bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of spring flood and water level draw‐down on methane dynamics in the littoral zone of boreal lakes
Authors: Juutinen  , Alm  , Martikainen  , Silvola
Published: March 2003

1. The annual dynamics of methane (CH4) in a temporarily flooded meadow, mire bank, lacustrine sedge fen, temporarily and continuously inundated sedge (Carex sp.) and reed (Phragmites australis) marshes were studied from June to November in the humic mesoeutrophic Lake Mekrijärvi and in eutrophicated parts of the mesotrophic Lake Heposelkä in the southern part of East Finland. The effects of water level and temperature on littoral CH4 fluxes were determined. Vegetation zonation along the moisture gradient, and associated CH4 fluxes, were evaluated.

2. The CH4 flux increased along the moisture gradient from –0.2 to 14.2 mg CH4 m–2 h–1, and was highest in the permanently inundated marshes. The duration of anoxia in the sediment caused differences in the CH4 flux. Estimated emissions for the period 1 June – 30 September in continuously inundated sparse reed and sedge marshes, drying sedge marsh, and lacustrine sedge fen were 13, 11 and 6 g CH4 m–2, respectively.

3. In continuously inundated vegetation, the fluxes were highest in late July/early August. The seasonal CH4 flux pattern suggested that the fluxes were regulated by the supply of organic matter during the course of the summer and the water level. In the temporarily flooded zone, the seasonal CH4 flux dynamics was greatly affected by changes in the lake water level, the fluxes being highest during the spring flood in early June.
Genetic evidence for `leaky' cohorts in the semivoltine stonefly Peltoperla tarteri (Plecoptera: Peltoperlidae)
Authors: SCHULTHEIS ALICIA S. , HENDRICKS ALBERT C. , WEIGT LEE A.
Published: March 2003

1. Genetic techniques are being used increasingly to address questions about dispersal and gene flow of freshwater invertebrates. However, population genetic structure can be affected by factors other than dispersal. Many stream insects have long life cycles that result in the simultaneous existence of multiple cohorts throughout the larval development period. If larval development is fixed, successive cohorts may be reproductively isolated and, as a result, genetically distinct. In such cases, significant levels of genetic differentiation between cohorts could confound estimates of dispersal based on population genetic structure.

2. Peltoperla tarteri is a stonefly that can be abundant in Appalachian headwater streams. Although P. tarteri is univoltine at the type locality (Big Paint Hollow, WV, U.S.A.), the study populations in southwestern Virginia, U.S.A., were semivoltine. This semivoltine life cycle results in the simultaneous existence of multiple cohorts with the potential for significant genetic differentiation among them.

3. Levels of genetic differentiation among P. tarteri cohorts were analysed with mitochondrial DNA (mtDNA) sequence data from the non‐coding origin of replication or `control' region from 93 individuals from two successive cohorts (collected in 1998 and 1999).

4. Analysis of molecular variance (AMOVA) indicated no genetic differentiation among cohorts (FST=0.0), and gene flow among cohorts was very high (Nm=∞).

5. High levels of gene flow among cohorts suggest that larval development of P. tarteri is not fixed. Gene flow among cohorts most likely occurs as a result of a cohort split in which some individuals complete development in one or three years instead of two.
Dormancy, dispersal and the survival of cyclopoid copepods (Cyclopoida, Copepoda) in a lowland floodplain
Authors: FRISCH D.
Published: March 2003

1. The survival of cyclopoid copepods was investigated in a floodplain for 2 years where flooding occurred during the cold season. The cyclopoid community was studied in three waterbodies with distinct hydroperiods: a permanent pond connected to the flooded area during inundation, a temporary pool that is part of the flooded area and an isolated temporary pool.

2. Field studies, including data obtained from samples of water, sediment and soil, showed the overall predominance of species with a summer diapause over those with a winter diapause or without diapause. Emergence of cyclopoid copepods at the onset of flooding, examined using emergence traps and data from recently filled or still isolated temporary pools, showed that some species can survive several months of drying.

3. The ability of the diapausing fourth copepodid stages of Cyclops strenuus and C. insignis, the two cyclopoids most abundant during winter and spring flooding, to survive terrestrial conditions was tested in laboratory experiments. Both species survived for several months, but rates differed among the species. A higher percentage of C. strenuus survived for a longer period, possibly explaining why this species was relatively more abundant in more temporary habitats.

4. Both dormancy and dispersal facilitated survival of cyclopoid copepods in transient habitats connected to each other during flood periods. Dormancy was the most important survival strategy, whereas dispersal could be more important following prolonged periods without flooding.
Assessing the influence of water and substratum quality on benthic macroinvertebrate communities in a metal‐polluted stream: an experimental approach
Authors: Courtney Lisa A. , Clements William H.
Published: March 2003

SUMMARY 1. Field and laboratory experiments were conducted to assess the relative influence of water quality and substratum quality on benthic macroinvertebrate communities in the Animas River, a metal‐polluted stream in south‐western Colorado (U.S.A.).

2. A community‐level in situ toxicity test measured direct effects of Animas River water on benthic invertebrates collected from a reference stream (Elk Creek). The effects of metal‐contaminated biofilm were examined by comparing macroinvertebrate colonisation of clean and contaminated substrata placed in Elk Creek. A feeding experiment with the mayfly Baetis tricaudatus Dodds (Ephemeroptera: Baetidae) examined metal bioaccumulation and effects of metal‐contaminated biofilm on growth and survival.

3. Animas River water was acutely toxic to most taxa, with greatest effects observed on mayflies (Heptageniidae, Ephemerellidae) and stoneflies (Taeniopterygidae and Capniidae).

4. Although Animas River biofilm was characterised by high concentrations of metals and low algal biomass, most taxa colonised substratum from the reference stream and the Animas River equally. The exceptions were Ephemerellidae, Taeniopterygidae and Simuliidae, which were less abundant on Animas River substratum. Mayflies grazing Animas River biofilm accumulated significantly more metals and showed reduced growth compared with organisms feeding on Elk Creek biofilm.

5. Results of our experiments demonstrated that effects of heavy metals on benthic community structure in the Animas River were complex, and that responses to metals in water and contaminated substratum were species‐specific. Predicting recovery of benthic communities following remediation requires an understanding of these species‐specific responses.
The fauna of dynamic riverine landscapes
Authors: ROBINSON C. T. , TOCKNER K. , WARD J. V.
Published: March 2003

1.  Riverine landscapes are heterogeneous in space (complex mosaic of habitat types) and time (expansion and contraction cycles, landscape legacies). They are inhabited by a diverse and abundant fauna of aquatic, terrestrial and amphibious species.

2.  Faunal distribution patterns are determined by interactive processes that reflect the landscape mosaic and complex environmental gradients. The life cycles of many riverine species rely upon a shifting landscape mosaic and other species have become adapted to exploit the characteristically high turn‐over of habitats.

3.  The complex landscape structure provides a diversity of habitats that sustains various successional stages of faunal assemblages. A dynamic riverine landscape sustains biodiversity by providing a variety of refugia and through ecological feedbacks from the organisms themselves (ecosystem engineering).

4.  The migration of many species, aquatic and terrestrial, is tightly coupled with the temporal and spatial dynamics of the shifting landscape mosaic. Alternation of landscape use by terrestrial and aquatic fauna corresponds to the rise and fall of the flood. Complex ecological processes inherent to intact riverine landscapes are reflected in their biodiversity, with important implications for the restoration and management of river corridors.
Temporal variation in the drift of plant litter and propagules in a small boreal river
Authors: Andersson E. , Nilsson C.
Published: March 2003

SUMMARY 1. Rivers are linear ecosystems across landscapes with an effective transport of organisms, sediment and organic matter. Dispersal is studied mostly during single events and for single species, and there is little knowledge on how the drift of plant litter and propagules varies within and between years for entire communities.

2. We used floating traps for collecting waterborne plant litter and propagules in a small boreal river over 2 years. We installed the traps at four different locations along the river, and emptied them at least once a week during the ice‐free season. We analysed propagule content by sorting and identifying species and through germination tests on bare soil.

3. In total, we recorded at least 54 taxa in the samples, and the highest density recorded in one sample was 5000 propagules per 100 g litter (dry weight). Large temporal variations in litter and propagule transport were revealed, both within and between years.

4. The longitudinal pattern was consistent between years, with an increasing mass of litter and number of propagule taxa downstream. The results highlight the importance of the temporal and longitudinal dimensions in river management.
Predatory interactions between a cyclopoid copepod and three sibling rotifer species
Authors: Lapesa S. , Snell T. W. , Fields D. M. , Serra M.
Published: March 2003

SUMMARY 1. Cyclopoid copepod predation on rotifers affects the dynamics and structure of zooplankton communities. We address the differential vulnerability of three sympatric rotifer sibling species belonging to the Brachionus plicatilis species complex. These co‐occur with their cyclopoid predator, Diacyclops bicuspidatus odessanus.

2. Using video recording and tracking, we analysed the steps in predation including attack distance, attack angle, and rotifer species swimming in the presence and absence of the predator. Our results show the greater vulnerability of B. rotundiformis (the smallest species) to D. b. odessanus predation, which is associated with a high percentage of attacks after contact. Brachionus plicatilis (the biggest species) is the less vulnerable prey, with low percentage of attacks after contact and captures after attacks. Branchionus ibericus, the intermediate sized species, had also intermediate vulnerability.

3. The differential vulnerability provides insight into the coexistence and seasonal succession of these competing rotifer species. Our results show that the competitive superiority of B. rotundiformis may be balanced by its greater vulnerability to copepod predation.
Effects of land cover on sediment regime and fish assemblage structure in four southern Appalachian streams
Authors: Sutherland Andrew B. , Meyer Judy L. , Gardiner Edward P.
Published: March 2003

SUMMARY 1. We examined the relationship between catchment land cover, sediment regime and fish assemblage structure in four small streams in the upper Little Tennessee River basin of North Carolina. Study streams drained similar sized catchments (17–31 km2) with different fractions of non‐forested land cover. Non‐forested land cover was <3% in two ‘reference’ streams, whereas it was 13 and 22% in two ‘disturbed’ streams. Land cover data were compared with sediment transport data (suspended and bedload), benthic habitat data (embeddedness, substratum composition and coverage of fines) and fishes collected in autumn 1997.

2. Suspended sediment concentration was significantly higher in disturbed streams during both baseflow and stormflow. During baseflow disturbed streams nearly always exceeded 10 nephelometric turbidity units (NTU), whereas reference streams never exceeded this threshold. The difference in suspended sediment concentration between reference and disturbed streams was more consistent at baseflow than at stormflow. Therefore, baseflow turbidity may be a useful indicator of potential stream degradation.

3. Disturbed sites had five‐ to nine‐fold more bedload transport than reference sites. Both embeddedness and streambed instability increased with increasing non‐forested land cover.

4. Relative abundance of fishes requiring clean cobble/gravel substratum for spawning was lower in disturbed streams, whereas relative abundance of mound‐building cyprinids, their nest associates and fishes that excavate nests in soft sediments (centrarchids) was higher. Relative abundance of fishes spawning in benthic crevices and gravel (BC + G) declined as the proportion of non‐forested land cover increased. This study supports growing evidence that human‐induced sedimentation alters stream fish assemblages.
Species‐specific changes in the phenology and peak abundance of freshwater copepods in response to warm summers
Authors: Gerten Dieter , Adrian Rita
Published: March 2003

SUMMARY 1. Climate warming is now widely recognised as a major factor influencing ecological processes in terrestrial, marine and freshwater habitats. Here, we investigated how a recent period of warm springs and summers has affected the population dynamics of various cyclopoid copepods in a central European lake. We compared (i) the duration of the period when the species were present in the water column, and (ii) their annual peak density in a period dominated by cool summers (1980–91) and one dominated by warm summers (1992–99).

2. The copepods under investigation were (i) Thermocyclops oithonoides, (ii) Mesocyclops leuckarti and (iii) Acanthocyclops robustus. These species differ in their thermal demand and seasonal phenology. Therefore, we hypothesised that enhanced summer warming would produce species‐specific responses.

3. The active phase of the copepods was usually prolonged both in spring and autumn. The earlier emergence of T. oithonoides (May in the warm years, July in the cool years) was probably related to high water temperature in late spring. The later onset of winter diapause in all species may have been coupled to raised temperature in late summer and autumn.

4. The annual peak abundance of the two thermophiles M. leuckarti and T. oithonoides increased significantly in the warm period. In the latter case, the increase was probably because of the early start to population growth. In contrast, M. leuckarti probably responded primarily to mid‐summer heat waves, in that its development time was likely to be short. We speculate that the increase in population size of both species resulted from the development of an additional generation (three instead of two cohorts per year). In contrast to these thermophiles, the coexisting A. robustus, which is adapted to a broader temperature range, did not respond noticeably to the warming trend.

5. In general, the nature of these responses to summer warming varied substantially among species, and depended on the detailed seasonal patterning of the warming. Our findings thus support the hypotheses that single species are sensitive indicators of climate change, and that the seasonal timing of warming is crucial in the context of climate–ecosystem relationships.

6. Moreover, our results add to the body of evidence that climate warming produces shifts in the seasonal phenology of aquatic and terrestrial organisms.
On the different nature of top‐down and bottom‐up effects in pelagic food webs
Authors: Maciej Gliwicz Z.
Published: March 2003

SUMMARY 1. Each individual planktonic plant or animal is exposed to the hazards of starvation and risk of predation, and each planktonic population is under the control of resource limitation from the bottom up (growth and reproduction) and by predation from the top down (mortality). While the bottom‐up and top‐down impacts are traditionally conceived as compatible with each other, field population‐density data on two coexisting Daphnia species suggest that the nature of the two impacts is different. Rates of change, such as the rate of individual body growth, rate of reproduction, and each species' population growth rate, are controlled from the bottom up. State variables, such as biomass, individual body size and population density, are controlled from the top down and are fixed at a specific level regardless of the rate at which they are produced.

2. According to the theory of functional responses, carnivorous and herbivorous predators react to prey density rather than to the rate at which prey are produced or reproduced. The predator's feeding rate (and thus the magnitude of its effect on prey density) should hence be regarded as a functional response to increasing resource concentration.

3. The disparity between the bottom‐up and top‐down effects is also apparent in individual decision making, where a choice must be made between accepting the hazards of hunger and the risks of predation (lost calories versus loss of life).

4. As long as top‐down forces are effective, the disparity with bottom‐up effects seems evident. In the absence of predation, however, all efforts of an individual become subordinate to the competition for resources. Biomass becomes limited from the bottom up as soon as the density of a superior competitor has increased to the carrying capacity of a given habitat. Such a shift in the importance of bottom‐up control can be seen in zooplankton in habitats from which fish have been excluded.
A comparative study of the functional response of four species of carnivorous stoneflies
Authors: Elliott J. M.
Published: March 2003

SUMMARY1. Comparisons were made of the functional responses of mature larvae ofPerlodes microcephalus,Isoperla grammatica,Dinocras cephalotesandPerla bipunctata. Experiments were performed in stream tanks with natural substrata and glass bottoms, so that feeding could be observed above and below the substratum. There was one stonefly per tank and one of 10 prey densities between 20 and 200 larvae of eitherChironomussp. orBaetis rhodaniper tank. Consumed prey were replaced in a first set of experiments but not in a second set. Additional experiments assessed intraspecific interference between larvae of each predator species (two to five predators per tank).

2. The number of prey eaten increased curvilinearly with prey density. The relationship was described by two models, a Type II instantaneous model and its integrated equivalent, for experiments with and without prey replacement, respectively. Handling time did not change significantly with prey density, and was the same for experiments with and without prey replacement. Estimates of attack rate were similar for the two models, but varied between prey type and predator species. Handling time varied considerably but was normally distributed for each prey type and predator species. Mean handling time varied forChironomusfrom 39 s forIsoperla, which rarely ate a whole larva, to 57 s forPerlodesand forBaetisfrom 116 s forPerlodesto 167 s forPerla. All predators were more efficient at capturingBaetis, but the longer handling time forBaetisensured that moreChironomuswere eaten. It was concluded that these variations in attack rate and handling time were related to activity and growth differences between the predator species, and that experiments with and without prey replacement could both be relevant to the field, depending on how the predators searched for food.

3. In the interference experiments, mean handling time did not change with increasing predator density, but attack rate decreased curvilinearly, the decrease varying from negligible forIsoperlato marked forPerlodes. Prey capture decreased with decreasing attack rate. Therefore, interference reduced prey consumption, but this effect was negligible forIsoperlaand increasingly severe in the orderDinocras,PerlaandPerlodes.
The integrated processing response of voles to fibre content of natural diets
Authors: Young Owl M. , Batzli G. O.
Published: March 2003

1. Two species of voles were fed high fibre (barnyard grass) and low fibre (alfalfa) diets to test the integrated processing response (IPR) hypothesis. This hypothesis states that many herbivores are able to maintain their required intake of digestible nutrients and energy on diets with very different fibre content because of compensatory changes in intake of food, size of gastro‐intestinal (GI) tract, passage rates of fibre and absorptive capacity of the GI tract.

2. As predicted by the IPR hypothesis, each species of vole maintained a similar intake of digestible dry matter on the two different diets. Both species also had greater intake, larger GI size, shorter mean retention times and greater GI mass (an indicator of epithelial mass and absorptive capacity) when fed grass than when fed alfalfa.

3. The two species differed in that meadow voles, the more active species, had greater total intake and obtained a greater amount of digestible dry matter from either diet than did prairie voles. Meadow voles also consume more grass in the field than do prairie voles, and they digested grass better than did prairie voles. Prairie voles, which consume more dicots in the field, digested alfalfa better than did meadow voles.

4. Meadow voles had longer GI tracts, particularly small intestines, than did prairie voles, which may be linked to their greater ability to digest grass. However, meadow voles did not have larger caeca than prairie voles, even though caecal size increased on grass diets for both species. The GI size of prairie voles fed grass increased more than did the GI size of meadow voles, and this may have enabled prairie voles to utilize a grass diet, though they prefer to eat dicots. Greater selection of leaves, which have less fibre than stems, and longer mean retention times of food may account for better digestion of alfalfa by prairie voles.
Host plant effects on the genetic variation and correlations in the individual performance of the Gypsy Moth
Authors: LazareviĆ J. , PeriĆ‐Mataruga V. , IvanoviĆ J. , AndjelkoviĆ M.
Published: March 2003

1.Quantitative genetic analysis of variation in host‐use ability was performed in an extremely polyphagous species – the Gypsy Moth. Various life‐history traits were investigated by applying a split‐family two‐environment experimental design, where 30 full‐sibling families were reared on oak and Locust Tree leaves.

2.Feeding on Locust Tree leaves decreased preadult viability, prolonged development time, decreased pupal mass both in males and females, and decreased reproductive effort in females.

3.The majority of broad‐sense heritabilities did not change across host plants.

4.Significant expression of genetic variation in diet breadth was observed for development time and pupal mass both in males and females, but not for female reproductive effort traits. The heritabilities of plasticities were, on average, lower than heritabilities of the traits themselves.

5.The majority of genetic correlations between the host plants were significantly positive. The only trade‐off was found between reciprocal value of reproductive index and the average mass of a fertilized egg within oak. This means that selection for the decrease in relative reproductive investment (under starvation during gradation) will be followed by laying larger eggs. Given that the Gypsy Moth has a cyclic population dynamics, this negative genetic correlation could have a role in maintaining genetic variability in this species.
Size dependence of reproductive allocation: the influence of resource availability, competition and genetic identity
Authors: Sugiyama S. , Bazzaz F. A.
Published: March 2003

1.Resource availability, competition and genetic difference are among the main factors causing size variation in plant populations. These factors also have great effects on the variation in reproductive allocation. We examined the effects of soil nutrient availability, competition and genetic identity on the size dependency of reproductive allocation inAbutilon theophrastifamilies grown under different conditions of soil nutrient and conspecific competition.

2.Soil nutrients, competition and genetic identity brought about a strong dependency of reproductive allocation on size. However, these factors differed in functional forms and signs of the size dependency.

3.An allometric (log–log) regression between seed mass and vegetative mass fit the data better than a linear regression. The slopes of allometric regressions for each nutrient treatment were lower than 1·0. Therefore, there was a negative relationship between plant size and reproductive allocation. However, the slopes calculated over different nutrient treatments were greater than 1·0 (i.e. positive relationship between plant size and reproductive allocation). We suggest that these two reproductive allometries indicate two different biological relationships: the former represents a physiological trade‐off between resource acquisition and reproductive allocation within a plant and the latter represents an allometric response to soil nutrients.

4.Genetic identity showed intrinsic effects on size dependency of reproductive allocation owing to trade‐off and not as a result of the allometric response to soil nutrients.

5.Nutrient availability changed the slopes of the allometric regressions. An increase in nutrient availability alleviated the negative relationship between plant size and reproductive allocation.

6.The slopes of the allometric regressions within nutrient treatments were significantly higher in competition treatments than in competition‐free treatments, although the slopes of the regressions over different nutrient levels did not differ between the two treatments. These results suggest that the effects of competition on reproductive allocation are owing to indirect effects of size difference on the allometric relationship rather than intrinsic effects.
Variation in bark thickness in a tropical forest community of Western Ghats in India
Authors: Hegde V. , Chandran M. D. S. , Gadgil M.
Published: March 2003

1. We examined the relation between bark thickness and girth in a large sample of trees from evergreen and semi‐evergreen rain forest.

2. There is a significant tendency for bark thickness to increase with tree girth. Removing this tendency, we find a significant trend for species from more disturbed habitats to possess thicker bark.

3. Species from more disturbed habitats also have a greater propensity for secreting gums and resins.

4. Nine of the 29 species occurring in more than one habitat type and with a sample size of at least 11 individuals show a tendency for possession of a thicker bark by individuals in the more disturbed habitats.

5. We conclude that bark thickness and occurrence of gums and resins are physiognomic–structural attributes of value in characterizing tree communities created by different levels of disturbance.
Body temperature and insulation in diving Great Cormorants and European Shags
Authors: GRÉmillet D. , Tuschy I. , Kierspel M.
Published: March 2003

1. Cormorants are typically considered as wettable diving birds with high thermoregulatory costs and are presumed to exert substantial predatory pressure on fish stocks.

2. The stomach temperatures of seven Great Cormorants and three European Shags were recorded during a total of 108 foraging trips undertaken near the Chausey Islands breeding colony (France).

3. Both species kept a constant body temperature during the dive series which lasted up to 158 min and were conducted in 12°C water. Consequently, assuming that heat loss to the water is equal to heat production in diving Great Cormorants, the minimal insulating plumage air volume was calculated to be 0·371 × 10–3 m3 (corresponding to a 1·62‐mm air layer) in males and 0·347 × 10–3 m3 (corresponding to a 1·90‐mm air layer) in females.

4. Furthermore, it is shown that plumage air volume and dive depth are the major factors influencing heat flux to the water and that the energetics of diving Great Cormorants may also vary substantially according to fat layer thickness, water temperature and body temperature. Swim speed plays only a minor role.

5. Considering these results, it is postulated that Great Cormorants may have optimized plumage air volume so as to minimize both mechanical costs (upthrust) and thermoregulatory costs of swimming in cold, shallow water.

6. Finally, body temperature patterns recorded in different cormorant species while diving are compared.
Ecological factors influencing the occurrence of ‘flash marks’ in wading birds
Authors: DE L. Brooke M.
Published: March 2003

1. Although the plumage of birds is important for flight and thermoregulation, it is also employed in inter‐ and intraspecific communication. The role in communication of particular plumage features can be studied by experiment or, as here, by correlational analysis.

2. The study was carried out on the 210 species of wading birds, such as plovers, sandpipers, thick‐knees and allies, that are placed within the traditional order Charadriiformes.

3. Species differ in the location and extent of ‘flash marks’, patches of white on the plumage that are typically conspicuous when the bird flies. These patches occur, in various permutations in different species, on the wing (primaries, secondaries, coverts), back, rump and tail.

4. Within a phylogenetic framework, it was asked which of several broad ecological variables (migration, habitat choice, feeding technique, propensity to flock) were correlated with the occurrence of flash marks. Only flocking correlated significantly. In particular, taxa that flock have flashier backs and coverts than their non‐flocking relatives.

5. Three non‐exclusive explanations for this correlation are: (i) individuals that take flight to avoid a predator may benefit from signalling their take‐off to flock mates which themselves then take flight; (ii) flash marks could enhance the confusion effect within flocks, making it more difficult for a predator to single out an individual; and (iii) flash marks may facilitate co‐ordinated flight within flocks.
Effects of floral morphology and display on outcrossing in Blue Columbine, Aquilegia caerulea (Ranunculaceae)
Authors: Brunet J. , Eckert C. G.
Published: March 2003

1. The effect of variation in floral morphology and display on the level of outcrossing was investigated in a Rocky Mountain population of the self‐compatible, protandrous, perennial herb, Aquilegia caerulea. ANOVA revealed substantial variation among 36 plants in floral traits including herkogamy (CV = 35%), protandry (23%), pollen production (12%), flower size (8%), the daily number of flowers in male phase (58%) and autofertility, seed production in the absence of pollinators (192%).

2. Whether this floral variation affected the outcrossing rates of individual plants was assessed using both a categorical analysis, in which outcrossing rates were estimated separately for groups of plants that differed with respect to floral features, and a correlation analysis involving outcrossing rates estimated for individual plants from large progeny arrays (n≥ 40). Both analyses indicated significant positive correlations between the outcrossing rate and herkogamy (r = + 0·71) and protandry (+ 0·54), negative correlations with the number of flowers in male phase during each day of female phase (– 0·42) and autofertility (– 0·36), but no correlation with flower size or pollen production.

3. Partial correlation indicated that both herkogamy and dichogamy, although weakly intercorrelated, were positively correlated with the outcrossing rate and that these effects were only partly mediated by their negative correlation with autofertility.

4. The extent to which floral features and the outcrossing rate covaried across the flowering sequence within plants was also examined in this study. As expected for a plant with strong protandry and sequential blooming, the number of flowers in male phase decreased strongly with flowering sequence position. However, categorical analysis did not support the prediction that the first flowers to open on an inflorescence outcrossed at a lower rate than later‐opening flowers.

5. These results suggest that self‐fertilization in A. caerulea is the result of all three major modes: autonomous and facilitated autogamy as well as geitonogamy. Although the geitonogamous component of selfing cannot be selected for directly, autogamy may be selected if it provides reproductive assurance.
A field fumigation system for elevated carbon dioxide exposure in chaparral shrubs
Authors: Roberts S. W. , Oechel W. C. , Bryant P. J. , Hastings S. J. , Major J. , Nosov V.
Published: March 2003

1. Modifications and improvements in the hardware and software of a free‐air CO2 enrichment (FACE) system are described. The modifications were undertaken to minimize the amount of structure required and to improve software control of CO2 set points.

2. A new low‐cost CO2 flow controller which provides increased reliability is described.

3. Analysis of system performance during a 79‐day evaluation period of operation (13 h day–1) showed that for 1 min averages, the system is capable of maintaining a 550 p.p.m. ± 10% CO2 set point during 78% of the operating time and a 550 p.p.m. ± 20% set point during 95% of the operating time. Ten‐minute averages were within ± 10% and 20% during 87% and 96% of the operating time, respectively.

4. Continuous measurements of the spatial variation in CO2 concentration inside the FACE ring over an 18‐day period showed that of the total 16‐m diameter treatment area, the central 11‐m diameter portion remains within the 550 p.p.m. ± 10% set point.

5. Daily course gas‐exchange measurements in matched individuals of the chaparral shrub Adenostoma fasciculatum just prior to and following a 6‐week fumigation period at 550 p.p.m. CO2 in the FACE treatment ring showed the FACE plants with reduced photosynthetic rates and higher (less stressful) water potentials compared with control A. fasciculatum plants measured at the same times and conditions, indicating the responsiveness of this species to elevated CO2 conditions.
Maternal and ambient environmental effects of light on germination in Plantago lanceolata: correlated responses to selection on leaf length
Authors: Van Hinsberg A.
Published: March 2003

1. Seeds from artificial selection lines were exposed to different maternal and ambient conditions, simulating sunlight and vegetation shade.

2. Lines selected for longer leaves also produced larger seeds, indicating a positive genetic correlation between leaf length and seed size.

3. Light conditions during maturation had no large effect on seed size.

4. Seed germination was reduced by a low ratio of red to far‐red light (R/FR ratio) in the ambient environment.

5. Seeds maturated under simulated vegetation shade germinated less readily and were more inhibited by a low ambient R/FR ratio than seeds maturated under full sunlight or R/FR‐neutral shade. Thus, low R/FR‐ratios in the maternal and ambient environment operated synergistically.

6. Large genotypic variation in the germination responses to both maternal and ambient light conditions was found among and within selection lines, indicating that such responses might have the potential to evolve in response to natural selection.

7. Artificial selection for leaf length had affected seed germination characteristics but correlated responses and thus genetic correlations largely depended on light conditions in the selective environment. Selection for longer leaves under a low R/FR ratio increased seed dormancy and plasticity of germination in response to the R/FR ratio. However, in the opposite selective environment selection for longer leaves reduced seed dormancy and plasticity to the R/FR ratio. It is argued that leaf length and seed germination characteristics are somehow linked by shared physiological mechanisms, which may facilitate concerted changes in shade avoidance responses.
The influence of the nutritional content of the adult male diet on testis mass, body condition and courtship vigour in a Hawaiian Drosophila
Authors: Droney D. C.
Published: March 2003

1. The effects of the nutritional quality of the adult diet (primarily protein content) on testis mass, body condition and courtship vigour were studied in a Hawaiian Drosophila, D. grimshawi, a lek‐forming species under strong sexual selection. The primary goals of this study were to determine whether there is a trade‐off between investment in reproductive and somatic tissues, and to examine whether this trade‐off is influenced by quality of the adult diet.

2. Quality of the adult diet had a major influence on male body condition, courtship vigour and testis mass, but males varied in their investment patterns even within diet treatment.

3. Body condition, a measure of phenotypic quality, was significantly related to how much males invested in testis and body tissues, but the nature of the relationships differed between males fed high‐ or low‐quality diets.

4. Paragonia volume was significantly smaller for adult males fed low‐quality diets than for males fed high‐quality diets. Nutrient‐deficient diets apparently forced males to trade off investment in testes and body condition, and in body condition and courtship vigour, but nutrient‐rich diets did not result in severe trade‐offs.

5. Collectively, the results suggest that fluctuation in adult diet quality of male D. grimshawi might influence male reproductive quality in ways that might limit female reproductive output and/or be a factor for female choice in this species.
Effects of enhanced UV‐B radiation on production‐related properties of a Sphagnum fuscum dominated subarctic bog
Authors: Gehrke C.
Published: March 2003

1. The aim of the study was to investigate effects of enhanced UV‐B radiation on the balance between biomass production and decay in an ombrotrophic bog which is dominated by one species of Sphagnum (S. fuscum). This paper concerns production.

2. Enhanced UV‐B radiation (simulating 15% ozone depletion under clear sky conditions) was applied by means of fluorescent tubes during two growing seasons.

3. In S. fuscum, shoot density, mass relations and length increment over time were measured and productivity was estimated. Pigment concentration, rates of dark respiration and maximum net photosynthesis were recorded.

4.
Sphagnum fuscum productivity was not changed by enhanced UV‐B radiation while properties determining production were highly influenced although in opposite directions.

5. Height increment was decreased by 20% in the first growing season and by 31% in the second growing season under enhanced UV‐B radiation. After two growing seasons spatial shoot density was decreased by 8% by enhanced UV‐B radiation. The shoots became stunted as capitulum dry mass and stem dry mass per unit length were increased by 21 and 17%, respectively, under enhanced UV‐B radiation.

6. Dark respiration was significantly decreased by 31% after growth under enhanced UV‐B radiation.

7. The UV‐B induced change in shoot biometry together with the reduced spatial shoot density involve potential long‐term effects on peat structure with possible feedback on productivity, decomposition and the strength of the system as a carbon sink.
Does photosynthetic acclimation to elevated CO2 increase photosynthetic nitrogen‐use efficiency? A study of three native UK grassland species in open‐top chambers
Authors: Davey P. A. , Parsons A. J. , Atkinson L. , Wadge K. , Long S. P.
Published: March 2003

1. The photosynthetic response to elevated CO2 and nutrient stress was investigated in Agrostis capillaris, Lolium perenne and Trifolium repens grown in an open‐top chamber facility for 2 years under two nutrient regimes. Acclimation was evaluated by measuring the response of light‐saturated photosynthesis to changes in the substomatal CO2 concentration.

2. Growth at elevated CO2 resulted in reductions in apparent Rubisco activity in vivo in all three species, which were associated with reductions of total leaf nitrogen content on a unit area basis for A. capillaris and L. perenne. Despite this acclimation, photosynthesis was significantly higher at elevated CO2 for T. repens and A. capillaris, the latter exhibiting the greatest increase of carbon uptake at the lowest nutrient supply.

3. The photosynthetic nitrogen‐use efficiency (the rate of carbon assimilation per unit leaf nitrogen) increased at elevated CO2, not purely owing to higher values of photosynthesis at elevated CO2, but also as a result of lower leaf nitrogen contents.

4. Contrary to most previous studies, this investigation indicates that elevated CO2 can stimulate photosynthesis under a severely limited nutrient supply. Changes in photosynthetic nitrogen‐use efficiency may be a critical determinant of competition within low nutrient ecosystems and low input agricultural systems.
Sex allocation and larval competition in a superparasitizing solitary egg parasitoid: competing strategies for an optimal sex ratio
Authors: Van Baaren J. , Landry B. L. , Boivin G.
Published: March 2003

1. Parasitic Hymenoptera reproduce by arrhenotokous parthenogenesis, and females of these species are able to control their progeny sex ratios. In structured populations of parasitic Hymenoptera, primary sex ratios are often highly biased toward females. However, sex ratio can be adjusted to the quality of encountered patches or hosts or be modified by differential developmental mortality.

2. In this paper, the effects were evaluated of the quality of encountered hosts and developmental mortality on the sex ratio in Anaphes victus, a solitary egg parasitoid whose first instar larvae present a sexual dimorphism and where superparasitism is regulated by larval fights between first instar larvae.

3. The results showed that a female‐biased sex ratio is allocated to unparasitized hosts. In the presence of parasitized hosts, the second (superparasitizing) female produced a significantly higher sex ratio than the first female but the tertiary sex ratio (sex ratio at emergence) was not significantly different from the sex ratio produced with unparasitized hosts. The increase in the primary sex ratio produced by the second female was mostly compensated by the higher mortality of male larvae.
Strategic sperm allocation in the Small White butterfly Pieris rapae (Lepidoptera: Pieridae)
Authors: Wedell N. , Cook P. A.
Published: March 2003

1. In species where females mate multiply, it is important for males to recuperate quickly in order to maximize their fertilization success. Butterflies produce a spermatophore at mating containing accessory secretions and sperm of two types: a large number of non‐fertile ‘apyrene’ sperm and fewer fertile ‘eupyrene’ sperm. Many butterfly species eclose with most nutrients for reproduction already present. Males must therefore decide how to allocate resources to the various spermatophore components at any given mating.

2. Recovery rates of apyrene and eupyrene sperm number and spermatophore size was studied in the polyandrous Small White butterfly Pieris rapae. The mass of the first spermatophore increases with time since eclosion, as does the number of both types of sperm. Similarly, on a male's second mating, both the mass of the spermatophore and the number of sperm increases with time since the first mating.

3. However, the rate of increase in eupyrene sperm numbers is higher after the first mating. The difference in rate of increase may be the result of different probabilities of virgin and non‐virgin males obtaining future matings.

4. Males have a sperm storage organ, the duplex, in which they retain sperm after their first mating. This ensures that high sperm numbers are available for their second mating, even when remating only 1 h later. Thus, males do not ejaculate all available sperm on any given mating, and seem to have different strategies on their first and second matings.

5. It can be argued that Small White butterfly males allocate sperm strategically according to the probability of obtaining subsequent matings, and the level of sperm competition.
The effect of male mating history on paternal investment, fecundity and female remating in the seed beetle Callosobruchus maculatus
Authors: SAVALLI U. M. , FOX C. W.
Published: March 2003

1. In many organisms, males provide nutrients to females via ejaculates that can influence female fecundity, longevity and mating behaviour. The effect of male mating history on male ejaculate size, female fecundity, female longevity and female remating behaviour in the seed beetle Callosobruchus maculatus was determined.

2. The quantity of ejaculate passed to females declined dramatically with successive matings. Despite the decline, a male’s ability to fertilize a female fully did not appear to decline substantially until his fourth mating.

3. When females multiply mated with males of a particular mated status, the pattern of egg production was cyclic, with egg production increasing after mating. Females multiply mated to virgins had higher fecundity than females mated to non‐virgins, and females mated to twice‐mated males had disproportionately increased egg production late in their life.

4. Females that mated to multiple virgins, and consequently laid more eggs, experienced greater mortality than females mated only once or mated to non‐virgins, suggesting that egg production is costly, and rather than ameliorating these costs, male ejaculates may increase them by allowing or stimulating females to lay more eggs.

5. Females mating with non‐virgin males remated more readily than did females mated to virgins. Females given food supplements were less likely to remate than females that were nutritionally stressed, suggesting that females remate in part to obtain additional nutrients.
Photosynthetic pathway diversity in a seasonal pool community
Authors: Keeley J. E.
Published: March 2003

1. Photosynthetic pathway diversity was evaluated for the dominant species in a seasonally aquatic community in the south‐western USA using 14C pulse‐chase techniques.

2. Under submerged conditions, only about half of the species were clearly C3, three of the 15 dominants were CAM, one species was C4 and three were potentially assimilating carbon with both C3 and C4 fixation.

3. During the brief terrestrial stage in the life history of these amphibious plants, both the CAM and the C3 + C4 species switched to C3, whereas the C4 species did not switch.

4. Numerous variations were apparent; for example, the C4 species, while exhibiting a biochemical pathway indistinguishable from terrestrial C4 plants, lacked Kranz anatomy in the aquatic foliage. Also, despite well‐developed CAM in several species, others exhibited low‐level diel changes in acidity, apparently not indicative of CAM.

5. Species with C4 or CAM CO2 concentrating mechanisms lacked the capacity for bicarbonate uptake, an alternative CO2 concentrating mechanism found in certain C3 species in this community.

6. Rubisco/PEPC in aquatic foliage was higher in C3 species than in C4, CAM or putative C3 + C4 species. In the terrestrial phase, as expected, the switch from CAM or C3 + C4 to strictly C3 assimilation was associated with a substantial increase in Rubisco/PEPC. Quite unexpected, however, was the substantial increase in this ratio in terrestrial C3 foliage. It is hypothesized that submerged C3 plants utilize PEPC for recycling of respiratory CO2 and/or C4 phototrophism under field conditions of limited CO2 and O2 saturation, and this is lost in the terrestrial foliage.