bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract1. 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

Abstract1. 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

Abstract1. 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

Abstract1. 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

Abstract1. 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

Abstract1. 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

Abstract

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

Summary 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

Summary1. 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

Summary 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

Summary 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

Summary

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.