bluuebunny/crossref_metadata_2025_split huggingface dataset:
Climate change and abundance of the Atlantic‐Iberian sardine (Sardina pilchardus)
Authors: Guisande C. , Vergara A. R. , Riveiro I. , Cabanas J. M. 
Published: December 2004

AbstractClimatic warming is affecting oceanic circulation patterns in coastal upwelling areas, but the impact of this climatic change on pelagic fish populations remains unclear. From juvenile landings collected over 38 years, the thresholds of environmental factors were determined that limited the optimal environmental window (OEW) for sardine (Sardina pilchardus recruitment success in the northwestern Iberian peninsula. The environmental factors considered were: water column stability in February, offshore water transport in March–April (QxMA), upwelling intensity in the preceding year from May to August (QxMJJA), and the winter North Atlantic Oscillation (NAO) index. From 1875 to the mid‐1920s, the mean number of years within the OEW was relatively constant. However, since the mid‐1920s, there have been oscillations and alternating decades with high and low number of years within the OEW, which were related to oscillations in sardine landings. From 1906 to 2000, there were four record, low sardine catches in the 1920s, 1950s, 1970s and 1990s, related to a high number of successive years with prevailing conditions out of the OEW. From 1875 to the present, a high year‐to‐year variation of the NAO, QxMJJA and water stability in February was observed, although with mean values usually within the OEW. The collapse in the 1950s was related, partly, to successive years with low QxMJJA. Successive years with high NAO values may be related to the collapse of the sardine fishery in the 1990s. QxMA has been the most significant factor controlling SRS in this area, being the factor related to the low catches observed in the 1920s, 1950s and 1970s. Water stability was not responsible for any of the collapses observed, but since the 1920s, there has been a significant trend toward decreasing water column stability before the onset of the spring bloom.
Water quality assessment using diatom assemblages and advanced modelling techniques
Authors: Gevrey Muriel , Rimet Frédéric , Park Young Seuk , Giraudel Jean‐Luc , Ector Luc , Lek Sovan 
Published: December 2004

Summary1. Two types of artificial neural networks procedures were used to define and predict diatom assemblage structures in Luxembourg streams using environmental data.2. Self‐organising maps (SOM) were used to classify samples according to their diatom composition, and multilayer perceptron with a backpropagation learning algorithm (BPN) was used to predict these assemblages using environmental characteristics of each sample as input and spatial coordinates (X and Y) of the cell centres of the SOM map identified as diatom assemblages as output. Classical methods (correspondence analysis and clustering analysis) were then used to identify the relations between diatom assemblages and the SOM cell number. A canonical correspondence analysis was also used to define the relationship between these assemblages and the environmental conditions.3. The diatom‐SOM training set resulted in 12 representative assemblages (12 clusters) having different species compositions. Comparison of observed and estimated sample positions on the SOM map were used to evaluate the performance of the BPN (correlation coefficients were 0.93 for X and 0.94 for Y). Mean square errors of 12 cells varied from 0.47 to 1.77 and the proportion of well predicted samples ranged from 37.5 to 92.9%. This study showed the high predictability of diatom assemblages using physical and chemical parameters for a small number of river types within a restricted geographical area.
Hydrological variability, organic matter supply and denitrification in the Garonne River ecosystem
Authors: Baker Michelle A. , Vervier Philippe 
Published: December 2004

Summary1. Groundwater nitrate contamination has become a worldwide problem as increasing amounts of nitrogen fertilisers are used in agriculture. Alluvial groundwater is uniquely juxtaposed between soils and streams. Hydrological connections among these subsystems regulate nutrient cycling.2. We measured denitrification using an in situ acetylene‐block assay in a nitrate‐contaminated portion of the Garonne River catchment along a gradient of surface water–ground water mixing during high (snowmelt) and low flow.3. During high flow (mid‐April to early June) the water table rose an average of 35 cm and river water penetrated the subsurface to a great extent in monitoring wells. Denitrification rates averaged 5.40 μgN2O L−1 min−1 during the high flow period, nearly double the average rate (2.91 μgN2O L−1 min−1) measured during base flow. This was driven by a strong increase in denitrification in groundwater under native riparian vegetation. Nitrate concentrations were significantly lower during high flow compared with base flow. Riparian patches had higher dissolved organic carbon concentrations that were more aromatic compared with the gravel bar patch closest to the river.4. Multiple linear regression showed that the rate of denitrification was best predicted by the concentration of low molecular weight organic acids. These molecules are probably derived from decomposition of soil organic matter and are an important energy source for anaerobic respiratory processes like denitrification. The second best predictor was per cent surface water, reflecting higher denitrification rates during spring when hydrological connection between surface water and ground water was greatest.5. Our results indicate that, while denitrification rates in Garonne River alluvium were spatially and temporally variable, denitrification was a significant NO3 sink during transport from the NO3‐contaminated floodplain to the river. DOC availability and river–floodplain connectivity were important factors influencing observed spatial and temporal patterns.
The influence of scale and geography on relationships between stream community composition and landscape variables: description and prediction
Authors: Townsend Colin R. , Dolédec Sylvain , Norris Richard , Peacock Kathi , Arbuckle Chris 
Published: December 2004

SUMMARY 1. We analysed an existing database of macroinvertebrates and fish in the context of a newly established geographical information system (GIS) of physical features to determine the relationships between stream community composition and physical factors measured at three landscape scales – catchment, reach and bedform. Both an exploratory (concordance analysis) and a predictive (ausrivas) approach were used.2. The environmental variables that most successfully accounted for variation in macroinvertebrate assemblages were mainly ‘natural’ and at the catchment‐scale (relief ratio, basin diameter, etc.) but the human‐induced physical setting of percentage of pasture in the riparian zone was also influential. For fish, ‘natural’ variables were also dominant, but these were mostly at the bedform or reach scales and land use featured strongly.3. Geographic location accounted for some of the variation in invertebrate assemblages, partly because geography and influential conditions/resources are correlated but also because different species may have evolved in different places and have not colonised every ‘ecologically appropriate’ location. Geographic location was not influential in accounting for variation in assemblages of strongly flying invertebrates, supporting the hypothesis that organisms having high dispersal potential can be expected to break down geographic barriers more readily than those with poor dispersal powers. In accord with what is known about the local evolution and restricted distributions of native and exotic species, history (reflected in geography) appeared to account for some variation in fish assemblages.4. Given their different mathematical bases, the fact that exploratory and predictive analyses yielded similar results provides added confidence to our conclusions.
Potassium dependence and phytoplankton ecology: an experimental study
Authors: Jaworski G. H. M. , Talling J. F. , Heaney S. I. 
Published: December 2004

SUMMARY 1. Unialgal cultures of three species common in the freshwater phytoplankton were used to test limitation of specific growth rate and final yield in defined media of low K+ concentration (range <0.3–6 μmol L−1 or mmol m−3).2. Growth rate of the diatom Asterionella formosa was independent of K+ concentration above 0.7 μmol L−1. Final yield was dependent on initial concentration when accompanied by K+ depletion below this concentration, but not by lesser depletion with more residual K+. Analyses of particulate K in the biomass indicated a mean final cell content of 2.8 μmol K 10−8 cells, approximately 1.0% of the organic dry weight.3. Less detailed work with the diatom Diatoma elongatum showed no dependence of growth rate or final yield upon the initial K+ concentration in the range 0.8–3.2 μmol L−1. The phytoflagellate Plagioselmis nannoplanctica suffered net mortality in the lowest concentration tested, 0.8 μmol L−1.4. Comparison with the range of K+ concentration in natural fresh waters, including a depletion induced by an aquatic macrophyte, suggests that K+ is unlikely to limit growth of phytoplankton. Nevertheless, there can be correlation of K+ with lake trophy.
Seasonal patterns of viruses, bacteria and dissolved organic carbon in a riverine wetland
Authors: Farnell‐Jackson E. A. , Ward A. K. 
Published: December 2004

SUMMARY 1. Viral and bacterial abundances were studied in relation to environmental attributes over an annual period, for both planktonic and attached (sediment, aquatic macrophyte and submerged wood) habitats, in a riverine wetland.2. Annual mean abundance of planktonic viruses ranged from 2.3 × 105−3.8 × 105 particles mL−1 and varied according to sampling site. Significant seasonal patterns in viral abundance were evident and appeared to be linked to variations in bacterial abundance, dissolved organic carbon and inorganic nutrients.3. Annual mean abundance of viruses associated with surfaces ranged from 1.3 × 106 particles cm−2 on aquatic macrophytes to 1.1 × 107 particles cm−2 on wood and also showed seasonal patterns. The difference in viral dynamics among the different sites emphasizes the importance of considering habitat diversity within wetlands when examining microbial communities.
The annual cycle of growth rate and biomass change in Planktothrix spp. in Blelham Tarn, English Lake District
Authors: Davis P.A. , Dent M. , Parker J. , Reynolds C.S. , Walsby A.E. 
Published: December 2004

SUMMARY 1. The changes in the vertical distributions of red coloured Planktothrix rubescens and green P. agardhii filaments in Blelham Tarn, English Lake District, were related to vertical profiles of temperature and light attenuation and to continuous records of the surface irradiance and windspeed, from August 1999 to October 2000.2. The potential growth rate of each organism was calculated from the irradiance and temperature at 0.5 m depths and hourly intervals throughout the year, using algorithms determined from growth rates in culture. The analyses indicated that there was sufficient irradiance for growth, integrated over the 24‐h cycle, at depths down to the metalimnion where the Planktothrix populations stratified in summer. The compensation depth for growth by P. rubescens reached a maximum of 9.3 m in spring and midsummer, and fell to a minimum of 1.6 m in midwinter; the corresponding values for P. agardhii were 7.9 and 0.5 m.3. The mixed depth (zm) exceeded the critical depth for growth (zb) by P. rubescens (the condition preventing population increase) on only 3 days of the year; for P. agardhii, however, zm exceeded zb on 31 days, contributing to its faster decline. The stratified population of P. rubescens was the major cause of light attenuation during the summer of 2000, and resulted in competitive exclusion of P. agardhii.4. The calculated growth rates integrated over the depth of the water column in Blelham Tarn equalled, or exceeded, the measured changes of the populations during periods when they were increasing, during summer and autumn. Close agreement between the two values was found for much of the year when allowance was made for dilution of the lake population by rainfall over the watershed. During periods of rapid decline, of P. agardhii in September 1999, P. rubescens in December 1999 and both in July–August 2000, additional losses (e.g. by chytrid parasitism and grazing) are invoked.
Effects of hydrogeomorphic region, catchment storage and mature forest on baseflow and snowmelt stream water quality in second‐order Lake Superior Basin tributaries
Authors: Detenbeck Naomi E. , Elonen Colleen M. , Taylor Debra L. , Anderson Leroy E. , Jicha Terri M. , Batterman Sharon L. 
Published: December 2004

SUMMARY1. In this study we predict stream sensitivity to non‐point source pollution based on the non‐linear responses of hydrological regimes and associated loadings of non‐point source pollutants to catchment properties. We assessed two hydrologically based thresholds of impairment, one for catchment storage (5–10%) and one for mature forest (<50% versus >60% of catchment in mature forest cover) across two different hydrogeomorphic regions within the Northern Lakes and Forest (NLF) ecoregion: the North Shore [predominantly within the North Shore Highlands Ecological Unit] and the South Shore (predominantly within the Lake Superior Clay Plain Ecological Unit). Water quality samples were collected and analysed during peak snowmelt and baseflow conditions from 24 second‐order streams grouped as follows: three in each region × catchment storage × mature forest class.2. Water quality was affected by a combination of regional influences, catchment storage and mature forest. Regional differences were significant for suspended solids, phosphorus, nitrogen: phosphorus ratios, dissolved organic carbon (DOC) and alkalinity. Catchment storage was significantly correlated with dissolved silica during the early to mid‐growing season, and with DOC, specific conductance and alkalinity during all seasons. Total nitrogen and dissolved nitrogen were consistently less in low mature forest than in high mature forest catchments. Catchment storage interacted with the influence of mature forest for only two metrics: colour and the soluble inorganic nitrogen : phosphorus ratio.3. Significant interaction terms (region by mature forest or region by storage) suggest differences in regional sensitivity for conductance, alkalinity, total organic carbon, and colour, as well as possible shifts in thresholds of impact across region or mature forest class.4. Use of the NLF Ecoregion alone as a basis for setting regional water quality criteria would lead to the misinterpretation of reference condition and assessment of condition. There were pronounced differences in background water quality between the North and South Shore streams, particularly for parameters related to differences in soil parent material and glacial history. A stratified random sampling design for baseflow and snowmelt stream water quality based on both hydrogeomorphic region and catchment attributes improves assessments of both reference condition and differences in regional sensitivity.
The ciliate epibiont Epistylis pygmaeum: selection for zooplankton hosts, reproduction and effect on two rotifers
Authors: Gilbert J. J. , Schröder T. 
Published: December 2004

SUMMARY1. A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis. Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs.2. Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta, and rarely or never settled on the rotifer Keratella, the cladocerans Bosmina and Scapholeberis, and the body of the copepod.3. Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 °C. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate (λ = 4.26 day−1); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare.4. Life‐table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.
Asymmetry, testis and sperm size in Yellow Dung Flies
Authors: Hosken D. J. , Garner T. W. J. , Blanckenhorn W. U. 
Published: December 2004

SummaryFluctuating asymmetry (FA), small random deviations from perfect bilateral symmetry, is a widely used measure of developmental stability, and has been linked to fitness measures including male primary reproductive traits such as sperm quality. However, there have been relatively few investigations of potential associations between these male traits and FA, and hence the current balance of evidence is equivocal.There is also evidence that levels of FA vary across populations with, for example, organisms inhabiting marginal populations often displaying increased FA. Moreover, environmental variation may select for different levels of developmental buffering across populations that are only revealed in ‘common garden’ experiments.Investigations of potential associations between male leg FA and testis and sperm size in Yellow Dung Flies are reported here. In addition, levels of FA in a mainland and two island populations were compared when flies were reared under common conditions.No associations were found between any measure of FA and sperm size (or variation) or testis size. Additionally, no evidence was found that FA varied across the three populations when flies were reared under identical controlled conditions.
Within‐colony transmission and the cost of a mutualistic bacterium in the leaf‐cutting ant Acromyrmex octospinosus
Authors: Poulsen M. , Bot A. N. M. , Currie C. R. , Nielsen M. G. , Boomsma J. J. 
Published: December 2004

Summary

Stable mutualistic interactions require the long‐term alignment of fitness interests of participating species. This condition is fulfilled when the benefits of the relationship exceed the costs for all partners.
One apparent stabilizing factor in mutualisms is the vertical (parent to offspring) transmission of symbionts, as this tends to reduce the expression of virulent traits and reproductive conflicts. This study examines the cost and mode of transmission of a mutualistic Streptomyces bacterium that grows on the cuticle of leaf‐cutting ants and produces antibiotics against a specialized fungal parasite of the ant fungus gardens.
It is shown that ant respiration rates are elevated by 10–20% when the bacterium is present on their cuticle. This increase is due to direct respiration of the bacterium and possible excess respiration by the ants. Although these two factors cannot be separated, it is clear that the total increase gives a reasonable quantification of the metabolic costs incurred by the Streptomyces symbiont.
Ants that actively maintain Streptomyces cultures on their cuticle tend to consume more of their mutualistic fungus garden than controls and this excess consumption increases with the amount of Streptomyces bacteria present.
Scanning electron microscopy showed that the mutualistic bacterium is not present on major workers immediately following eclosion, indicating that the bacterium is not transferred to callow workers until later.
The results of an experiment simulating within‐colony transmission to callow workers suggest that the bacterium is predominantly transmitted from older to newly eclosed major workers, but that transmission may also occur via the fungus garden. The presence of Streptomyces bacteria in the fungus garden implies that rare events of horizontal transmission of the fungal cultivar of attine ants may also imply horizontal transmission of strains of the mutualistic bacterium.
The consequences of crown traits for the growth and survival of tree saplings in a Mexican lowland rainforest
Authors: Sterck F. , Martinéz‐Ramos M. , Dyer‐Leal G. , Rodríguez‐Velazquez J. , Poorter L. 
Published: December 2004

Summary

Many studies discuss the adaptive value of plant architecture, but few have actually measured architectural effects on plant growth and survival. In this study, sapling growth and survival are related to crown traits for two tree species, Trophis mexicana (Liebm.) Bur. and Pseudolmedia oxyphyllaria Donn. Sm., in the Los Tuxtlas lowland rainforest of Mexico. The traits investigated were crown width, crown depth, number of leaves, number of leaves per unit crown area (horizontal self‐shading), and number of leaves per unit silhouette area (vertical self‐shading).
Self‐shading indices decreased with crown size, but were unaffected by the number of leaves per tree. Larger crowns thus had more diffuse foliage, with less self‐shading.
The number of leaves had positive effects on growth and survival, while self‐shading indices had no effect. This indicates that shaded leaves do not necessarily have negative carbon balances.
Negative effects of crown width on horizontal crown growth, and positive effects on vertical crown growth, suggest that saplings tend to grow towards a shape intermediate between the narrow and wide crown extremes.
Survival was positively correlated with crown width in Pseudolmedia, and with the number of leaves in Trophis. Apparently, dependence of survival on crown traits differed among species.
Crown traits affected plant growth and survival, but the hypothesis emerging from light‐limited carbon acquisition was confounded by other factors, such as tree size and the inherent branching patterns.
Crown traits are good and rather simple predictors of future sapling growth and survival, and may help foresters to select potential crop trees.