bluuebunny/crossref_metadata_2025_split huggingface dataset:
Competition as an amplifier of short‐term vegetation responses to climate: an experimental test
Authors: Dunnett N. P. , Grime J. P. 
Published: March 2003

1. Responses to a spring warming treatment were measured on five common herbaceous species grown in outdoor microcosms in Northern England. Although elevated temperature had a beneficial effect on canopy height and plant cover in monospecific cultures of all species, strongly divergent responses to warming occurred in mixtures. 2. We show that the effect of interspecific competition was to modify and amplify the vegetation response to the warming treatment through effects on phenology and morphological development. 3. The observed responses between the species to warming are consistent with predicted differential responses linked to genome size. 4. We conclude that the mechanism of competitive interaction proposed by Boysen‐Jensen (1929) coupled with the insights related to genome size provide a basis for explaining and predicting the role of interannual variation in temperature in determining year to year fluctuations in the relative abundance of species in productive perennial herbaceous vegetation.
Chemical differentiation between leaves of seedlings and spatially close adult trees from the tropical rain‐forest species Nectandra ambigens (Lauraceae): an alternative test of the Janzen–Connell model
Authors: Sánchez‐Hidalgo M. E. , Martínez‐Ramos M. , Espinosa‐García F. J. 
Published: March 2003

1. We tested the hypothesis of Langenheim and Stubblebine that differences in chemical composition between maternal trees and the seedlings under them arise from differential mortality; only seedlings different from the mother survive. Such mortality could explain at least some of the cases where seedlings accumulate under adult conspecifics, contrary to the extreme form of the Janzen–Connell hypothesis. 2. We investigated Nectandra ambigens (Lauraceae), an upper‐canopy tree at Los Tuxtlas tropical rain forest, Mexico, whose seedlings survive under the canopy of conspecific trees. We analysed chromatographic profiles of leaf terpenoids of 15 groups, each formed by an adult tree and its surrounding seedlings. 3. We predicted that seedlings chemically similar to the adult would be absent under the tree canopy and that they would be present outside that canopy. We also predicted that younger seedlings would be more similar to the adult than the older ones. 4. Chemical similarity analyses showed that most seedlings were significantly different from their closest adult and thus supported the Langenheim and Stubblebine hypothesis. However, we did not find chemical differentiation among seedlings regarding their age or their position inside or outside the tree canopy.
Carbon and water fluxes in Beech–Spruce model ecosystems in response to long‐term exposure to atmospheric CO2 enrichment and increased nitrogen deposition
Authors: Maurer S. , Egli P. , Spinnler D. , Körner CH. 
Published: March 2003

1. We present data on the gas exchange of 32 Beech–Spruce model ecosystems including understorey species, which were planted on acidic or calcareous soil in 16 (half‐split) open‐top chambers in 1994 and were continuously exposed to the combinations of two CO2 concentrations and two wet nitrogen deposition rates for 3 years. 2. Instantaneous mid‐season net ecosystem carbon‐exchange rates (NEC) were determined during the day (11.00–16.00 h, NECd) and at night (22.00–02.00 h, NECn) with a mobile chamber in July 1996 and August 1997 for both soil types and, in addition, in August and September 1996 on acidic soil only. 3. Elevated CO2 increased NECd at all sampling dates on both soil types and under both N deposition rates. Increased nitrogen deposition stimulated NECd on acidic soil but not on calcareous soil, irrespective of the CO2 level. NECn was increased in elevated CO2 on both soil types (but more on the calcareous soil), but did not respond to increased nitrogen deposition in both years. The daytime instantaneous ecosystem evapotranspiration (ETd) was not significantly affected by the CO2 and nitrogen treatments at any sampling date. Year to year differences in NECn and ETd were small, but a doubling in NECd occurred throughout the observation period. 4. Elevated CO2 caused a small but significant increase in stem dry mass on calcareous soil only and increased nitrogen deposition stimulated stem biomass production on acidic soil only. Leaf area index was not affected by CO2, but was increased under high nitrogen deposition. 5. Our results suggest that nitrogen deposition and soil type are major co‐determinants of the carbon balance of forests in a future CO2‐rich world.
More on the meanderings of mangabeys: how to test whether bounded walks are random
Authors: Hutchinson J. M. C. 
Published: March 2003

Abstract1. Barrett & Lowen (1998)andWaser (1976)attempted to explain the net monthly and yearly displacements of Grey‐Cheeked Mangabeys using observed short‐term step lengths and assuming a random walk, with and without boundaries. This paper reanalyses their data.2. Analytic approaches require the root‐mean‐square step length, not the mean. However, a more flexible approach to making and testing predictions is Monte‐Carlo simulation. With a random walk long‐term displacements have a large variance, so a single observation is unlikely to disprove this null hypothesis.3. Restricting movement to a square lattice is a reasonable approximation even when rectangular boundaries are incorporated. Describing the boundary configuration accurately is more important.4. The observed non‐uniformity in turning angles should have been incorporated as it has a large effect on predicted net displacements, unless the arena is tightly constricted. Randomness of movement within a day can be distinguished from that between days. For Waser's population it makes sense to predict long‐term displacements using only long‐distance daily displacements.5. There are better approaches to establish both whether boundaries exist and whether movements follow a random walk.
The carbon balance of a young Beech forest
Authors: Granier A. , Ceschia E. , Damesin C. , Dufrêne E. , Epron D. , Gross P. , Lebaube S. , Le Dantec V. , Le Goff N. , Lemoine D. , Lucot E. , Ottorini J. M. , Pontailler J. Y. , Saugier B. 
Published: March 2003

Abstract1. We present measurements of CO2 fluxes over 2 years above and within a young Beech stand in the east of France. This site is part of the Euroflux network set up to monitor fluxes over representative European forests.2. The net ecosystem carbon (C) exchange was derived from continuous eddy flux measurements. Major components of the total flux (i.e. soil and above‐ground biomass respiration and assimilation of leafy branches) were measured independently using chambers. The main C stocks (i.e. root, stem and branch biomass) were also quantified.3. Daily minima of CO2 flux were typically around −20 µmol CO2 m−2 s−1 during the period of full leaf expansion, while night‐time ecosystem respiration varied between 5 and 15 µmol CO2 m−2 s−1. The seasonal pattern of net ecosystem assimilation was very close to that of net assimilation at the single branch scale. The seasonal variation of net ecosystem exchange was closely related to leaf expansion and soil water content during the dry year of 1996.4. Measurements of ecosystem respiration (eddy flux) were corrected for CO2 storage within the stand. This C flux showed a seasonal pattern, the maximum rates (4–7 g C m−2 day−1) occurring in spring and summer, and appeared to be correlated with soil temperature. Temporal variation of soil respiration showed the same pattern, and effects of both temperature and soil drying were found. Annual soil respiration was ≈ 70% of ecosystem respiration. Root respiration was 60% of the total below‐ground respiration.5. Annual net C exchange was −218 and −257 g C m−2 in 1996 and 1997, respectively, corresponding to net C uptake by the forest. These values are much lower than the annual biomass increment (stems and large roots) of the stand: 427 and 471 g C m−2 year−1, respectively. The difference may be explained by a release of CO2 from the decomposition of woody debris.6. Ecosystem C loss by respiration was 800–1000 g C m−2 year−1. Gross C gain was 1000–1300 g C m−2 year−1. Ecosystem respiration therefore played a major role in the annual C balance of this forest.
Leaf‐level resource use for evergreen and deciduous conifers along a resource availability gradient
Authors: Kloeppel B. D. , Gower S. T. , Vogel J. G. , Reich P. B. 
Published: March 2003

Abstract1. We compared leaf‐level carbon, nitrogen and water use for a deciduous (Larix occidentalis Nutt.) and sympatric evergreen (Pseudotsuga menziesii, Beissn., Franco, or Pinus contorta Engelm.) conifer along a resource availability gradient spanning the natural range of L. occidentalis in western Montana, USA.2. We hypothesized that leaf photosynthesis (A), respiration (r), specific leaf area (SLA) and foliar nitrogen concentration (N) would be higher for deciduous than sympatric evergreen conifers in mixed stands, and that these interspecies differences would increase from high to low resource availability. We also hypothesized that leaf‐level nitrogen and water‐use efficiency would be higher for the co‐occurring evergreen conifer than L. occidentalis.3. In general, mass‐based photosynthesis (Am) was significantly higher for L. occidentalis than co‐occurring evergreen conifers in the drier sites, but Am was similar for evergreen and deciduous conifers at the mesic site.4. Mass‐based foliar nitrogen concentration (Nm) was positively correlated to SLA for all species combined across the gradient (R2 = 0·64), but the relationship was very weak (R2 = 0·08–0·34) for evergreen and deciduous species separately. Mass‐based Am and rm were poorly correlated to Nm for all species combined across the gradient (R2 = 0·28 and 0·04, respectively).5. For each site‐species combination, daily maximum Am was negatively correlated to vapour pressure deficit (VPD) (R2 = 0·36–0·59), but was poorly correlated to twig predawn water potential (R2 < 0·04).6. Instantaneous nitrogen‐use efficiency (NUEi; Am divided by Nm) and water‐use efficiency (δ13C) increased significantly (P = 0·05) from high to low resource availability for both evergreen and deciduous conifers, except for NUEi in L. occidentalis.
Indirect, physiological assessment of reproductive state and breeding chronology in free‐living birds: an example in the Marbled Murrelet (Brachyramphus marmoratus)
Authors: Vanderkist B. A. , Williams T. D. , Bertram D. F. , Lougheed L. W. , Ryder J. L. 
Published: March 2003

AbstractAn indirect, physiological method to assess reproductive state in individuals of unknown status is described. The plasma levels of two main yolk precursors, vitellogenin (VTG) and very‐low density lipoproteins (VLDL), are focused on as indices of egg production, for the characterization of fecund females.Data for a species where breeding chronology could be directly assessed, at the population level (Cassin’s Auklet,Ptychoramphus aleuticus), confirmed the validity of this approach: plasma VTG levels were highest during the defined egg‐laying period, and the highest proportion of females were defined as ‘egg‐producing’ in this period.Analysis of samples for Marbled Murrelets (Brachyramphus marmoratus) caught off‐nest (i.e. where all individuals were of unknown status), clearly identified a putative egg‐laying phase, with a single, protracted laying period (cf. multiple‐broodiness).Analysis of body mass confirmed our characterization of ‘egg‐producing’ females: birds with elevated plasma VTG were on average 40 g heavier than other females, equivalent to the mass of the single egg (36–41 g).Indirect, physiological assessment of reproductive state provided valuable information on the breeding biology of Marbled Murrelets which would have been difficult to obtain in any other way (e.g. proportion of fecund females, breeding phenology, singlevsmultiple‐clutch breeding pattern). Despite some limitations, this technique should be applicable to any oviparous vertebrate population where essential information on breeding biology cannot be obtained by more traditional methods.
Carbon allocation in calcareous grassland under elevated CO2: a combined 13C pulse‐labelling/soil physical fractionation study
Authors: P. A. Niklaus , E. Glöckler , R. Siegwolf , C. Körner 
Published: March 2003

Summary

To test whether plant–soil C fluxes in natural grassland increase under elevated atmospheric CO2 concentration, intact calcareous grassland monoliths exposed to ambient or elevated CO2 were pulse‐labelled and the dynamics of the 13C label followed throughout the rest of the growing season.
The experiment revealed no increased fluxes of C to soils at elevated CO2. The only changes found were relatively small shifts towards increased C allocation to roots by the end of the growing season. This effect was probably because wetter soil under elevated CO2 prolonged the growing period. At elevated CO2, plant C pools increased below ground (+28%) at the end of the season, resulting in slightly increased root : shoot ratios. Plant 13C pools increased significantly below ground. There were no effects of CO2 enrichment on 13C in soil microbes, fine roots or earthworms.
Elevated CO2 caused a shift in soil particle size distribution towards smaller aggregate sizes, but had no effect on the total C and 13C content of low‐ and high‐density soil fractions.
The absence of effects of CO2 on the labelling of soil microbial biomass, and of C and 13C accumulation in low‐density macro‐organic fractions, suggest that there is no significant effect of elevated CO2 on root exudation or turnover, agreeing with published labelling studies, but conflicting with CO2‐exchange budgets.
Nectar ‘theft’ by hummingbird flower mites and its consequences for seed set in Moussonia deppeana
Authors: C. Lara , J. F. Ornelas 
Published: March 2003

Summary

Mites (Acari: Mesostigmata: Ascidae) that live and feed in the flowers of about 100 plant species are transported in the nares of hummingbirds (Trochilidae). Mites may compete with hummingbirds for nectar secreted by the host plants, and this could affect the dynamics and reproductive outcomes of the mutualism between plants and their pollinating hummingbirds.
Here we combined field observations and experimental manipulations to assess the role of hummingbird flower mites (Tropicoseius sp. nov.) on nectar secretion and reproductive output of protandrous Moussonia deppeana (Schlecht. & Cham.) Hanst. (Gesneriaceae) during their flowering period in a cloud forest remnant.
During the 4 days that the flowers of M. deppeana last, flowers were visited exclusively by hummingbirds (Lampornis amethystinus). Bud production per inflorescence peaked in December. There were few open flowers per inflorescence in November, but numbers increased as the flowering season progressed (December and January).
The availability of each flower phase differed over the flowering season. Staminate‐phase flowers were more abundant over the flowering season than pistillate‐phase flowers. These differences were statistically significant over time.
Nectar availability was reduced by up to 50% in the presence of hummingbird flower mites. Over the 4 days of observation, significantly more nectar was secreted to flowers from which mites were excluded than to flowers with no mite exclusion. The same effect was observed during flowering, but mites consumed a greater percentage of the total nectar secreted in December.
Significantly more nectar was secreted during the staminate phase than in the pistillate phase, independent of time and treatment.
A manual pollination experiment suggested that mites act like secondary pollinators in this self‐compatible, non‐autogamous plant, at least in flowers that were not pollinated manually and had no access to pollinating hummingbirds.
Although seed production was not reduced significantly by flower mites, our results suggest that the presence of floral mites can affect pollen transmission, as the amount of nectar available to hummingbirds was reduced drastically. This can directly affect hummingbird foraging patterns and reduce the fitness of the host plants.
Contrasting effects of different types of resource depletion on life‐history traits in Daphnia
Authors: Urabe J. , Sterner R. W. 
Published: March 2003

Abstract1. Life‐history traits of animals are known to change according to food quantity, but there is another type of resource depression, namely depletion of food quality. To examine life‐history responses of herbivores to changes in resource quality, Daphnia obtusa Kurz, a common planktonic herbivore, were reared individually under several algal food regimes with different quantity and quality in terms of chemical composition.2. Compared with Daphnia fed on a small quantity of nitrogen (N) and phosphorus (P) sufficient food, Daphnia fed on a large amount of P deficient food grew more slowly at young ages but continually grew until older ages. This trend was also found for Daphnia fed on a large amount of N deficient food.3. However, the size‐specific reproductive investment (measured as biomass accrued per unit time) of Daphnia fed on a large amount of N or P deficient algae was similar to those fed on a small amount of N and P sufficient food, indicating complex life‐history responses to food quality and suggesting that nutritional requirements for reproduction differ from somatic growth.4. Compared with individuals fed high‐quality and high‐quantity food, Daphnia fed on a large amount of P deficient food produced smaller eggs, while individuals fed on a small amount of P and N sufficient food produced larger eggs. Furthermore, 15–30% of eggs produced by individuals fed on P or N deficient food ceased to develop and were aborted.5. These results demonstrate that life‐history responses to food quality differ from responses to food quantity. Since the chemical composition of algae is highly variable in nature, herbivorous plankton demographics may not be predictable from resource quantity alone.
Soil dilution as a surrogate for root competition: effects on growth of seedlings of Australian tropical rainforest trees
Authors: Metcalfe D. J. , Grubb P. J. , Metcalfe S. S. 
Published: March 2003

Summary

Previous studies on the combined effects of light and nutrient supply on the growth rates of plants have involved adding nutrients to soils to levels rarely (or never) met by the plants in nature. As a better test of the likely response of plants to root competition for nutrients, we grew for 1 year seedlings of six species of Australian rainforest tree on forest topsoil undiluted and on soil diluted 50/50, 25/75 and 5/95 with coarse sand. Seedlings were grown in tall tubes in 6 and 9% daylight, equivalent to gap‐edge and gap‐centre conditions.
The six species varied in their light requirements for establishment and onward growth.
One species grew significantly and markedly more quickly on soil diluted 50/50 with sand (Elaeocarpus grandis). Improved aeration is the most likely explanation.
The extent of inhibition by soil dilution correlated positively with the absolute amount of new dry mass accreted in one year, whether the larger accretion resulted from a combination of high relative growth rate (RGR) and small embryo size, or moderate RGR and larger embryo size.
Soil dilution generally reduced leaf mass fraction and leaf area ratio, but had no significant effect on specific leaf area.
In all species the overall concentration of nitrogen in the whole plant declined with soil dilution; in the four species tested, N concentration in leaves declined, and it is likely that the reduction in growth arose partly from a reduced unit leaf rate. Most species showed increases in the concentrations of P, K, Ca and Mg with soil dilution, or no change, but in Diploglottis bracteata the concentrations of Ca and Mg, especially in the older leaves, declined markedly with soil dilution, and one of these cations could have been limiting growth.
Extrapolation of the results to the field suggests that in single‐treefall gaps the fastest growing species will the most inhibited by root competition.
The soil‐dilution technique is likely to be more appropriate than nutrient addition as an indicator of sensitivity to root competition on a given soil.
Flowering, growth and defence in the two sexes: consequences of herbivore exclusion for Salix polaris
Authors: Dormann Carsten F. , Skarpe Christina 
Published: March 2003

Summary

For a long time, dioecious plants have been a model system for understanding the interactions between plants and herbivores. Differences in growth rate and, consequently, investment in defence between sexes may lead to skewed sex ratios due to differential herbivory.
In this study we evaluated the applicability of this idea to polar willow (Salix polaris), which in the study site, Svalbard, displays a female‐biased sex ratio.
Excluding reindeer for 3 years increased the abundance of male flowers in one of two vegetation types investigated. Growth rates differed only slightly between the sexes, with females investing more in inflorescences.
The concentration of chemical defence compounds (phenolics and condensed tannins) did not differ between the sexes.
On the basis of these findings, the idea that growth rate‐dependent herbivory caused the unbalanced sex ratio in S. polaris has to be rejected. Possibly an interaction of niche differentiation between male and female willows, in combination with reindeer grazing, produced the observed female‐biased sex ratio, but the mechanism remains unclear.
Species‐specific patterns of litter processing by terrestrial isopods (Isopoda: Oniscidea) in high intertidal salt marshes and coastal forests
Authors: Zimmer M. , Pennings S. C. , Buck T. L. , Carefoot T. H. 
Published: March 2003

Summary

The species‐specificity of litter processing by three species of isopods at the interface between salt marsh and coastal forest habitats in the south‐eastern United States was examined.
To quantify isopod performance, measurements were taken of feeding, digestion and growth of isopods fed on three litter types (Juncus roemerianus, Quercus virginiana and Pinus palustris) and on artificial diets containing one of three classes of model phenolic compounds (simple phenolics and hydrolysable and condensed tannins).
To quantify the ecosystem impact of isopods, promotion of microbial respiration, changes in detritus chemistry, and the quantity of litter processed by isopod populations were measured.
The results support three hypotheses concerning isopod–litter interactions. (i) Isopod performance on different litter types can be predicted based on chemical litter traits, e.g. phenolic concentrations and C : N ratios. (ii) Fully terrestrial isopods are better adapted to the range of phenolics found in angiosperm litter than are semiterrestrial species inhabiting the supralittoral. (iii) Isopod species differ with respect to their impact on decomposition processes due to species‐specific digestive capabilities, different effects on microbial decomposition and different rates of net litter processing.
Because isopods are transitional between semiterrestrial and terrestrial habitats, unlike most other salt marsh detritivores, they are likely to play a unique role in decomposition processes and in the flux of materials between salt marsh and terrestrial habitats.