bluuebunny/crossref_metadata_2025_split huggingface dataset:
Abundance and distribution of desert annuals: are spatial and temporal patterns related?
Authors: Guo Qinfeng , Brown James H. , Valone & Thomas J. 
Published: March 2003

Summary 1  Spatial distribution–abundance relationships have been intensively studied. Workers have now begun to study temporal relationships but little is known about how these are related to spatial patterns. We examined these relationships both over space and time using 15 years of data from permanent quadrats in the Chihuahuan Desert. 2
Winter and summer annual communities were analysed. Within single years, the species in each community exhibited a positive relationship between distribution and abundance at two spatial scales, 0.25‐ha plots and 0.25‐m2 quadrats. Over 15 years, the species in each community also exhibited a positive relationship between abundance and the number of years in which they were present. Species frequency distributions, both in space and over time, were scale‐dependent. 3  Over space, the frequency distribution was bimodal at large (plot) scales, but unimodal at small (quadrat) scales in both communities. Over time, the frequency distribution was bimodal for winter annuals but unimodal for summer annuals, a difference we attribute to the marked difference between the two communities in the temporal consistency of rank abundance of species. We conclude that both niche and metapopulation models can be used in explaining the distribution patterns of species but at different scales. The factors and processes in these models are not mutually exclusive in determining the overall abundance and distributions of these species in space and over time.
Fluctuating resources in plant communities: a general theory of invasibility
Authors: Davis Mark A. , Grime J. Philip , Thompson Ken 
Published: March 2003

Summary 1 The invasion of habitats by non‐native plant and animal species is a global phenomenon with potentially grave consequences for ecological, economic, and social systems. Unfortunately, to date, the study of invasions has been primarily anecdotal and resistant to generalization. 2 Here, we use insights from experiments and from long‐term monitoring studies of vegetation to propose a new theory in which fluctuation in resource availability is identified as the key factor controlling invasibility, the susceptibility of an environment to invasion by non‐resident species. The theory is mechanistic and quantitative in nature leading to a variety of testable predictions. 3 We conclude that the elusive nature of the invasion process arises from the fact that it depends upon conditions of resource enrichment or release that have a variety of causes but which occur only intermittently and, to result in invasion, must coincide with availability of invading propagules.
The demographics of resprouting in tree and shrub species of a moist tropical forest
Authors: Paciorek Christopher J. , Condit Richard , Hubbell Stephen P. , Foster Robin B. 
Published: March 2003

Summary1 Individuals of many woody plant species have the ability to respond to damage which causes removal of the crown by producing new branches (sprouts) along the remaining stem. Resprouting by woody plants has received little attention in relatively undisturbed tropical forest.2 To assess the importance of resprouting for forest dynamics, we estimated resprouting rates and mortality rates of resprouted individuals for the forest as a whole and for individual species in a 50‐ha permanent plot in tropical moist forest on Barro Colorado Island, Panama. We tested for differences between species and asked whether the differences were related to phylogeny, growth form or shade tolerance.3 Among individuals not known to have resprouted previously, we estimate that the annual rate of resprouting is 1.7% for individuals in both small and large size classes (1–9.9 cm d.b.h. and ≥ 10 cm d.b.h.). For small and large individuals, respectively, annual mortality of previously undamaged individuals is 2.2% and 1.5%, while that of resprouted individuals is 9.6% and 10.3%. This resulted in survival of 62% of resprouted individuals over 5 years, compared to 90% survival among individuals not known to have resprouted recently.4 Resprouting rates varied by species and family, but little between growth forms. Species in the families Lauraceae and Piperaceae had high rates of resprouting. Resprouting was common across the spectrum of shade tolerance.5 Damage to woody forest plants on Barro Colorado Island is frequent, and many species are able to respond by resprouting. Resprouting ability may be an important life history characteristic of woody species on BCI, with individuals experiencing both increases and decreases in size.
Colonization constraints during primary succession on coastal Lake Michigan sand dunes
Authors: Lichter John 
Published: March 2003

Summary 1 Primary succession on coastal sand dunes has generally been presumed to be driven by autogenic environmental change associated with dune stabilization and gradual soil development. 2 An extensive chronosequence of dune‐capped beach ridges is found adjacent to northern Lake Michigan and the youngest 13 ridges (aged 30–440 years old) show a clear pattern of primary succession and development of a forest ecosystem. 3 Seed‐addition and seedling‐transplant experiments indicated that colonization of young sand dunes by late‐successional Pinus and Quercus species is constrained by limited seed dispersal, seed and seedling desiccation, and seed predation rather than seedling success being constrained by low soil nitrogen availability. Their establishment may therefore depend on coincidence of chance seed dispersal, favourable weather conditions and low rodent densities. 4 In addition, episodic burial by sand prevents most species from colonizing young dune ridges, while burial of seedlings by litter limits recruitment on older dune ridges with developing forest. The intensity of competition increases during succession. 5 Dune succession is better described as the transient dynamics of colonization and competitive displacement rather than the result of gradual soil development and competitive displacement.
Effects of fine‐scale disturbances on the demography and population dynamics of the clonal moss Hylocomium splendens
Authors: Rydgren Knut , De Kroon Hans , Økland Rune H. , Van Groenendael Jan 
Published: March 2003

Summary

The boreal forest is subject to disturbance but the effects on population dynamics are poorly understood. We investigated how a prominent species of the forest floor, the clonal moss Hylocomium splendens, responded to different types of fine‐scale disturbance.
Canopy gap formation was simulated in H. splendens populations by removing 50% of the bryophyte layer (Removal treatment) and herbivory by clipping all of its growing points (Clipped treatment). Demographic parameters and population dynamics were compared with an unmanipulated reference population (Ref).
Both types of disturbance caused a significant decrease in mean segment size (particularly following clipping) and an increase in branching rates. Branching rates in the Removal population were enhanced at all architectural opportunities for enhanced branching, but only the Clipped segments themselves were affected during the 2 years following disturbance.
The population effects of disturbance were analysed by a periodic matrix model, with 3‐year as the period, followed by elasticity analysis. The Ref population was approximately stable (growth rate, λ = 1.012), with the survival of mature segments making an overwhelming contribution to its growth rate. The higher λ (1.740) in the Removal population was associated with higher elasticities of branching. Clipping reduced λ to 0.841 by blocking segment survival, although regeneration of new growing points on the remnant main shoot axis after 1 year, and its subsequent maturation in the next year, then made a major contribution.
Life table response experiment analyses revealed that almost all demographic processes including branching and the survival of mature segments contributed to the increased λ in Removal treatment. The relatively small decrease in λ following clipping was mainly due to the absence of mature segment survival, being almost balanced by the pulse of regeneration of growing points the year after disturbance.
We conclude that H. splendens populations show a good ability to recover from common types of disturbances in their environment. The general mechanisms behind the responses are discussed.
Relationships between plant nitrogen economy and life history in three deciduous‐forest herbs
Authors: Rothstein David E. , Zak Donald R. 
Published: March 2003

SummaryWe compared nitrogen (N) uptake and whole‐plant N dynamics in three deciduous‐forest herbs of contrasting life histories: the spring ephemeralAlliumtricoccum, the summergreenViolapubescensand the semievergreenTiarellacordifolia. We predicted that differences in above‐ground physiology would translate into differences in N acquisition and partitioning, such that nitrogen‐use efficiency (NUE) would increase fromAlliumtoViolatoTiarella.Patterns of N uptake were generally the opposite of our predictions.Alliumhad the lowest N uptake capacity in both laboratory and field experiments whereas roots ofTiarellahad the highest specific N uptake capacity.Violawas the only species in which the specific uptake capacity of roots was related to photosynthetic activity of leaves, both decreasing by a factor of two from spring to summer. In contrast,Tiarellaconsistently had the lowest photosynthetic capacity and the highest specific uptake capacity whereasAlliummaintained substantial root uptake capacity throughout the summer when it had no photosynthetic activity.There were no significant differences between species in overall NUE. However, there were differences in the components of NUE: nitrogen productivity (A) and mean residence time of N in the plant (MRT). Nitrogen productivity increased, and MRT decreased, fromAlliumtoViolatoTiarella.In all three species, there was a balance between acquisition of N and building of biomass over the annual growth cycle, despite dramatic disjunctions between the tissue‐specific rates of carbon and N acquisition inAlliumandTiarella. The variation in A and MRT we observed among co‐occurring species of a single N‐rich habitat was comparable with that observed by other researchers studying plants adapted to habitats of widely varying N availability.
Habitat requirements for establishment of Sphagnum from spores
Authors: Sundberg Sebastian , Rydin Håkan 
Published: March 2003

Summary1 The ecological significance of the spore in perennial bryophytes has been questioned. In Sphagnum, protonemata have rarely been observed in the field and P‐concentrations in natural waters are insufficient for spore establishment.2 We determined requirements for establishment of Sphagnum spores in growth chamber experiments. Up to 17 species were tested on peat with various natural substrates added and with different mire waters. In a field experiment, the effect of cover of nutrient depleted Eriophorum‐litter was also tested.3 There were large differences between substrates, and establishment appeared to be limited by the amount of phosphate released. Added moose dung or litter of Betula pubescens promoted establishment well above the low level seen on peat alone, or with added litter from Pinus sylvestris.4 Species differed slightly in response to different mire waters and to added substrates, but these differences could not be attributed to the natural habitat of the species or their breeding system. There was a weak negative relationship between spore size and establishment success.5 In the field experiment, about 1% of the sown, viable spores established in the presence of moose dung or Betula litter. With moose dung there was an indication that protonemata and plants of other bryophytes had a negative effect on the establishment of Sphagnum.6 Nutrient release from litter and cover provided by vascular plants are needed to generate safe sites for the establishment of Sphagnum from spores, especially on wet, acidic and relatively nutrient‐poor soils and peat. Recruitment from spores may therefore be important in Sphagnum, particularly following disturbance.
The relationship between growth and mortality for seven co‐occurring tree species in the southern Appalachian Mountains
Authors: Wyckoff Peter H. , Clark James S. 
Published: March 2003

SummarySlow growth is associated with high mortality risk for trees, but few data exist to assess interspecific differences in the relationship between growth and mortality. Here we compare low growth tolerance for seven co‐occurring species in the southern Appalachian Mountains:Acer rubrum,Betula lenta,Cornus florida,Liriodendron tulipifera,Quercus prinus,Quercus rubraandRobinia pseudo‐acacia.For all species, mortality was greater for understorey individuals than for canopy trees. Species varied widely in the length of growth decline prior to death, ranging from 6 years forL. tulipiferato more than 12 years forQ. rubra.Growth‐mortality functions differ among species, but we found little evidence of a trade‐off between tolerance of slow growth and an ability to show rapid growth in high light conditions.A. rubrumstands out in its ability both to grow rapidly and to tolerate slow growth, suggesting that its density may increase at our study site as in other parts of the eastern United States. In contrast,C. floridashows high mortality (15% per annum) as a result of infection with dogwood anthracnose.We modified a forest simulation model, LINKAGES (which assumes that all species have the same ability to tolerate slow growth), to include our functions relating growth and mortality. The modified model gives radically altered predictions, reinforcing the need to rethink and re‐parameterize existing computer models with field data.
Carbon limitation in trees
Authors: Körner Christian 
Published: March 2003

Summary

The ongoing enrichment of the atmosphere with CO2 raises the question of whether growth of forest trees, which represent close to 90% of the global biomass carbon, is still carbon limited at current concentrations of close to 370 p.p.m. As photosynthesis of C3 plants is not CO2‐saturated at such concentrations, enhanced ‘source activity’ of leaves could stimulate ‘sink activity’ (i.e. growth) of plants, provided other resources and developmental controls permit. I explore current levels of non‐structural carbon in trees in natural forests in order to estimate the potential for a carbon‐driven stimulation of growth.
The concentration of non‐structural carbohydrates (NSC) in tree tissues is considered a measure of carbon shortage or surplus for growth. A periodic reduction of NSC pools indicates either that carbon demand exceeds con‐current supply, or that both source and sink activity are low. A steady, very high NSC concentration is likely to indicate that photosynthesis fully meets, or even exeeds, that needed for growth (surplus assimilates accumulate).
The analysis presented here considers data for mature trees in four climatic zones: the high elevation treeline (in Mexico, the Alps and Northern Sweden), a temperate lowland forest of central Europe, Mediterranean sclerophyllous woodland and a semideciduous tropical forest in Panama.
In all four climatic regions, periods of reduced or zero growth show maximum C‐loading of trees (source activity exceeding demand), except for dry midsummer in the Mediterranean. NSC pools are generally high throughout the year, and are not significantly affected by mass fruiting episodes.
It is concluded that, irrespective of the reason for its periodic cessation, growth does not seem to be limited by carbon supply. Instead, in all the cases examined, sink activity and its direct control by the environment or developmental constraints, restricts biomass production of trees under current ambient CO2 concentrations.
The current carbohydrate charging of mature wild trees from the tropics to the cold limit of tree growth suggests that little (if any) leeway exists for further CO2‐fertilization effects on growth.
Individual patient data meta‐analysis of randomized anti‐epileptic drug monotherapy trials
Authors: Williamson Paula R. , Marson Anthony G. , Tudur Catrin , Hutton Jane L. , Chadwick David 
Published: March 2003

AbstractMeta‐analysis may be based on either aggregate data or individual patient data (IPD). Three reasons why IPD are desirable for the meta‐analysis of anti‐epileptic drug (AED) monotherapy trials are: (1) to undertake a more complete analysis of time‐to‐event outcomes; (2) to investigate the interaction between AED and type of epilepsy; and (3) to undertake re‐analysis of the trial to obtain results for all relevant outcomes. We demonstrate that IPD meta‐analysis is possible in AED research. Problems arose from missing data at four levels: (1) unknown trials; (2) known trials but no IPD supplied; (3) known trials but missing outcome data for some individuals within trials; and (4) known trials but missing covariate data for some individuals within trials. Empirical evidence of the reliability of meta‐analyses based on aggregate rather than individual patient data is still lacking. Examples of other benefits such projects may bring include improvements to the design of a new trial in the area, in terms of the sample size considerations, the definition of outcomes and data collection.
Identifying meaningful intra‐individual change standards for health‐related quality of life measures
Authors: Wyrwich Kathleen W. , Wolinsky Fredric D. 
Published: March 2003

Abstract Although numerous measures have been developed for the evaluation of health‐related quality of life (HRQoL), strategies for identifying meaningful intra‐individual change in these measures have not kept pace with instrument development. As a result, clinical trial researchers, quality assurance assessment teams and practising clinicians are without established standards to evaluate individual patient change in HRQoL measures as improved, stable or declined. This article reviews and critiques the methods that have been applied to establish intra‐individual HRQoL change standards. These methods include within‐person and between‐persons anchor‐based studies, as well as distribution‐based techniques using the effect size, the standard error of measurement, the mean squared error or individual slope coefficients derived from hierarchical linear modelling. Practical approaches to improving and advancing HRQoL change evaluations that enhance the interpretation of intra‐individual change are provided. Two future methodological challenges in this area of HRQoL research are examined: (1) the development of individual change standards for generic HRQoL measures; and (2) the incorporation of individual clinical assessments into the process for establishing significant intra‐individual change standards.
Choosing a doctor: an exploratory study of factors influencing patients’ choice of a primary care doctor
Authors: Bornstein Brian H. , Marcus David , Cassidy William 
Published: March 2003

AbstractWe assessed the relative importance healthcare consumers attach to various factors in choosing a primary care doctor (PCD) in a cross‐sectional, in‐person survey. Three survey locations were used: doctors’ offices, a public shopping area, and meetings of a women’s organization. A total of 636 community residents, varying across major demographic categories, participated. Participants completed a 23‐item survey, designed to assess which factors consumers perceive as most relevant in choosing a PCD. Participants perceived professionally relevant factors (e.g. whether the doctor is board certified, office appearance) and management practices (e.g. time to get an appointment, evening and weekend hours) as more important than the doctor’s personal characteristics (race, age, gender, etc.). Participants’ own characteristics bore little relationship to the perceived importance of doctor characteristics. Factors patients perceive as most important to their choice of a PCD are also those that have the greatest effect on the quality of healthcare they will receive. However, they do not always have access to this information. A better understanding of the factors that influence people’s choice of a PCD can contribute to efforts to provide them with the resources to make well‐informed decisions in selecting among healthcare options.
The effect of a hepatitis serology testing algorithm on laboratory utilization
Authors: Walraven Carl van , Goel Vivek 
Published: March 2003

Abstract Rationale, aims and objectives Laboratory testing algorithms use patient and laboratory data to identify the optimal testing strategy for patients. Studies have shown that these algorithms can decrease test utilization. Since over‐utilization of hepatitis serological tests was suspected, a hepatitis serology testing algorithm was initiated in Ontario, Canada. This study determined the effects of this algorithm on utilization. Methods  Population‐based retrospective observational study, involving all patients having viral hepatitis serological testing at private laboratories in Ontario, Canada, between July 1991 and December 1999. Prior to the testing algorithm, physicians listed the required specific antigens and antibodies on the test requisition form. In September 1996, the form was changed so that physicians identified the clinical indication – acute hepatitis, chronic hepatitis or immune status testing – for hepatitis serology testing. Therefore, the algorithm introduced a new ‘tick‐box’ to the requisition form. Tests conducted by the laboratory depended upon which indication was chosen. Rates for hepatitis serological testing were calculated using population‐based claims data. Results Time‐series modelling showed that the testing algorithm was associated with a slight but significant increase in the use of hepatitis serology (P < 0.05). The algorithm was associated with an increase of 30 serological tests per 100 000 population per month. Conclusions Introducing a testing algorithm for hepatic viral serology in Ontario did not significantly decrease hepatitis serology utilization and may be associated with a slight, but significant, increase in serology utilization rates.