bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mode of Competition and Size‐structure Dynamics in Plant Communities
Authors: HARA TOSHIHIKO 
Published: February 2005

Abstract Competition between individual plants is defined as a mathematical function for the mean growth rate of individuals in a vertically mono‐layered crowded stand as compared with growth of an isolated individual of the same size. The degree of competitive asymmetry can be described mathematically by using this definition. A canopy photosynthesis model for individual growth in a mono‐layered stand shows that physiological and environmental variations have little effects on the size‐structure dynamics of plant populations undergoing strongly asymmetric competition. These variations affect greatly the size‐structure dynamics under symmetric competition. It has also been shown that one‐sided competition (the most asymmetric competition) is never realised in a mono‐layered stand. A spatial competition model shows that variation in the spatial distribution pattern of individuals greatly affects the size‐structure dynamics of populations undergoing symmetric competition, whilst it has little effect on populations undergoing strongly asymmetric competition. Therefore, it can be concluded that a population undergoing strongly asymmetric competition is a stable system little affected by variations in various factors and that a population undergoing symmetric competition is an unstable system greatly affected by these variations.Based on these theoretical results, the relationships between the mode of competition, species diversity and community stability are discussed and a hypothesis on these processes and mechanisms is proposed for grassland and forest plant communities. One‐sided competition is associated with the stability of community structure, and this type of competition works as a structuring force for plant communities. Symmetric competition is associated with species diversity, and this type of competition cannot be a structuring force of plant communities, i.e. symmetric competition is irrelevant to the deterministic community dynamics. Distinctly multi‐layered forests show “apparent” one‐sided competition between layers (i.e. little direct interactions between canopies in different layers, but higher‐layer trees suppress lower‐layer trees one‐sidedly), bringing about structural stability, but trees in each layer undergo symmetric competition, bringing about species diversity. Mono‐layered grassland shows symmetric competition, bringing about small‐scale spatio‐temporal changes in species' abundance and hence species diversity. The real world lies between the two extreme types of competition, one‐sided and completely symmetric, and each plant community has its own position in this continuous spectrum of the competition mode.
Does Physiological Integration Enable Clonal Herbs to Integrate the Effects of Environmental Heterogeneity?
Authors: HUTCHINGS MICHAEL J. , PRICE ELIZABETH A.C. 
Published: February 2005

Abstract The effects of physiological integration on clone behaviour are examined at various structural scales, using data from the stoloniferous herb Glechoma hederacea. The consequences for clone expansion of traumatic fragmentation of the connections between clonal ramets are also illustrated. These results, together with information from other species, are used to refute the commonly‐quoted view that physiological integration between the ramets of clonal herbs evens out the effects of variation in environmental quality, and promotes equitable ramet performance. Instead, clonal species are responsive, at a variety of structural scales, to environmental quality. Therefore, in a heterogeneous habitat, within‐clone variation in the performance of ramets and clonal sub‐structures is to be expected. The seminal study which purports to demonstrate environmental averaging in clonal herbs is shown to be both inadequately designed and inappropriately analysed to accomplish its aim.Physiological and architectural reasons for the local responses to environmental quality seen in the majority of clonal herbs are discussed.
Reproductive Systems and Sibling Competition in Plants
Authors: CHEPLICK G.P. 
Published: February 2005

Abstract Competition among relatives can modify the genetic structure of plant populations; in turn, competitive outcomes can depend on the genetic relatedness of the individuals competing. The offspring from individual parents exhibit a continuum of genetic relatedness, depending on parental reproductive systems. Competition among relatives may have evolutionary significance as a selection pressure; sibling competition, for example, has been invoked to explain the evolution of sexual systems, seed packaging within fruits, seed dispersal dimorphisms, and germination behavior.Density‐dependent fitness consequences of sibling competition have been documented in a population of the annual grass Sporobolus vaginiflorus. This species produces seeds matured in cleistogamous spikelets within leaf sheaths along tillers in autumn: when seeds along the tillers of a maternal parent (i.e. a sibship) germinate in situ the following spring in close proximity to one another, sibling competition results in a high‐density zone centered around the original senescent parent. Both intra‐ and intersibship interactions can occur within a population. Although fitness is much reduced for siblings inside the zone of competition, potential seed rain and net primary productivity per unit area are significantly higher relative to outside the zone. This annual is functionally analogous to a perennial ramet producer with a phalanx growth strategy and the unit of selection may be the sibling group. It is not yet known whether sibling competition is a significant selection pressure in other species, but indirect evidence suggests it may be relatively widespread.
Seedling Establishment of a Canopy Tree Species in Malaysian Tropical Rain Forests
Authors: KACHI NAOKI , OKUDA TOSHINORI , YAP S.K. 
Published: February 2005

Abstract Unlike many other canopy tree species in tropical rain forests, Dryobalanops aromatica (Dipterocar‐paceae, local name: Kapur) establishes monospecific dominant (monodominant) forests in Peninsular Malaysia. In natural conditions, monodominance of Kapur does not necessarily mean low species diversity of the Kapur forests. While the emergent canopy layer is occupied by Kapur, many other plant species, which are common to lowland dipterocarp primary forests in the same region, are found in lower canopy layer and understory.To understand the ecological implications of the monodominance of Kapur, we monitored post dispersal survival and seedling establishment in a pure stand of Kapur in a plantation in Kepong, near Kuala Lumpur. Immediately after seed fall, seeds and cotyledon‐stage seedlings suffered high predation by vertebrates such as rodents. The predation pressure was higher in a more general fruiting year (1991) than in a sporadic fruiting year (1992). In contrast to the high mortality of seeds and newly emerged seedlings, seedlings surviving to the six‐leaf stage showed low mortality, which allowed the establishment of a sapling bank.The occurrence of saplings of Kapur with a wide range of size classes in natural forests indicates that this species is more shade tolerant than other dipterocarp species such as the Shorea group and that it could well respond to enhanced light conditions caused by canopy opening. These characteristics may partly contribute to maintaining monodominance of Kapur.
Temporal Hierarchies of Variation and the Maintenance of Diversity
Authors: CHESSON PETER , HUNTLY NANCY 
Published: February 2005

Abstract A general model shows how the long‐term growth rate of a population can be partitioned into components representing various mechanisms of maintenance of species diversity. One component summarises the effects of fluctuation‐independent mechanisms, which include classical resource partitioning and frequency‐dependent herbivory. Two other components represent fluctuation‐dependent mechanisms, the storage effect and relative nonlinearity of competition.The general model shows how a community will track an equilibrium set by fluctuation‐independent mechanisms and the environmental state when community dynamics are faster than the rate of environmental change. Fluctuation‐dependent mechanisms can be important for diversity maintenance with or without such tracking, but on long timescales their effects are indistinguishable from those of fluctuation‐independent mechanisms.These considerations lead to a hierarchical view of mechanisms of diversity maintenance where the effects of different timescales are partitioned or merged depending on the timescale of observation. These issues are illustrated with model examples involving various combinations of resource partitioning, fluctuations in recruitment rates, variation in the timing of germination, and seasonality. The very long timescales associated with climate change contain many complexities but nevertheless many ideas applicable to shorter timescales may be useful in a modified form.
Life History Evolution in Amphicarpic Plants
Authors: CHEPLICK GREGORY P. 
Published: February 2005

Abstract Plants with dimorphic flowers or seeds provide excellent material for the study of life history evolution because the dimorphism often involves measurable differences in morphology, size, number, or genetic relatedness. For amphicarpic plants, the proportion of aerial: subterranean morphs produced is highly variable (from 0 to > 100) and related to both environmental and genetic factors. Plants from aerial seeds produce lower ratios of aerial: subterranean morphs than those from subterranean seeds. Despite substantial variation, subterranean seeds are generally heavier than aerial seeds (but fewer) and produce vigorous seedlings with high survivorship and high fitness. Adaptive advantages of subterranean seeds include retention of offspring in favorable parental microhabitats, protection of seeds from herbivory, predation, or fire, and avoidance of desiccating conditions on the soil surface; potential disadvantages include lack of gene exchange, high energy costs, limited dispersal, and sibling competition. For the few species studied, aerial reproduction is more plastic than subterranean reproduction and more likely to be affected by environmental conditions.Quantitative genetic analyses of a population of the annual grass Amphicarpum purshii have revealed lower heritabilites for subterranean relative to aerial reproductive traits. Subterranean seed number and mass show genetic correlations with shoot mass while aerial seed number and mass do not; seed set percentages of both seed types as well as percentage allocation to both reproductive morphs show negative genetic correlations with shoot mass. In this Amphicarpum population, directional selection on shoot mass may indirectly select for increased subterranean (but not aerial) seed output.
Molecular Variation in Isolated Plant Populations
Authors: SCHAAL BARBARA A. , LEVERICH WESLEY J. 
Published: February 2005

Abstract Isolated plant populations face a series of demographic and genetic challenges. They potentially may suffer from a loss of allelic and genotypic diversity or from inbreeding depression. The demographic stability associated with migration between components of a metapopulation is lost as fragmentation increasingly isolates populations. Such isolated populations are then increasingly subject to demographic stocasticity and to more frequent population bottlenecks. Some plant species clearly endure this challenge better than others. In studies of native plant species whose populations have long endured isolation, population numbers very often appear stable and populations often contain ample genetic variation. Of course, such observations are biased, since those species which did not accommodate isolation are presumed extinct and thus not studied.When one considers species which have recently undergone habitat fragmentation and population isolation, the ability to accommodate such change is clearly not present in many species. Such populations often show a dramatic decline in numbers as well as erosion of genetic variability. In these populations the role of somatic processes in the generation of genetic variation may assume an increased importance. Since only a few isolated studies have documented such somatic genomic changes in plants, the importance of such changes is subject to speculation.
A Case Study in Experimental Evolution: Reproductive Effort and Induced Responses in Drosophila melanogaster
Authors: STEARNS STEPHEN C. , KAISER MARCEL , BLARER ALBERT 
Published: February 2005

Abstract To understand the causes of tradeoffs, particularly those involved in ageing, to test the reproductive effort model of life history evolution, and to measure the rate of evolution of induced life history responses, we have been performing an artificial selection experiment on Drosophila melanogaster since November 1993. It consists of four treatments, each with three replicates.The first treatment consists of constant high adult mortality; the second treatment of constant low adult mortality. In all four treatments, propyl acetate is present in the medium for 4 weeks, then absent for 4 weeks. In the third treatment, propyl acetate in the larval medium is associated with high adult mortality. In the fourth treatment, propyl acetate is associated with low adult mortality. To ensure that the effects of treatments are due to differences in mortality and not in density, adult and larval density are kept the same in all treatments.In the first two treatments, the evolution of reproductive effort and age and size at maturity has been rapid and has confirmed the predictions of the reproductive effort model. The relationships between age and size at eclosion and between size at eclosion and fecundity have also evolved. Because the only difference between the first two treatments was the level of adult mortality, this establishes differences in mortality rates as a sufficient cause for the evolution of age and size at eclosion and for the age‐distribution of fecundity rates.In the second two treatments, the evolution of induced responses has been slow, and responses are not yet consistent. The reasons for the slower evolution of induced responses suggest two new theoretical questions.
Genetic Variation and Relationships of Japanese Populations of Oxalis corniculata L. (Oxalidaceae) Detected by Random Amplified Polymorphic DNA (RAPD)
Authors: SHIBAIKE HIROYUKI , ISHIGURI YOSHIO , KAWANO SHOICHI 
Published: February 2005

Abstract RAPD analysis was applied to estimate the genetic variability in Japanese populations of Oxalis corniculata. This species comprises two floral morphs, homostyled and long‐styled, with different breeding systems (i.e., autogamy in the homostyled populations and mixed mating in the long‐styled populations). The number of RAPD phenotypes tended to be larger in homostyled populations than in long‐styled ones, and genetic diversity expressed by Simpson's indices of diversity was also generally larger in the former than in the latter.To examine the effects of breeding system on the levels of genetic differentiation among populations, two‐ and one‐level hierarchical variance partitionings were performed by the analysis of molecular variance (AMOVA). In two‐level AMOVA, significant variance component between the floral morphs was observed. In one‐level AMOVA, the proportions of variance partitioned among populations within each floral morph and among individuals within populations were similar in the homostyled and long‐styled populations, despite the difference in breeding system.To obtain insight into the relationships among individuals and/or populations, principal co‐ordinate analysis using 184 individuals (PCOA), and clustering analysis of 12 populations (UPGMA) were performed. PCOA indicated that the range of variation for homostyled individuals was more inclusive than that for long‐styled ones. A UPGMA dendrogram that consisted of two clusters showed that the long‐styled populations were nested in the homostyled ones.
Demographic Genetics of the Japanese Beech, Fagus crenata, at Ogawa Forest Preserve, Ibaraki, Central Honshu, Japan. I. Spatial Genetic Substructuring in Local Populations
Authors: KITAMURA KEIKO , SHIMADA KENICHI , NAKASHIMA KIYOSHI , KAWANO SHOICHI 
Published: February 2005

Abstract The demographic genetic substructuring of local Fagus crenata populations at Ogawa Forest Preserve, Ibaraki Prefecture, central Honshu, Japan, was analyzed by means of demographic parameters and genetic markers using protein polymorphisms (allozymes). All individuals, including seedlings, various sizes of juveniles, and adult trees within two transects were mapped; size‐class structures were analyzed based on DBH and DGH measurements, and their genotypes determined for 11 different allozyme loci (a total of 46 alleles), i.e., Aap1(3 alleles), Adh (3), Amy2 (6), Dia (4), Fum (3), Got1 (5), Got2 (3), Lap (6), Pgi (4), Pgm1 (4), and Pgm2 (5).Critical analyses were conducted to test whether genetic substructuring patterns in these two transects are correlated with the underlying environmental regimes of the habitats. Measurements of relative light intensity, soil moisture, pH, and C‐N content were made for each block in the two transects. Principal component analyses (PCA) of the environmental variables revealed that two components (Z1 and Z2) were closely related to variations in light intensity and soil moisture. The projection diagrams obtained by the environmental variables were then overlaid with the spatially localized patterns of size‐classes and genotype distributions of 11 allozyme loci examined.The results revealed that genetic variations are pooled in the juvenile trees of certain size‐classes, consisting of overlapping generations which occur in the particular sites characterized by environmental regimes. Throughout the regeneration processes, new genetic diversities are introduced through seedlings with new genotypes into the population.
Markoff chain modelling of NDI techniques
Authors: ROCHA M. M. , SCHUËLLER G. I. 
Published: February 2005

ABSTRACTA procedure for non‐destructive inspection by taking into account the effects of stochastic fatigue crack growth is presented. For this purpose a Markoff chain model is used to update the crack statistics, allowing an efficient computational implementation and a clear account of the involved concepts. In this context, perfect and imperfect removal of cracks, respectively, are considered, which represent idealizations defining bounds for actual situations.
Finite‐element analysis of fatigue crack closure under plane strain conditions: stabilization behaviour and mesh size effect
Authors: LEE H.‐J. , SONG J.‐H. 
Published: February 2005

ABSTRACTAn elastic–plastic finite‐element analysis of fatigue crack closure is performed for plane strain conditions. The stabilization behaviour of crack opening level and the effect of mesh size on the crack opening stress are investigated. It has been well reported that the crack opening level under plane stress conditions becomes stable after the crack advances beyond the initial monotonic plastic zone. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behaviour is influenced by the crack growth increment and discontinuous opening behaviour is observed.
Guard cell metabolism and CO2 sensing
Authors: Vavasseur Alain , Raghavendra Agepati S. 
Published: February 2005

SummaryIn this review we concentrate on guard cell metabolism and CO2 sensing. Although a matter of some controversy, it is generally accepted that the Calvin cycle plays a minor role in stomatal movements. Recent data emphasise the importance of guard cell starch degradation and of carbon import from the guard cell apoplast in promoting and maintaining stomatal opening. Chloroplast maltose and glucose transporters appear to be crucial to the export of carbon from both guard and mesophyll cells. The way guard cells sense CO2 remains an unresolved question. However, a better understanding of the cellular events downstream from CO2 sensing is emerging. We now recognise that there are common as well as unique steps in abscisic acid (ABA) and CO2 signalling pathways. For example, while ABA and CO2 both trigger increases in cytoplasmic free calcium, unlike ABA, CO2 does not promote a cytoplasmic pH change. Future advances in this area are likely to result from the increased use of techniques and resources, such as, reverse genetics, novel mutants, confocal imaging, and microarray analyses of the guard cell transcriptome.

Contents

Summary
665

Abbreviations
665

I.
Introduction
666

II.
Guard cell metabolism
666

III.
Guard cell CO2 sensing
672

IV.
Prospects in guard cell metabolism and CO2 sensing
676

Acknowledgements
677

References
677
Legume nodule senescence: roles for redox and hormone signalling in the orchestration of the natural aging process
Authors: Puppo Alain , Groten Karin , Bastian Fabiola , Carzaniga Raffaella , Soussi Mariam , Lucas M. Mercedes , De Felipe Maria Rosario , Harrison Judith , Vanacker Hélène , Foyer Christine H. 
Published: February 2005

SummaryResearch on legume nodule development has contributed greatly to our current understanding of plant–microbe interactions. However, the factors that orchestrate root nodule senescence have received relatively little attention. Accumulating evidence suggests that redox signals contribute to the establishment of symbiosis and senescence. Although degenerative in nature, nodule senescence is an active process programmed in development in which reactive oxygen species (ROS), antioxidants, hormones and proteinases have key roles. Nodules have high levels of the redox buffers, ascorbate and glutathione, which are important in the nodulation process and in senescence. These metabolites decline with N‐fixation as the nodule ages but the resultant decrease in redox buffering capacity does not necessarily lead to enhanced ROS or oxidative stress. We propose models by which ROS and antioxidants interact with hormones such as abscisic acid in the orchestration of nodule senescence.

Contents

Summary
683

I.
Introduction
684

II.
The characteristics of legume nodule senescence
685

III.
Redox homeostasis and programmed cell death
688

IV.
Antioxidants and programmed cell death during the senescence process
692

V.
Perspectives for manipulating nodule senescence
695

VI.
Conclusions and perspectives
696

Acknowledgements
697

References
697
Infection: friend or foe in the development of allergic disorders?
Authors: Von Mutius E. 
Published: February 2005

SummaryThere is still a controversial debate as to the potential contribution of the ‘hygiene hypothesis’ to the development of childhood asthma and allergies. Viral infections have for long time been recognized as potent triggers of asthma exacerbations. Whether viral infections also induce the development of new cases of asthma remains unclear, particularly for respiratory syncytial virus (RSV) infections. Other infections have been proposed to have protective effects on the development of asthma and allergies such as Hepatitis A, Helicobacter pylori or Toxoplasma. The available evidence is reviewed in the following paragraphs. To date there is no indication that immunizations of all kinds may exert a negative or positive effect on the incidence of asthma and allergies. In turn, the finding that children in farming environments exposed to a variety of microbial compounds have substantially lower rates of respiratory allergies strongly supports the ‘hygiene hypothesis’.