bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ life table of a subtropical copepod
Authors: WYNGAARD GRACE A.
Published: May 2006

A life table of a subtropical population of Mesocyclops edax(Copepoda: Cyclopoida) was constructed from a cohort of individuals reared in enclosures in a small, eutrophic lake.

The lake population was sampled concurrently to determine age structure, per capita birth, death and growth rates, body size and clutch size.

Maturation times of enclosed males and females were 9.3 and 11.4 days, respectively. The population growth rate. r. was estimated to be 0.18 females day‐1 for the enclosed population, but approximated zero on most dates in the lake population. Mortality was low in the enclosures which excluded predators and high in the field population exposed to planktivorous fish and Chaoborus.

The means and variances of several fitness traits are related to the specific environment. The enclosure approach promises to be a useful tool in the study of zooplankton life history variation.
The age, growth and reproduction of the stone loach Noemacheilus barbatulus (L.) in a Dorset chalk stream
Authors: MILLS C. A. , WELTON J. S. , RENDLE E. L.
Published: May 2006

SUMMARY.

In this highly productive chalk stream the stone loach, sampled by electrofishing over a 30 month period, had a high growth rate reaching a mean length of 65 mm in 1 year and 93 mm in 2 years. The fish were short‐lived in contrast to most slow‐growing populations in the U.K. and Finland with 11 group fish comprising 8.8% and III group fish only 1.1% of the total number.

The loach were fractional spawners: a 75 mm female produced an estimated 10,620 eggs between late April and early August totalling 46% of the loach's initial weight.

In March and April some small 0 group females contained only poorly developed eggs and up to 10% of 0 group fish may have failed to spawn.

Amongst loach >52 mm in length in March and April there was an exponential relationship between absolute fecundity and fish length but no relationship between relative fecundity and length. There was. however, a relationship between fish length and both gonadosomatic index and maximum egg size, which may indicate that large fish began to spawn first.
The logseries distribution and Mountford's similarity index as a basis for the study of stream benthic community structure
Authors: SHEPARD RICHARD B.
Published: May 2006

SUMMARY. 1. Of the various approaches to studying species‐abundance patterns in aquatic ecosystems (particularly streams) the logseries distribution is the most appropriate. The distribution parameter, α, is readily estimated and goodness‐of‐fit of the model to the data can be estimated.

2. A method exists which uses a to calculate an index of similarity from which cluster dendrograms can be constructed and the clusters tested for significant differences. Assumptions and calculations are presented.

3. Procedures are illustrated, with examples from Idaho streams, and approaches to interpreting the results are included.

4. Studies of stream macro invertebrates can fulfill the assumptions of the logseries distribution but cannot meet those of commonly used diversity indices.
The effect of temperature on photosynthetic and respiratory electron transport system activity in the shallow and deep‐living phytoplankton of a subalpine lake
Authors: PRISCU JOHN C. , GOLDMAN CHARLES R.
Published: May 2006

SUMMARY. 1. The influence of temperature on in vivo photosynthetic and in vitro respiratory electron transport system (ETS) activity was determined over the season for the 3 m (warm‐water) and a 20m (cold‐water) phytoplankton communities in Castle Lake. The optimum temperature of photosynthesis at 3 m (X̄=20.8°C) was significantly higher than the average optimum at 20 m (X̄=14.8°C).

2. Seasonally, the photosynthetic temperature optimum increased when the blue‐green alga Chroococcus limneticus Lemm. was present. The temperature characteristics of this organism were maintained even after it had settled into the cold water of the hypolimnion.

3. Temperature optima were not significantly different in experiments conducted under limiting or saturating photosynthetic photon flux densities (PPFD).

4. Short‐term (1 h) preincubations with dissolved inorganic nitrogen (DIN) (≃80 μg NH4NO3‐N l−1) had little effect on the temperature characteristics of photosynthesis while the longer (>24 h) incubations provided by a whole‐lake epilimnetic DIN addition (≃75 μg NH4NO3‐ N l−1) significantly lowered the photosynthetic temperature optimum to 12.5°C. Once this epilimnetic DIN was depleted the optimum roseto25°C, a value higher than that present before the enrichment, which coincided with the growth of C limneticus.

5. Respiratory ETS activity usually began to inactivate between 19 and 20°C. However, when C. limneticus was abundant the inactivation temperature was often greater ihan 25°C.

6. The average energy of activation (E) and Q10 value for the 3 m community (15.9 kcal mol−1 and 2.6 respectively) were significantly higher than those at 20 m (14.2 kcal mol−1 and 2.4 respectively). Seasonally, the highest E and Q10 values of ETS activity occurred during the late‐summer bloom of C. limneticus.

7. These results demonstrate that the epilimnetic and hypolimnetic phytoplankton communities in Castle Lake are physiologically distinct with regards to their temperature characteristics.
Community structure in some southern English streams: the influence of species interactions
Authors: HILDREW ALAN G. , TOWNSEND COLIN R. , FRANCIS JEANETTE
Published: May 2006

SUMMARY. 1. The results of a survey of thirty‐four stream sites, differing in pH and invertebrate species richness, indicated that the pool of locally available, suitably adapted species was smaller in the acid streams. This plays a part in determining the general pattern of lower species richness at more acid sites.

2. Diversity of feeding categories increased with species richness, indicating that a greater range of food resources was available in the less acid, more species‐rich communities.

3. The pattern of predation varied with pH and species richness. The numbers of large insect predators were lower in the less acid, more species‐rich communities and this was correlated with the presence of fish.

4. A detailed study of the guild of detritivorous stoneflies in four streams differing in species richness provided evidence that density compensation occurs, niche width decreases and niche overlap declines as species richness increases.

5. We discuss the roles that competition and predation play in determining the structure and richness of stream invertebrate communities.
Embryonic development, larval growth and life cycle of Coenagrion puella (Odonata: Zygoptera) from an Austrian pond
Authors: WARINGER J. A. , HUMPESCH U. H.
Published: May 2006

SUMMARY. 1. Newly‐laid eggs of Coenagrion puella (L.) from a pond near Herzogenburg (Lower Austria) were kept at constant water temperatures (range c.3.5°C to c.28°C)in the laboratory. Hatching success varied with temperature; no eggs hatched below 12°C and nearly all hatched at c.l6°C. Hatching time decreased with increasing temperature and the relationship between the two variables within the range 12–28 °C was well described by a power law. The length of the hatching period was less than 12 days. Hatching times estimated from the power‐law equations and those obtained in the field experiments were similar. Therefore both the hatching time and the length of the hatching period in the field could be estimated from the laboratory data for the range 12–28°C.

2. The maximum number of instars from egg to imago was 11; the average body length increment (mm) per moult was proportionately constant at c.26% and Dyar's rule was applicable. The interval between moults decreased with increasing temperature up to the seventh instar and the relationship between the two variables within the range 12–28°C was well described by a power law. The moulting interval for instars 8–11 ranged from 23 to 48 days and was relatively independent of temperature. No moulting occurred at temperatures below 12°C.

3. Larval growth was logistic in the laboratory and variations in mean logistic growth rate (range 0–2.5% length day−1) were related to mean temperature with no growth at temperatures <12°C. Larval growth rates in pond experiments were similar to those estimated from laboratory data, and therefore the regression equations obtained from the laboratory experiments are probably applicable to larval growth in the field.

4. Information on the life cycle of C. puella is briefly reviewed and it is concluded that C. puella from the pond near Herzogenburg has an univoltine life cycle.
Assay for biologically available phosphorus using proteolytic Aeromonas hydrophila
Authors: RATSEP A.I. , SJOGREN R. E.
Published: May 2006

SUMMARY. 1. A simple and inexpensive assay was developed to determine the amount of biologically available phosphorus (BAP) present in freshwater.

2. BAP was measured by using Aeromonas hydrophila in a proteolytic assay system in which the release of the chromogen from an insoluble azure dye derivative of hide powder (HPA) was determined spectrophotometrically. The time necessary to hydrolyse 50% of the HPA was found to be directly dependent on the amount of BAP present. BAP within the range 2–250 μg 1−1 phosphate‐phosphorus was detected.

3. Our data suggest that the application of this assay for the measurement of BAP in freshwater offers the potential of monitoring the biological response of a freshwater ecosystem to phosphorus.
Spatial variations in the water quality of Lough Erne, Northern Ireland, on the basis of surface sediment diatom analysis
Authors: BATTARBEE RICHARD W.
Published: May 2006

SUMMARY. 1. Constrained cluster analysis of thirty‐five surface sediment diatom assemblages shows that Lough Erne, a complex multi‐basin lake in Northern Ireland, can be sub‐divided into four main zones.

2. All areas of the lake system have planktonic diatoms typical of eutrophic lakes but the lack of small Stephanodiscus species in zone 4 suggests that this area of the system is least productive.

3. Surface sediment diatom assemblages can be used to assess spatial variations in complex lake systems and can thereby be used as a guide to the choice of sites for water quality monitoring and sediment coring.
The relationship between food particle size and larval size in Simulium noelleri Friederichs
Authors: WOTTON R.S.
Published: May 2006

SUMMARY. 1. In a laboratory experiment, larvae of Simulium noelleri were fed on polystyrene latex microspheres of a range of diameters from 5 to 100 μm.

2. Examination of the particle size distribution in the water used in the experiment showed those <13μm to be the most numerous (87% of all particles present). Particles of this size made up 57±2% (mean ±SE)of the total of those in the gut of larvae.

3. Comparison of particle composition in the gut contents and the water of the experiment, using Jacob's index of electivity, showed that larvae of all sizes filtered proportionally fewer of the particles <13 μm and more of those >13μm.

4. As larvae increased in size they became better able to filter the largest particles present (>52μm in diameter) and less well able to filter the smallest particles (<13μm in diameter).

5. Gut retention time was longer in larger larvae.

6. The biology of S. noelleri, which inhabits lake outlets in high population densities, is considered in the light of these findings.
Adenylate energy charge in streambed sediments
Authors: KAPLAN LOUISA , BOTT THOMAS L.
Published: May 2006

SUMMARY.

The adenylate energy charge (ECA) of microbial communities from streambed sediments was measured during three different seasons, under experimental manipulation and in culture.

The ECA values of sediments (x±S.E.) in the autumn, winter and spring were low and constant; 0.22±0.03 (n=12), 0.32±0.04 (n= 12) and 0.28±0.03 (n=6) respectively.

A 5 h exposure of sediments to an algal lysate at 3.0–4.0°C and a 48 h exposure of sediments to tryptone‐yeast extract at 8.0–18.0°C failed to increase ECA even though respiration increased 3.7‐fold during the latter exposure.

The cellular ECA of a bacterial monoculture, sampled in log phase, was 0.90±0.10 (n=3), but cxtracclluhir AMP depressed the total culture ECA to 0.21±0.01 (n=4).

Attempts to isolate extracellular AMP from the interstitial waters of sediments were unsuccessful.

The data suggest that under natural conditions ECA is of limited use as a monitor of subtle changes in the physiological state of microbial communities in streambed sediments.
Uptake of phosphate and inorganic nitrogen by a sediment‐algal system in a subarctic lake
Authors: BJÖRK‐RAMBERG SUSANNA
Published: May 2006

SUMMARY.

The uptake of phosphate and inorganic nitrogen by sediment and phytoplankton was studied under natural conditions (1977) and during lake fertilization with phosphorus and nitrogen (1978–79) in Lake Gunillajaure, a small, stratified, subarctic lake in northern Sweden. The experiments were performed in situ in plexiglass cylinders, to which additions of nutrients were made, and the uptake followed by consecutive sampling and analysis of the water phase.

Additions of HgCl2 to the experimental vessels reduced the phosphate uptake to the sediment to less than 10% and it could therefore be concluded that the sediment uptake was mainly of biological nature.

Dark assimilation was 30–40% of that in light. Since light clearly stimulated the sediment uptake the epipelic algae were probably responsible.

The phosphate uptake to the sediment could be described by Michaelis‐Menten kinetics and the calculated constants (Vmax, ks) were very alike in 1977 and 1978 but appeared to have increased in 1979.

The sediment uptake of ammonium and nitrate was very slow indrcating that the epipelic algae were not nitrogen starved.

Even though the epipelic algae had a potential for efficient uptake of phosphorus, the phytoplankton took up 92–96% of the phosphate added to the lake on each fertilization occasion due to the relatively large water volume in the epilimnion in relation to the bottom area available for the epipelic algae.
Aspects of nitrogen fixation in Lough Neagh. II. Competition between Aphanizomenon flos‐aquae, Oscillatoria redekei and Oscillatoria agardhii
Authors: RIDDOLLS ANTHEA
Published: May 2006

SUMMARY.

The effect of nutrient availability on the growth of natural samples of Lough Neagh plankton (Aphanizomenon flos‐aquae, initial innoculum 0.98 mm3 l‐1, Oscillatoria redekei, 2.52 mm3 l‐1 and Oscillatoria agardhii, 4.96 mm3 l‐1) was studied, using ecologically realistic conditions of temperature (15°C), nitrate‐N (<0.35g m‐3) and orthophosphate‐P (<0.55g m‐3), in which the combinations –N–P, –N+P, +N–P, and +N+P were used.

After 8 days A. flos‐aquae had become dominant in treatments lacking N. After 12 days with N available the mean yields of O. redekei (37.7 mm3 l‐1) and O. agardhii (10.82 mm3 l‐1) were significantly greater (P=5%) than their respective yields (3.6 and 2.6 mm3 l‐1) in the absence of N. Somewhat surprisingly the mean yield of A. flos‐aquae when N was present (0.15 mm3 l‐1), was significantly less (P=5%) than in the absence of N (13.26 mm3l‐1).

The relative rates and duration of growth, the availability of P and N, and heterocyst frequency as an index of nitrogen fixation are considered in relation to the seasonal succession and dominance of these three principal cyanophyte members of the Lough Neagh phytoplankton.
Distribution, biomass and production of the freshwater mussel, Hyridella menziesi (Gray), in Lake Taupo, New Zealand
Authors: JAMES M. R.
Published: May 2006

SUMMARY.

A study of the distribution, biomass and production of the freshwater mussel Hyridella menziesi (Gray) was carried out at six sites in Tapuaeharuru Bay, Lake Taupo, New Zealand.

H. menziesi is common in the littoral zone, with clean sand and angle of slope being the most important environmental variables measured which are positively associated with mussel density. These variables are related to the accumulation of fine material which can clog the filtering mechanism of mussels. The angle of slope may also influence the movement and supply of food.

Density (5.6 m‐2), biomass (2.8 g dry weight shell free tissue m‐2) and potential production (0.50 g dry weight shell free tissue m‐2 yr‐1) are high compared to values found for mussels from other oligotrophic lakes.

The age structure of Hyridella suggests recruitment has declined in recent years. A periodicity in generations is proposed.
The organization of macroinvertebrate communities in the major tributaries of the LaTrobe River, Victoria, Australia
Authors: MARCHANT R. , METZELING L. , GRAESSER A. , SUTER P.
Published: May 2006

SUMMARY.

Seventeen sites were each sampled six times over 2 years for macroinvertebrates. A range of physicochemical variables was also measured to determine which factors were related to the distribution of species.

Numerical classification of the faunal data indicated that four groups of sites or communities were distinguishable: lowland sites; sandy upland sites; cobble upland sites from the northern catchment; cobble upland sites from the southern catchment.

Multiple discriminant analysis and multiple regression analysis demonstrated that particle size of the sediment, concentration of dissolved ions and altitude were the physicochemical features that were most strongly associated with changes in the faunal distribution.

Abundances of shredders and predators did not vary between the site groups while those of scrapers, gatherers and filterers did: scrapers were most abundant at cobble sites while gatherers and filterers were least abundant on sand and increased in abundance downstream. The distribution of the feeding groups showed some similarity with that predicted by the River Continuum Concept, but the fact that the shredders did not decrease in abundance downstream was a notable difference.

Abundance of the total fauna at a site was inversely related to the amount of benthic organic matter. This feature is contrary to the pattern usually reported from rivers in the northern hemisphere.
The role of lipids as feeding stimulants for shredding aquatic insects
Authors: CARGILL AUSTEN S. , CUMMINS KENNETH W. , HANSON BOYD J. , LOWRY ROBERT R.
Published: May 2006

SUMMARY.

Caddisflies (Trichoptera) that shred leaf detritus preferentially ingested lipid‐coated detritus during the last larval in star. This is the interval when these insects accumulate the triglyceride reserves necessary for metamorphosis and reproduction. Early in star larvae, which do not accumulate lipids, showed no preference for any lipids. This behaviour indicates food selection based on changing nutritional needs.

Pure unsaturated 18‐ and 20‐carbon fatty acids, either as free acids or triglycerides, were most strongly preferred. Crude lipid and the neutral lipid fraction from aquatic hyphomycete fungi, an important component of aquatic leaf detritus, were also preferred.

Tipula abdominalis (Diptera: Tipulidae) did not prefer any lipids during the last instar.
Spatial variations in and controls on the calcite saturation index in Acton Lake, Ohio
Authors: GREEN WILLIAM J. , CANFTELD DONALD E. , STEINLY BRUCE A.
Published: May 2006

SUMMARY.

Acton Lake is a small, hardwater, eutrophic reservoir located in the southwestern corner of Ohio. Over a period of 5 weeks in mid‐summer 1979, water samples were collected from the lake and its streams and analyzed for seven major ionic species and for temperature, dissolved O2, pH and conductivity. Geochemically the waters are characterized by high calcium and bicarbonate concentrations.

Data obtained on all samples were used to compute calcite saturation indices (SI) and to map the spatial distribution of this function throughout the system. The saturation indices were corrected for activity and ion pairing effects and yet are still to our knowledge among the highest values reported for a natural water.

The good correlations obtained between the SI and both the pH and dissolved oxygen clearly indicate that biological activity is the dominant control on the degree of saturation in this largely isothermal lake. To account for the extreme departure from chemical equilibrium, it is proposed that dissolved organic matter may be poisoning freshly formed calcite surfaces and preventing them from serving as effective nucleation centers.
Formation of thermal stratification in a small temperate lake
Authors: SZUMIEC MARIA ANNA
Published: May 2006

SUMMARY.

The origin of vertical temperature stratification in Erstwhile Water (Lake District, Cumbria, England) was observed.

At the first stage of the spring warming of the whole water column some discontinuity in the vertical temperature distribution appears in the surface and bottom layers.

Persistent summer stratification occurred for the first time at the lee end of the lake immediately after a change of wind direction, when the cumulative potential energy deficit dominated the cumulative kinetic energy by about 110‐8 Jcm‐2.

The results show the importance of the proper choice of initial conditions in computations of total energy, as well as the necessity to consider the spatial distribution of potential and mechanical energy responsible for the summer stratification in the lake.
The effects of vegetation removal by grass carp and herbicides on the water chemistry of four Florida lakes
Authors: SMALL JAMES W. , RICHARD DAVID I. , OSBORNE JOHN A.
Published: May 2006

SUMMARY.

Four lakes in central Florida each received a different weed control treatment consisting of herbicide and/or different stocking ratios of grass carp (Ctenopharyngodon idella Val.).

Submersed vegetation was eliminated by grass carp within 6 months In Lake Orienta and within 14 months in Clear Lake. Because Little Lake Fairview, treated with herbicide and a smaller stocking ratio of grass carp, retained abundant vegetation levels over the first two study years, grass carp which had been introduced initially were replaced with a greater number of fish at the beginning of the third year. Submersed vegetation was subsequently eliminated in this lake within LO months. Aquatic vegetation was reduced but not eliminated in Lake Mann which was treated with herbicide only.

Where macrophytes were removed there tended to be increased bottom dissolved oxygen, higher and more stable total alkalinity values, increased turbidity, lowered transparency, higher specific conductivity and increased chlorophyll levels. Significant increases in pH were probably due to low water levels resulting from a severe drought rather than weed control. Low water also affected specific conductivity. Annual means for nutrients did not differ significantly between years in the four lakes.
Feeding efficiencies of Chironomus plumosus (L.) and C. anthracinus Zett. (Diptera: Chironomidae) in mesotrophic Lake Erken
Authors: JOHNSON RICHARD K.
Published: May 2006

SUMMARY.

Absorption efficiencies of nitrogen and carbon in two Chironomus species found dominating in the profundal zone of mesotrophic Lake Erken were determined gravimetrically.

Absorption efficiencies for C. plumosus showed greater seasonal variation than those of C. anthracinus, with low efficiencies coinciding with the summer dominance of flagellate phytoplankton and with high C:N ratios.

Overall mean absorption efficiencies (±SE) for carbon and nitrogen, respectively, were 26.8% (±1.9) and 29.3% (±1.9) for C. plumosus, 24.6% (±1.7) and 28.1% (±1.8) for C. anthracinus.

Significant differences were found to exist between the C: N ratios of the superficial 2 cm sediment layers and those of Chironomus anterior midgut contents.

C. anthracinus appears to be a deposit feeder ingesting particulate matter scraped from the recently deposited surface sediments. The greater seasonal variation found in the absorption efficiencies of C. plumosus, together with the lower C:N ratios, support the contention that this species is a filter feeder with the nutritional quality of ingested matter depending primarily on pelagic inputs.
Limnological investigations on the Rosetta branch of the Nile. II. Seasonal variations of nutrients
Authors: SAAD MASSOUD A H. , ABBAS MAHDI H.
Published: May 2006

SUMMARY.

Nitrate tended to be low in the estuarine region compared with the freshwater stretches and seasonally was low in October. Nitrite broadly showed patterns similar to NO3 but at lower values.

Reactive phosphate and silicate tended to be much higher in fresh compared with saline stretches and was high in January.

These changes are broadly interpreted in relation to river discharge and the seasonality of phytoplankton although other, and as yet unstudied, causes will probably be found to be involved.
Fine‐layer depth relationships of lakewater chemistry, planktonic algae and photosynthetic bacteria in meromictic Lake Fidler, Tasmania
Authors: BAKER ALAN L. , BAKER KATHLEEN KROMER , TYLER PETER A.
Published: May 2006

SUMMARY.

Use of a multi‐column thin‐layer pneumatic sampler and modified analytic procedures has enabled resolutions of chemical and biological strata at 2.5 or 5.0 cm depth intervals. Examination of meromictic Lake Fidler, Tasmania, indicates the presence of a thin, intense stratum of bacteriochlorohyll d in the upper monimolimnion, associated with a discrete stratum of Chlorobium cf. limicola at the microaerobic interface between the oxygenated and sulphide‐rich zones.

Algae included small populations of Chlorophyceae, Chrysophyceae, Bacillariophyceae and Cryptophyceae. Bacteria included microaerophils and obligate anaerobes, pigmented and colourless, in well‐defined strata in the upper monimolimnion. A population of the microcrustacean Calamoecia tasmanica tasmanica was present in the mixolimnion. Chaoborus larvae were concentrated within the Chlorobium layer.

The chemical profile of Lake Fidler was stable, with a chemocline constant in position relative to the lake bottom. The surface water levels rose and fell through a distance of 1m in conjunction with heavy rainfall in the rainforest, and with river level variation, but had no measurable effect on the absolute position of the chemocline. Marked heterogeneity of dissolved substances at depths in the vicinity of bacteria suggested endogenous influence on pH and gelbstoff (‘gilvin’ in Australia).

Downwelling light attenuation was influenced primarily by gelbstoff (‘gilvin’) in the mixolimnion, with only red light (peak at 700 nm) measurable below 2 m. Light was absorbed mainly by Chlorobium in the monimolimnion, and was unmeasurable deeper than 3 m.

The absorption spectrum of the bacteriochlorophyll d in vivo, with a maximum absorbance at 721 nm, corresponds with the available downwelling light penetrating the mixolimnion to the Chlorobium layer.
The retrieval of material from the surface micro layer with screen and plate samplers and its implications for partitioning of material within the micro layer
Authors: ESTEP K. W. , MAKI J. S. , DANOS S. C. , REMSEN C. C.
Published: May 2006

SUMMARY.

The surface micro layers of two small ponds in Wisconsin were sampled over several years using screen and plate samplers. These devices performed identically for dissolved substances but for particulate material the glass plate sampler produced values 4 times those obtained with the screen.

These differences in sampling efficiency are probably the result of the failure of the screen sampler to release all of the particulate material it has collected and also to differences in the partitioning of dissolved and particulate material within the micro layer.

Results suggest that particulates are concentrated at the air‐water interface and that there is a four‐fold dilution with subsurface water in the screen samples when compared to the plate samples. Dissolved material, in contrast, is concentrated in a thicker layer below the surface mono layer, resulting in equal sampling efficiency with the plate and screen samplers.
Predator‐prey ratios in communities of freshwater invertebrates: the role of enemy free space
Authors: JEFFRIES M. J. , LAWTON J. H.
Published: May 2006

SUMMARY.

The ratio: number of predator species/number of prey species is reviewed using comprehensive faunal lists for a range of freshwater habitats in Britain and North America. Prey species are defined as detritivores, herbivores and fungivores; predators eat metazoan animals as the main component of their diet. Our data refer only to invertebrates.

The numbers of predators and prey species are apparently very closely correlated in freshwater communities (r=0.84, In transformed data), with an average ratio of predators to prey of 0.36. The average ratio of predators to prey changes from 0.48 in small (species‐poor) collections to 0.29 in large (species‐rich) collections.

We suggest that an approximately constant ratio of predators to prey may be generated by: (a) the number of predator species being a function of the number of broad classes or kinds of prey; and (b) the number of prey species being constrained by competition between prey for ‘enemy free space’, i.e. species that are too similar are unable to coexist with shared predators.
A 25,000‐year history for Lake Victoria, East Africa, and some comments on its significance for the evolution of cichlid fishes
Authors: STAGER J. C. , REINTHAL P. N. , LIVINGSTONE D. A.
Published: May 2006

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 13,000 bp. 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 mouths.
Microhabitat selection by a stream‐dwelling amphipod: a muitivariate analysis approach
Authors: WILLIAMS D. DUDLEY , MOORE KATHRYN A.
Published: May 2006

SUMMARY. 1. Colonization of microhabitat implants by the amphipod Gammarus pseudolimmnaeus in 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 small Gammarus (<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 selections seen.
Effects of overhead canopy on macroinvertebrate production in a Utah stream
Authors: BEHMER DAVID J. , HAWKINS CHARLES P.
Published: May 2006

SUMMARY. 1. Macroinvertebrate abundance and production were compared between an open and shaded site of a stream in the Wasatch Mountains, Utah. Mean biomass was significantly higher at the open site for midges (Chironomidae), 4.6×; Baetis bicaudatus, 5.7×; Baetis tricaudatus, 2.3×; Drunella coloradensis, 12× and Cinygmula sp., 1.6×, Abundance of most other macroinvertebrates (except black flies: Simuliidae) was also greater at the open site, but differences were not significant. Black fly biomass was 1.7× greater at the shaded site.

2. Seasonal production, estimated by the size‐frequency and instantaneous growth rate methods, was greater at the open site than the shaded site for most taxa (except black flies) and reflected differences in standing crops between the sites rather than differences in rate of growth. Excluding black flies, production at the open site was twice as high as at the shaded site.

3. The greater abundance and production of most invertebrate taxa at the open site is probably associated with either higher quality food (algae and algal detritus), or a phototactic attraction to sunlit areas.

4. Sampling of large cobbles was an efficient method of sampling all taxa except Cinygmula sp. which was more abundant on smaller substrate particles.
Quantitative observations on the ability of epiphytic bacteria to contribute to the populations of suspended bacteria in two dissimilar headstreams
Authors: RIMES CARRIE A. , GOULDER R.
Published: May 2006

SUMMARY. 1. Concentration of suspended bacteria in a calcareous headstream increased linearly from the source to 48 m; this indicated a diffuse origin of bacteria.

2. Drift loss of suspended bacteria and glucose‐mineralization capacity from this length of stream were measured, and estimates were also made of the total number and glucose‐mineralization capacity of epiphytic bacteria associated with the luxuriant submerged aquatic vegetation.

3. Mean drift loss per day represented 11–12% of total epiphytic bacteria and 8–18% of epiphyte glucose‐mineralization capacity, hence the epiphytic population should be well able to sustain the observed downstream losses.

4. In a 90 m length of a contrasting acid, granitic, headstream, in which submerged vegetation was principally a leafy liverwort, there was no downstream change in concentration of suspended bacteria.

5. A substantial population of epiphytic bacteria was found in the acid stream, sufficient for only a 1–2% daily release to produce a doubling in concentration of suspended bacteria; reasons are suggested for the apparent non‐release of epiphytes.
Population dynamics, life histories and species richness in an epiphytic chironomid community
Authors: TOKESHI MUTSUNORI
Published: May 2006

SUMMARY. 1. The chironomid fauna on the spiked water‐milfoil Myriophyllum spicatum was studied quantitatively for a year in a small lowland stream in eastern England.

2. A total of nineteen species, comprising fourteen Orthocladiinae, four Chironominae and one Tanypodinae, was recorded. Population dynamics and life histories of the eight most abundant species were described: Orthocladius (O.) Pe 9, O. (O.) sp. A, Cricotopus (C.) annulator, Rheocricotopus chalybeatus, Tvetenia calvescens, Eukiefferiella ilkleyensis, Thienemanniella majuscula and Rheotanytarsus curtistylus. The number of generations per year ranged from one (O. (O.) Pe 9, O. (O.) sp. A, C, (C.) annulator) to five (T. calvescens, T. majuscula). Temporal variation in population density often reflected characteristic patterns of the life cycle of each species.

3. Species richness (number of species) for each month ranged between six and fifteen. These observed species richnesses were compared with a null species occurrence model and it was revealed that a significantly higher number of species than expected coexisted in April and May. This may be related to the abundance of diatoms in spring.
Population dynamics of the gastropod Theodoxus jordani (Sowerby) in the Shatt Al‐Arab river
Authors: AL‐DABBAGH KHALID Y. , LUKA JAMAL Y.
Published: May 2006

SUMMARY. 1. Measurements of the population density of Theodoxus jordani were made for the period July 1980 until June 1981. Numbers showed a well‐defined pattern of fluctuation and varied between 390 in February and 1804 snails m−2 in May after recruitment.

2. The population age structure revealed that the snail was semelparous, and that one generation dominated the population for most of the year.

3. The breeding season was long. Snails laid eggs from early December to the end of April. Eggs were laid in protective capsules and one snail developed per capsule. Total population natality estimated from field samples was 9813 snails m−2.

4. Age specific mortality was high immediately after recruitment, low during the juvenile stages, and increased sharply at the adult stage with the onset of reproduction.
The effects of temperature and photoperiod on life history parameters of Daphnia magna (Crustacea: Cladocera)
Authors: KORPELAINEN HELENA
Published: May 2006

SUMMARY. 1. The life history responses of two common and three rare Daphnia magna clones to constant conditions of temperature and photoperiod were investigated, and intraspecific variation in the genes controlling growth, survivorship and reproduction was observed.

2. Rearing temperature had a significant effect on growth, survivorship and on all reproductive parameters measured (generation time, intrinsic rate of increase and male production), while photoperiod influenced significantly only survivorship and male production.

3. The maximum proportion of male offspring was produced at a low temperature (14°C) and at a mid‐range photoperiod (L:D16:8).

4. The likely mechanism whereby clones with different life histories are maintained in the population is discussed.
Spatial and temporal variation in the macroinvertebrate fauna of streams of the northern jarrah forest, Western Australia: functional organization
Authors: BUNN STUART E.
Published: May 2006

SUMMARY. 1. Spatial and temporal changes in functional organization of the invertebrate community of streams of the northern jarrah forest, Western Australia, were examined in the light of predictions of the river continuum concept (Vannote et al., 1980).

2. The composition of the fauna was largely as predicted for forested headwater streams with detritivores, principally collectors, dominating the fauna. Although shredders are generally considered to be codominant in such streams, they were not abundant in the riffle areas sampled in this study.

3. Some of the observed temporal changes in the composition of functional feeding groups were in agreement with those predicted by the generalized model. The abundance and richness of collectors were higher during the summer than winter, whereas the converse was true for filterers. This corresponded to the presumed availability of deposit and suspended fine‐particulate organic matter during summer and winter respectively. Scrapers and predators showed no consistent temporal pattern among sites. However, the density of the latter was highly correlated with the density of other invertebrates, particularly collectors.

4. Temporal changes in the abundance and richness of shredders were not synchronized with the marked summer input of coarseparticulate organic matter. The possible reasons for this, and the role of shredders in Australian stream systems, are discussed.
Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake
Authors: LENZ PETRA H. , MELACK JOHN M. , ROBERTSON BARBARA , HARDY ELSA A.
Published: May 2006

SUMMARY. 1. Regeneration of ammonium and phosphate by macro‐zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×104 and 3×105 individuals m−2.

2. Phosphate regeneration ranged from 0.2 to 1.3μ mol PO4 m−2 b−1at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO4 m−2 h −1 at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH4 m−2 h−1. respectively.

3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.
Egg development of the stoneflies Siphonoperla burmeisteri(Chloroperlidae) and Dinocras cepùnalotes(Perlidae)
Authors: LILLEHAMMER ALBERT
Published: May 2006

SUMMARY. 1. The duration of egg incubation (Y) in Dinocras cephalotes and Siphonoperla burmeisteri was related to constant temperatures from 4 to 24°C, by the regression equations Y=2382 T −1, 402(r2=0.992, P<0.001) and y= 2683 T−1.667 (r2=0.994, P<0.001), respectively. No diapause was observed in either species.

2. Egg incubation in D. cephaloles was slow and took 784.9±92.7 (mean ± SD) degree days between 12 and 20°C. significantly more than in S. burmeisteri(445±76.17 degree days: t= 7.44. d.f.=13,P<0.001).

3. For D. cephalotes hatching occurred at temperatures between 12 and 24°C, and for S. burmeisteri between 8 and 20°C. The mean volume of the eggs of D. cephalotes was about 5 times greater than that of S. burmeisteri and the mean body lengths of the newly‐hatched nymphs were 1.13 mm and 0.95 mm respectively.

4. This study shows that the freshwater fauna of northern Fennoscan‐ dia also contains species with warm stenotherm eggs. D. cephalotes. which is of a Mediterranean origin (Zwick, 1981a), may exist at the limit of its distribution in northern Fennoscandia.
Unsuitability of introduced tiles for sampling blackfly larvae (Diptera: Simuliidae)*
Authors: MORIN ANTOINE
Published: May 2006

SUMMARY. 1. Blackfly larvae were collected from twenty‐one stations in five lake outlets in Southern Quebec. Tiles (total area=500cm2) were introduced in early March, and collected 4 weeks later: randomly selected rocks (30–500cm) from the surrounding area were collected at the same time.

2. Larval densities on tiles were significantly less variable than on rocks. The variance of density estimates on tiles averaged 36% of the observed variance on natural rocks, or 67% when variance on rocks was corrected for average rock size.

3. Tiles significantly overestimated densities on rocks in some streams, and significantly underestimated them in others. These differences could not be explained by microhabitat differences (distance from the lake, depth, current velocity) between rock and tile samples. The bias that tiles introduce in density estimates precludes their use in comparisons among sites.
Zooplankton grazing on [methyl‐3H]thymidine‐labeIled natural particle assemblages: determination of filtering rates and food selectivity
Authors: BERN LARS
Published: May 2006

SUMMARY. 1. The grazing of [methyl‐3H]thymidine‐labelled bacteria by zooplankton was studied in Lake Norrviken. Sweden.

2. Animals did not ingest bacteria attached to large colonies of the cyanobacterium Microcystis wesenbergii Kom. but small aggregates of hacteria and free bacteria were readily consumed.

3. Diaphanosoma brachyurum (Liévin). Daphnia cucullata Sars. and Daphnia galeata Sars grazed free bacteria more quickly than aggregates, but Endiaptomus gracilis (Sars), Chydorus sphaericus Müll. and Bosmi‐ na coregoni s.l. Baird grazed the aggregates more readily.

4. Filtering rate determinations varied from LA to 123 μl ind. −1h − 1for various species.
Factors affecting the microdistribution of Gammarus pulex (Amphipoda): an experimental study
Authors: ADAMS JONATHAN , GEE JOHN , GREENWOOD PAUL , McKELVEY SIMON , PERRY RICHARD
Published: May 2006

SUMMARY. 1. The tnierodistribution of Gammarus species is size assortative: larger animals are associated with larger substrate particles. Using an artificial stream with scrubbed substrate we investigate the hypothesis that the assortative mechanism is stimulated by current avoidance rather than food searching.

2. In uniformly mixed substrate, G. pulex tend to move upstream, but in patchy substrate they are found in a predictable substrate grade. There is no discrimination between patches by different size classes of G. pulex in static water. The size assortative field pattern can only be reproduced under flow conditions in the laboratory. It occurs in the absence of food and irrespective of the sequence or location of substrate patches.

3. As density increases, G. pulex are displaced from the optimal patches but move into the open stream rather than into the cover of alternative patch types.

4. We discuss the significance of these results and suggest that some earlier models explaining mechanisms for microdistribution patterns tnay have been unnecessarily complex. Contrasts between natural and simulated stream situations and their experimental advantages are noted.
Importance of dissolved organic matter produced by duckweed (Lemna minor) in a southern English river
Authors: BAKER J. H. , FARR I. S.
Published: May 2006

SUMMARY. 1. The quantity of dissolved organic carbon (DOC) released by axenic Lemna minor cultures in the laboratory has been determined by an absolute method and by 14C labelling.

2. Good agreement was obtained between the two methods and from 1.1% to 2.6% of the total carbon fixed was released.

3. The DOC produced by L. minor has been analysed by ultrafiltra‐ tion and compared with a similar analysis of DOC in natural river water.

4. The results of ullrafiltration analyses indicate that the proportion of low molecular weight (<1000 Daltons) material in DOM produced by axenic L. minor is significantly greater than is found in its natural habitat.
Field experiments on the relationship between drift and henthic densities of aquatic insects in tropical streams (Ivory Coast). III Trichoptera
Authors: STATZNER BERNHARD , ELOUARD JEAN‐MARC , DEJOUX CLAUDE
Published: May 2006

SUMMARY. 1. Based on in situ gutter 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 Hydropsychidae.
An inexpensive water circulation system for studies of chemical exchange using intact sediment cores
Authors: FOWLER B. , DRAKE J. , HEMENWAY D. , HEANEY S. I.
Published: May 2006

SUMMARY. 1. An inexpensive pumping and reservoir system has been developed for circulating water over intact sediment cores. The system facilitates both measurement and manipulation of supernatant properties and flow velocities.

2. The apparatus has been used to evaluate the effect of flow velocity and pH on nutrient exchange at the sediment‐water interface.