bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow rate and vertical position influence ingestion rates of colonial zebra mussels (Dreissena polymorpha)
Authors: Tuchman Nancy C. , Burks Romi L. , Call Christopher A. , Smarrelli John 
Published: December 2004

Summary1. Zebra mussels aggregate to form dense colonies where, depending on the flow rate, individuals in different vertical locations within the colony may experience restricted food availability.2. Using 32P‐labelled Chlamydomonas angulosa, we found ingestion rates of individual mussels located at the surface to exceed those in the bottom of a 6 cm thick colony by up to 75%.3. Higher velocities (10 and 20 cm s−1) increased algal delivery to the colony's middle layer (2–4 cm depth), subsequently increasing ingestion rates to equal those in the surface layer, while increasing ingestion only for the smallest mussels in the bottom (4–6 cm).4. At all vertical locations within the colonies, smaller mussels showed higher ingestion rates per unit mass than larger mussels, particularly at higher flow rates.
Effects of light and microcrustacean prey on growth and investment in carnivory in Utricularia vulgaris
Authors: Englund Göran , Harms Sabine 
Published: December 2004

SUMMARY 1. In a 5‐week enclosure experiment, we studied the effects of light (ambient light, low light) and prey availability (no prey, prey added) on growth and investment in carnivory in Utricularia vulgaris.2. Investment in carnivory, measured as the proportion of biomass allocated to bladders, was strongly affected by our manipulations of light intensity and prey density. In the treatment with high prey density the light reduction decreased the investment in bladders from 25% to zero. The effect of prey density on investment in bladders was negative. Because prey addition increased the concentration of nutrients, especially phosphorus, we propose that the effect of the prey treatment on investment reflected altered nutrient concentrations.3. Availability of prey increased growth and apical biomass of Utricularia. As Utricularia had very few bladders in some treatments we suggest that the effect was due to a combination of live prey trapped and increased nutrient availability from dead prey.4. Abundance of periphyton on Utricularia and on the enclosure walls was highest in the treatments with high prey density where nutrient concentrations were highest. Thus we interpret the response of periphyton as primarily reflecting nutrient availability.
A mass‐balance model for phosphorus in lakes accounting for biouptake and retention in biota
Authors: Håkanson Lars , Ostapenia Alexander P. , Boulion Viktor V. 
Published: December 2004

SUMMARY 1. A new mass‐balance model was developed to predict phosphorus fluxes to, within and from lakes and lake concentrations of phosphorus.2. The model is driven by data easily accessed from standard monitoring programmes or maps, so it should be useful in many contexts of lake management.3. The phosphorus model gives seasonal (weekly) variations and accounts for all fundamental abiotic/biotic interactions and feedbacks for lakes in general for phosphorus. The model has been developed within the framework of a more comprehensive ecosystem model, LakeWeb, which accounts for production values and biomasses of nine functional groups of organisms (phytoplankton, bacterioplankton, herbivorous and predatory zooplankton, prey and predatory fish, zoobenthos, macrophytes and benthic algae).4. The LakeWeb‐model has been critically tested in a wide limnological domain and shown to predict very well. By using this model, it is possible for the first time to predict realistic values of biouptake and retention of phosphorous in biota in lakes on a weekly basis.
Response of the flora and macroinvertebrate fauna of a chalk stream site to changes in management
Authors: Wright J. F. , Clarke R. T. , Gunn R. J. M. , Winder J. M. , Kneebone N. T. , Davy‐Bowker J. 
Published: December 2004

SUMMARY1. Temporal changes in a series of habitats and their macroinvertebrate assemblages were examined on a 50‐m section of a chalk stream in Berkshire, England between June 1975–79 and June 1997–2001.2. The site was part of a trout fishery in 1975–79, when river management included instream weed cutting together with control of bankside trees and riparian vegetation. Management ceased in the 1980s and by 1997–2001, the site was heavily shaded by trees and riparian vegetation.3. The mean area of instream macrophytes decreased by 50% between the first and second sampling period. In contrast, gravel and silt increased and invading marginal vegetation formed a new habitat.4. Changes in macroinvertebrate family richness between sampling periods were scale dependant. Although there were, on average, significantly more families in individual replicates in 1975–79 than in 1997–2001, total family richness for the site in each year did not differ significantly between sampling periods.5. Sixty families of macroinvertebrates were recorded during the study, 50 in both sampling periods, 53 in 1975–79 and 57 in 1997–2001. This small increase in site family richness may be due to the invading marginal plants.6. Total macroinvertebrate abundance was significantly lower in the second sampling period. A major drought in 1976 resulted in significantly higher densities of macroinvertebrates, partly through the exploitation of epiphytic diatoms by chironomid larvae. A drought in 1997 failed to elicit a similar response because of the limited macrophytes and diatoms under heavy shading by trees and marginal vegetation.7. Significant increases in important shredders and decreases in some scrapers between the early and later sampling years largely reflected changes in available food resources.8. Whereas macroinvertebrate family richness has been conserved under the recent ‘no management’ regime, the site is now less attractive as a fishery because of poor access and lower densities of some macroinvertebrates taken by brown trout.
Relationships between locomotor performance, microhabitat use and antipredator behaviour in lacertid lizards
Authors: Vanhooydonck B. , Van Damme R. 
Published: December 2004

SummaryMicrohabitat use and antipredator behaviour (i.e. behavioural response to a bird model and refuge microhabitat) was measured in an experimental set‐up for 11 lacertid lizard species. Additionally, locomotor performance (sprint speed, climbing and clambering speed, manoeuvrability and endurance) of the same species was quantified.The results showed considerable interspecific variation in microhabitat use, behavioural response and choice of refuge microhabitat. Part of that variation could be linked to differences in locomotor capacity.Species that frequently made use of open microhabitats tended to be fast sprinters, but had limited endurance. The behavioural data suggest these species will not start running before the predator is close at hand, and thus having high sprint capacities might be more beneficial than great endurance.Species that spent most of their time on vertical elements appeared to be fast climbers. As such microhabitats tend to be quite exposed, lizards living there are conspicuous to predators and being able to escape fast seems relevant.Contrary to our expectations, species mostly observed in the vegetated microhabitats did not excel in clambering capacity or manoeuvrability. Possibly, dense vegetation constitutes a safe harbour and species may no longer be under selection for locomotor speed.Behavioural response when confronted with an aerial predator was context‐dependent in most species: most lizards fled more when in open or vertical microhabitats than when in densely vegetated ones. Moreover, when fleeing most species sought refuge in the vegetation. These findings support our idea that vegetated patches may constitute a safe harbour for lacertids.
Energetics and water economy of common spiny miceAcomys cahirinusfrom north‐ and south‐facing slopes of a Mediterranean valley
Authors: Scantlebury M. , Shanas U. , Speakman J. R. , Kupshtein H. , Afik D. , Haim A. 
Published: December 2004

SummaryA comparison was made of the daily energy expenditure (DEE), resting metabolic rate (RMR) and water turnover (WTO) of two populations of Common Spiny MiceAcomys cahirinusfrom north‐ and south‐facing slopes (NFS and SFS) of the same valley, which represented ‘Mediterranean’ and ‘desert’ habitats, respectively.An examination was made as to whether these physiological characteristics differed between mice that had been in the laboratory (outdoor conditions) for 2 months compared with mice captured from the field.Mice from the field had greater RMR values than mice in the laboratory and NFS mice had greater RMR values than SFS mice. In the field, NFS individuals had greater DEE values than SFS individuals. Mass‐specific RMR values of SFS mice were 20% less than the allometrically predicted value, whereas those of NFS were not. WTO and sustained metabolic scope (DEE/RMR) were lower in the field than in the laboratory.The results indicate that physiological capabilities are phenotypically plastic, as differences exist between the field and laboratory and between NFS and SFS mice. Furthermore, they highlight the importance of using field studies for understanding the link between energetics and physiological adjustment to environmental conditions.
High dosage Rhp51 suppression of the MMS sensitivity of DNA structure checkpoint mutants reveals a relationship between Crb2 and Rhp51
Authors: Smeets Monique F.M.A. , Francesconi Stefania , Baldacci Giuseppe 
Published: December 2004

AbstractBackground: In eukaryotic cells DNA structure checkpoints organize the cellular responses of DNA repair and transient cell cycle arrest and thereby ensure genomic stability. To investigate the exact role of crb2+ in the DNA damage checkpoint response, a genetic screen was carried out in order to identify suppressors of the conditional MMS sensitivity of a crb2‐1 mutant. Here we report the isolation of rhp51+ as a multicopy suppressor.Results: We show that suppression is not specific for the checkpoint mutant while it is specific for the MMS treatment. Rescue by rhp51+ over‐expression is not a consequence of increased recombination repair or checkpoint compensation and epistasis analysis confirms that crb2+ and rhp51+ function in different pathways. A tight linkage between the two pathways is nevertheless suggested by the complementary expression or modification of Crb2 and Rhp51 proteins. Crb2 protein stability is down‐regulated when Rhp51 is over‐expressed and up‐regulated in the absence of Rhp51. The up‐regulation of Crb2 is independent of the activation of DNA structure checkpoints. Conversely Rhp51 is more readily activated and differentially modified in the absence of Crb2 or other checkpoint proteins.Conclusions: We conclude that fission yeast Crb2 and Rhp51 function in two parallel, tightly connected and coordinately regulated pathways.
Nucleocytoplasmic shuttling and phosphorylation of BMAL1 are regulated by circadian clock in cultured fibroblasts
Authors: Tamaru Teruya , Isojima Yasushi , Van Der Horst Gijsbertus T. J. , Takei Kohtaro , Nagai Katsuya , Takamatsu Ken 
Published: December 2004

AbstractBackground:  Recent discoveries of clock proteins have unveiled an important part of the mammalian circadian clock mechanism. However, the molecular clockwork that cause these fundamental feedback loops to stably oscillate with a ∼24 h‐periodicity remain unclear.Results:  Serum‐shocked fibroblasts were used as a cellular clock model. Circadian changes in the subcellular localization and phosphorylation of BMAL1 protein in these cells were assessed by immunocytochemistry and immunoblotting. A significant time lag between Bmal1 transcription and the cytoplasmic/nuclear accumulation of BMAL1 was observed. After its nuclear accumulation, BMAL1 accumulated in the cytoplasm again, mainly by nucleoexport, before the increase of Bmal1 transcripts. Nuclear accumulation of BMAL1 matched nuclear accumulation of CLOCK and the peak of Per1 transcription. Nuclear BMAL1 was gradually phosphorylated and then dephosphorylated in a temporally regulated manner, although cytoplasmic BMAL1 was not. In serum‐shocked mCry1/mCry2 (CRY)‐deficient fibroblasts, which lack a functional clock, both the cytoplasmic and nuclear BMAL1 were only present as hyperphosphorylated forms and their circadian nucleocytoplasmic shuttling was absent.Conclusions:  We propose that the nucleocytoplasmic shuttling and phosphorylation states of BMAL1 are regulated by circadian clock, and that this temporally regulated and time‐delayed nuclear entry of BMAL1 is important in the maintenance of a stably oscillating clock.
Adaptive subtraction of multiples using the L1‐norm
Authors: Guitton A. , Verschuur D. J. 
Published: December 2004

ABSTRACTA strategy for multiple removal consists of estimating a model of the multiples and then adaptively subtracting this model from the data by estimating shaping filters. A possible and efficient way of computing these filters is by minimizing the difference or misfit between the input data and the filtered multiples in a least‐squares sense. Therefore, the signal is assumed to have minimum energy and to be orthogonal to the noise. Some problems arise when these conditions are not met. For instance, for strong primaries with weak multiples, we might fit the multiple model to the signal (primaries) and not to the noise (multiples). Consequently, when the signal does not exhibit minimum energy, we propose using the L1‐norm, as opposed to the L2‐norm, for the filter estimation step. This choice comes from the well‐known fact that the L1‐norm is robust to ‘large’ amplitude differences when measuring data misfit. The L1‐norm is approximated by a hybrid L1/L2‐norm minimized with an iteratively reweighted least‐squares (IRLS) method. The hybrid norm is obtained by applying a simple weight to the data residual. This technique is an excellent approximation to the L1‐norm. We illustrate our method with synthetic and field data where internal multiples are attenuated. We show that the L1‐norm leads to much improved attenuation of the multiples when the minimum energy assumption is violated. In particular, the multiple model is fitted to the multiples in the data only, while preserving the primaries.
Reassessing the impact of North Atlantic Oscillation on the sub‐Saharan vegetation productivity
Authors: WANG GUILING 
Published: December 2004

AbstractThe Northern Atlantic Oscillation (NAO) has been shown to have a significant impact on the terrestrial ecosystem in the Sahelian region of Africa during the 1980s, and it has been strongly suggested that NAO may be a reliable predictor for the response of the Sahelian ecosystem to global climate variability. Using data from an extended period, we provide a reassessment for the impact of NAO on the Sahelian climate and ecosystem, and show that there is no consistent relationship between NAO and the ecosystem over Sahel. Statistical analysis on the NAO, vegetation, and precipitation data indicates that NAO influences the Sahelian vegetation productivity exclusively through its impact on precipitation. However, the relationship between the NAO index and Sahelian precipitation varies substantially with time. The correlation coefficient fluctuates between positive and negative values, and does not pass the 5% significance test during most of the twentieth century. The NAO system, although documented to govern the ecosystem dynamics over many other regions, does not have a consistent impact on the ecosystem over the Sahel. Therefore, the NAO index cannot produce a useful prediction on the ecosystem variability and changes in this region. This study provides an example that correlations based on short climate and ecological records (less than 20 years in this case) can be spurious and potentially misleading.
Why are estimates of the terrestrial carbon balance so different?
Authors: HOUGHTON R. A. 
Published: December 2004

AbstractThe carbon balance of the world's terrestrial ecosystems is uncertain. Both top‐down (atmospheric) and bottom‐up (forest inventory and land‐use change) approaches have been used to calculate the sign and magnitude of a net terrestrial flux. Different methods often include different processes, however, and comparisons can be misleading. Differences are not necessarily the result of uncertainties or errors, but often result from incomplete accounting inherent in some of the methods. Recent estimates are reviewed here. Overall, a northern mid‐latitude carbon sink of approximately 2 Pg C yr−1 appears robust, although the mechanisms responsible are uncertain. Several lines of evidence point to environmentally enhanced rates of carbon accumulation. Other lines suggest that recovery from past disturbances is largely responsible for the sink. The tropics appear to be a small net source of carbon or nearly neutral, and the same uncertainties of mechanism exist. In addition, studies in the tropics do not permit an unequivocal choice between two alternatives: large emissions of carbon from deforestation offset by large sinks in undisturbed forests, or moderate emissions from land‐use change with essentially no change in the carbon balance in undisturbed forests. Resolution of these uncertainties is most likely to result from spatially detailed historical reconstructions of land‐use change and disturbance in selected northern mid‐latitude regions where such data are available, and from systematic monitoring of changes in the area of tropical forests with satellite data of high spatial resolution collected over the last decades and into the future.
The annual carbon budget of a French pine forest (Pinus pinaster) following harvest
Authors: KOWALSKI S. , SARTORE M. , BURLETT R. , BERBIGIER P. , LOUSTAU D. 
Published: December 2004

AbstractEddy covariance measurements of net ecosystem exchange (NEE) of carbon dioxide and sensible and latent heat have operated since clear felling of a 50‐year old maritime pine stand in Les Landes, in Southwestern France. Turbulent fluxes from the closed‐path system are computed via different methodologies, including those recommended from EUROFLUX (Adv. Ecol. Res. 30 (2000) 113; Agric. Forest Meteorol. 107 (2001a, b) 43 and 71), and sensitivity analysis demonstrates the merit of post‐processing for accurate flux calculation. Footprint modeling, energy balance closure, and empirical modeling corroborate the eddy flux measurements, indicating best reliability in the daytime.The ecosystem, a net source of atmospheric CO2, is capable of fixing carbon during fair weather during any season due to the abundance of re‐growing species (mostly grass), formerly from the understorey. Annual carbon loss of 200–340 g m−2 depends on the period chosen, with inter‐annual variability evident during the 18‐month measurement period and apparently related to available light. Empirical models, with weekly photosynthetic parameters corresponding to seasonal vegetation and respiration depending on soil temperature, fit the data well and allow partitioning of annual NEE into GPP and TER components. Comparison with a similar nearby mature forest (Agric. Forest Meteorol. 108 (2001) 183) indicates that clear‐cutting reduces GPP by two thirds but TER by only one third, transforming a strong forest sink into a source of CO2. Likewise, the loss of 50% of evapotranspiration (by the trees) leads to increased temperatures and thus reduced net radiation (by one third), and a 50% increase in sensible heat loss by the clear cut.
Climate and CO2 controls on global vegetation distribution at the last glacial maximum: analysis based on palaeovegetation data, biome modelling and palaeoclimate simulations
Authors: HARRISON SANDY P. , PRENTICE COLIN I. 
Published: December 2004

AbstractThe global vegetation response to climate and atmospheric CO2 changes between the last glacial maximum and recent times is examined using an equilibrium vegetation model (BIOME4), driven by output from 17 climate simulations from the Palaeoclimate Modelling Intercomparison Project. Features common to all of the simulations include expansion of treeless vegetation in high northern latitudes; southward displacement and fragmentation of boreal and temperate forests; and expansion of drought‐tolerant biomes in the tropics. These features are broadly consistent with pollen‐based reconstructions of vegetation distribution at the last glacial maximum. Glacial vegetation in high latitudes reflects cold and dry conditions due to the low CO2 concentration and the presence of large continental ice sheets. The extent of drought‐tolerant vegetation in tropical and subtropical latitudes reflects a generally drier low‐latitude climate. Comparisons of the observations with BIOME4 simulations, with and without consideration of the direct physiological effect of CO2 concentration on C3 photosynthesis, suggest an important additional role of low CO2 concentration in restricting the extent of forests, especially in the tropics. Global forest cover was overestimated by all models when climate change alone was used to drive BIOME4, and estimated more accurately when physiological effects of CO2 concentration were included. This result suggests that both CO2 effects and climate effects were important in determining glacial‐interglacial changes in vegetation. More realistic simulations of glacial vegetation and climate will need to take into account the feedback effects of these structural and physiological changes on the climate.
Uncertainties in interpretation of isotope signals for estimation of fine root longevity: theoretical considerations
Authors: LUO YIQI 
Published: December 2004

AbstractThis paper examines uncertainties in the interpretation of isotope signals when estimating fine root longevity, particularly in forests. The isotope signals are depleted δ13C values from elevated CO2 experiments and enriched Δ14C values from bomb 14C in atmospheric CO2. For the CO2 experiments, I explored the effects of six root mortality patterns (on–off, proportional, constant, normal, left skew, and right skew distributions), five levels of nonstructural carbohydrate (NSC) reserves, and increased root growth on root δ13C values after CO2 fumigation. My analysis indicates that fitting a linear equation to δ13C data provides unbiased estimates of longevity only if root mortality follows an on–off model, without dilution of isotope signals by pretreatment NSC reserves, and under a steady state between growth and death. If root mortality follows the other patterns, the linear extrapolation considerably overestimates root longevity. In contrast, fitting an exponential equation to δ13C data underestimates longevity with all the mortality patterns except the proportional one. With either linear or exponential extrapolation, dilution of isotope signals by pretreatment NSC reserves could result in overestimation of root longevity by several‐fold. Root longevity is underestimated if elevated CO2 stimulates fine root growth. For the bomb 14C approach, I examined the effects of four mortality patterns (on–off, proportional, constant, and normal distribution) on root Δ14C values. For a given Δ14C value, the proportional pattern usually provides a shorter estimate of root longevity than the other patterns. Overall, we have to improve our understanding of root growth and mortality patterns and to measure NSC reserves in order to reduce uncertainties in estimated fine root longevity from isotope data.