bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Context‐dependent aggregation in Common Frog Rana temporaria tadpoles: influence of developmental stage, predation risk and social environment
Authors: Nicieza A. G.
Published: March 2003

1. This study examines the aggregation behaviour and activity of larvae of the Common Frog Rana temporaria in relation to the early social environment, ontogeny and the presence of chemical cues from a predatory fish to address three main questions: (i) Does previous social interaction influence aggregation behaviour in later developmental stages? (ii) To what extent does aggregation behaviour depend upon the risk level perceived by the individual? (iii) Does aggregation behaviour change through ontogeny?

2. Tadpoles were reared from eggs either in small groups or in complete isolation. In relatively early stages of development, tadpoles showed no preference for the side of the test container containing siblings over the side containing no larvae regardless of the social context experienced (isolation or contact with siblings).

3. The presence of chemical cues from a potential predator did not trigger the aggregation behaviour of tadpoles, but it had a remarkable effect on their activity and spatial distribution. Tadpoles exposed to water preconditioned by a predator spent significantly less time swimming and avoided the central area of the test container more frequently than did controls exposed to unconditioned water.

4. Tadpoles were more active, avoided the central section and associated preferentially with conspecifics (siblings) at later stages of development regardless of the social conditioning they had previously experienced.

5. Individuals reared in groups were twice as active as individuals reared in isolation. This suggests that the early social environment experienced by larvae can influence future behaviour and thereby growth and development rates.

6. The expression of conspecific attraction is probably linked to an ontogenetic shift in larval behaviour. However, reduced activity, rather than aggregation, appears to be the basic antipredator mechanism in larval Common Frog.
The effect of tissue complexity and sward height on the functional response of Wood Bison
Authors: Bergman C. M. , Fryxell J. M. , Gates C. C.
Published: March 2003

1. Little is known about the interplay between tissue complexity and tissue selection and its effect on the ungulate functional response. Effects of sward height and of bison tissue selectivity on the functional response of bison Bison bison athabascae Rhoads were examined.

2. The height of stem present in a sward was varied. Grazing depth of bison was negatively related to height of stem, and this relationship was more pronounced in tall swards. Bison preferred leaf to stem tissue at all sward heights, though preference of leaf was positively related to sward height.

3. While controlling for selectivity, a factorial design was used effectively to uncouple sward height from sward biomass. Intake rates and bite sizes obtained on simple swards were used to quantify functional responses. Without tissue selection, sward height had no effect on the functional response. Sward biomass explained 90% of the variation in intake rates.

4. Rates of bison food intake on complex swards with both stem and leaf tissue were significantly depressed at low sward biomass, relative to those obtained on simpler leaf‐only swards. Thus, sward tissue composition is a crucial covariate for characterizing intake rates of grazing ungulates.
Carbon and water exchanges of two contrasting central Siberia landscape types: regenerating forest and bog
Authors: Valentini R. , Dore S. , Marchi G. , Mollicone D. , Panfyorov M. , Rebmann C. , Kolle O. , Schulze E.‐D.
Published: March 2003

1. In central Siberia Pinus sylvestris forests and bogs are common elements of the landscape and they show different functional behaviour in terms of energy and carbon exchanges.

2. The two ecosystems show a remarkable difference in energy dissipation, with average Bowen ratios of 0·6 and 2·9, respectively.

3. The alternation of bogs and forests with different energy partition at the surface could affect rainfall distribution and the disturbance regimes (lightening and fires) and drive the ecology of such a complex landscape.

4. During summer, water shortage and poor nutrient conditions in the soil heavily affect carbon exchange rates of the regenerating forest (− 7·7 mmol m−2 day−1). Consequently the bog becomes a significant dominant carbon sequestration element of this particular landscape with higher rates of carbon uptake (− 104·2 mmol m−2 day−1).
Stable isotope ratios of carbon and nitrogen in natural populations of Drosophila species and their hosts
Authors: Markow T. A. , Anwar S. , Pfeiler E.
Published: March 2003

1. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were determined in seven species of wild‐caught Drosophila (see Patterson & Stone 1952) and their natural hosts in order to assess if any relationships existed between isotope signatures of the flies and their hosts. The species included the cosmopolitan D. hydei, D. arizonae, D. simulans and D. pseudoobscura collected from rotting fruit (commercial melons), and the cactophilic D. nigrospiracula, D. mojavensis and D. pachea collected from their specific host plants (Saguaro, Organpipe and Senita Cactus, respectively).

2. Isotope signatures were clearly different among the natural hosts, with fruit and each species of cactus segregating into a non‐overlapping pattern on plots of δ13C vsδ15N.

3. Wild‐caught Drosophila exhibited interspecific differences in isotope signatures that reflected the patterns observed for their natural hosts. For most species, values for δ15N were 3·0–5·‰ higher in the flies, in agreement with the expected δ15N enrichment with increased trophic level.

4. For D. nigrospiracula, changing food resources from the natural host (Saguaro) to a laboratory diet of yeast for only 24 h resulted in a shift in stable isotope signatures toward the values of the new resource.

5. The results suggest that stable isotope analysis can be a valuable tool in studies of resource ecology and feeding habitats in Drosophila, and is sensitive enough to detect recent feeding history.
Site history affects soil and plant 15N natural abundances (δ15N) in forests of northern Vancouver Island, British Columbia
Authors: Chang S. X. , Handley L. L.
Published: March 2003

1. About 10 years after establishment, plantations of Western Redcedar (Thuja plicata Donn ex D. Don) on northern Vancouver Island, British Columbia become nutrient deficient and chlorotic, grow slowly, and are susceptible to invasion by the ericaceous shrub Salal (Gaultheria shallon Pursh.).

2. To test the hypothesis that δ15N can be related to site histories (site disturbance, soil N dynamics and plant development), we measured soil and foliar δ15N in the summer of 1992 in 3‐year‐old (nutrient‐sufficient) and 10‐year‐old (nutrient‐deficient) plantations and in old‐growth stands. The foliar and soil δ15N values of the plantations and old‐growth forests were different and closely reflected site histories. Salal invasion and nutrient deficiency interacted to depress the growth of Redcedar in 10‐year‐old plantations.

3. Site preparation destroyed the top soil organic layers (fresh and decaying litter) and forced Salal (ecto‐ and ericoid mycorrhizal) into the humus layer, where it was in direct competition with Redcedar, thereby disadvantaging arbuscular mycorrhizal/non‐mycorrhizal Redcedar in its nutrient acquisition during a period when N and P are severely limited.

4. There was a large seasonal range of foliar δ15N (5·5 and 4·3‰ for 10‐year‐old Redcedar and Salal, respectively), and there was no relationship between foliar δ15N and measured rooting depth, demonstrating that rooting depths cannot be used to explain foliar δ15N variation among coexisting woody taxa.

5. Foliar and soil δ15N declined with site age and with a presumed change from ‘open’ to ‘closed’ N cycling; the 15N‐depleting effects of mycorrhizal N transformations contributed to the observed δ15N decline.
A framework for understanding the relationship between environment and vegetation based on the surface area to volume ratio of leaves
Authors: Roderick M. L. , Berry S. L. , Noble I. R.
Published: March 2003

1. Existing data show that the surface area to volume ratio (Λ) of leaves generally decreases along both aridity and altitudinal gradients. That results in the relations: Λ decreases as it gets drier and hotter, as well as wetter and colder. Thus variations in rainfall and temperature do not explain the gross trends in Λ in a consistent manner. We hypothesized that Λ should vary in a regular manner with variations in light, water, nutrients and CO2, because recent work has shown regular relationships between Λ and the carbon, nitrogen and water contents of leaves.

2. To test the hypothesis we used existing measurements of leaves from various eucalypt species along aridity, altitudinal and fertility gradients in south‐east Australia. The measurements were converted from a dry mass to a volumetric basis using an empirical leaf model known as the RSBS‐model leaf.

3. Variation in leaf composition and morphology generally followed that predicted by the RSBS‐model leaf.

4. We found that Λ increased with site fertility. Analysis of data from the literature showed that increasing the supply rate of nitrogen also results in an increase in Λ. We conclude that increases in site fertility are associated with increases in Λ.

5. Leaf thickness increased (hence Λ decreased) with light along the aridity and altitudinal gradients, in agreement with theoretical predictions. The increase in light along the aridity gradient is attributed to a decrease in cloud cover, while the increase in light with altitude is due to a decline in the optical thickness of the atmosphere.

6. Along the altitudinal gradient, the soils became increasingly boggy and anoxic with elevation, leading to increased soil acidity and a consequent decline in oxygen and nutrient availability. In contrast, along the aridity gradient decreases in nutrient availability were related to dry soil.

7. Both an excess and shortage of soil water can lead to reductions in the availability of oxygen and/or nutrients. When that relationship was considered, we found that a consistent framework linking Λ with the availability of light, water, nutrients and CO2/O2 could be established. In that framework, leaf area is controlled jointly by the availability of water and nutrients, while leaf thickness is controlled by the availability of carbon (i.e. light, CO2). Λ is the result of interactions between those two factors. The resulting framework should be useful in the development of models linking vegetation with environmental conditions.

8. A method for extending these results to the modelling of vegetation communities is proposed.
Trade‐offs between egg size and number in waterfowl: an interspecific test of the van Noordwijk and de Jong model
Authors: Christians J. K.
Published: March 2003

1. Van Noordwijk & de Jong proposed a model to predict the sign of an intraspecific correlation between two life‐history traits, given that a trade‐off between the two traits exists. In this paper, the model is adapted to egg size/number trade‐offs.

2. The predictions of the model are tested within various clades of waterfowl. Although the relationship between egg mass and clutch size in this group has been examined previously, prior analyses have either failed to take phylogenetic structure into account or relied upon phylogenies that lack resolution. Phylogenetic structure is adjusted for using recently constructed phylogenies and the method of phylogenetically independent contrasts.

3. Van Noordwijk and de Jong's model was successful in explaining between‐clade variation in the relationship between egg mass and clutch size. Even if a trade‐off between egg size and number exists, a negative relationship will only be observed if the variation in the pattern of allocation (i.e. few large eggs vs many small eggs) is high relative to the variation in the amount of resources invested in the clutch. Thus, this model may be useful for understanding interspecific relationships as well as intraspecific patterns.
Temporal, spatial and biotic variations in extrafloral nectar secretion by Macaranga tanarius
Authors: M. Heil , B. Fiala , B. Baumann , K. E. Linsenmair
Published: March 2003

Many plants produce extrafloral nectar (EFN) to nourish ants and other animals which defend them against herbivores. We aimed to find reasons for the high variability in amounts of EFN produced by most plant species. We investigated the influence of several biotic and abiotic factors (time of day, leaf age, nectar removal and leaf damage) on secretion rates of EFN in the common south‐east Asian pioneer tree species, Macarangatanarius (L.) Muell. Arg.

In most experiments leaves were washed with pure water and bagged in nets to protect them against nectar‐collecting insects, and nectar was collected and quantified 24 h later. Six soluble sugars and up to eight amino acids were detected in nectar samples derived from untreated, field‐grown plants. Total amounts of soluble substances varied more than the relative composition of EFN.

Nectar secretion rates were highest on young, expanded leaves. A diurnal pattern with a secretion peak in the first 2 h after dusk was detected in the field. Nectar removal had a positive effect and its accumulation a negative effect on further EFN production. Artificial leaf damage (punching leaves with a needle or removing parts of the leaf blade with scissors) led to a significant induction of EFN production for the next 3 days.

Extrafloral nectar of M. tanarius was secreted in complex patterns influenced by different biotic and abiotic factors; its production appeared to be adapted temporally and spatially in order to ensure optimal use of invested resources.
The capture and gratuitous disposal of resources by plants
Authors: H. Thomas , Sadras V. O.
Published: March 2003

Every plant will die if light, water or nutrients are withheld for long enough. It is natural to think of plants in general as having evolved a strong drive for resource acquisition as a survival mechanism. All else being equal, an individual that sequesters more material from the environment than its neighbour must be at a competitive advantage.

 But the resource capture imperative seems at odds with the profligacy of some characteristic developmental and metabolic processes in many plants. Here, using leaf senescence as a vantage point, we consider whether a kind of wilful inefficiency of resource use may not be essential for success as a terrestrial autotroph.
Determinants of within‐ and among‐clutch variation in levels of maternal hormones in Black‐Headed Gull eggs
Authors: T. G. Groothuis , H. Schwabl
Published: March 2003

1. Females of egg‐laying vertebrates may adjust the development of their offspring to prevailing environmental conditions by regulating the deposition of hormones into their eggs. Within‐ and amng‐clutch variation in levels of steroid hormones were studied in the egg yolks of the Black‐Headed Gull (Larus ridibundus, Linnaeus) in relation to environmental conditions at the nest site. This species breeds in colonies of different densities and in different habitats, and the chicks hatch asynchronously.

2. Egg yolks contained very high levels of androstenedione, substantial levels of testosterone and moderate levels of 5α‐dihydrotestosterone. Oestrogen (17β‐oestradiol) was not detected.

3. Androgen levels increased strongly with laying order, irrespective of egg or yolk mass. This may compensate for the disadvantages of the later hatching chicks. These results have implications for adaptive hypotheses that were proposed for asynchronous incubation.

4. Eggs of lighter clutches contained more androgens, perhaps to compensate for a lower nutritional quality of these eggs.

5. Birds breeding in the periphery of a colony, being relatively more aggressive and having relatively large territories, laid eggs that contained more androgens than those of birds breeding in the centre. These high yolk androgen levels may facilitate growth and motor development of the chicks, which may be especially important for chicks developing at the periphery of a colony. Reduced levels may be adaptive for birds breeding in the centre, where risk of infectious diseases is high, since steroids may be immunosuppressive.

6. Corrected for nest distance, clutches of birds in high vegetation, where predation risk is less severe and therefore competition for nest sites perhaps high, contained relatively high levels of androgens. It is suggested that the level of yolk androgens reflects the hormonal condition of the female, that in turn is influenced by her characteristics such as her age and aggressiveness, and the level of social stimulation.
The functional response does not predict the local distribution of European Rabbits (Oryctolagus cuniculus) on grass swards: experimental evidence
Authors: Iason G. R. , Manso T. , Sim D. A. , Hartley F. G.
Published: March 2003

1. The relationship between available biomass and short‐term rate of intake (functional response) of herbivores is expected to provide a link between their food supply, and their distribution.

2. The functional response of captive wild rabbits (Oryctolagus cuniculus L.) on artificially produced broad‐leaved (Lolium perenne L.) and narrow‐leaved (Festuca ovina L.) grass swards was quantified.

3. The general prediction that habitat selection varied with biomass, and reflected the potential rate of intake defined by the functional response, was also tested. The main alternative predictions, that both intake rate and habitat selection increased asymptotically with biomass, or were biased towards intermediate habitat standing crop biomasses, were distinguished.

4. There was no relationship between biomass and short‐term rate of intake on the narrow‐leaved Festuca swards, but on the broad‐leaved Lolium sward the short‐term rate of intake increased asymptotically with biomass.

5. In a field experiment on Lolium swards, a population of free‐living wild rabbits selected the shortest swards with the lowest biomasses, and which provided the lowest potential rates of intake.

6. Results demonstrate that free‐living wild rabbits do not select habitats that provide the maximum potential rate of intake, nor did they select foraging habitat with intermediate standing crops. It is suggested that their selection of foraging areas in these grasslands which typify rabbit foraging habitat, is dominated by antipredator considerations rather than purely by rate of intake.
Do shade‐tolerant tropical tree seedlings depend longer on seed reserves? Functional growth analysis of three Bignoniaceae species
Authors: Kitajima K.
Published: March 2003

1. A functional growth analysis was used to determine the duration of strict dependency on seed reserves for energy and nitrogen in three woody Bignoniaceae species (Tabebuia rosea DC., Challichlamys latifolia K. Schum. and Pithecoctenium crucigerum A. Gentry) which differed in cotyledon function (photosynthetic, semi‐photosynthetic and storage) and shade tolerance (probability of seedling establishment and survival in the understorey).

2. Seedlings were raised from seeds in sand culture under combinations of three nitrogen levels (daily supply of nutrient solution containing 100, 10 and 0% of 2·6 mm N) and two irradiances (27 and 1% full sun). Time course of biomass, non‐cotyledonous biomass and leaf area for 40 days post‐germination were compared to identify when the external availability of nitrogen or light began to affect seedling growth.

3. Seedlings of all species became dependent on external energy supply earlier than they did on nitrogen supply. In all species seed nitrogen was sufficient to support positive seedling growth for 40 days in shade, but not in sun.

4. Tabebuia rosea with photosynthetic cotyledons responded to light availability earlier than more shade‐tolerant species with storage cotyledons. Challichlamys latifolia, the most shade‐tolerant species, had the highest nitrogen concentration in seeds and was the last to respond to external nitrogen availability. Thus seedlings of the most shade‐tolerant species depended on seed reserves for the longest period for both energy and nitrogen.

5. Relative growth rate after seedlings initiated autotrophic growth was in a trade‐off relationship with seedling survivorship in the understorey across the three species. Tabebuia rosea, the least shade‐tolerant species, had the highest positive net carbon balance in sun and shade.

6. Functional morphology of cotyledons and concentration of seed nitrogen deserve as much attention as seed size as correlates of contrasting seedling regeneration strategies.
Host provenance effects on germination and establishment of two New Zealand mistletoes (Loranthaceae)
Authors: Norton D. A. , Ladley J. J. , Sparrow A. D.
Published: March 2003

The influence of host genotypes (provenances) on mistletoe establishment, or the susceptibility of different host provenances to mistletoe infection, has not previously been documented.

We quantified the germination and establishment of two New Zealand mistletoes [Alepis flavida (Hook. f.) Tiegh. and Peraxilla tetrapetala (L. f.) Tiegh.] on different provenances of their main host Nothofagus solandri (Hook. f.) Oerst. in a ‘common garden’ host experiment.

Germination was high for both species (96·9% for A. flavida and 97·4% for P. tetrapetala), but establishment was much lower (13·2 and 2·3%, respectively).

Deviance explained in statistical models of germination with respect to light, branch growth rate, host tree provenance and tree effects was lower than that explained in models of establishment (20·3 compared with 33·2% for A. flavida; 35·9 compared with 73·7% for P. tetrapetala).

While branch growth rate and host tree provenance were significant variables in the P. tetrapetala establishment model, the most significant effect for both species was due to individual trees within provenances (24·9 and 42·8% of total deviance, respectively, for A. flavida and P. tetrapetala).

Even when a range of factors are accounted for (including branch growth rate and host tree provenance), there is still a large degree of unpredictability in mistletoe establishment that reflects either inherent or environmental conditions associated with individual trees.
Leaf‐level nitrogen‐use efficiency of canopy and understorey species in a beech forest
Authors: Yasumura Y. , Hikosaka K. , Matsui K. , Hirose T.
Published: March 2003

In a forest stand, canopy and understorey species grow at completely different irradiances and consequently with different carbon and nitrogen availability ratios. We studied how the difference in growth irradiance influenced plant N use in a mature beech forest.

We defined leaf‐level nitrogen‐use efficiency (NUEL) as the amount of the leaf dry mass produced per unit N taken up by leaves. NUEL was similar between the canopy species (Fagus crenata) and the understorey species (Lindera umbellata and Magnolia salicifolia).

NUEL was analysed further as the product of two components: leaf‐level N productivity (NPL) and mean residence time of leaf N (MRTL). The canopy species had significantly larger NPL and significantly shorter MRTL than the understorey species.

As the photosynthetic capacity was similar among the species, different NPL between the species was attributable largely to the difference in light conditions to which their leaves were exposed.

The difference in MRTL was not attributable to potential efficiency of N resorption (REFF) determined at leaf senescence, but to actual REFF, which depended on the amount of green leaf lost before full senescence. The canopy species had significantly smaller actual REFF because of strong wind actions in the canopy.

Although the canopy species realized higher NPL by virtue of high irradiance, it had shorter MRTL due to wind damage to pre‐senescent leaves. On the other hand, the canopy species had shorter NPL under shady conditions, but had longer MRTL with little wind damage. Interplay of local environmental factors such as light and wind strongly influenced N use by plants in the beech forest.
A broadening view of recombinational DNA repair in bacteria
Authors: Cox Michael M.
Published: March 2003

Recombinational DNA repair is both the most complex and least understood of DNA repair pathways. In bacterial cells grown under normal laboratory conditions (without a DNA damaging treatment other than an aerobic environment), a substantial number (10–50%) of the replication forks originating at oriC encounter a DNA lesion or strand break. When this occurs, repair is mediated by an elaborate set of recombinational DNA repair pathways which encompass most of the enzymes involved in DNA metabolism. Four steps are discussed: (i) The replication fork stalls and/or collapses. (ii) Recombination enzymes are recruited to the location of the lesion, and function with nearly perfect efficiency and fidelity. (iii) Additional enzymatic systems, including the φX174‐type primosome (or repair primosome), then function in the origin‐independent reassembly of the replication fork. (iv) Frequent recombination associated with recombinational DNA repair leads to the formation of dimeric chromosomes, which are monomerized by the XerCD site‐specific recombination system.
Molecular cloning of cDNA and tissue‐specific expression of the gene for SII‐K1, a novel transcription elongation factor SII
Authors: Taira Yuichiro , Kubo Takeo , Natori Shunji
Published: March 2003

Background

Transcription elongation factor SII has been shown to promote read‐through by RNA polymerase II of pausing sites within various eukaryotic genes in vitro by inducing cleavage of the 3′‐end of the nascent transcript in the ternary elongation complex. Recently, we showed that various mouse tissues contain multiple SII‐related proteins. Of these, ‘general SII’ was ubiquitously expressed, whereas the others were expressed in a tissue‐specific manner. We have identified testis‐specific SII (SII‐T1) and shown that it was expressed exclusively in spermatocytes.

Results

A new SII cDNA clone (pSII‐K1) was isolated from mouse kidney. This clone contained an open reading frame which encoded a protein consisting of 347 amino acid residues (SII‐K1). A comparison of the amino acid sequences of SII‐K1 with those of general SII and SII‐T1 revealed that their amino‐ and carboxy‐terminal regions were very similar, but that the sequence of the 95 internal residues (87/181) was unique to each. The recombinant SII‐K1 produced in Escherichia coli stimulated RNA polymerase II as did general S‐II. The gene for SII‐K1 was found to be expressed strongly in the heart, liver, skeletal muscle and kidney, but not in other tissues examined. Contrary to the expression of the general SII gene, the SII‐K1 gene was expressed only in 15‐ and 17‐day‐old embryos during mouse embryonic development.

Conclusions

We identified a novel member of SII family transcription elongation factor named SII‐K1. This factor was expressed exclusively in the heart, liver, kidney and skeletal muscle. During mouse embryonic development, no significant expression of the SII‐K1 gene was detected before the formation of these tissues.
Developmental patterning in chondrocytic cultures by morphogenic gradients: BMP induces expression of Indian hedgehog and Noggin
Authors: Kameda Takashi , Koike Chika , Saitoh Kanako , Kuroiwa Atsushi , Iba Hideo
Published: March 2003

Background

The maturation of chondrocytes is essential for endochondral bone formation. The Indian Hedgehog (Ihh) gene is expressed in prehypertropic chondrocytes and has been proposed to regulate chondrocyte maturation. While such secretary factors as PTHrP and BMP are thought to be involved in Ihh expression, the mechanism of the restricted expression of Ihh is not clear.

Results

Using primary chondrocytes, we have developed here a modified micromass culture (MM‐C) system that allows the formation of concentration gradients of secreted factors, expressed either endogenously or retrovirally, from each of plural micromass cultures on a single plate. Using this system, we determined that chondrocytes create the inhibitory micro‐environment, partly dependent on PTHrP secretion, for the Ihh expression. We also showed that retrovirally induced BMP‐2 induces the expression of both Ihh and Noggin (encoding the BMP‐inactivating protein), and we further present evidence that a negative‐feedback loop involving Noggin might account for the precise localization of BMP signalling for Ihh induction.

Conclusion

These results suggest that the expression of the Ihh gene in cartilage is regulated by several mechanisms that include the secretion of inhibitory factors (including PTHrP) and the negative‐feed back loop formed by BMPs and Noggin.