bluuebunny/crossref_metadata_2025_split huggingface dataset:
Female control of the embryonic environment in a terrestrial amphipod, Mysticotalitrus cryptus (Crustacea)
Authors: Morritt D. , Richardson A. M. M. 
Published: March 2003

1. In amphipod crustaceans the ventral chamber plays an integral role in a number of physiological processes and in the female forms the marsupium in which eggs are brooded. The ventral chamber can be viewed as a pre‐adaptation to the colonization of land by the family Talitridae. The hypothesis that the female of the terrestrial species, Mysticotalitrus cryptus, can control the osmotic concentration of the marsupial fluid ([MF]) bathing the eggs, thereby buffering the brood from potential physiological stresses presented by the terrestrial environment, is examined. 2.[MF] was maintained significantly higher than the concentration of the external medium ([Medium]) on both dechlorinated tap‐water and 400 mOsm kg–1 media. In each case, [MF] was intermediate to [Medium] and the concentration of the female haemolymph ([Haem]): when [Medium] = 40 mOsm kg–1, [MF] = 277 mOsm kg–1 and [Haem] = 590 mOsm kg–1, respectively, and when [Medium] = 413 mOsm kg–1, [MF] = 516 mOsm kg–1 and [Haem] = 722 mOsm kg–1, respectively. 3. Evidence is provided that females produce urine that is isosmotic with the haemolymph and that the urine is directed, by capillarity, into the marsupium via cuticular channels. It is suggested that this urine plays a role in controlling [MF] in combination with other behavioural mechanisms. 4. Some preliminary observations are presented on the ontogeny of embryonic osmoregulation in M. cryptus which suggest that osmoregulatory ability improves with developmental stage. There is also limited evidence for the ability of the late embryonic stages to hypo‐osmoregulate on concentrated media, even though adults lack this capacity. 5. The results are discussed in relation to the colonization of the terrestrial environment by the Talitridae.
Effect of nectar‐robbing birds on fruit set of Fuchsia magellanica in Tierra Del Fuego: a disrupted mutualism
Authors: Traveset A. , Willson M. F. , Sabag C. 
Published: March 2003

1. This paper investigates spatial habitat variation in flower visitation by avian pollinators (mainly Hummingbirds) and nectar robbers to Fuchsia magellanica at the southern limit of its range, Tierra del Fuego, and their effects on plant reproductive success. 2. The plant‐pollination mutualism appears to be disrupted as Hummingbirds (Sephanoides galeritus) are rare at this high latitude and the frequencies of a nectar‐robbing bird (Phrygilus patagonicus) are high, especially in open areas where F. magellanica is most abundant. 3. Nectar robbery by P. patagonicus reduced fruit set about 20%, mainly because this fringillid can damage the ovary when piercing a flower. This bird was more abundant in open areas than inside the forest and, as expected, flower piercing was also more frequent in the former habitat. 4. Spatial variation was also found in the frequency of flower visitation by Hummingbirds; these birds foraged chiefly in the forest presumably because of the greater probability of finding intact (non‐robbed) flowers there. This suggests that cross‐pollinations in this self‐compatible plant are more likely to occur in the forest. Nectar robbers therefore may influence not only the quantity of seeds produced but also, indirectly, their quality. 5.
Fuchsia magellanica is polymorphic in flower colour. Robbery was significantly lower in the pale than in the normal (red) morph, although fruit set was similar between morphs.
The functional morphology of light capture and carbon gain in the Redwood forest understorey plant Adenocaulon bicolor Hook
Authors: Pearcy R. W. , Yang W. 
Published: March 2003

1. A three‐dimensional geometric simulation model of crown architecture was utilized to investigate the efficiency of light capture and its relationship to whole‐plant CO2 assimilation of Adenocaulon bicolor. 2. Positioning of the leaves by the combined effects of ontogenetic variations in petiole length and angle and leaf size, and the leaf divergence angles were shown to be effective in minimizing self shading. The efficiency of light absorption varied from 0·64 to 0·70 among individual plants that were sampled. 3. Plant to plant variation in simulated daily carbon gain was strongly influenced by variations in the direct and diffuse PFD received by the individual plants. When simulations were run for all plants under a single common light environment, the carbon gain was strongly dependent on the efficiencies of light absorption of the different plants. 4. Simulations in which petiole length was varied showed a non‐linear dependence of light absorption efficiency on petiole length. When both petiole length and leaf size were varied in a way that maintained a constant biomass then an optimal petiole length that corresponded to the observed petiole length was apparent. The observed divergence angle between successive leaves also maximized light absorption efficiency as compared to greater or lesser angles, but increases in internode length had no significant effect. 5. The results of this study provide evidence for selection for an ‘optimal design’ of crown architecture in Adenocaulon bicolor that maximizes light capture.
Effects of a 4 °C increase in temperature on partitioning of leaf area and dry mass, root respiration and carbohydrates
Authors: Gunn S. , Farrar J. F. 
Published: March 2003

1. Plants of Bellis perennis, Dactylis glomerata and Poa annua were grown from seed in controlled‐environment cabinets at either 16 or 20 °C; at the higher temperature all three species had increased total dry mass and leaf area when assessed on the basis of chronological time. On the basis of thermal time (summation of degree‐days above 0 °C; days °C) temperature decreased the dry mass in P. annua. 2. Partitioning was assessed as a change in the allometric coefficients relating shoot and root dry mass, leaf and plant mass, leaf area and plant mass, and leaf area and leaf mass. Of the 12 relationships examined only three were affected by temperature: there was increased partitioning towards the shoot relative to the root in D. glomerata and increased partitioning towards leaf area rather than leaf mass in D. glomerata and B.perennis. 3. Root respiration was unaffected by temperature of growth in D. glomerata and P.annua but was lower in B. perennis grown at elevated temperature. 4. Root respiration acclimated to temperature in P. annua and B. perennis (i.e. when measured at the same temperature, respiration was higher in plants grown at 16 °C). 5. Root soluble carbohydrate concentration was unaffected by temperature of growth in any of the species. Feeding sucrose to the roots for a short period had no effect on the rate of respiration of B. perennis or D. glomerata but increased root respiration of P. annua.
Temperature, nitrogen availability and mixture effects on the decomposition of heather [Calluna vulgaris (L.) Hull] and bracken [Pteridium aquilinum (L.) Kuhn] litters
Authors: Anderson J. M. , Hetherington S. L. 
Published: March 2003

1. Heather moorlands in the upland regions of the United Kingdom are under threat from changes in land use and management, the potential effects of atmospheric nitrogen deposition and climate warming. Displacement of heather (Calluna vulgaris) stands by bracken (Pteridium aquilinum) is also widespread. 2. Field (Upper Teesdale National Nature Reserve) and laboratory studies were carried out to investigate decomposition rates of heather and bracken litters. The effects of fertilization with mineral N (50 kg ha–1 year–1 added in four increments) and temperature responses of microbial respiration in decomposing litters were determined. 3. The qualities of heather and bracken litters were similar with 1·5% N, 22·3% cellulose and 40·6% lignin in heather, and 1·32% N, 28·9% cellulose and 49·0% lignin in bracken. Total concentrations of phenylpropanoid derivatives (PPDs) from lignin (by alkaline CuO oxidation) and total hydrolysable carbohydrates (using TFA) were similar for the two litter types, but there were qualitative differences in the constituents of the lignins and hemicelluloses. 4. Bracken and heather litters in 1 mm mesh bags both lost about 34% of initial mass over 18 months but 1:1 mixtures of the two litters showed 14% higher losses over the same period. These mixture effects could not be explained in terms of litter quality. Laboratory studies, on litter mixtures incubated on sterile sand and soil organic matter, suggested that the mechanisms involved interactions between components of litter microbial communities; possibly fungal endophytes. 5. The decomposition rates of heather and bracken litters were about 10% higher in the N‐fertilized plots than control plots while the mixtures showed nearly 15% higher mass losses. 6. Heather and bracken litters incubated in the laboratory with temperature cycles varying from 2 °C to 24 °C for heather and 2 °C to 27 °C, for bracken, showed rapid depletion of available carbohydrates over 2 months. Despite the changes in litter quality the temperature response coefficient (Q10≅ 2·5) showed little change over this period. 7. It is concluded that synergistic interactions between litter types, which may occur when bracken invades heather stands, can significantly increase surface litter decomposition rates and that N fertilization can further enhance mass losses. The extent to which these interactions affect litter standing crops, plant species interactions and organic matter dynamics in peaty upland soils, remains to be determined.
In memory of C. S. Pittendrigh: Does exposure in forest canopies relate to photoprotective strategies in epiphytic bromeliads?*
Authors: Griffiths H. , Maxwell K. 
Published: March 2003

1. Photoprotective strategies were investigated in 10 epiphytic bromeliad species in Trinidad with contrasting preferences for the light environment, according to exposure groups categorized by C.S. Pittendrigh in 1948 (viz. Exposure, Sun and Shade‐Tolerant). 2. Chlorophyll a/b ratios were relatively consistent under both high and low light, despite large differences in total chlorophyll content. 3. Diurnal patterns of photosynthesis were examined in three C3 species. Carboxylation limitation was ubiquitous and despite some evidence for the operation of alternative electron sinks, utilization of photon energy was minimal. 4. Irrespective of exposure group and photosynthetic pathway (C3 or CAM), all species exhibited a very high capacity for thermal dissipation of excess excitation. 5. Non‐photochemical quenching of chlorophyll fluorescence in leaves of Exposure and Sun Group species was largely rapidly relaxing, indicative of a photoprotective down‐regulation of photosynthesis. In contrast more slowly relaxing quenching (qI) was the major component in the Shade‐Tolerant Group, suggesting a greater probability of photodamage for species within this group. 6. C.S. Pittendrigh supported the view that many bromeliads low in the canopy were shade‐tolerant, suggesting that the epiphytic ancestor originated in exposed, open regions. Our fluorescence quenching data support this assertion.
Lichen respiration in relation to active time, temperature, nitrogen and ergosterol concentrations
Authors: Sundberg B. , Ekblad A. , Näsholm T. , Palmqvist K. 
Published: March 2003

1. Respiration in eight lichen species was related to thallus hydration status, external temperature and to total nitrogen, chitin and ergosterol concentrations. Chitin is a nitrogenous and major compound of the fungal cell wall, and ergosterol is a sterol of the plasma membrane in fungi and sometimes in algae. 2. Hydration of previously dry thalli resulted in an initially high rate of respiration. Both the amplitude of this resaturation respiration and the time required to reach steady state varied among species. Generally, peak rates were one to three times higher than steady‐state rates, which were reached 3–7 h after hydration. 3. Increases in external temperature also resulted in transient bursts in respiration. Again, both the amplitude of the burst and the time required to reach steady state varied among species. Also depending on species, a temperature increase from 5 to 15 °C resulted in two‐ to fivefold increases in steady‐state respiration. 4. Steady‐state respiration, at optimal thallus hydration and a given temperature, varied three‐ to sixfold among the species, when related to thallus dry mass. This difference correlated best (r2 = 0·89) with their ergosterol concentration, where a doubling in ergosterol resulted in more than a doubling in respiration. Respiration correlated less well to total nitrogen or chitin. 5. The chitin to ergosterol ratio varied more than one order of magnitude between the species, where species with high nitrogen concentrations had the highest ratio. This implies that species with access to ample amounts of nitrogen can make more fungal cell walls in relation to plasma membrane surface area.
The effect of water supply on seed‐bank analysis using the seedling‐emergence method
Authors: Ter Heerdt G. N. J. , Schutter A. , Bakker J. P. 
Published: March 2003

1. When using the seedling‐emergence method to analyse a soil seed bank the greenhouse conditions should match the germination requirements of the species involved. Although the seedling‐emergence method is common practice in ecological studies, the germination characteristics of many species are not known, or are only partly known. 2. Before carrying out a large‐scale seed‐bank study in a wet dune slack, we tested the water requirements of the species in the seed bank, comparing a waterlogged soil with a moist soil. Four species germinated in significantly larger numbers in a waterlogged soil, seven species in a moist soil and 11 species showed no significant difference. When a species was present in low densities, it was often missed using the less appropriate treatment. 3. These results emphasize the need for a preliminary study before carrying out a seed‐bank analysis and show the danger of using a ‘standard’ method to analyse soil samples from different habitats.
Energy regulation by traplining hummingbirds
Authors: Gass C. L. , Garrison J. S. E. 
Published: March 2003

1. A published model of constant diurnal energy accumulation by territorial hummingbirds does not accurately reflect the temporal distribution of feeding behaviour of traplining hummingbirds, Phaethornis longirostris (Long‐Tailed Hermit Hummingbirds). 2. In an enclosure study, gross nectar intake by P. longirostris decreased through the day, mirroring nectar production rates in its natural food‐flowers and mimicking its natural foraging patterns. 3. Using a simulation model, the energetic consequences of constant and decreasing net energy intake rates for traplining hummingbirds are compared. 4. Given natural patterns of nectar production, model birds with decreasing diurnal net intake rates met their energetic needs with fewer flowers than those with constant net intake, and spent less time foraging. 5. It is concluded that P. longirostris do not satisfy the physiological assumptions of the published model, and that in this way they are different from the territorial species on which the model has previously been tested.
Patch use in a diurnal rodent: handling and searching under thermoregulatory costs
Authors: Bozinovic F. , Vásquez R. A. 
Published: March 2003

1. The role of physiological complexity in animal foraging ecology was investigated through experiments to determine how animals manage time and energy during patch use under thermoregulatory costs. The Degu Octodon degus (Molina 1782), a diurnal rodent inhabiting the semiarid environments of central Chile, was studied. 2. Previous studies reported that Degus are constrained to specific foraging areas mainly by limits to thermal tolerance and food quality. Predation risk may also be important. Because new evidence shows that physiological processes are important in shaping foraging ecology, it was hypothesized that Degu foraging behaviour is influenced by the risk of hyperthermia as well as by the advantages of gathering food efficiently. 3. Feeding trials were conducted in an experimental arena with food offered in an experimental patch containing sand and placed under a heater. Using video cameras, the overall time budget was measured, including frequency and duration of patch visits, and events of food gathering. Besides ambient temperature (high or low), handling time was manipulated by using husked and unhusked sunflower seeds, and searching time by using two seed distributions. 4. Ambient temperature and husk state as well as ambient temperature and seed distribution interacted in their influence on both handling time and searching efficiency. These results imply that a thermally risky patch affects both parameters associated with patch use and diet selection and that this effect disappears when animals are not risking hyperthermia. 5. Degus decreased the frequency of patch visits under thermoregulatory costs. This behaviour resulted exclusively from the effect of ambient temperature. Data on time use suggest that direct exposure to higher environmental temperatures is avoided through changes in the duration of patch visits. Degus harvested food items in shorter foraging bouts when food was under a stressful thermal patch. 6. In conclusion, a time‐minimizing foraging behaviour, in face of Degus’ thermoregulatory physiology and related risks, was observed.
Plant species and nitrogen effects on soil biological properties of temperate upland grasslands
Authors: Bardgett R. D. , Mawdsley J. L. , Edwards S. , Hobbs P. J. , Rodwell J. S. , Davies W. J. 
Published: March 2003

1. The aim was to assess the extent to which the microbial biomass and activity, and community structure of fertilized upland grasslands are directly related to changes in soil N availability or indirectly related to individual plant species effects caused by changes in plant species composition and dominance. We investigated the short‐term interactive effects of dominant plant species (Lolium perenne, Agrostis capillaris, Holcus lanatus and Festuca rubra) and nitrogen (N) amendment using an N‐limited upland grassland soil. 2. In soils planted with different grass species, soil microbial biomass, and to some extent microbial activity, were determined by temporal changes in plant productivity. Variations in the way that individual plants influenced soil microbial biomass and activity were highly inconsistent over time, and largely independent of N‐additions and differences in plant productivity. At the final sample date, those grass species which co‐dominate the total plant biomass of intermediate fertility (H. lanatus) and semi‐improved grasslands (A. capillaris and F. rubra) had a beneficial effect on the soil microbial biomass. In contrast, the dominant plant species of improved grasslands, L. perenne, had zero or a negative effect on soil microbial biomass. Two plant species (A. capillaris and H. lanatus) increased the proportion of fungi relative to bacteria in the soil microbial community, relative to the unplanted control soil and the other plant species. Lolium perenne and A. capillaris reduced the evenness of microbial PLFAs, suggesting negative effects of these plant species on the diversity of the soil microbial community. 3. The addition of N had no consistent effect on measures of soil microbial biomass or activity, but significantly altered the structure of the microbial community in favour of fungi. The lack of effects of N‐addition on microbial biomass and activity were despite the finding that nitrogen addition reduced root biomass in all plant species and increased rhizosphere acidity. 4. The results suggest that in the short term, the abundance and activity of soil micro‐organisms in upland grasslands are regulated more by plant species traits than by a direct effect of nitrogen. These effects are likely to be related to variations amongst plant species in root exudation patterns and/or efficiency of nutrient aquisition. 5. Our study provides evidence that the functional characteristics of dominant plant species are important determinants of soil biological properties, and hence ecosystem functioning in temperate upland grasslands.
Contrasting adaptation of twoEucalyptussubgenera is related to differences in respiratory metabolism
Authors: Anekonda T. S. , Criddle R. S. , Bacca M. , Hansen L. D. 
Published: March 2003

1.The largest eucalypt subgenusSymphyomyrtussurvives and grows better in diverse native and exotic environments than the second largest subgenusMonocalyptus. Previously postulated reasons for this difference, including differential resistance to native insect pests and dependence on specific ectomycorrhizal symbiotic associations with soil fungi, do not fully explain the marked adaptive differentiation.2.This work shows that differences between the subgenera in survival and growth performance are related to respiratory parameters. We propose that effects of climatic temperature on respiratory metabolism result inSymphyomyrtusbeing more successful thanMonocalyptusin adapting to diverse environments. This suggests a new paradigm for adaptation and evolution of eucalypts.
Reducing losses to offspring mortality by redistributing resources
Authors: Greeff J. M. , Storhas M. G. , Michiels N. K. 
Published: March 2003

1. It is shown that reallocation of resources from dying offspring to their surviving siblings leads to significant reductions of fitness losses due to early developmental errors. 2. The reason resource reallocation can improve offspring fitness is because mothers do not provide offspring with the optimal amount of resources from the offspring’s point of view. Rather, mothers trade their investment per offspring off against the number of offspring. Hence, surviving offspring can use reallocated resources fruitfully. 3. Animals suffering high offspring mortality can reduce this cost by producing large packages of resources shared by offspring. This allows for better reallocation of resources. Furthermore, by overstocking their resource packages with eggs they can anticipate embryo mortality and obtain offspring that will on average be more optimal in size. 4. In accordance with our prediction, parthenogenetic flatworms studied here produce larger cocoons than sexuals and they overstock smaller cocoons with eggs. However, higher embryo survival in large cocoons may also explain both these phenomena.