bluuebunny/crossref_metadata_2025 huggingface dataset:
River regulation and fish larvae: variation through space and time
Authors: HUMPHRIES PAUL , SERAFINI LUCIANO G. , KING ALISON J.
Published: March 2003

1. Patterns in abundance and distribution of larval fish in a heavily regulated and a mildly regulated Australian lowland river were compared over four breeding seasons to gain some insight into how river regulation affects fish populations.

2. Larvae from a total of 13 species from nine families were recorded from the two rivers. The mildly regulated Broken River supported twice as many species as the heavily regulated Campaspe River. The two rivers shared three introduced species but only two native species. The dominant species in the Campaspe was not found in the Broken River.

3. The two most abundant species in the Campaspe were classified as `opportunists'. They are small, short‐lived species, which spawn for up to 9 months, encompassing extremes in temperature and flow. The extended spawning period may place a subset of larvae in optimal conditions for recruitment and is hypothesised as being the key to the success of these species.

4. Most species spawned each year, despite large interannual variation in flow and temperature conditions. Poor recruitment over several decades, rather than a failure to spawn, is considered the most likely explanation for differences in the larval fish faunas between the two rivers.

5. The highly regulated section of the Campaspe River downstream of the regulating impoundment is thought to provide suboptimal habitat conditions for larvae relative to the less regulated downstream sections.

6. The timing of occurrence of larvae of the dominant species varied by breeding season and may be the result of flexibility in the timing of spawning.
Development and validation of a fish‐based index for the assessment of ‘river health’ in France
Authors: Oberdorff Thierry , Pont Didier , Hugueny Bernard , Porcher Jean‐Pierre
Published: March 2003

SUMMARY 1. In Europe, water policy is currently undergoing considerable change as emphasised by the recent European Water Framework Directive (WFD), which requires the restoration and maintenance of ‘healthy’ aquatic ecosystems by the assessment of their hydromorphological, chemical and biological characteristics. If the requirements of the WFD are to be met, effective biological tools are needed to measure the ‘health’ of rivers at scales large enough to be useful for management. These tools need to be ecologically based, efficient, rapid and applicable in different ecological regions. Among potential indicators, fish assemblages are of particular interest because of their ability to integrate environmental variability at different spatial scales. To meet the goals of the WFD, the French Water Agencies and the Ministry of the Environment initiated a research programme to develop a fish‐based index that would be applicable nationwide.

2. A variety of metrics based on occurrence and abundance data and reflecting different aspects of the fish assemblage structure and function were selected from available literature and for their potential to indicate degradation.

3. Logistic and multiple linear regression procedures were applied, using an initial data set of 650 reference sites fairly evenly distributed across French rivers and defined by some easily measured regional and local characteristics, to elaborate the simplest possible response model that adequately explained the observed patterns of each metric for a given site.

4. Models obtained for each metric were validated using two independent data sets of 88 reference sites and 88 disturbed sites. These procedures allowed us to select the most effective metrics in discriminating between reference and disturbed sites.
Sampling variation in macroinvertebrate data and implications for river quality indices
Authors: Clarke R. T. , Furse M. T. , Gunn R. J. M. , Winder J. M. , Wright J. F.
Published: March 2003

SUMMARY 1. The EC Water Framework Directive (2000/60/EC) recognises the need for biological monitoring. Indices derived from standard samples of macroinvertebrates are frequently used for the appraisal of the ecological quality of rivers. However, information on the errors or chance variation that can influence the value of an index is also important.

2. This paper describes a study to quantify the observed sampling variation in three ecological indices based on the Biological Monitoring Working Party (BMWP) score system across a wide range of river types and qualities. The indices are number of BMWP taxa, BMWP score and Average Score Per Taxon (ASPT).

3. The study sites were selected to encompass the four major groups within the River InVertebrate Prediction And Classification System (RIVPACS) site classification for Britain. Within each group, four sites which differed in ecological quality grade were chosen (total of 16 sites). At each site three standard RIVPACS samples were taken in each of spring, summer and autumn by trained staff. In each season, two samples were taken by one biologist and the third by a different individual to allow for within and between‐operator variation.

4. The effects of sampling variation within a season on the number of taxa, BMWP score and ASPT across all sites, irrespective of operator, could be represented by some simple parameters. We found that the sampling SD of the square root of the number of taxa, square root of BMWP score and the untransformed ASPT were roughly constant in each case, irrespective of site type or quality. For each index, SD for two and three seasons combined samples were smaller than for single season samples.

5. Inter‐operator influences on sample values were negligible (4–12% of total sampling SD) in this study. This underlines the importance of adequate training for all staff involved in extensive monitoring programmes which use standard procedures from one year to the next, but may involve different staff.

6. Indices for number of taxa, BMWP score and ASPT were all estimated with greater precision from combined season samples than from the averages of two or three seasons' samples.

7. This study enables us to estimate confidence intervals for the values of the number of taxa, BMWP score and ASPT based on single season, two or three season combined samples collected using standard RIVPACS procedures for any river site in Britain. The results can also be used in simulation models which incorporate the effects of sampling variation into assessments of the ecological quality of river sites based on the ratio of observed to RIVPACS expected values of these BMWP indices.
Riverine landscape diversity
Authors: WARD J. V. , TOCKNER K. , ARSCOTT D. B. , CLARET C.
Published: March 2003

1. This review is presented as a broad synthesis of riverine landscape diversity, beginning with an account of the variety of landscape elements contained within river corridors. Landscape dynamics within river corridors are then examined in the context of landscape evolution, ecological succession and turnover rates of landscape elements. This is followed by an overview of the role of connectivity and ends with a riverine landscape perspective of biodiversity.

2. River corridors in the natural state are characterised by a diverse array of landscape elements, including surface waters (a gradient of lotic and lentic waterbodies), the fluvial stygoscape (alluvial aquifers), riparian systems (alluvial forests, marshes, meadows) and geomorphic features (bars and islands, ridges and swales, levees and terraces, fans and deltas, fringing floodplains, wood debris deposits and channel networks).

3. Fluvial action (erosion, transport, deposition) is the predominant agent of landscape evolution and also constitutes the natural disturbance regime primarily responsible for sustaining a high level of landscape diversity in river corridors. Although individual landscape features may exhibit high turnover, largely as a function of the interactions between fluvial dynamics and successional phenomena, their relative abundance in the river corridor tends to remain constant over ecological time.

4. Hydrological connectivity, the exchange of matter, energy and biota via the aqueous medium, plays a major though poorly understood role in sustaining riverine landscape diversity. Rigorous investigations of connectivity in diverse river systems should provide considerable insight into landscape‐level functional processes.

5. The species pool in riverine landscapes is derived from terrestrial and aquatic communities inhabiting diverse lotic, lentic, riparian and groundwater habitats arrayed across spatio‐temporal gradients. Natural disturbance regimes are responsible for both expanding the resource gradient in riverine landscapes as well as for constraining competitive exclusion.

6. Riverine landscapes provide an ideal setting for investigating how complex interactions between disturbance and productivity structure species diversity patterns.
Aquatic invertebrates in riverine landscapes
Authors: MALMQVIST BJÖRN
Published: March 2003

1. Riverine systems consist of a mosaic of patches and habitats linked by diverse processes and supporting highly complex communities. Invertebrates show a high taxonomic and functional diversity in riverine systems and are in several ways important components of these systems. Their distribution patterns, movements and effects on ecological flows, testify to their importance in various landscape ecological processes. This paper reviews the invertebrate literature with respect to patterns and processes in the riverine landscape.

2. The distribution of invertebrates in riverine habitats is governed by a number of factors that typically act at different scales. Hence, the local community structure can be seen as the result of a continuous sorting process through environmental filters ranging from regional or catchment‐wide processes, involving speciation, geological history and climate, to the small‐scale characteristics of individual patches, such as local predation risk, substratum porosity and current velocity.

3. Dispersal is an important process driving invertebrate distribution, linking different ecological systems across boundaries. Dispersal occurs within the aquatic habitat as well as into the terrestrial surrounding, and also over land to other waterbodies. New genetic techniques have contributed significantly to the understanding of aquatic invertebrate dispersal and revealed the importance of factors such as physical barriers, synchrony of emergence and taxonomic affiliation.

4. Invertebrates affect the cycling of nutrients and carbon by being a crucial intermediate link between primary producers, detritus pools or primary consumers, and predators higher up in the trophic hierarchy. Suspension feeders increase the retention of carbon. The subsidies of aquatic invertebrates to the terrestrial ecosystem have been shown to be important, as are reciprocal processes such as the supply of terrestrial invertebrates that fall into the water.

5. Future studies are needed both to advance theoretical aspects of landscape ecology pertaining to the invertebrates in riverine systems and to intensify the experimental testing of hypotheses, for example with respect to the scaling of processes and to linkages between the terrestrial and aquatic systems. Another promising avenue is to take advantage of naturally steep environmental gradients, and of systems disturbed by humans, such as regulated rivers. By comparison with unimpaired reference sites, the mechanisms involved might be identified. The use of `natural' experiments, especially where environmental gradients are steep, is another technique with great potential.
Genetic population structure and dispersal in Atlantic Island caddisflies
Authors: Kelly Lucy C. , Rundle Simon D. , Bilton David T.
Published: March 2003

SUMMARY 1. Population genetic structure of Wormaldia tagananana, a caddis with a narrow geographic range and endemic to the Canary Islands, was investigated by studying allozyme variation at 11 putative loci in five of the eight extant populations on Tenerife and La Gomera. Genetic variability, population structure and gene flow were compared with those reported previously in more widespread Trichoptera, particularly Canarian populations of the non‐endemic limnephilid Mesophylax aspersus, to examine the hypothesis that the Wormaldia, with its restricted range, would exhibit relatively little genetic variability and gene flow.

2. Despite it being a narrow‐range island endemic, genetic variability in populations of W. tagananana is broadly similar to values reported for more widespread caddis.

3. Significant genetic population structure was observed in W. tagananana (overall FST = 0.387), greater than that seen in M. aspersus and amongst the highest reported for lotic caddis to date. Several site‐ and island‐specific alleles were reported, providing further evidence for the relative isolation of individual Wormaldia populations.

4. Significant deviations from Hardy–Weinberg equilibrium were found in four of five populations (overall FIS = 0.675). This could result from within‐locality population substructuring, or offspring within a reach being the product of a limited number of matings.

5. This genetic evidence supports the hypothesis that the restricted range of W. tagananana is, at least in part, because of limited dispersal ability.
Riverine landscapes: an introduction
Authors: TOCKNER K. , WARD J. V. , EDWARDS P. J. , KOLLMANN J.
Published: March 2003

1. This paper is an introduction to a special issue of Freshwater Biology containing selected papers from the First International Symposium on Riverine Landscapes held in March 2001 in Switzerland.

2. The primary goal of the symposium was to synthesise present understanding of riverine landscapes from the perspectives of different disciplines. A landscape approach was used to address interactions between patterns and processes, in the context of spatial heterogeneity, across scales in physical and biological systems.

3. The three main themes were: (i) hydrogeomorphic processes, (ii) biological dynamics and (iii) human influences in riverine landscapes.
A comparison of statistical approaches for modelling fish species distributions
Authors: Olden Julian D. , Jackson Donald A.
Published: March 2003

SUMMARY1. The prediction of species distributions is of primary importance in ecology and conservation biology. Statistical models play an important role in this regard; however, researchers have little guidance when choosing between competing methodologies because few comparative studies have been conducted.

2. We provide a comprehensive comparison of traditional and alternative techniques for predicting species distributions using logistic regression analysis, linear discriminant analysis, classification trees and artificial neural networks to model: (1) the presence/absence of 27 fish species as a function of habitat conditions in 286 temperate lakes located in south‐central Ontario, Canada and (2) simulated data sets exhibiting deterministic, linear and non‐linear species response curves.

3. Detailed evaluation of model predictive power showed that approaches produced species models that differed in overall correct classification, specificity (i.e. ability to correctly predict species absence) and sensitivity (i.e. ability to correctly predict speciespresence) and in terms of which of the study lakes they correctly classified. Onaverage, neural networks outperformed the other modelling approaches, although all approaches predicted species presence/absence with moderate to excellent success.

4. Based on simulated non‐linear data, classification trees and neural networks greatly outperformed traditional approaches, whereas all approaches exhibited similar correct classification rates when modelling simulated linear data.

5. Detailed evaluation of model explanatory insight showed that the relative importance of the habitat variables in the species models varied among the approaches, where habitat variable importance was similar among approaches for some species and very different for others.

6. In general, differences in predictive power (both correct classification rate and identity of the lakes correctly classified) among the approaches corresponded with differences in habitat variable importance, suggesting that non‐linear modelling approaches (i.e. classification trees and neural networks) are better able to capture and model complex, non‐linear patterns found in ecological data. The results from the comparisons using simulated data further support this notion.

7. By employing parallel modelling approaches with the same set of data and focusing on comparing multiple metrics of predictive performance, researchers can begin to choose predictive models that not only provide the greatest predictive power, but also best fit the proposed application.
Biomanipulation of lake ecosystems: an introduction
Authors: Kasprzak P. , Benndorf J. , Mehner T. , Koschel R.
Published: March 2003

SUMMARY 1. This paper is an introduction to a special issue of Freshwater Biology containing selected papers from an international symposium on Food Web Effects of Fish in Lake Ecosystems: Research Progress, Water Quality and Fisheries Management held from 31 May to 3 June 2000 in Rheinsberg, Germany. The primary goal of the workshop was to enlarge the current view of fish‐induced effects on lake ecosystems. An additional goal was to promote biomanipulation as a multiple‐use tool for managing freshwater ecosystems.

2. The three main topics addressed at the workshop were: (i) mechanisms involved in biomanipulation, (ii) whole‐lake case studies and (iii) management aspects in water quality and fisheries.

3. Mortality of Daphnia, nutrient recycling, habitat selection and fish predation are reported as important mechanisms governing food‐web effects as a result of biomanipulation.

4. Whole‐lake case studies indicate that repeated fish removal can help improve water quality of shallow lakes, but successful biomanipulation of deep, thermally stratifying lakes remains difficult.

5. In many cases, biomanipulation of lakes has proved to provide benefits in addition to improving water quality. As all lake users are potentially affected when biomanipulation is used as a lake management tool, their concerns need to be clearly recognised if biomanipulation is to be successful in practice.
Hypolimnetic anoxia hampers top–down food‐web manipulation in a eutrophic lake
Authors: Dawidowicz Piotr , Prejs Andrzej , Engelmayer Andrzej , Martyniak Andrzej , Kozłowski Jacek , Kufel Lech , Paradowska Małgorzata
Published: March 2003

SUMMARY 1. A biomanipulation experiment was carried out in a small (10 ha), but relatively deep (17 m) and highly eutrophic lake in northern Poland. The lake had been stocked in 1996, 1997 and 1998 with a variety of piscivorous fish (pike, catfish, trout and pikeperch), in order to reduce numbers of cyprinid planktivores.

2. Piscivore stocking was associated with a threefold decrease in the offshore fish density (night echosounding). Despite this reduction, the large planktonic cladoceran, Daphnia hyalina, remained scarce, whereas the density of small‐sized zooplankton increased greatly.

3. The lack of demographic response in D. hyalina was probably due to the anoxia in the hypolimnetic refuge of this vertically migrating species. The anoxic hypolimnion, below 3–4 m depth, was inhabited day and night by numerous Chaoborus flavicans larvae.

4. Changes in zooplankton were associated with shifts in the taxonomic composition (from single‐cell green algae to filamentous cyanobacteria), size structure (from nano‐ to net phytoplankton) and seasonal dynamics of phytoplankton, but not in the average biomass of planktonic algae. A clear‐water phase, which was absent in the prestocking years, developed in spring, with Secchi depth reaching 2.5 m, a value which had never been recorded in the 20 years preceding the biomanipulation. In general, the lake's status was switched from hypertrophic to eutrophic.

5. Deteriorating food conditions, resulting from qualitative changes in the phytoplankton community, combined with predation pressure by the remaining fish and Chaoborus larvae were associated with the ultimate elimination of D. hyalina from the lake.
Genetic population structure of the net‐winged midge, Elporia barnardi (Diptera: Blephariceridae) in streams of the south‐western Cape, South Africa: implications for dispersal
Authors: Wishart M. J. , Hughes J. M.
Published: March 2003

SUMMARY 1. The net‐winged midges (Diptera: Blephariceridae), with highly specific habitat requirements and specialised morphological adaptations, exhibit high habitat fidelity and a limited potential for dispersal. Given the longitudinal and hierarchical nature of lotic systems, along with the geological structure of catchment units, we hypothesise that populations of net‐winged midge should exhibit a high degree of population sub‐structuring.

2. Sequence variation in the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA) was examined to determine patterns of genetic variation and infer historical and contemporary processes important in the genetic structuring of populations of Elporia barnardi. The DNA variation was examined at sites within streams, between streams in the same range, and between mountain ranges in the south‐western Cape of South Africa.

3. Twenty‐five haplotypes, 641 bp in length, were identified from the 93 individuals sampled. A neighbour‐joining tree revealed two highly divergent clades (∼5%) corresponding to populations from the two mountain ranges. A number of monophyletic groups were identified within each clade, associated with individual catchment units.

4. The distribution of genetic variation was examined using analysis of molecular variance (amova). This showed most of the variation to be distributed among the two ranges (∼80%), with a small percentage (∼15%) distributed among streams within each range. Similarly, variation among streams on Table Mountain was primarily distributed among catchment units (86%). A Mantel's test revealed a significant relationship between genetic differentiation and geographical distance, suggesting isolation by distance (P < 0.001).

5. Levels of sequence divergence between the two major clades, representing the two mountain ranges, are comparable with those of some intra‐generic species comparisons. Vicariant events, such as the isolation of the Peninsula mountain chain and Table Mountain, may have been important in the evolution of what is now a highly endemic fauna.

6. The monophyletic nature of the catchment units suggests that dispersal is confined to the stream environment and that mountain ridges provide effective physical barriers to dispersal of E. barnardi.
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

1. 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

1. 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.
Scaling of visual acuity with body size in mammals and birds
Authors: Kiltie R. A.
Published: March 2003

1. Kirschfeld (1976)suggested that visual acuity is directly proportional to body length across a wide range of animal species. A survey of eye size, visual acuity and body size of birds and mammals that is consistent with Kirschfeld's suggestion is reported. Hypoallometry (scaling factor < 1) for eye sizevsbody size combines with hyperallometry (scaling factor > 1) for acuityvseye size to produce roughly linear scaling between acuity and body size.

2. Kirschfeld (1976)also suggested that the distance at which important objects are typically viewed is a linear function of body length. ‘Subjective distance’ (viewing distance/body length) was therefore thought to be independent of body size across species. However, for prey detection by mammalian and avian predators, it is doubtful that subjective visual distances are size independent because prey size and visual acuity both scale by factors > 0·5 with predator body size; hence, detection distance should scale with size by a factor > 1. Scaling analyses also suggest that subjective visual distances for intraspecific social interactions are size dependent.

3. A positive association between body size and viewing distance has implications for the scaling of coat pattern features. In environments with fractal visual backgrounds (in which perceived sizes of background pattern elements do not change as distance from the background changes), larger animal species should have larger coat patches than smaller species if they are adapted to be cryptic at greater viewing distances than smaller species are.