bluuebunny/crossref_metadata_2025 huggingface dataset:
Costs and consequences of superparasitism in the polyembryonic parasitoidCopidosoma koehleri(Hymenoptera: Encyrtidae)
Authors: KEASAR TAMAR , SEGOLI MICHAL , BARAK ROI , STEINBERG SHIMON , GIRON DAVID , STRAND MICHAEL R. , BOUSKILA AMOS , HARARI ALLY R.
Published: May 2006

Abstract1. Polyembryonic wasps provide dramatic examples of intra‐specific developmental conflict. In these parasitoids, each egg proliferates into a clonal lineage of genetically identical larvae. If more than one egg is laid in a host (superparasitism), individuals of different clones may compete for food resources.

2. In the polyembryonic encyrtidCopidosoma koehleri, one larva per clone can differentiate into a sterile soldier. It is shown that soldiers are always females, and that they attack intra‐specific competitors.

3. Research hypotheses were that (a) clones that develop in superparasitised hosts suffer heavier mortality than clones that develop in singly parasitised hosts, and (b) female clones cause higher mortality to their competitors than male clones, hence larval survival is lower in superparasitised hosts that contain females than in male‐only broods.

4. The potential frequency of superparasitism inC. koehleriwas manipulated by varying parasitoid–host ratios and exposure durations.

5. As parasitoid densities and exposure durations increased, the frequency of superparasitism rose, brood sizes increased, but the number of hosts that completed development was reduced. The number of offspring per parasitoid female decreased with increasing parasitoid–host ratios. Offspring size and longevity were inversely correlated with brood size. As superparasitism rates increased, fewer all‐male broods were produced. Male–female broods were female‐biased, suggesting selective killing of males by female soldiers. All‐female broods were significantly smaller than all‐male broods at high parasitoid densities only, possibly reflecting aggression among soldiers of competing clones.

6. The results support the working hypotheses, and suggest that female larvae outcompete males in superparasitised hosts.
Observations on some aquatic Actinomycetes of streams and rivers
Authors: WILLOUGHBY L. G.
Published: May 2006

Actinomycetes of the family Actinoplanaceae, especially Actinoplanes, are readily isolated from the flowing waters of local rivers and streams and it seems clear that such lotic environments are favoured for colonization by these organisms. In this contribution evidence is produced that part at least of this activity can be ascribed to the utilization of wood as a growth substratum. Some other aquatic Actinomycetes of less certain affinity were also shown to be capable of growth on wood, under the conditions of pure culture.
The ecology of newt tadpoles
Authors: AVERY R. A.
Published: May 2006

Food consumption of newt tadpoles caught during July and August was estimated as C=34W1·11±0·12 where C is food consumption in milligrams wet weight/day and W is the live weight in grams.

Well‐fed tadpoles assimilated the food with an efficiency of 90–6%, but at low rates of feeding, the efficiency fell. Gross growth efficiency was about 35 % at maximum rations.
Factors affecting the distribution of some Phryganeaeid (Trichoptera) in Malham Tarn, Yorkshire
Authors: BRAY R. P.
Published: May 2006

This paper describes a distribution problem involving Agrypnetes crassicornis and Phryganea obsoleta (Trichoptera : Phryganeidae) in Malham Tarn, Yorkshire. The only suitable habitat for their larvae is the offshore vegetation, chiefly Chara delicatula, but owing to the specialized egglaying behaviour of this family and the absence of other sites, the eggs of Agrypnetes crassicornis are laid on the exposed rocky shoreline. The situation with Phryganea obsoleta differs in that the emergence of Potamogeton spp. provides new oviposition sites away from the shore. Investigations on both species however have provided further support for an hypothesis which postulates the importance of wind‐induced water movements in rapidly dispersing newly hatched insect larvae to the favourable habitats in deep water.
Vertical migration of Chaoborus flavicans in a Scottish loch
Authors: GOLDSPINK C. R. , SCOTT D. B. C.
Published: May 2006

The pattern of diel vertical migration of Chaoborus flavicans larvae in a shallow Scottish loch varies according to the instar and, in third and fourth instars, according to the season.

The planktonic phase of the migration is not exclusively concerned with predation, the larvae feeding at least equally actively in the benthos. Although there is no conclusive evidence as to the role of vertical migration in Chaoborus flavicans, it has some of the characteristics of an epideictic display.

Upward and downward locomotion can be induced experimentally in a plankton wheel by manipulating light intensity alone. However, the responses are complex and there is a great deal of individual variation, suggesting that additional factors are involved.
On a new genus of freshwater hoplonemertean from Campbell Island
Authors: MOORE JANET , GIBSON RAY
Published: May 2006

A new freshwater hoplonemertean from Campbell Island, to the south of New Zealand, i s described and named Campbellonemertes jolinsi gen. et sp. nov. The morphology of this tiemertean relates it with the family Prosorhochmidae and the occurrence of this form, the second freshwater prosorhochmid genus from the Antipodes, strongly supports an earlier hypothesis on the evolution of freshwater hoplonemerteans.
Bacterial dynamics in two high‐arctic lakes
Authors: MORGAN KEITH C. , KALFF JAPP
Published: May 2006

The heterotrophic planktonic bacteria in two high‐arctic lakes were studied by direct microscope count and the enzymatic uptake of 14C labelled glucose which generally conformed to Michaelis‐Menten kinetics. Bacterial numbers and activity in oligo‐trophic Char Lake ranged from 0.1 to 2.0×10−3 bacteria/l and a maximum uptake velocity (Vmax) of 1.8 × 10−3μg glucose l− h−1. Nearby Meretta Lake received waste water from the Department of Transport Base at Resolute and this eutrophication was reflected in higher bacterial numbers of 2‐80 × 108/1 and Kmax of 0.1 × 10−1‐7.5 × 10−1 fig glucose l−1 h−1 The Kmax per cell in Char Lake was 3 × 10−11μg glucose l−1 h−1 and changed little between the period of solid ice cover in May and ice‐free conditions in August. Bacterial cycles could not be related to phytoplankton cycles in either lake. Comparison of kinetic data from several lakes suggests a relationship between the bacterial uptake rate of glucose and phytoplankton production. Both bacterial numbers and activity in Char Lake may be very close to the minima to be expected in undisturbed freshwater environments.
Etude expérimentale de Tincubation des oeufs de Baetis rhodani Pictet
Authors: BENECH V. , VIGNES J. C.
Published: May 2006

The eggs of Baetis rhodani were collected from natural conditions just after laying and incubated at different constant temperatures (from 7‐5°C to 27‐5°C) with a constant photoperiod. The incubation period was shorter at higher temperatures up to 25°C (8 days); above this eggs no longer hatched. The slowest development (determined by extrapolation) was at about 3°C (theoretically 130 days). The hatching period was always very short (about 3‐5 days). Fewer eggs hatched at higher temperatures.
La Fecondité de Baetis rhodani Pictet
Authors: BENECH V.
Published: May 2006

Résume

La fécondité de Baetis rhodani Pictet a étéétudiée sur tout un cycle saisonnier dans le lissurage, ruisseau du Sud‐Ouest de la France.

La variation de la fécondité suit celle de la taille; les femelless les plus grandes sont les plus fécondes et pondent les plus gros oeufs. Le maximum est atteint en hiver; le minimum estival résulte à la fois d'une diminution du nombre d'ovarioles et d'ovules produits par ovariole.

Des lignes de régression ont étéétablies entre la fécondité et plusieurs mensurations larvaires et adults, elles ont permis de calculer chaque mois le potentiel de reproduction de la population d'après des prélèvements quantitatifs de larves au dernier stade.

Une relation nombre d'oeufs pondus‐‐‐numbre de larves au dernier stade qui en sont issues a fourni a base d'une estimation de la production de la génération printanière en utilisant la méthode de la courbe d'Allen. La part prise par les jeunes stades non capturables dans la production de cette cohorte a été calculée è partir de cetteestimation.

The fecundity of Baetis rhodani throughout a seasonal cycle is measured and the production by the spring generation is calculated from the figures obtained. Females of B. rhodani cannot be identified with certainty and therefore they were not cauht wild but bred from mature nymphs in the laboratory. Various measurements were made(Fig. 1). Eggs range in number from 4500 in February and March to 200 per female in July. This decrease coincides with a diminution in size and a rise in temprature (Fig. 2). In summer there are about 200 fewer ovarioles per female and production per ovariole is about half what it is early in the year. Smaller females produce not only fewer eggs but also smaller eggs (Fig. 3).

The relation between certain dimensions and number of eggs is found to remain close (Table 4), and it is therefore possible to predict how many eggs will be laid per square metre from a quantitative sample of full‐grown nymphs that have been measured (Table 6). Continuous sampling and measuring therefore make it possible to calculate the number of eggs at the beginning of a given generation and the number of adults that ultimately emerge. Calculation of production is based on the assumption that mortality follows the Allen curve (Fig. 10). It is shown that the very small nymphs, ignored in many other calculations of production could contribute up 18% to the total production of the spring generation.
An ecological investigation of the Portneuf River, Idaho: a semiarid‐land stream subjected to pollution
Authors: WAYNE MINSHALL G. , ANDREWS DOUGLAS A.
Published: May 2006

The Portneuf River (mean monthly discharge near mouth 1.4‐15.4 m3/s) in southeastern Idaho, U.S.A., flows through an area of reduced precipitation (approx. 33 cm/year) and is dependent on underground aquifers and snowmelt runoff from the surrounding mountains for its water. The stream was examined at ten locations, distributed over its 156‐km course, during the period 1967‐1971. The Portneuf River is shown to have undergone a number of changes from its natural state as evidenced by alterations in water quality and the distribution of benthic invertebrates along the stream course. Of particular interest are changes brought about by the use of the stream for irrigation and by runoff from agricultural lands, factors whose effects are magnified by the semiarid conditions of the region and by poor soil‐conservation practices. However, the stream also is affected by wastes from a sewage‐treatment plant, phosphate‐processing operations, and an assortment of scattered urban sources. Benthic invertebrates were collected during all four seasons by means of artificial substratum samplers and during summer and autumn by a qualitative dip‐net technique. In general, the samplers were more effective in obtaining a representative picture ofthe fauna. However, neither procedure alone gave as much information as the combined results. The artificial substratum collections are not believed to be representative of the usual effects of stream devvatering by irrigation withdrawal in as much as the samplers provide refugia for the benthos during the periods of reduced habitat.
Diurnal changes in dissolved organic and inorganic carbon and nitrogen in a hardwater stream
Authors: MANNY B. A. , WETZEL R. G.
Published: May 2006

Organic and inorganic carbon and nitrogen parameters were sampled simultaneously at 6 h intervals over a diurnal period at seven stations in a small hardwater stream in southern Michigan. Concentrations and budget values (kg/day) varied up to 10‐fold at individual stations and between stations. The most constant parameters were total dissolved organic carbon and nitrogen. The most variable parameter was particulate organic carbon.

Significant changes were noted in all parameters as the stream passed through different stream‐side habitats. Budget values facilitated interpretation of these changes over time between stations. High variability in the concentration values was introduced by large allochthonous inputs of dissolved organic matter (DOM) and water alternately adding to or diluting parameters. Distance from upstream terrestrial DOM sources, DOM residence time, the pulsed nature of DOM inputs and biological utilization of DOM have important effects on the quality and quantity of DOM that enters recipient lakes and rivers. The importance of ground‐water flux and DOM content is stressed. The DOM input and turnover within hardwater streams appears t o be in rapid, dynamic equilibrium.
A new method for establishing a permanent laboratory culture of Chironomus riparius Meigen (Diptera: Chironomidae)
Authors: CREDLAND PETER F.
Published: May 2006

A new technique for the establishment of a permanent laboratory culture of Chirono‐mus riparius is described. Larvae and pupae were reared in plastic tanks containing tap water, filamentous algae and a commercially prepared fishfood. The tanks were aerated, maintained at a constant temperature of 24°C and subjected to a constant lighting regime of 13 h of light followed by 11 h of darkness. Adults flew freely in a modified handling box, mated, and oviposited on strips of filter paper placed in the plastic tanks containing the aquatic stages. It has proved unnecessary to change the water or medium, which has saved both time and effort. Moreover, larvae established themselves in ail parts ofthe alga, and therefore more could be kept in each tank than when, as in previous methods, they are provided only with a substratum on the floor of the container.
Surface nitrogen and plankton in Skaha Lake, British Columbia (Canada)
Authors: FINDLEY DAVIS L. , FINDLEY DIANE I. , STEIN JANET R.
Published: May 2006

This study (1970–71) of an oligotrophic lake subject to cultural enrichment indicates the presence of complex interrelations between plankton and nitrogen levels in surface waters. Generally inorganic nitrogen was high in the winter (0.4–0.5 ppm) and Iow in summer (less than 0‐1 ppm). However, in late July and August a large increase in nitrogen (1.5 ppm) was recorded. This correlated with the Gloeotrichia echinulata J. E. Smith ex P. Richt. bloom (Cyanophyceae) and the increase in nitrogen fixation, or nitrogenase activity (measured as acetylene reduction). It was calculated that the cyanophyte bloom could have contributed a minimum of 2350 kg nitrogen to the lake in August 1970 which is c. 62% of the nitrate‐nitrogen occurring at any time.
Lakes of south‐western Uganda
Authors: DENNY PATRICK
Published: May 2006

The vegetation of Lake Bunyonyi, a high altitude lake in Kigezi, S.W. Uganda, is described. The lake had two distinct plant communities. In the shallow sheltered bays and inflows extensive floating swamps of Cyperus papyrus L. and Cladium janiaicen. se Cranz. existed. On the steep, exposed shores there was only a narrow band of vegetation, dominated by firmly rooted Phragmites australis (Cav.) Steud., usually with papyrus behind. Floating‐leaved Potamogeton and Nymphaea sometimes occurred outside the emergent species, and submerged species, including Ceratophyllum demersum L. grew down to 8 m. The pattern of vegetation, and the contribution of floating islands to the distribution of plants in the lake is discussed. Susceptibility to fragmentation, and distribution by wind are thought to be major factors governing the pattern.

Oxygen proflies measured at the fringe of swamps indicated that the swamps did not cause appreciable deoxygenation of the water.
Observations on the vertical distribution of the benthos in a Malaysian stream
Authors: BISHOP JOHN E.
Published: May 2006

An apparatus is described wbich is capable of sampling tbe bentbic fauna to a depth of 50 cm by providing a natural substrate for colonization. Tbe results obtained from an area of visually uniform sediments demonstrate that stream animals occur in significant numbers deep in tbe bottom sediments and that, at most, only about half tbe bentbos lives in tbe upper 10 cm usually ‘quantitatively’ sampled in stream surveys. The significance of a deep‐living fauna in regulating community density, in recolonizing denuded areas and in optimizing utilization of available food resources is discussed.
Gastropod associations within Malham Tarn, Yorkshire
Authors: CALOW P.
Published: May 2006

A survey of gastropod species associations was undertaken in one locus, i.e. Malham Tarn, Yorkshire. This ranged through both the major weed beds and the rocky shores. A semiquantitative analysis, in terms of both presence‐absence and relative abundance indices, suggested a clear distinction between the snail fauna present in the weed beds and that on the rocky shores, and also indicated a separation of faunas within these two major habitat types. The latter was closely correlated with degree of exposure. From this, and other evidence, it was suggested that wind, via wave action, may be a critical determinant of both the qualitative and quantitative aspects of biocoenotic structure in large bodies of fresh water.
The fine structure of the periphyton of Chara sp. and Potamogeton natans from Wytham Pond, Oxford, and its significance to the macrophyte‐periphyton metabolic model of R. G. Wetzel and H. L. Allen
Authors: ALLANSON B. R.
Published: May 2006

The fine structure of the periphyton of Chara sp. from Wytham pond, Oxford, is examined using transmission and stereoscan electron microscopy. As a result of this investigation the structural proximity of each periphyte component as required by Wetzel and Allen's metabolic model of macrophyte‐periphyton interaction is amply confirmed. The application of stereoscan electron microscopy to a study of feeding in periphyton consumers is also examined.
Studies on mountain streams in the English Lake District
Authors: SUTCLIFFE D. W. , CARRICK T. R.
Published: May 2006

Sodium and potassium in streamwater were measured over a period of 2 years, and concentrations of other major ions were occasionally monitored. The supply of sodium, potassium and calcium in rainfall was measured over a period of 1 year. A tentative budget is given for annual income and output of sodium, potassium and calcium in the Duddon catchment. Sodium and potassium concentrations in streamwater were independent of stream discharge; both ions displayed an annual cycle of high concentrations in winter and low concentrations in summer. The input of sodium was dependent on rainfall, wind direction and wind speed; 40% of the annual supply in rain was precipitated in the autumn. Sodium income in rainfall during the remaining 9 months of the year was insufficient to balance the output in streamwater. Annual income of potassium in rainfall was equal to annual output in streamwater. But potassium was retained on the catchment during spring and summer and was slowly released to the streams in autumn and winter. Only about 10% of the annual calcium output was derived from atmospheric sources.
Vertical distribution and abundance of Ceriodaphnia quadrangula (O. F. Muller) (Crustacea, Cladocera)
Authors: SMYLY W. J. P.
Published: May 2006

Distribution and abundance of C. quadrangula (O. F. Muller) has been studied in two small lakes in the southern part ofthe English Lake District. Esthwaite Water (maximal depth 15 m) was sampled from 1958 to 1969 and Blelham Tarn (maximal depth 12 m) from 1961 to 1963. Samples in both lakes were taken with a 5‐1 water bottle at a fixed station in deep water.

No difference in vertical distribution between day and night samples was observed. The majority of individuals were located below 7 m in Esthwaite Water and above 8 m in Blelham Tarn. The seasonal cycle in the open water was from May to December with maximal abundance in September and October. Males and ephippial females regularly appeared in early October, irrespective of population density, water‐temperature or the time of the overturn.
Calorific, chemical and physical values of potential duck foods
Authors: DRIVER E. A. , SUGDEN L. G. , KOVACH R. J.
Published: May 2006

Calorific values of thirty‐three species of aquatic invertebrates, representing various life stages, from small prairie wetlands are given. The values for twenty‐seven species are new to the literature. Percentage crude protein for fifteen species and the amino acid composition for eleven taxa are presented. The majority of the species dealt with are eaten by waterfowl.
On the food of Chironomus costatus (Chironomidae: Diptera) from a shallow freshwater pond in South India
Authors: ALFRED J. R. B.
Published: May 2006

A study has been made of the feeding of Chironomus costatus in a temporary fresh‐water pond in South India. It was found that, irrespective of the size of the larvae, the food composition was the same. The larvae were non‐selective feeders in that the organisms enumerated in the water were also found in the gut.
Diurnal stratification, photosynthesis and nitrogenfixation in a shallow, equatorial Lake (Lake George, Uganda)
Authors: GANF G. G. , HORNE A. J.
Published: May 2006

From a series of experiments and measurements covering one 24‐h period in Lake George the diurnal patterns of photosynthesis, nitrogen‐fixation and stratification are described. The thermal cycle shows three distinct phases of isothermy, intense stratification and mixing. During stratification the surface water temperature reached 36°C, whereas the bottom temperature remained at 25°C. The phytoplankton are evenly distributed at dawn, sink out during the day and tend towards an even redistribution as thermal stratification breaks down. Depth‐time profiles of oxygen concentration and pH values showed that intense photosynthetic and respiratory activity occurred. The shortness of the predominant limnological cycle is thought to be instrumental in restricting species fluctuations.

Changes of total CO2 concentration in situ within the euphotic zone indicated that 2.25 g C/m2.12 h were photosynthetically fixed during daytime. From changes of in situ oxygen concentration, gross photosynthesis was estimated to be 12 g O2/m2.12 h and net particulate production over 24 h as zero.

Photosynthetic activity was also measured with the i^C and oxygen techniques by enclosing algal samples in light and dark bottles. The patterns of activity recorded by the two methods were similar, although quantitatively the oxygen method gave rather higher values than did the method. Daily gross photosynthesis was estimated as 15.56 g O2/m2.12 h and 4.5 gC/m2.12 h. These figures are compatible with one another and with the production estimates calculated from Tailing's model of integral daily photosynthesis.

The balance between respiration and photosynthesis is described as a function of the underwater light climate and the relative rate of respiration. Both the experimental and theoretical approaches suggest that the column 24‐h net particulate production is an extremely small percentage of gross photosynthesis.

Nitrogen‐fixation was measured using both the 15N2 and the acetylene reduction techniques. The day‐long incubation of the 15N2 experiment showed that 11 mg N/m2.day were fixed. The series of shorter acetylene reduction experiments gave a value of 58 mg N/m2.day. The acetylene technique showed relatively high nitro‐genase activity at very low light intensities. The 15N2 results indicated little N2‐fixation at low light intensities. The differences between the two techniques are discussed.

Gross photosynthesis estimates calculated from seven different methods run simultaneously are compared. The figures show reasonable agreement, but since the gaseous environment in the euphotic zone is particularly suitable for photo respiration the values are not considered reliable estimates of phytoplankton photosynthesis.
Annual cycles of macro‐invertebrates of a river in southern Ghana
Authors: HYNES J.D.
Published: May 2006

The results of a quantitative study of the benthic invertebrates of a riffle area in the upper reaches of the Pawmpawm River in the forest of southern Ghana are presented. The investigation was carried out over a period of 17 months with a Surber Sampler. The seasonal fauna changes are discussed in relation to changes both in water flow and in the vegetational substrate, and a model for the succession of recolonization of the river after the resumption of flow is outlined. The earliest colonizers of the river were primary consumers, Chironomidae, Centroptilum and Simulium., which were followed after a few weeks (once a mat of vegetation had become established) by the carnivorous Cheumatopsyche (Trichoptera) and Centroptiloides (Ephemeroptera). After 2 to 3 months, the attached vegetation matured and was able to support a greater diversity of fauna. The strategy of survival in intermittent tropical rivers is discussed and it is concluded that recolonization from eggs laid by flying adults is the most important method.
The determination of nucleic acids in freshwater plankton and its ecological implications *
Authors: BAUDOUIN MARIE‐FRANCE , SCOPPA PIETRO
Published: May 2006

Nucleic acid concentrations show large variations between different planktonic species. RNA concentration is much higher in phytoplankton than in zooplankton. DNA varies to a considerable extent, being five to six times higher in copepods than in cladocerans. In Daphnia hyalina, nucleic acid contents are proportional to dry weight during the whole life cycle except in newborn Daphnia where DNA concentration is abnormally high. Seasonal variations affect, to a large extent, nucleic acid concentrations. These results rule out the possibility of using nucleic acids as indicators of biomass in mixed planktonic populations.
Salinity tolerance and osmoregulatory ability of Galaxias maculatus (Jenyns) (Pisces, Salmoniformes, Galaxiidae)
Authors: CHESSMAN B. C. , WILLIAMS W. D.
Published: May 2006

The salinity tolerance and osmoregulatory ability of Galaxias maculatus were investigated. In the field this species has been recorded from salinities of less than 1‰ to 49‰. In the laboratory, upper L.D.50 salinity values of 62‰ after gradual acclimation and 45‰ after direct transfer were established. Within the salinity range of its field occurrence the species is a powerful osmoregulator, being able both to hypo‐ and hyper‐osmoregulate.
Dominant diatoms in Tjeukemeer
Authors: MOED J. R. , HOOGVELD H. L.
Published: May 2006

Diatoma elongatum has been observed in Tjeukemeer (The Netherlands) from time to time. Its intermittent presence is probably a consequence of the local hydrology. In early 1972, besides the usual increase of Melosira spp. and of unicellular centric diatoms, a development of D. elongatum took place. Its maximum was found 5‐6 weeks later than those of the centric diatoms. Possible factors causing the decrease in number of cells are discussed.
Quantitative aspects of the distribution of invertebrates in the benthos of a small stream system in western Ireland
Authors: FAHY EDWARD
Published: May 2006

The invertebrate community of a small stream system in western Ireland is described from the results of two sampling programmes. The investigation was conducted at four sites which occurred within the same range of altitude (between 60 and 130 m O.D.) and the greatest differences between them were rock size, current intensity and the amount and type of detritus in the substratum. Approximately 60,000 invertebrates were identified and almost 100 taxa were listed. Attempts which were made to relate the occurrence of certain taxa to three factors (rock size, current intensity and detrital content) showed that detrital content was the most significant. Using empirical clustering techniques efforts were made to demonstrate zonation of the invertebrates taken during one of the two sampling programmes and the groups which were so obtained were further amalgamated subjectively. The resemblance of the resulting pattern to lotic zonation is briefly discussed.
The Plecoptera community of a small stream in Oregon, U.S.A. *
Authors: KERST CARY D. , ANDERSON N. H.
Published: May 2006

The Plecoptera community of a small woodland stream in Oregon was studied by examining density and species composition. Four sites were studied using benthos sampling for larvae and emergence trap collections for adults. Sixteen genera and forty‐three species were identified with most species occurring in relatively low numbers. A comparison with the species list from an earlier study suggested that the species composition has not changed markedly in 40 years but there were several changes in relative abundance.

Species diversity of stoneflies decreased with distance from the headwaters. These changes were correlated with decrease in habitat complexity, decrease in stability of the substrate, and increase in water depth. Examples of longitudinal succession are given as a method enabling the large number of species to partition the habitat. Concurrent benthos and emergence sampling demonstrated differences in emergence success that were correlated with habitat suitability.
An experimental study of the role of gradient and substratum in the distribution of two stream‐dwelling triclads, Crenobia alpina (Dana) and Polycelis felina (Dalyell) in North Wales
Authors: LOCK MAURICE A.
Published: May 2006

A laboratory stream is described which has simulated steep‐ and shallow‐gradient bottoms whose gradients can be varied. It was found that Polycelis felina, the principal triclad of shallow‐gradient streams had a much reduced ability to colonize the simulated steep‐gradient bottoms when compared to Crenobia alpina, which is the principal triclad of the steep‐gradient bottoms in the field. P. felina is unable to move in the steep‐gradient bottoms to any great extent, while C. alpina showed considerable ability to do this. When a reduction in flow was made this did not increase the proportion of P. felina to be found in the steep‐gradient regions. The triclads were also tested for possible acclimatory responses and it was found that their responses were more fundamentally based. On the basis of the above evidence it is suggested that the absence of P. felina from the steep‐gradient regions of streams in North Wales is due to a behavioural inability to tolerate the current regimes present in the steep‐gradient bottoms.
The influence of microbial food sources and aeration on the growth of Ceriodaphnia quadrangula (O.F.Müller) (Crustacea: Cladocera) under experimental conditions
Authors: SMYLY W. J. P. , COLLINS VERA G.
Published: May 2006

Casual observations had shown that, in laboratory cultures, populations of Ceriodaphnia quadrangula (O. F. Muller) rarely persisted for more than a month at most. It is shown here that populations of C. quadrangula can be maintained in static water on a diet of mixed algae (mainly Scenedesmus quadricauda (Turp.) Brev., but if the water is disturbed by a slow current of ascending air bubbles, the numbers of C. quadrangula decline. Death is not, however, immediate, and at high densities populations may persist in disturbed water for several weeks before numbers start to decline.

Numbers of C. quadrangula did not decline in disturbed water when the food was changed from the alga Scenedesmus to the animal Artemia salina (L.). Individuals of C. quadrangula in the presence of decomposing naupliar larvae of A. salina grew as well in disturbed as in static water and in static water their numbers increased at a greater rate on this animal diet than on an algal diet of Scenedesmus. When the bacterial populations associated with Scenedesmus were greatly reduced, there was no increase in the numbers of C. quandrangula. Microbes associated with Scenedesmus, and not the alga per se, seem to be used as food by C. quandrangula.
Number of meals in a day, maximum weight of food consumed in a day and maximum rate of feeding for brown trout, Salmo trutta L.
Authors: ELLIOTT J. M.
Published: May 2006

Brown trout (live weight 9–302 g) were fed to satiation in each of four meals at seven different water temperatures (range 3.8–18.1°C). The period (Ih) from the start of one meal to the start of the following meal was not significantly affected by the weight (Wg) of the trout, but was negatively correlated with water temperature (T°C). A regression equation described the exponential relationship between I and T, and also estimated the number of meals {N) in a day. Values ranged from one meal at about 4°C t o three meals at about 18°C, The greatest increase in appetite occurred at the end of the period I.

The maximum weight offood (Drng) eaten in a day was positively correlated with both W and T, a relationship which was well described by a multiple regression equation. The maximum rate of feeding (Fmg h−1) was not significantly affected by W, but increased from 3.8 to 6.8°C, was fairly constant from 6.8 to 19.3°C, and decreased markedly above 19.3°C. Estimates of D and F(with 95% confidence limits) were applicable to a wide variety offood organisms with the exception of mealworms. From comparisons with the results of other workers, it was concluded that the upper limit ofthe daily energy intake determines the optimum temperature for growth.
Primary production studies on a new reservior; Bighorn Lake‐Yellowtail Dam, Montana, U.S.A. *
Authors: SOLTERO RAYMOND A. , WRIGHT JOHN C.
Published: May 2006

A definite algal succession pattern was established for all 3 years of study. Volume‐based phytoplankton density and chlorophyll concentration decreased down‐reservoir. However, the depth of the euphotic zone increased down‐reservoir as silt settled out. Consequently, the euphotic zone standing crops were greatest mid‐reservoir. Insufficient light penetration was established as the principal limiting factor to primary production in the upper end of the reservoir. Decreased primary production in the lower end of the reservoir did not appear to be due to nutrient limitation. Comparison of sampling periods common to all years of the study showed that estimated net primary production increased 84% in 1970 over 1968.
Algal nitrogen fixation in Californian streams: seasonal cycles
Authors: HORNE ALEXANDER J. , CARMIGGELT COEN J. W.
Published: May 2006

Using the acetylene reduction technique, nitrogen fixation was measured in Rocky Creek, a small seasonally dry Californian stream. In the 3 years since 1970 nitrogen fixation varied seasonally and spatially, being highest in the early stages of colony growth in shallow, clear regions where there was little shade. The annual rate of N2‐fixation was similar to that found recently for Arctic tundra, but was greater than rates for Antarctic rivulets and less than rates for temperate rocky shores. A hetero‐cystous Nostoc appeared to be the sole organism responsible for this fixation. Nostoc occurred in variously sized gelatinous clumps on the stable boulders on which the co‐dominant alga, Ulothrix zonata, also grew. Maximum nitrogenase activity yielded 70 nmoles C2H4 mg‐1 drywt day‐1 and 123 nmoles C2H4cm‐2 day‐1. Estimated annual amounts of nitrogen fixed in 1971 ranged from 42 in shade to 360 mg N fixed m‐2y‐1 in the most favourable areas. Nostoc biomass reached 33 g dry wt m‐2 and peeled off each year in June‐July. Because Nostoc was confined to stable rocks the biomass per unit area of the stream as a whole was much less, ranging from 0.054 to 1.26 g dry wt m‐2 in the most favourable site. Nostoc was common throughout the length of Rocky Creek and also plentiful in eight out of ten adjacent streams but not in the main river (Eel River South Fork), probably due to high turbulence and turbidity. N2‐fixation in these streams makes a significant, but probably small contribution to the nitrogen income of the nitrogen‐deficient Eel River system. Nostoc colony establishment appears to be controlled by a combination of reduced turbulence and firmer attachment of the colonies to the substrate. Nostoc colony disappearance in June is probably due to nutrient depletion.
A survey of the invertebrates of four streams in The Moor House National Nature Reserve in Northern England
Authors: ARMITAGE P. D. , MacHALE ANGELA M. , CRISP DIANE C.
Published: May 2006

The Moor House Nature Reserve, Westmorland, is situated in typical north Pennine moorland and experiences a rigorous climate. Three of the streams arise between 700 and 750 m O.D. and the fourth at 590 m O.D. The sampling sites lie between 570 and 540 m O.D. and conditions in the streams range from slow‐flowing peaty‐bottomed reaches to typical fast‐flowing stony streams. Samples were taken in riffles and pools in May, August and October using the kick method. 111 taxa were recorded from the four streams, 90 of which were identified to the species level. The most abundant and widespread taxa were Leuctra inermis, L. fusca, Rhithrogena semicolorata, Elmis aenea and Chironomidae. Seasonal and annual variation in abundance of several species was marked with L. inermis most numerous in May, E. aenea and Chironomidae in August and R. semicolorata most abundant in October. The total number of animals caught was generally higher in riffles than in pools and the mean number per 60‐sec kick for riffles and pools, based on May, August and October samples between 1967 and 1970, ranged from 110 to 128 in the four streams. Capnia bifrons, Paraleptophlebia submarginata, P. cincta, Leptophlebia marginata, Centroptilum pennulatum, Plectrocnemia geniculata, Cyrnus trimaculatus, Lepidostoma hirtum, Hydropsychidae (larvae indet.) and Philopotamidae (larvae indet.), are all additions to the lists of previously studied groups on the Reserve. All the species of Tricladida, Annelida, Coleoptera, Hydrachnellae and Pisidium are here recorded for the first time for the Reserve.

Great Dodgen Pot Sike supported the largest number of species and species groups (88) and was characterized by having water with the lowest pH (6.75) of all the streams and by having the most gentle gradient and a relatively stable bottom. The fauna is discussed and compared with that of the adjacent Cow Green area. Some of the differences between these areas may be attributable to the slightly greater variation in flow‐conditions and water chemistry in the Cow Green basin. Comparison with other areas in the British Isles are made briefly and it is suggested that habitat diversity may account for the species richness of the Moor House streams.
Variation in chemical composition of the River Frome, England, from 1965 to 1972
Authors: CASEY H.
Published: May 2006

This study covers a 7‐year period from 1965 to 1972, and shows the variation in flow, water chemistry and throughput of nutrients. The annual discharge of the River Frome varied considerably from year to year, ranging from a mean value of 4.48 m3 sec−1 in 1971 to one of 8.38 m3 sec−1 in 1966. The mean annual nutrient losses calculated over all 7 years of study from the River Frome catchment were: Nitrate 11.4 kg ha−1, phosphorus 0.49 kg ha−1 and potassium 8.4 kg ha−1. There has been an increase in annual throughput (in years of similar flow) of 21% in phosphate and 41% in nitrate from 1965 to 1972.
Laboratory experiments on factors affecting the activity of Gammarus pseudolimnaeus Bousfield
Authors: WALLACE RON R. , HYNES H. B. N. , KAUSHIK N. K.
Published: May 2006

Factors such as current, light, food, substrate and time of year were found to influence the activity of specimens of Gammarus pseudolimnaeus maintained in stream tanks in the laboratory. Although there was seasonal variation, levels of diurnal and nocturnal activity were generally much higher when there was no current than when the water was running. Diurnal periodicity occurred but was not as pronounced as had been indicated in the field studies of previous workers. Although there was activity during the day, nocturnal levels were higher especially in specimens collected during the summer. When there was no current, and the lights were left on for 24 h, peak activity occurred at precisely the times when the lights normally would have been off. This strongly suggests that there is an endogenous component in the activity. The nocturnal activity showed a bigeminus pattern, and there was a seasonal change, with the general activity at its highest levels in summer. Activity was significantly greater during daylight both with and without current when there was no substrate present in the tanks. The behaviour of Gammarus appears to be complex and greatly influenced by combinations of the various factors.
Methods of sampling aquatic beetles in the transitional habitats at water margins
Authors: LANDIN JAN
Published: May 2006

Populations of water‐beetles (Hydrophiloidea) were studied during the ice‐free seasons of 2 years at a lake shore near Stockholm, Sweden. They were sampled by means of an absolute quantitative method (twenty‐four bottom cores/sample), extracted by Berlese‐Tullgren funnels, and a relative searching method (time‐catch or catch per unit effort). The sampling efficiency was tested by charging empty samples with known numbers of beetles. ‘Smaller’ species were less efficiently extracted than ‘larger’ ones. Absolute and relative population estimates of eight species were compared by means of regression analysis, the relative estimate being considered as the dependent variable. Only three statistically significant correlations were found, but a correlation always seemed to exist, and the relative estimates are considered as crude estimates. To obtain better ones when studying several species in one habitat much work is required, and then the advantages of the simple relative method disappears. The different sizes of the species were evaluated as sources of errors affecting the relative estimates. The estimates of the 'smaller’ species were more affected than the ‘larger’ ones. It is considered that relative population estimates would gain much if compared with independent absolute estimates. This seems to have been done rarely with invertebrates in aquatic habitats. Further, it is thought that behavioural extraction methods might be applied to several aquatic animal groups in eulittorals and littorals, saving much time compared with mechanical methods or hand sorting.
Seasonal patterns in abundance of water‐beetles belonging to the Hydrophiloidea (Coleoptera)
Authors: LANDIN JAN
Published: May 2006

Populations of Hydraena britteni Joy., Limnebius aluta Bedel (Hydraenidae), and Helophorus brevipalpis Bedel, H. strigifrons Thoms., Hydrobius fuscipes L. and Anacaena limbata Fabr. (Hydrophilidae) were studied from the break up of the ice until autumn or freezing at three different shores of a lake near Stockholm, Sweden. The beetles were generally found to frequent the zone immediately at the water's edge. Both larvae and imagines inhabit the uppermost 2 or 3 cm of the substrate. Two patterns in the seasonal abundance were found. (a) Maximal abundance during spring, minimal during summer, and sometimes a new, smaller maximum during late summer and autumn (Hydraena britteni, Helophorus strigifrons, Hydrobius fuscipes, Anacaena limbata, and perhaps Limnebius aluta). (b) An abrupt peak in abundance during July‐August and very low abundance at other times (Helophorus brevipalpis). Type (a) is probably the general one in this region and type of habitat. It fits a univoltine life cycle, where the beetles breed during early summer and hibernate as adults. In other climates this life cycle seems to be modified, partial second generations may occur or development is retarded and a new generation does not emerge until next spring. Type (b) is shown by a univoltine species much disposed to flight. The peak coincides both with its dispersal phase and the emergence of the new generation. The species is thought not to belong to a closed, stable habitat but to ephemeral waters in open landscapes. Its ecology is quite different to that of H. strigifrons, which is considered to belong to more closed, stable habitats. Patterns similar to type (a) are also shown by Laccophilus spp. (Dytiscidae) and Haliplus spp. (Haliplidae) according to the literature. This may be an adaptation to the probable danger of being trapped in ice during winter. Like the water‐beetles these two beetle groups also mostly leave the water margin during autumn. The pattern of type (a) of most Hydrophiloidea seems to be geared to the amounts of plant remnants in the littoral, imagines and some larvae being most abundant when the amounts are maximal, i.e. during spring. The plant material probably offers food and cover. It disintegrates rapidly during summer and a new maximum is reached next spring. The pond‐like habitat, which may develop behind reeds is compared with ephemeral ponds. Both may be regarded as unstable habitats, each passing through a series of predictable changes. The difference is the final stage, often disastrous when a pond dries out, but seldom so in a lake when the water line moves outwards in the littoral during summer.
Nitrogen nutrition of Myriophyllum spicatum: variation of plant tissue nitrogen concentration with season and site in Lake Wingra
Authors: NICHOLS DALE S. , KEENEY DENNIS R.
Published: May 2006

Samples of water, sediment and Myriophyllum spicatum were collected from four weedbed sites in Lake Wingra, a small hypereutrophic hardwater lake in Madison, Wisconsin, several times during the 1972 and 1973 growing seasons, and analysed for various forms of N. The concentrations of inorganic N in the lake water were quite similar at all sites. The differences in the total N content of the Myriophyllum tissue from site to site directly related to the levels of available sediment N, indicating a dependence upon the sediment as a N source. Myriophyllum tissue N concentrations (ash and moisture‐free basis) were highest in spring, decreased steadily during the summer, and increased again in the fall. Myriophyllum apparently grows very little during the winter, but continues to accumulate N. The death and decay of a considerable portion of the Myriophyllum in the fall contributes insignificant amounts of N directly to the lake water. Nitrogen does not appear to be limiting Myriophyllum spicatum growth in Lake Wingra.
Environmental dependence of manganese and zinc in the scales of Atlantic salmon, Salmo salar (L) and Brown trout, Salmo trutta (L)
Authors: ABDULLAH M. I. , BANKS J. W. , MILES D. L. , O'GRADY K. T.
Published: May 2006

Analysis of manganese and zinc concentrations in the scales of salmon and trout from a number of sites showed significant dependence of the levels of these metals in the scales on the levels in the environment. There is some evidence to suggest that in trout scales there is a minimum concentration of zinc above which there is a direct proportion between environmental and scale concentration. It is also possible that the response of trout to environmental zinc differs from that of salmon.