bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mate guarding and sperm displacement in the water striderGerris lateralisSchumm. (Heteroptera: Gerridae)
Authors: ARNQVIST GÖRAN 
Published: May 2006

SUMMARY.1. Field and laboratory observations on the mating behaviour of Gerris lateralis Schumm. allowed three distinct phases to be distinguished: (i) a precopulatory phase (1.5min, SD=1.3), (ii) copulation (16.2min, SD=12.9), and (iii) a postcopulatory phase. The duration of the postcopulatory phase, during which the male rode passively on the back of the female without genital contact, varied considerably (11 min to > 48h). Females appeared reluctant in all matings, and matings were forced by males.2. Laboratory experiments showed that the females were able to store sperm for more than 30 days without decrease in fertilization rate. In double mating experiments, where partially sterilized males were used, it was demonstrated that sperm displacement was extensive. The last male to mate fertilized approximately 80% of the eggs.3. It is concluded that the postcopulatory behaviour is beneficial to males in terms of paternity assurance, and it is interpreted as a mate guarding behaviour.
Seasonal allocation of energy to respiration, growth and reproduction in the freshwater clams, Pisidium variabile and P. compressum (Bivalvia: Pisidiidae)
Authors: WAY CARL M. 
Published: May 2006

SUMMARY. 1. The ecological energetics of the pisidiid clams, Pisidium variabile and P. compressum, from permanent ponds in southwestern Ohio were studied from July 1978 to July 1980. Productivity (P; as g C m−2 yr −1) was 1.82 (0.80 and 1.02 for the spring and autumn generations) and 4.22 (2.69 and 1.53 for the spring and autumn generations) for P. variabile and P. compressum, respectively.2. The average biomass (B; as g C m−2) of P. variabile was 0.54 (0.30 and 0.24 for the spring and autumn generations) and of P. compressum 1.09 (0.69 and 0.40 for the spring and autumn generations). P:B ratios for the spring and autumn generations of P. variabile were 2.7 and 4.2 and of P. compressum 3.9 and 3.8, which are below those reported for other iteroparous invertebrates.3. Reproductive effort (Re:Px100) was 5.1 and 5.7 for the generations of P. variabile and 7.7 and 8.8 for the generations of P. compressum. These low values relative to other molluses can be attributed to a viviparous mode of reproduction and exposure to local environmental variability. In addition, the differences between the reproductive efforts of the spring and autumn generations of both species can be ascribed to season of birth and altometric constraints on reproductive capacity.4. The data from this and related studies on pisidiid clams are used to generate several hypotheses concerning the evolution of life cycles in the family: (1) reproductive effort is limited by allometric constraints on clam size; (2) individuals of different ages can have different demographies and physiological rate functions; and (3) current one‐dimensional life history theories are largely inappropriate when dealing with an organism that has a wide range of phenotypic responses to environmental variability as well as complex age structure.
Population dynamics and morphometries of Gammarus pulex L.: evidence of seasonal food limitation in a freshwater detritivore
Authors: GEE JOHN H. R. 
Published: May 2006

SUMMARY. 1. Seasonal changes in population size structure of Gammarus pulex L. in a Cotswold stream appeared to indicate a growth check in late summer.2. The relationships between dry weight and body length, and between the number of primary flagellar segments on the first antenna and either dry weight or body length provided further evidence of a reduction in growth in mid and late summer.3. Body fat content was minimal (4% of dry weight) at the end of summer, when large particulate organic detritus was scarce or of poor quality, and maximal in late winter (17.9% dry weight in females; 9.4% in males), after a period of high food availability. In a field experiment, the fat content of animals in summer was raised to levels typical of winter by providing high quality food.4. Field and experimental evidence together strongly infer that this population of G. pulex was subject to severe food limitation from early summer until leaf fall in autumn.
Age, growth and reproduction of Aphanius iberus (Cuv. & Val., 1846) in the lower reaches of the Guadalquivir river (south‐west Spain)
Authors: FERNANDEZ‐DELGADO C. , HERNANDO J. A. , HERRERA M. , BELLIDO M. 
Published: May 2006

SUMMARY. 1. Age, growth and reproduction in an Atlantic population of the small fish, Aphanius iberus (Cuv. & Val., 1846), from the estuary of the Guadalquivir river were studied.2. The growth period was from April to September and the annulus on the scales was formed in April.3. The life‐span was short with a winter age‐structure of 95.9% 0+ fish, 3.9% 1+ and 0.2% 2+.4. The fecundity of this stock, before the beginning of reproduction, is represented by the formula: Fec=0.907 TL (cm)4.099. During the reproductive period 1+ females contained more, smaller eggs g−1 of gonad than 0+ fish.5. Males matured before females, but females were larger than males. The overall sex ratio did not differ from 1:1 but males dominated significantly during most of the spawning period.6. Aphanius iberus spawned intermittently during the reproductive period. From April to July, 1+ group specimens (7–12 months old) reproduced. Their offspring (0+ group; 3–4 months old) reproduced from July to September. Very few of the 1+ group specimens survived to spawn the following year.7. Mean gonadosomatic indices were much higher in the 1+ group than in the 0+ group and in females compared to males.8. The loss of condition and the disappearance of the 1 + group during spawning, may indicate the cost of a prolonged high level of reproductive effort.9. In this productive environment, the life history of Aphanius iberus is similar to that of Gambusia affinis (Baird & Girard, 1853) and Fundulus heteroclitus (Linnaeus) found in the same area.
Grazing on filamentous algae by herbivorous zooplankton
Authors: FULTON ROLLAND S. 
Published: May 2006

SUMMARY. 1. Feeding experiments were conducted to examine filtering rates and selectivity of a variety of zooplankton taxa (including cladocerans, copepods and a rotifer) for filamentous diatoms, green and blue‐green algae.2. Most herbivores were capable of consuming some filamentous algae at rates similar to or higher than those on unicellular algae. Only feeding of Diaphanosoma brachyurum Liéven and Moina micrura Kurz seemed to be primarily limited by the filamentous morphology.3. Filtering rates and selectivities of most herbivores were much higher for the diatom Melosira granulata angustissima Müller than for similarly sized blue‐green algal filaments, indicating that chemical factors strongly influence consumption of filamentous algae.4. The toxic blue‐green algal filament Anabaena flos‐aquae De Brébisson NRC 44–1 had a much strong inhibitory effect on zooplankton feeding than other filaments. The only herbivores that were not inhibited by this strain have been shown to be resistant to blue‐green algal toxins, or strongly avoided consuming the blue‐green alga. These results indicate that the inhibitory effect of filamentous algae is due more to toxic or noxious chemicals than to the filamentous morphology.5. Selectivities of zooplankton for filamentous algae were largely independent of herbivore body size. The small‐bodied cladoceran Bosmina longirostris Müller had the highest selectivities for filamentous algae.
Digestive ability of the freshwater crayfish Paranephrops zealandicus (White) (Parastacidae) and the role of microbial enzymes
Authors: MUSGROVE RICHARD J. 
Published: May 2006

SUMMARY. 1 Ingestion rate, assimilation efficiency and digestive enzyme activity were investigated in the New Zealand freshwater crayfish, Paranephrops zealandicus (White). Rates of ingestion of fresh and decaying Elodea canadensis Michx. were highly variable at 15°C and assimilation efficiency averaged 21%.2.Hepatopancreas extracts showed enzyme activity towards each of nine substrates tested; microcrystalline cellulose (MCC), carboxymethyl cellulose (CMC), cellobiose, amylose, pectin, mannan, laminarin, chitin and‘Azocoll’ (a dye‐collagen complex).3. Three genera of Enterobacteriacae were isolated from digestive juices and hepatopancreas samples and microbial activity was implicated in the breakdown of MCC, laminarin and protein. Host‐specific activity was not detected in the assays with MCC suggesting a solely microbial source for this enzyme.4. Although cellulose cannot be broken down without some degree of prior conditioning, the polytrophic feeding strategy of P. zealandicus is indicated by the presence of host‐specific enzymes that hydrolyse storage and structural sugars of algae, fungi and higher plants as well as animal protein.
Distribution of planktonic ciliates in highly coloured subtropical lakes: comparison with clearwater ciliate communities and the contribution of myxotrophic taxa to total autotrophic biomass
Authors: BEAVER JOHN R. , CRISMAN THOMAS L. , BIENERT RAYMOND W. 
Published: May 2006

SUMMARY 1. The planktonic ciliate communities of eleven organically coloured north and central Florida lakes representing a variety of trophic conditions were examined during 1979–80. The total abundance and biomass of ciliates were not significantly different from comparable clearwater lakes and only minor taxonomic replacements were noted at the order level.2. Timing of population peaks of oligotrophic lakes was dissimilar to clearwater lakes of the same trophic state, but seasonality in meso‐trophic and eutrophic lakes resembled patterns described for comparable clearwater lakes.3. Various ciliate components were strongly correlated with chlorophyll a concentrations, but only moderately correlated to dominant phytoplankton groups. No significant correlations were found between ciliate components and bacterial abundance.4. Myxotrophic taxa numerically dominated oligotrophic systems, particularly during midsummer, and accounted for a large percentage of the total ciliate biomass. Estimates of the ciliate contribution to total autotrophic biomass indicate that these zoochlorellae‐bearing protozoa may account for much of the autotrophic biomass during midsummer periods in coloured lakes, and thus may lead to an overestimation of phytoplankton standing crops available to zooplankton grazers if chlorophyll a is used as a surrogate measure of algal biomass.
Habitat utilization by sympatric arctic charr Salvelinus alpinus L. and brown trout Salmo trutta L. in Lake Atnsjø, south‐east Norway
Authors: HEGGE OLA , DERVO BØRRE K. , SKURDAL JOSTEIN , HESSEN DAG O. 
Published: May 2006

SUMMARY. 1. Habitat utilization, as well as inter‐ and intraspecific relations of different size groups of arctic charr (Salvelinus alpinus (L.)) and brown trout (Salmo trutta L.) in Lake Atnsjø, south‐east Norway, were investigated by analysing food and spatial niches from monthly benthic and pelagic gillnet catches during June‐October 1985.2. Small individuals (150–230 mm) of both arctic charr and brown trout occurred in shallow benthic habitats. However, they were spatially segregated as arctic charr dominated at depths of 5–15 m and brown trout at depths of 0–5 m.3. Larger (>230 mm) arctic charr and brown trout coexisted in the pelagic zone. Both species occurred mainly in the uppermost 2‐3 m of the pelagic, except in August, when arctic charr occurred at high densities throughout the 0–12 m depth interval. On this occasion, arctic charr were segregated in depth according to size, with significantly larger fish in the top 6 m. This was probably due to increased intraspecific competition for food.4. The two species differed in food choice in both habitats, Arctic charr fed almost exclusively on zooplankton, whereas brown trout had a more variable diet, consisting of surface insects, zooplankton. aquatic insects and fish.5. The data suggest that the uppermost pelagic was the more favourable habitat for both species. Large individuals having high social position occupied this habitat, whereas small individuals lived in benthic habitat where they were less vulnerable to agonistic behaviour from larger individuals and less exposed to predators. The more aggressive and dominant brown trout occupied the more rewarding part of the benthic habitat.
Microhabitat availability in Welsh moorland and forest streams as a determinant of macroinvertebrate distribution
Authors: RUTT G. P. , WEATHERLEY N. S. , ORMEROD S. J. 
Published: May 2006

SUMMARY. 1 Eighteen streams in mid‐Wales were sampled for macro‐invertebrates in both riffles and margins in April 1985–87. Stream macro‐flora, substrata and marginal habitats were surveyed in May 1988.2. TWINSPAN classification of the macroinvertebrate data indicated three major stream groups. One was distinguished by circumneutral pH and had a flora and fauna typical of such conditions. The other two groups consisted of acidic streams with moorland and conifer afforested catchments respectively. The forest streams were the more acidic but the two groups also differed significantly in the composition of their marginal habitats.3 The acidic moorland streams had more vegetation (‘soft’ features) in the margins and supported several invertebrate taxa which were relative more abundant there than in the riffles. These taxa may be excluded from forest streams because the margins are ‘hard’ due to greater erosiveness and shading.4. In view of the increasing cover by conifer afforestation in Britain, it is clearly necessary to elucidate all its effects on stream ecosystems, which include changes to the physical environment.
Genetic evidence of variation in the contributions of sexual and asexual reproduction to populations of the freshwater ostracod Candonocypris novaezelandiae
Authors: CHAPLIN JENNIE A. , AYRE DAVID J. 
Published: May 2006

SUMMARY. 1 Genetic (electrophoretic) and sex ratio data were used to assess the contributions of sexual and asexual reproduction to recruitment to populations of the freshwater ostracod Candonocypris novaezelandiae in temporary and permanent water bodies of varying size.2. Two distinct types of population structure were found. Populations from eight permanent ponds, a reservoir and a temporary pond, apparently comprised only females and were dominated by a few highly replicated genotypes. Significant departures from Hardy‐Weinberg equilibria were observed for at least one locus in all populations, and multi‐locus genotypic diversity ranged between 16% and 48% of that expected in a population with the same underlying gene frequencies reproducing solely by sexual means. These results were consistent with the predicted consequences of predominantly asexually derived recruitment.3. In contrast, sexual reproduction was probably most important in a population inhabiting a large temporary swamp. This population displayed 79% of the genotypic diversity expected for a sexually reproducing population, and contained both males and females.4. Most theoretical models predict that sexually reproducing individuals should have a selective advantage in unstable environments. The results of this study do not provide a perfect association of sexually derived recruitment with unstable habitats.
Hydrolytic extracellular enzyme activity in heterotrophic biofilms from two contrasting streams
Authors: JONES SUSAN E. , LOCK MAURICE A. 
Published: May 2006

SUMMARY. 1. Extracellular hydrolytic enzyme activities and cell densities were monitored during undisrupted biofilm formation on pristine surfaces in two contrasting river sites in North Wales: an oligotrophic mountain stream (Nant Waen) and a mildly eutrophic river (River Clywedog).2. Bacterial densities generally increased at both sites over a 33‐day monitoring period. Densities in the eutrophic site were approximately 14 times greater than in the mountain stream.3. Using fluorescent substrate analogues, biofilms from Nant Waen produced low, variable xylosidase and β‐glucosidase activities. Biofilms from the more eutrophic River Clywedog produced higher xylosidase and β‐glucosidase activities and detectable endopeptidase, though these activities also fluctuated during the colonization period.4. Unlike the other activities measured, esterase activities in the River Clywedog were correlated with cell densities (P<0.05). When extracellular esterase activities per cell were calculated, the oligotrophic biofilm was found to contain about twice as much extracellular esterase activity as the more eutrophic River Clywedog biofilm.
Fish predation and reduction in body size in a Cladoceran population: palaeoecological evidence
Authors: SALO JUKKA , WALLS MARI , RAJASILTA MARJUT , SARVALA JOUKO , RÄSÄNEN MATTI , SALONEN VELI‐PEKKA 
Published: May 2006

SUMMARY. 1 We studied the recent history (1852‐1982) of Lake Pyhä‐järvi, south‐west Finland, using both cladoceran microfossils and independent historical data. The objective of the study was to assess the impact of introduced planktivorous whitefish Coregonus lavaretus s.1. on zooplankton, especially on the main prey species Bosmina coregoni Baird s.str.2. A size‐frequency analysis of carapace remains preserved in the sediments clearly shows a size shift in a Bosmina coregoni population. The carapace length of B. coregoni decreased by 11.0% after the introduction of the size‐selective planktivorous whitefish, indicating a parallel body‐size reduction.3.During the study period no changes could be found in the carapace length of Chydorus sphaericus O. F. Müller, which was not preyed upon.
Classification and ordination of profundal macroinvertebrate communities in nutrient poor, oligo‐mesohumic lakes in relation to environmental data
Authors: JOHNSON RICHARD K. , WIEDERHOLM TORGNY 
Published: May 2006

SUMMARY. 1. Profundal macroinvertebrates and water chemistry of sixty‐eight nutrient poor, poorly buffered lakes were sampled in 1983 or 1986. Assemblages of profundal zoobenthos were classified using two‐way indicator species analysis (TWINSPAN), ordinated by canonical correspondence analysis (CCA), and related to physico‐chemical factors using CCA. discriminant analysis, and regression.2. 90% of zoobenthos (TWINSPAN) groups were classified correctly using discriminant analysis. Depth (Function 1), soluble reactive Si(OH)4 and HCO3, ‐(2), and phytoplankton biovolume and pH (3) were the strongest correlates with the three discriminant functions.3. Regression analysis showed that depth, KmnO4, consumption, and phytoplankton biovolume were the best estimators of zoobenthos biomass in the profundal.4. Multivariate analyses showed species assemblages amongst the profundal zoobenthos to be good indicators of lake type, particularly depth, pH, and phytoplankton biovolume.
Oxygen concentration profiles and exchange in sediment cores with circulated overlying water
Authors: SWEERTS JEAN‐PIERRE R. A. , LOUIS VINCE ST , CAPPENBERG THOMAS E. 
Published: May 2006

SUMMARY. 1. The overlying water of intact sediment cores was constantly stirred with an impeller at a rate sufficient to mix turbulently the water column and maintain the diffusive boundary layer at a determined thickness. The system allowed standardization of water circulation in laboratory sediment core experiments.2. Both oxygen concentration and oxygen penetration depth in the sediments decreased, the former by 70% and the latter from 4.2 mm to 2.0 mm, when the overlying water was not stirred for 24 h, as measured with oxygen microelectrodes in a lake sediment core.3. Oxygen profiles measured in sediment cores in the laboratory were similar to those measured in situ when the overlying water was stirred with an impeller at such a rate that a similar thickness of the diffusive boundary layer at the sediment‐water interface developed in the laboratory as that in situ.4. Sediment oxygen consumption was calculated from: (1) measured oxygen profiles in the diffusive boundary layer and the molecular diffusion coefficient for oxygen in water; (2) the measured oxygen decrease in the top of the sediments and the estimated diffusion coefficient in the sediment; and (3) by oxygen differences in the overlying water after incubation of sediment cores.
The influence of copper exposure on predator‐prey interactions in aquatic insect communities
Authors: CLEMENTS WILLIAM H. , CHERRY DONALD S. , JR CAIRNS JOHN 
Published: May 2006

SUMMARY. 1. Vulnerability of two species of net‐spinning caddisflies (Chimarra sp. and Hydropsyche morosa) to predation by the stonefly, Paragnetina media, was significantly greater in experimental streams dosed with copper (target concentration=6 μg 1‐1) than in control streams.2. Results of stomach analyses showed that Hydropsychidae was the major component of stonefly diets in experimental streams and that the number of Hydropsychidae per stonefly gut was significantly greater in dosed streams than controls.3. Since these results could not be predicted using single species bioassays, we suggest that such simple tests be supplemented with more environmentally realistic procedures that account for species interactions.
Changes in phytoplankton over various time scales in a shallow, eutrophic: the Loch Leven experience with special reference to the influence of flushing rate
Authors: BAILEY‐WATTS A. E. , KIRIKA A. , MAY L. , JONES D. H. 
Published: May 2006

SUMMARY. 1. The pattern of fluctuations in the total biomass and species composition of phytoplankton in the shallow, eutrophic Loch Leven exhibits considerable inter‐annual and within‐year variability. Nevertheless, studies over the 18‐year period reviewed here (1968–85) show that many of the observed changes can be explained in ‐terms of light regimes and the concentrations and fluxes of nutrients. On occasion, the incidence of fungal parasitism and of protozoan, rotiferan and crustacean grazing is also important.2. Changes in annual mean algal biomass from very high levels in the late 1960s and early 1970s to somewhat lower levels in the late 1970s, followed by occasional high peaks in the present decade, are attributed to shifts in phosphorus loading‐particularly from a P‐rich industrial source.3. In spite of complex and erratic sequences of algal species, seasonal patterns in the size distribution of the phytoplankton assemblage have been identified. However, these also changed. During the 4 years prior to 1971, Daphnia hyalina was not recorded in the plankton, and small algae have been abundant only in late winter or early spring.4. The potential importance of the weather is highlighted as one of the possible causes of the irregular appearance of algal species. The effect of the characteristically variable, oceanicclimate of Northern Britain on this large (13.3 km2), shallow (&#x007a;̄= 3.9 m) loch is thought to be of particular importance.5. The influence of the weather on phytoplankton sequences is explored by comparing records of monthly flushing rate values with time‐series data on aspects of the aquatic environment and plankton populations. The preliminary assessment suggests that variation in flushing rate (p) has a considerable effect on temperature regimes and the supplies and in‐loch dynamics of nutrients; through such changes, p controls major features of phytoplankton succession such as the temporal abundance of diatoms, as well as detailed sequences of events relating to the development and collapse of particular algal species ‐ and. as a consequence, in some cases, of the animals preying on them.6. Concluding remarks emphasize how little would have been understood about the functioning of shallow lakes, had the long‐term commitment to Loch Leven research been abandoned. The view is also expressed that the findings are of considerably greater relevance to research on ‘classic’ stratifying lake systems, than the focus on the shallow waterbody might hitherto have suggested.