for twenty species of aquatic insect species, it was found that the nitrogen content (N) of the food was significantly and positively correlated (r=0.97. P<0.001) with assimilation efficiency (Ase).2. Therefore, the Ase of aquatic insects can be predieted, if the nitrogen content of the food is known, using the equation: Ase (%)=9.29+8.82

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00950.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Dominant chemical gradients in the peats of a flood‐plain fen in Broadland, Norfolk were poor‐fen (oligotrophic)  rich‐fen (minerotrophic) and freshwater  brackish water. These gradients were to some extent obscured by a complex of factors governing the concentrations of ions in the peats and peat waters.2. The peats were almost totally organic and cation exchange capacities (CEC) varied with their macrofossil composition.Cladium mariscitsL. peats had higher CEC thanPhragmites communisTrin. peats of similar bulk density.3. Amounts of dissolved and extractable N and P were very low. but total amounts of N and P were high and closely related to bulk density.4. Large seasonal variation in concentrations of ions in the peat waters was due to dilution at times of flooding. There was strong evidence that little river water penetrated directly across the study area, contrary to classical descriptions of flood‐plain mires.5. Amplitude of fluctuations in concentration varied between study sites although the pattern of change was similar. Fluctuations were small in poor‐fen.Sphagnumdominated sites.6. An incursion of brackish water up river due to unusually high tides was observed, but it is likely that brackish conditions in the fens are caused by release of ions from underlying es

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00951.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Colonization of microhabitat implants by the amphipodGammarus pseudolimmnaeusin a small southern Ontario stream was studied in order to analyses the factors controlling habitat selection. The variables substrate particle size, current speed, presence of food and light were used in an analysis of covariance, with percentage weight of organic matter of silt and percentage interstitial space occluded by silt as the covariates.2. Greatest numbers of amphipods settled on microhabitats featuring large substrate particles, no current and presence of food. There was also a positive relationship between total numbers and the volume of silt deposited on the microhabitats by the stream; small quantities of silt had a beneficial effect on colonization but larger quantities became detrimental.3. The change from a positive effect occurred at approximately 25% occlusion of the interstitial space in large gravel (x̄ diameter=3.2 cm) and at approximately 55% occlusion in small gravel (x̄ diameter = 0.34 cm).4. Large animals (6–16.0 mm long) were found predominantly in microhabitats featuring food and large substrate. Medium‐sized animals (3–6.0 mm) were most commonly associated with no current and presence of food, and were positively affected by the amount of silt but, at the same time, were negatively affected by increasing occlusion of interstitial spaces by silt. Numbers of smallGammarus(<3.0 mm) were affected only by silt and in a similar manner to medium‐sized animals.5. Amphipod biomass was greatest in microhabitats featuring food and no current. Previous data on the behaviour of this species in laboratory stream‐tanks are compared with the microhabitat sele

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00952.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY