bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crayfish as geomorphic agents and ecosystem engineers: effect of a biomass gradient on baseflow and flood‐induced transport of gravel and sand in experimental streams
Authors: Statzner B. , Peltret O. , Tomanova S. 
Published: March 2003

SUMMARY 1. Using experimental streams, we studied the impact of the crayfish Orconectes limosus on (i) the transport of gravel and sand at baseflow; (ii) the sediment surface (bedform, particle consolidation, proportion of sand, algal and gravel cover); and (iii) the critical shear stress (τC) causing incipient gravel and sand motion during simulated floods. We examined (i) and (ii) in experimental outdoor flumes that replicated riffle‐pool sequences and (iii) in a larger laboratory flume, in which we exposed sediments retrieved from the outdoor flumes to a progressively increasing discharge.2. Habitat changes induced by crayfish, such as bedform alterations in riffles (downstream displacement of riffle heads) and the increase of gravel on sand dunes in pools, had major impacts on the spatial and temporal patterns of the baseflow transport of gravel and sand.3. In addition to their impact on bedform in riffles and on gravel cover in pools, crayfish prevented the physical consolidation of particles in riffles and reduced the algal cover and the proportion of sand in the surface layer in both riffles and pools. These crayfish impacts on sediment surface variables had complex, interacting effects on the mobilisation of gravel and sand during subsequent flood simulations. For sand, crayfish progressively decreased the τC (i.e. the sum of bedform drag and skin friction) by about 50% along the entire biomass gradient in pools, whereas the presence of crayfish abruptly decreased the τC by about 75% in riffles. For gravel, the discharge causing motion in riffles produced a shear stress (in terms of skin friction) on an even bedform that was about 75% lower in all flumes with crayfish compared with the flumes without crayfish. Crayfish had no impact on τC for gravel in pools.4. Scaling‐up these experimental results to real streams suggests that crayfish could affect the patch dynamics of major sediment transport events and habitat suitability for other organisms that, at larger spatial scales, could increase the overall spatio‐temporal habitat diversity and thus the overall structural and functional biodiversity of lotic communities.
Leaf litter decomposition and microbial activity in nutrient‐enriched and unaltered reaches of a headwater stream
Authors: Gulis V. , Suberkropp K. 
Published: March 2003

SUMMARY 1. Decomposition of red maple (Acer rubrum) and rhododendron (Rhododendron maximum) leaves and activity of associated microorganisms were compared in two reaches of a headwater stream in Coweeta Hydrologic Laboratory, NC, U.S.A. The downstream reach was enriched with ammonium, nitrate, and phosphate whereas the upstream reach was not altered.2. Decomposition rate, microbial respiration, fungal and bacterial biomass, and the sporulation rate of aquatic hyphomycetes associated with decomposing leaf material were significantly higher for both leaf types in the nutrient‐enriched reach. Species richness and community structure of aquatic hyphomycetes also exhibited considerable changes with an increase in the number of fungal codominants in the nutrient‐enriched reach.3. Fungal biomass was one to two orders of magnitude greater than bacterial biomass in both reaches. Changes in microbial respiration rate corresponded to those in fungal biomass and sporulation, suggesting a primary role of fungi in leaf decomposition.4. Nutrient enrichment increased microbial activity, the proportion of leaf carbon channelled through the microbial compartment and the decomposition rate of leaf litter.
Vegetation abundance in lowland flood plan lakes determined by surface area, age and connectivity
Authors: Van Geest G. J. , Roozen F. C. J. M. , Coops H. , Roijackers R. M. M. , Buijse A. D. , Peeters E. T. H. M. , Scheffer M. 
Published: March 2003

SUMMARY 1. We analysed the vegetation structure of 215 lakes in the flood plain of the river Lower Rhine in relation to environmental variables related to hydrological connectivity, lake morphometry, lake age and land use on adjacent land.2. The frequency distribution of the cover of submerged macrophytes was not normal, implying that submerged macrophytes in any one lake were either scarce or abundant.3. We observed clear water lakes with submerged macrophyte dominance over a wide range of total P concentration (0.020–0.40 mg total P L−1).4. Multiple logistic regression indicated that the probability of dominance by submerged macrophytes decreased markedly with the surface area, depth and age of the lakes. The surface area effect occurred independently of the depth. Further, there was a negative relationship between submerged macrophyte dominance and the long‐term annual duration of inundation by the river.5. Nymphaeid cover showed a distinct optimum with respect to mean lake depth, being almost absent in lakes shallower than 0.5 m. In contrast to what was found for submerged plants, the probability of occurrence of nymphaeids increased with lake age.6. The probability of helophyte occurrence increased with lake age, and decreased with the presence of trees, cattle grazing, surface area, use of manure and mean lake depth.7. In all cases the critical level of one factor (e.g. mean lake depth) depended on other factors (e.g. surface area or age of lake). Thus, in the present study, small lakes tended to remain dominated by submerged macrophytes up to a greater depth than large lakes, and helophytes colonised smaller lakes in an earlier phase.8. The effect of inundation by the river was modest. This could be because most of our lakes are rarely inundated during the growing season and experience only moderate current velocities while flooded.9. The results have practical implications for future management of flood plains for conservation purposes. In new water bodies, macrophyte domination will be promoted if many small shallow lakes, rather than few large deep ones, are excavated.
Colony performance and immunocompetence of a social insect, Bombus terrestris, in poor and variable environments
Authors: Schmid‐Hempel R. , Schmid‐Hempel P. 
Published: March 2003

1. Feeding and defence against parasites are among the major simultaneous requirements for survival and successful reproduction of any animal, including colonies of social insects. Harsh environments may therefore not only negatively affect overall success, but force animals to allocate resources in different ways, for example, to reduce immune defence under adverse conditions while maintaining growth rate. 2. This study examines how colony growth, reproduction and immune defence of the bumble bee, Bombus terrestris, varies with environmental condition. In particular, the manner in which limited or unpredictable food availability affects the number and size of workers and sexuals produced, the timing of reproduction, and the level of encapsulation of a novel antigen was tested. A new experimental paradigm was applied by splitting colonies into two halves while ensuring integrity by regular swaps of the residing queen. 3. The results show that limited food availability, as expected, led to fewer and smaller workers and sexuals. Unpredictable food availability, in contrast, was associated with higher numbers of workers and heavier sexuals. Also, reproductive success was highest under unpredictable conditions, due to an increased rate of collection of resources. 4. The timing of reproduction did not vary among treatments. Contrary to expectation, also immunocompetence did not vary among treatments.
The effect of time and digestion constraints in Common Eiders while feeding and diving over Blue Mussel beds
Authors: Guillemette M. 
Published: March 2003

1. To maintain energy intake Common Eiders (Somateria mollissima) in winter should compensate for reduced day‐length by increasing both the proportion of time spent feeding and diving efficiency, defined as the proportional duration of a dive bout within a dive cycle. Common Eiders swallowed Blue Mussel (Mytilus edulis) whole with their shells where any behavioural compensation in relation to short days may be limited by digestive processes. 2. Based on time budget studies conducted from mid‐December to the end of April in the Gulf of St. Lawrence, Québec, Canada, diving and feeding efficiency were compared for three seasonal periods varying in day‐length (from 557 to 890 min). 3. Results showed that eiders were compensating for short days by feeding 56% of the time in mid‐winter compared with 33% in spring. However, diving efficiency remained constant through the season and apparently no compensation occurred at this level of their foraging behaviour. Despite this, the daily rate of prey ingestion was much higher in mid‐winter than in spring. 4. Ingestion rate values for mid‐winter individuals approached or even exceeded the rate at which prey items are defecated and it was concluded that shell crushing performed by the muscular gizzard is physiologically more demanding during that period. On this basis, gizzard mass should be larger in winter when ingestion rates are higher. Data presented support that hypothesis and suggest that compensation in relation to short days can be both behavioural and physiological.
Consistencies in post‐dispersal seed predation of temperate fleshy‐fruited species among seasons, years and sites
Authors: Kollmann J. , Coomes D. A. , White S. M. 
Published: March 2003

1. Seed predation of 12 fleshy‐fruited species was recorded in experimental dishes under early successional forest in south‐west Germany (four seasons 1992 and 1993) and in south England (summer 1995). On each occasion, 200 dishes were laid out, each containing five seeds of a given species. The mean time for three or more seeds to be removed was taken as a measure of granivore preferences. We tested correlations of these preferences with several physical and nutritional seed traits. 2. Live trapping and selectively accessible dishes indicated that rodents were the major granivores (Apodemus sylvaticus, Apodemus flavicollis, Clethrionomys glareolus); no predation by birds or insects was observed. The rank order of the rodents’ seed preferences was consistent among sites, seasons and years, but mean predation differed between species, sites and seasons. Seed predation was highest in summer and lowest in winter. Possible implications of the seasonal pattern in predation risk are discussed. 3. The preferences of rodents were significantly correlated with the species‐specific viability of seeds (i.e. percentage of sound seed) in five of eight experiments and with the percentage of water in the embryo‐plus‐endosperm fraction (EEF) in four of eight experiments. Surprisingly, preferences were not correlated to seed mass, EEF mass or nitrogen concentration. Predation was lowest among toxic species (Berberis vulgaris, Euonymus europaeus, Sambucus nigra) and among species with woody endocarps (Cornus sanguinea, Crataegus spp.).
Energetic stress, immunosuppression and the costs of an antibody response
Authors: Svensson E. , RÅberg L. , Koch C. , Hasselquist D. 
Published: March 2003

1. Recently, there has been much interest in physiological trade‐offs between parasite resistance and fitness‐related traits such as secondary sexual characters or reproductive effort. More specifically it has been suggested that (i) energetically costly activities may suppress the immune system and (ii) that this immunosuppression is caused by costly immune defences competing with other bodily demands for scarce resources, e.g. energy. 2. The possibility was investigated of an energetically based trade‐off between humoral (antibody‐based) immunocompetence and other costly activities, by immunizing Blue Tits, Parus caeruleus, with novel antigens (proteins) thereby inducing antibody responses, and performing two experiments. In experiment 1, one group of birds was subjected to cold stress, thereby increasing their daily energy expenditure and the effect on immune responsiveness was investigated. In experiment 2, the basal metabolic rate (BMR) of immunized birds was measured to investigate the energetic costs of mounting the antibody responses. 3. In experiment 1, birds subject to increased energy turnover had significantly lower antibody responses, consistent with the hypothesis that environmental stress could suppress immunocompetence. However, in experiment 2 the energetic costs of these antibody responses were found to be low and at most 8–13% of BMR, indicating that adaptive resource allocation of energy was an unlikely explanation for the lowered immune responsiveness in the cold stress treatment (experiment 1). 4. It is concluded that our data provide some support to the idea that there may be a trade‐off between immunocompetence and energetically costly activities such as thermoregulation, reproduction or mate attraction, although this trade‐off may not necessarily be based on energy or nutrient limitation (i.e. resource allocation models). Two non‐energetic explanations are briefly discussed, one adaptive and one non‐adaptive, that could explain the immunosuppression in our study as well as in other behavioural and ecological contexts.
Ejaculate production schedule and the degree of protandry in fishflies (Megaloptera: Corydalidae)
Authors: HAYASHI F. 
Published: March 2003

1. To examine the relationship between male–female emergence patterns and ejaculate dynamics, patterns producing sperm and seminal fluids in male internal reproductive organs, the size of a spermatophore transferred at mating and the fate of spermatophore contents moved into female storage organs were compared among the fishflies (Megaloptera: Corydalidae: Chauliodinae), Parachauliodes continentalis, P. japonicus and Neochauliodes sinensis. 2. Spermatophore contents moved into female storage organs decreased rapidly in P. japonicus and N. sinensis, but hardly at all in P. continentalis. This suggests that the females of the former two species may remate sooner than the latter species as it is known in insects that material remaining in the storage organs mechanically inhibits receptivity to mating. 3. Male P. japonicus and N. sinensis increased in internal reproductive organ mass continuously after adult eclosion, and the spermatophore size produced at the first mating increased with male age. In contrast, the internal reproductive organs of P. continentalis were relatively small and did not increase in mass after emergence. P. continentalis transferred a constantly smaller spermatophore at any copulation than the former two species. 4. Males of P. japonicus and N. sinensis emerged earlier than females, while P. continentalis showed a nearly simultaneous emergence pattern between the sexes. It seems that males of P. japonicus and N. sinensis (more polyandrous than P. continentalis) inhibit female receptivity for a longer time period by emerging earlier and transferring larger ejaculates. In these two species, the number of sperm ejaculated at the first mating also increased with male age. The increase in sperm number by emerging earlier may be adaptive for the males owing to numerical sperm competition when the female remates.
A novel indicator of reducing conditions and water‐table depth in mires
Authors: Belyea L. R. 
Published: March 2003

1. Direct measurements of water‐table depth in a mire were compared with depth to discolouration of polyvinyl chloride (PVC) tape left in situ for 15 months. Discolouration depth was highly correlated with positions of highest and lowest water tables; estimates were systematically biased but generally within 5 cm of measured values. 2. The annual range in water‐table position indicated by discolouration depth varied 10‐fold along a 30 m transect. Discolouration of PVC tape is an indicator of reducing conditions that could be applied in extensive surveys at very low cost.
Reproductive allocation and seed production in Bromus madritensis ssp. rubens at elevated atmospheric CO2
Authors: Huxman T. E. , Hamerlynck E. P. , Smith S. D. 
Published: March 2003

1. Two trends are consistent across the response of plant species to growth at elevated CO2: decreased leaf nitrogen content and increased photosynthetic gas exchange. While both of these are very important to the understanding of plant and ecosystem responses to climate change, little research has evaluated the consequences of these patterns on reproductive allocation and seed production. 2. For this reason, Bromus madritensis ssp. rubens was grown in ambient (360 μmol mol–1), × 1·5 ambient (550 μmol mol–1) and elevated (700 μmol mol–1) CO2 environments to compare the relationship between allocation to growth and reproduction as a function of CO2 growth environment. 3. There were no differences in final total biomass or reproductive mass between CO2 growth environments. There were significant decreases in reproductive mass per unit total mass and per unit vegetative mass, but not per unit leaf surface area (LSA), as growth CO2 environment increased from 360 to 700 μmol mol–1 CO2. Despite these decreases, the number of seeds produced per unit LSA in elevated CO2 significantly increased as compared to ambient CO2. These results may be owing to a shift in allocation to greater investment in vegetative growth as compared to reproduction under elevated levels of atmospheric CO2. 4. Prior to reproduction, there were no significant differences between CO2 treatments in carbon uptake by leaves. In contrast, plants grown in elevated CO2 did not show a decline in photosynthetic rate during seed filling, suggesting that nitrogen may not have been re‐translocated from leaves to seeds as apparently occurred in ambient plants. 5. Patterns measured here may partially explain the parental effect of CO2 environment exhibited in Bromus. Seeds produced from elevated parental CO2 growth conditions lead to seedlings that produce smaller leaves that are delayed in development and smaller roots as compared to structures produced by seeds from ambient‐grown parents. 6. Because the success of Bromus is partially owing to its ability to produce large numbers of viable seeds, these changes in reproductive allocation and subsequent seedling performance with respect to growth in an elevated CO2 environment may have impacts on community composition in the Mojave Desert.
Settlement of barnacle larvae is governed by Euclidean and not fractal surface characteristics
Authors: Hills J. M. , Thomason J. C. , Muhl J. 
Published: March 2003

1. Extensive research has been carried out on the biological, physical and chemical characteristics of surfaces that promote, or prevent, marine fouling. The texture of the substratum is probably the most important factor affecting settlement of the Acorn Barnacle Semibalanus balanoides in the field. The aim of this study was to examine the relationship between fractal and Euclidean descriptions of substratum surface complexity and settlement of the Acorn Barnacle. 2. Replicate settlement panels with smooth, fine, medium and coarse surfaces were manufactured using a precise and accurate technique. Two‐dimensional profiles were measured using a laser profilometer, and two surface complexity indices, potential settling sites (PSS) and the Minkowski fractal dimension (MFD) were calculated. PSS is a Euclidean measure of the surface complexity taking into account the body size and settlement behaviour of the barnacle larvae, whereas MFD is a fractal dimension related to the complexity of the surface at a variety of scales. 3. In a field experiment, settlement density of S. balanoides was positively related to both PSS and MFD. To break the correlation between PSS and MFD, surfaces were modified by sandblasting with either 64–125‐μm or 250–500‐μm grains. This decreased MFD but did not affect PSS. 4. A further field experiment found that this erosion using small‐scale sand particles had no effect on settlement of the barnacle. It was concluded that S. balanoides larvae were responding to characteristics of the surface related to PSS and not MFD. 5. Although a correlation was found between species abundance and the fractal complexity of its habitat, further experimentation showed that there was no causality in this relationship. Many surveys, with no experimentation, of aquatic and terrestrial communities have shown relationships between organisms and their habitat and assumed causality; however, care must be taken in interpretation of such studies.
Acclimation for heat resistance in Trichogramma nr. brassicae: can it occur without costs?
Authors: Hoffmann A. A. , Hewa‐Kapuge S. 
Published: March 2003

Abstract1. It is well known that animals can increase their stress resistance by prior exposure to sub‐lethal conditions, but this acclimation process is often accompanied by deleterious fitness effects. These may reflect a cost of acclimation, or more general costs arising from damage due to sub‐lethal exposures.2. Acclimation for increased adult resistance to a 40 °C heat shock was tested in the egg parasitoid, Trichogramma nr. brassicae, following exposure of immature stages to 33 °C for different periods. Prepupal exposure did not increase heat resistance, but daily exposures at the pupal stage for 2 h day−1 and 3 h day−1 over 4 days increased survival of the shock.3. Pre‐pupal exposure for 3 h day−1 over 4 days led to decreased parasitism reflecting general damage costs. Pupal exposure for 3 h day−1 and 4 h day−1 also decreased parasitism rates, but there were no deleterious effects when pupae were acclimated for 2 h day−1.4. These findings indicate that acclimation can occur without costs in Trichogramma nr. brassicae and suggest a general phenotypic approach for separating acclimation costs from other fitness costs caused by sub‐lethal exposures. The potential for using acclimation to increase field parasitism success of this important group of parasitoids is discussed.
Is hormesis an evolutionary expectation?
Authors: Forbes V. E. 
Published: March 2003

Abstract1. This paper approaches the phenomenon of hormesis (i.e. stimulatory effects occurring in response to low levels of exposure to agents that are harmful at high levels of exposure) from an evolutionary perspective and addresses three questions related to its occurrence and consequences: (1) Is the occurrence of hormesis to be expected on the basis of evolutionary arguments? (2) Considering selection as a driving force in the evolution of hormesis, is it likely that certain aspects of organism performance have a greater tendency than others to exhibit hormesis? (3) What are the practical implications of hormesis for ecological risk assessment?2. Several hypotheses are presented to explain the observations of hormesis, and a literature review is used to assess the evidence for hormesis of various fitness‐related traits.3. To avoid statistical artefacts, it is essential that the underlying distribution of traits that appear to show hormesis be examined, particularly as many of them may be expected to deviate from normality.4. The occurrence of hormesis of individual life‐history traits can be explained as an evolutionary adaptation that acts to maintain fitness in a changing environment.5. As a result of energetic trade‐offs among life‐history traits, not all traits are likely to exhibit hormesis simultaneously, and therefore overall fitness is not likely to be enhanced at low levels of exposure to toxic agents. Because toxic agents affect different traits in different directions and to different degrees, interpreting the ecological consequences of hormesis of any single trait is not possible without examining it in relation to overall effects on fitness.