bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reproductive mode in populations of Daphnia pulex and Daphnia obtusa from the East Midlands of Britain
Authors: WARD ROBERT D. , GEISSLER PAUL A. 
Published: May 2006

SUMMARY 1. Two populations of Daphnia pulex, one from a permanent pond and one from a temporary pond, and two temporary pond populations of Daphnia obtusa in the East Midlands of Britain were examined by enzyme electrophoresis. The three temporary pond populations showed good fits to Hardy‐Weinberg expectations, suggestive of cyclic parthenogenesis, while the permanent pond population showed deviations bordering on statistical significance.2. Laboratory characterization of the ephippiai offspring of heterozy‐gous mothers from each population showed normal Mendelian segregation and males were produced. This indicates that in both species ephippiai egg production was a sexual process, and confirms that these populations reproduce by cyclic, rather than obligate, parthenogenesis.
An inexpensive device for sampling large volumes of lake water from discrete depths
Authors: DODDS WALTER K. , PRISCU JOHN C. 
Published: May 2006

SUMMARY 1. A sampler was developed that displaces surface water which is replaced with water from a sampling tube at a set depth.2. The displacement sampler is inexpensive, easy to build, and is capable of collecting water at 7.5 I min−1.3. Phytoplankton photosynthesis was higher in water from the displacement sampler than in water collected with a Van‐Dorn bottle. Subsequent experiments indicated this was due to inhibition caused by the Van‐Dorn bottle.
Depth selection by larval Ischnura verticalis (Odonata: Coenagrionidae): effects of temperature and food
Authors: BAKER ROBERT L. , FELTMATE BLAIR W. 
Published: May 2006

SUMMARY. 1. Water temperatures in a shallow, weedy bay of a reservoir in southern Ontario were related to depth; mid‐day temperatures in summer were approximately 30°C at the water surface and 20°C below 25 cm.2. In the laboratory, larval Ischnura verticalis released in a thermal gradient (warmest water near the surface) did not remain near the surface any more than larvae in isothermal conditions. However, larvae in both isothermal and gradient conditions tended to spend more time close to the surface than expected by chance.3. Larvae provided with food at all depths spent more time near the surface than did larvae with no food. Larvae provided with one feeding site in the coldest water remained near the food as much as did larvae provided with a single feeding site in the warmest water.4. Results suggest that selection of microhabitats is based primarily on food availability and secondarily on proximity to the surface.
The susceptiblity of Keratella cochlearis to interference from small cladocerans
Authors: GILBERT JOHN J. , MACISAAC* HUGH J. 
Published: May 2006

SUMMARY. 1. Even at high population densities (300–2000 ind. 1−1), only one of five small cladoceran species (adult body length <1 mm) significantly suppressed population growth of the rotifer Keratella cochlearis through interference (encounter) competition. At 500 ind. H, adults of D. ambigua (0.96 mm body length) imposed an instantaneous per capita death rate of 0.21 day−1 on this rotifer. These short‐term experiments may have underestimated cladoceran interference because newborn rotifers were rarely present.2. Newborn rotifers (<12 h old) were much more susceptible than adult rotifers (> 24 h old) to interference from Ceriodaphnia dubia. All of the small cladoceran species tested were very much less likely than large Daphnia (body lengths >1.2 mm) to interfere with K. cochlearis, but perhaps at high population densities they could suppress population growth of susceptible rotifer species by damaging, and possibly eating, relatively small and soft‐bodied newborn individuals.3. K. cochlearis of the tecta form, without a posterior spine, produced offspring of the typica form, with a posterior spine, in the presence of C. dubia. This developmental response is stimulated by at least several, and possibly all, cladocerans and probably reduces the susceptibility of the rotifer to cladoceran interference.
On the occurrence, causes and potential consequences of low zooplankton to phytoplankton ratios in New Zealand lakes
Authors: MALTHUS TIMOTHY J. , MITCHELL STUART F. 
Published: May 2006

SUMMARY. 1. New Zealand lakes are shown to have lower average zooplankton biomasses than north‐temperate lakes of similar average phytoplankton biomass, expressed as cell volume or chlorophyll a, or similar average total phosphorus concentration, typically by a factor of 5 or more.2. Evidence suggests that the relatively low zooplankton biomasses of New Zealand lakes may be related to a tendency for them to be dominated by large algae that are not directly available as food for zooplankton, with oligotrophy lakes in particular differing from north‐temperate lakes in this respect.3. This difference in turn may be related largely to their mixing regimes. All of the New Zealand lakes are polymietic or monomietic, whereas the northern lakes used for comparison are mostly dimietic. Also, hetero‐cystous cyanobacteria are favoured by the low inorganic nitrogen concentrations that are typical of New Zealand lakes.4. Poor nutritional quality of the phytoplankton, relating to nitrogen limitation in many New Zealand lakes, might supplement the effects of cell size.5. Low exploitation of phytoplankton by zooplankton can be expected to produce a shift in the metabolism of New Zealand lakes towards the sediments. Among the potential consequences of this effect are increased hypolimnetic oxygen demand with increased susceptibility to development of large internal loads of nutrients, and consequently, increased sensitivity to accelerated eutrophication from any increase in external nutrient loads.
Effects of nutrients and grazers on periphyton phosphorus in lake enclosures
Authors: MAZUMDLR ASIT , TAYLOR W. D. , McQUEEN D. J. , LEAN D. R. S. 
Published: May 2006

SUMMARY. 1. Periphyton. measured as particulate phosphorus (PP) and expressed as periphyton PP, growing on vertically oriented substrata (polyvinyl impregnated nylon) under different nutrient loadings, light intensities (exposures), and grazer communities was examined in eight large enclosures (750 m3) where nutrients (N and P) and planktivorous fish (1+yellow perch) were added in a 2x2 factorial design.2. During the first 3 weeks of the experiment (25 June to 15 July), there was a significantly higher accumulation of phosphorus into periphyton (periphyton PP) with fertilization, but fish addition had no effect. During the fourth to seventh weeks (16 July to 12 August), addition of fish was associated with lower abundance of amphipods and chironomids and higher concentration of periphyton PP. In the enclosures without fish, these invertebrates were over 25 times more abundant, and periphyton PP decreased substantially compared to the June‐July period. Fertilization increased periphyton PP only at high exposures in the enclosures with fish.3. Exposure had a significant effect on periphyton PP. In the enclosures with fish, high abundance of nanoplankton reduced water transparency, and periphyton PP was lower in the deeper waters which may have been due to limitation by low light. Lower periphyton PP was also observed at the surface on sunny sides of enclosures without fish, and therefore with high water transparency. This pattern may have been due to inhibitory effects of high light intensity.4. Periphyton communities in the enclosures with fish had higher uptake rates for planktonic phosphorus, and lower rates of phosphorus release, suggesting that periphyton with high phosphorus demand may have high internal cycling of assimilated phosphorus.
Environmental stress and the survival of brown trout, Salmo trutta
Authors: PICKERING A. D. 
Published: May 2006

SUMMARY. 1. The hypothalamic‐pituitary‐interrenal axis of the brown trout, Salmo trutta, is activated in response to most forms of environmental stress. This results in an elevation of blood cortisol levels.2. Experimental elevation of blood cortisol levels in otherwise unstressed brown trout caused a dose‐dependent increase in mortality rate due to disease. In our studies., Saprolegnia‐infection, furunculosis and bacterial fin‐rot were the principal diseases.3. Chronic cortisol elevation also suppressed several of the endocrine processes controlling sexual maturation, resulting in a significant reduction in the size of the gonad in both male and female fish.4. It is argued that many of the deleterious effects of sublethal pollution (including acidification) on natural trout populations can be attributed to chronically‐elevated blood cortisol levels and that a knowledge of such physiological changes would allow an assessment of the impact of pollution events and act as an early warning of potential disease and recruitment problems.
Conservation and management of brown trout, Salmo trutta, stocks in Wales by the Welsh Water Authority
Authors: CRESSWELL R. C. 
Published: May 2006

SUMMARY. 1. The diversity, value and status of the trout resource within the Welsh Water Authority area is described.2. Reported angling catches of sea trout have increased in recent years but there is an apparent decline in brown trout stocks. Factors affecting the distribution, status and diversity of the trout resource are identified and discussed.3. Investigations are being carried out to evaluate the apparent problems and to provide information required to formulate management solutions. A management strategy is proposed which allows for the maintenance and development of the resource, whilst ensuring the preservation of strains of trout which have conservation value in their own right.
Changes in diatom‐inferred pH and add neutralizing capacity in a dilute, high elevation, Sierra Nevada lake since A.D. 1825
Authors: HOLMES R. W. , WHITING M. C. , STODDARD J. L. 
Published: May 2006

SUMMARY. 1. We developed equations which describe relationships between the relative abundance of diatom assemblages in the surface sediments of twenty‐seven Sierra Nevada lakes and the present pH and acid neutralizing capacity in these lakes.2. These equations were employed to reconstruct pH and acid neutralizing capacity at twenty‐four depth intervals in a 20 cm long sediment core from Emerald Lake, a dilute, high elevation lake, located in Sequoia National Park, California, U.S.A.3. The diatom‐inferred pH and acid neutralizing capacity values indicated that neither pH nor acid neutralizing capacity exhibited significant trends since about A.D. 1825. We conclude from our diatom analysis that Emerald Lake has not been affected by acidic deposition.
Timing of emergence of males and females of Ephoron shigae (Ephemeroptera: Polymitarcyidae)
Authors: WATANABE NAOSHl C. , YOSHITAKA ICHIRO , MORI IKUE 
Published: May 2006

SUMMARY. 1. The winged adults of Ephoron shigae swarming over the water surface were collected by successive random sweeps during their daily emergence period, and the changes in sex and stage composition were examined, in the lower reach of the Asahi River in western Japan.2. The emergence occurred mainly during a 11/2 h period beginning some time after sunset. Male sub‐imagos emerged synchronously and moulted to imagos in a 25 min period immediately prior to an abrupt increase of female emergence.3. This timing of male emergence may be considered the result of selection of males to decrease the risk of death before mating, and for all the males to have an equal opportunity to mate.
Long‐term investigations of trophic relationships in southern chalk streams
Authors: LADLE M. 
Published: May 2006

SUMMARY. 1. An understanding of the feeding relationships of organisms is fundamental to our capability to conserve and manage aquatic systems. At one extreme we must study the cyclic and erratic physical processes which govern the reproduction, survival and growth of consumers and their‘prey’and at the other the rates of food consumption, the assimilation of nutrients and the energetic interactions of plants, animals and micro‐organisms.2. Since the commencement of freshwater science in this country, our understanding of the mechanisms by which producers and consumers interrelate has increased greatly. Information is required basically on three levels: (1) Short‐term laboratory and field studies designed to provide detailed data on aspects such as habitat selection, growth, feeding behaviour, etc. (2) Investigation of patterns of change which show periodicities of weeks, months or even a few years associated with the life cycles of many plants and animals and with the seasonal variations in physical and chemical parameters. (3) Long‐term surveillance and monitoring, often in a superficial manner, of particular aspects of river ecology in order to detect trends of change or patterns of variation over tens or hundreds of years and, if possible, to relate these to recorded climatic changes.3. Long‐term data collection, in the scale of human longevity, is most appropriate to phenomena which show readily indentifiable periodic maxima or minima or which occur at well defined times (for example the discharge of a river or the start and finish of flow in a winterbourne). Alternatively, information which is amenable to automatic or semi‐automatic monitoring (temperature, water chemistry, fish migration) or integrated sampling (insect abundance, annual removal of cut water weeds) may also provide valuable evidence of long‐term change.
Diatoms as indicators of water quality in some English urban lakes
Authors: GUZKOWSKA M. A. J. , GASSE F. 
Published: May 2006

SUMMARY. 1. The paper describes diatom communities from a series of linked urban lakes in relation to water chemistry and uses multivariate statistical techniques to show how indicator groups can he defined.2. Diatoms are classified into ecological groups using two‐way species indicator analysis (TWINSPAN). Each ecological group is associated with a specific range of water‐quality conditions. The headwater stream environments are differentiated from the lake habitats at level 1. At level 2 of TWINSPAN. the sampling sites are grouped into five ecological groups, according to their water chemistry and irrespective of the time of year.3. Detrended correspondence analysis (DCA) and principal components analysis (PCA) provide two statistically independent methods of assessing the environmental gradients along which the ecological groups are distributed. The most important physico‐chemical parameters are total hardness, specific conductance and pH, followed by phosphates and nitrates.4. Ecological groups I‐V correspond to an environmental gradient ranging from the forested headwaters, which are acidic, of low specific conductance, total hardness and nutrient content, through the urban lakes, which are alkaline and of relatively high total hardness, specific conductance and nutrient content.5. Twelve site groups are identified at level 3 of TWINSPAN, each of which corresponds to a narrower range of water‐quality conditions within the ecological groupings. A specific diatom assemblage is associated with each site group.6. Benthic diatoms form an integral part of the diatom assemblages found in the water column and this is identified as a topic for further study.
Influences of seasonal flooding on macroinvertebrate abundance in wetland habitats
Authors: NECKLES HILARY A. , MURKIN HENRY R. , COOPER JAMES A. 
Published: May 2006

SUMMARY. 1. We studied the effects of seasonal flooding on macro‐invertebrate abundance by manipulating water regime and detrital level within three contiguous experimental marshes in Manitoba, Canada, over 2 years. One area was seasonally flooded (standing water present through midsummer) with emergent vegetation left undisturbed throughout the study, one was semipermanently flooded (standing water present through the ice‐free season) with the vegetation left undisturbed, and one was seasonally flooded with the vegetation harvested at the end of the first summer.2. Abundances of frequent macroinvertebrate taxa were compared between the seasonally flooded‐undisturbed treatment area and each of the other areas.3. Densities of total invertebrates and of the dominant taxa (Cladocera, Ostracoda and Culicidae) were reduced dramatically by a year of semipermanent flooding, despite high levels of paniculate organic food resources and low populations of predators. Densities were not reduced by lowering the availability of detritus under seasonally flooded conditions.4. Taxa unaffected by water regime included Dytiscidae, Corixidae, Chironomidae, Ceratopogonidae and Ephydridae.5. Semi‐permanent flooding may have eliminated environmental cues necessary for oviposition, embryonic development and hatch among dominant taxa. High invertebrate densities in temporary waters may be more dependent upon life history traits of resident fauna than upon habitat features such as food availability or predation pressure.
Different colonization patterns of two closely related stream insects (Austrosimulium spp.) following disturbance
Authors: DOWNES BARBARA J. , LAKE P.S. 
Published: May 2006

SUMMARY.
In many streams, blackfly larvae rapidly colonize scoured surfaces, then decline in numbers as other species are still increasing. Such a colonization pattern may be generated by species that seek disturbed substrata because they prefer scoured surfaces having low epilithon cover (i.e. they are opportunists) or because of lowered faunal densities (i.e. they are fugitives), but this has rarely been tested.
In the Acheron River, south‐eastern Australia, the larvae of the blackfly Austrosimulium torrentium show the typical pattern of increase and decline whereas A. victoriae shows a different pattern of more gradual increase.
An experiment showed that A. torrentium, consistent with its colonization pattern, responded strongly to treatments that mimicked the effects of disturbance; it colonized bricks with few other animals present regardless of epilithon cover and therefore is potentially a fugitive species. A. victoriae did not respond convincingly to treatments, which is also consistent with its colonization pattern.
Blackfly larvae of both species preferentially colonized bricks that were in fast‐moving water. Hence, A. torrentium only responded to the densities of other fauna when bricks occurred in currents greater than approximately 30 cm s−1.
Whilst epilithon cover did not affect abundance of blackfly larvae, it did affect attachment positions. In one experimental treatment, epilithon was reduced on one half of the top surfaces of bricks. More than 50% of larvae on these bricks were attached to the epilithon‐reduced halves.
Our results show that functional feeding or taxonomic groups do not necessarily contain ecologically equivalent taxa; colonization patterns may provide a more useful way of categorizing species for the purposes of modelling these assemblages.
Effects of temperature, age and body size on moulting and growth in the freshwater amphipods Gammarus fossarum and G. roeseli
Authors: PÖCKL MANFRED 
Published: May 2006

SUMMARY1. The total body length, cephalic length, wet weight and dry weight was measured in juveniles, males and females of Gammarus fossarum and G. roeseli kept in the laboratory. Numbers of flagellar segments on the first and second pairs of antennae of G. fossarum and G. roeseli were quantitatively related to body size and in stars. The addition of segments cannot be used to identify particular instars of individuals or to determine their ages in natural populations.2. At experimental temperatures ranging from 3.8 to 20.2°C, the number of moults, duration of intermoults, maturation times and specific growth rates were studied from birth in isolated specimens. Sexual maturity was reached after 9 or 10 moults, at a mean wet weight of c. 5mg for females and c. 7mg for males of G. fossarum, and at c. 10 mg for females and c. 13 mg for males of G. roeseli. At 3.8°C neither species reached sexual maturity within 550 days.3. The mean interval between moults was observed from birth to sexual maturity and was linearly related to moult number and exponentially related to age. The relationship between each intermoult interval, or the maturation time, and the experimental water temperature was described by a power function. Maturation times increased from 96 days at 20.2°C to 355 days at 7.9°C in G. fossarum, and 85 days to 403 days in G. roeseli.4. Over the range 3.8–20.2°C there was a log—log relationship between temperature and specific growth rates. Growth was maximal at 20.2°C in newborn animals as well as in small sexually mature animals; interspecific differences were highly significant.5. Increase in body wet weight of G. fossarum and G. roeseli fed ad libitum on a constant mixture of autumn‐shed, naturally decaying, tree leaves and aquatic macrophytes was followed to senescence and death. The instantaneous or specific growth rate was maximal near birth, at c. 7.98% wet weight day−1 in G. fossarum and 9.03% in G. roeseli. At ≥12°C, growth conformed to a logistic curve; maximum absolute increments in weight occurred about half‐way through a life span of 280–300 days at 20°C, 380–420 days at 16°C and 550–600 days at 12°C. Some individuals lived longer than 850 days at ≤12°C. The wet weight at birth was 0.112mg for G. fossarum and 0.123mg for G. roeseli. Asymptotic mean body weights of males and females were, respectively, 61 and 41 mg for G. fossarum and 87 and 58 mg for G. roeseli. However, G. roeseli reached the inflection point of the logistic curve significantly faster than G. fossarum. In the latter species, growth and maturation were relatively faster at temperatures below 12°C, whereas they were faster in G. roeseli at 16–20°C. Thus G. fossarum is adapted to summer‐cool streams and G. roeseli is adapted to summer‐warm streams.
The RCE: a Riparian, Channel, and Environmental Inventory for small streams in the agricultural landscape
Authors: PETERSEN ROBERT C. 
Published: May 2006

SUMMARY1. The Riparian, Channel and Environmental (RCE) Inventory has been developed to assess the physical and biological condition of small streams in the lowland, agricultural landscape. It consists of sixteen characteristics which define the structure of the riparian zone, stream channel morphology, and the biological condition in both habitats.2. The inventory is based on the view that in landscapes where non‐point source pollution and agriculture dominate, the environmental condition of small streams can be assessed by an appraisal of the physical condition of the riparian zone and stream channel. It is assumed that disturbance of this physical structure is a major cause for reduction of stream biological structure and function. This assumption is supported by a case study using fifteen Italian stream locations in which the RCE was found to be positively correlated to the benthic macroinvertebrate community as measured by the Extended Biotic Index (r = 0.80, P < 0.001) and the Shannon Diversity Index (r = 0.73; P < 0.001).3. The inventory is designed for quick use to cover a large number of streams in a short period of time. When used it generates a numerical score which can be used to compare the physical and biological condition between different streams within a region. The numerical score is divided into five, colour‐coded classes to facilitate use in streammonitoring programmes and to allow comparison with biological indices.