bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in species richness of vascular plants under the impact of air pollution: a global perspective
Authors: Zvereva Elena L. , Toivonen Eija , Kozlov Mikhail V. 
Published: April 2008

ABSTRACTAim To investigate the general pattern of changes in species richness and diversity of vascular plants due to environmental contamination and associated habitat changes imposed by point polluters, and identify the sources of variation in the response of plant communities to industrial pollution.Location Global.Methods We collected species richness and diversity data from 86 studies that were conducted around 60 atmospheric point polluters worldwide and reported in 95 papers (published in 1953–2007). We used meta‐analysis to search for a general effect and to compare between polluter types and plant groups, and linear regression to describe the latitudinal gradient and to quantify relationships between pollution and effect size.Results Although the species richness of vascular plants generally decreased with pollution, the effects were not uniform across the studies. Polluters that cause soil acidification imposed a stronger detrimental effect on plant diversity than industries whose emissions increased soil pH. An overall adverse effect was primarily due to the contribution of non‐ferrous smelters and aluminium plants; the effects of other SO2‐emitting industries were less detrimental, albeit negative, and the effects of chemical plants, fertilizer factories and cement industries did not differ from zero. Longevity of the pollution impact only made a slight contribution to the detected variation, while adverse effects increased with increase in pollution load.Main conclusions This study is the first demonstration of geographical variation in the responses of plant communities to aerial emissions: adverse effects increased from high to low latitudes, and this pattern was explained primarily by increases in both the diversity of original (undisturbed) communities and mean summer temperatures. The latter result suggests that under a future warmer climate the existing pollution loads may become more harmful. Model calculations indicate that a detectable depauperation of plant communities is unlikely if the polluter emits < 1500 t of SO2annually.
Why does the unimodal species richness–productivity relationship not apply to woody species: a lack of clonality or a legacy of tropical evolutionary history?
Authors: Laanisto Lauri , Urbas Pille , Pärtel Meelis 
Published: April 2008

ABSTRACTAim  To study how differences in species richness patterns of woody and herbaceous plants may be influenced by ecological and evolutionary factors. Unimodal species richness–productivity relationships (SRPRs) have been of interest to ecologists since they were first described three decades ago for British herbaceous vegetation by J. P. Grime. The decrease in richness at high productivity may be due to competitive exclusion of subordinate species, or diverse factors related to evolution and dispersal. Unimodal SRPRs are most often reported for plants, but there are exceptions. For example, unimodal SRPRs are common in the temperate zone but not in the tropics. Similarly, woody species and forest communities in the Northern Hemisphere do not tend to show unimodal SRPRs.Location  Global.Methods  We used data from the literature to test whether a unimodal SRPR applies to woody species and forest communities on a global scale. We explored whether the shape of SRPRs may be related to the lack of clonality in woody species (which may prevent their being competitively superior), or the legacy of evolutionary history (most temperate woody species originate from tropical lineages, and due to niche conservatism they may still demonstrate ‘tropical patterns’). We used case studies that reported the names of the dominant or most abundant species for productive sites.Results  Woody species were indeed less clonal than herbaceous species. Both clonality and the temperate evolutionary background of dominating species were associated with unimodality in SRPRs, with woodiness modifying the clonality effect.Main conclusions  The unimodal SRPR has been common in the ecological literature because most such studies originate from temperate herbaceous communities with many clonal species. Consequently, both evolutionary and ecological factors may influence species richness patterns.
The maintenance of a positive spatial correlation between South African bird species richness and human population density
Authors: Hugo Sanet , Van Rensburg Berndt J. 
Published: April 2008

ABSTRACTAim  To investigate explanations for the maintenance of a positive spatial species richness–human population density correlation at broad scales, despite the negative impact of humans on species richness. These are (hypotheses 1–4): (1) human activities that create a habitat mosaic and (2) a more favourable climate, and (3) adequate conservation measures (e.g. sufficient natural habitat), maintain the positive species richness–human density correlation; or (4) the full range of human densities decrease the slope of the correlation without changing its form.Location  South Africa.Methods  Avian species richness data from atlas distribution maps and human population density data derived from 2001 census results were converted to a quarter‐degree resolution. We investigated the number of land transformation types (anthropogenic habitat heterogeneity), irrigated area (increasing productivity), and other covarying factors (e.g. primary productivity) as predictors of species richness. We compared species richness–human density relationships among regions with different amounts of natural habitat, and investigated whether the full range of human densities decrease species richness in relation to primary productivity.Results  Hypotheses 1, 2 and 3 were supported. Human densities and activities that increase habitat heterogeneity and productivity are important beneficial factors to common species, but not to rare species. The species richness–human density relationship persists only at low land transformation levels, and no significant relationship exists at higher levels. For common species, the relationship becomes non‐significant at lower land transformation levels than for rare species.Main conclusions  The persistence of the species richness–human density relationship depends mostly on the amount of remaining natural habitat. In addition, certain human activities benefit especially common species. Common species seem to be more flexible than rare species in response to human activity and habitat loss.
Model selection and information theory in geographical ecology
Authors: Diniz‐Filho José Alexandre Felizola , Rangel Thiago Fernando L. V. B. , Bini Luis Mauricio 
Published: April 2008

ABSTRACTAim Although parameter estimates are not as affected by spatial autocorrelation as Type I errors, the change from classical null hypothesis significance testing to model selection under an information theoretic approach does not completely avoid problems caused by spatial autocorrelation. Here we briefly review the model selection approach based on the Akaike information criterion (AIC) and present a new routine for Spatial Analysis in Macroecology (SAM) software that helps establishing minimum adequate models in the presence of spatial autocorrelation.Innovation  We illustrate how a model selection approach based on the AIC can be used in geographical data by modelling patterns of mammal species in South America represented in a grid system (n = 383) with 2° of resolution, as a function of five environmental explanatory variables, performing an exhaustive search of minimum adequate models considering three regression methods: non‐spatial ordinary least squares (OLS), spatial eigenvector mapping and the autoregressive (lagged‐response) model. The models selected by spatial methods included a smaller number of explanatory variables than the one selected by OLS, and minimum adequate models contain different explanatory variables, although model averaging revealed a similar rank of explanatory variables.Main conclusions  We stress that the AIC is sensitive to the presence of spatial autocorrelation, generating unstable and overfitted minimum adequate models to describe macroecological data based on non‐spatial OLS regression. Alternative regression techniques provided different minimum adequate models and have different uncertainty levels. Despite this, the averaged model based on Akaike weights generates consistent and robust results across different methods and may be the best approach for understanding of macroecological patterns.
Incentives to Reduce Crop Trait Durability
Authors: Ambec Stefan , Langinier Corinne , Lemarié Stéphane 
Published: April 2008

AbstractTo reduce the competition from farmers who self‐produce seed, an inbred line seed producer can switch to nondurable hybrid seed. In a two‐period framework, we first investigate the impact of crop durability on self‐production, pricing and switching decisions. Second, we study how the introduction of a fee paid by self‐producing farmers affects those decisions. We find that the monopolist may produce technologically dominated hybrid seed in order to extract more surplus from farmers. Further, the introduction of a self‐production fee improves efficiency.
Differentiation and Synergies in Rural Tourism: Estimation and Simulation of the Israeli Market
Authors: Tchetchik Anat , Fleischer Aliza , Finkelshtain Israel 
Published: April 2008

AbstractThis article applies a discrete‐choice equilibrium model with product differentiation to study the rural tourism industry in Israel and to jointly estimate the effect of lodging and farm characteristics on consumer preferences and firms' costs. The model accounts for heterogeneity in tastes and technologies and allows for unobservable product characteristics. We find evidence for technological synergy in the joint production of agricultural goods and rural tourism services, but none in the demand. The differentiation in the industry is the major contributor to the price‐cost margin, which averages 62%. An additional minor cause is government regulations, which restrict supply. Simulation results demonstrate the growth potential of the industry and show that the government can play an important role in catalyzing growth via investment subsidization, deregulation of supply and information distribution.
Risk Rationing and Wealth Effects in Credit Markets: Theory and Implications for Agricultural Development
Authors: Boucher Stephen R. , Carter Michael R. , Guirkinger Catherine 
Published: April 2008

AbstractWe develop a model that shows that asymmetric information can result in two types of credit rationing: conventional quantity rationing, and “risk rationing,” whereby farmers are able to borrow but only under high‐collateral contracts that offer them lower expected well‐being than a safe, subsistence activity. After exploring its incidence with respect to wealth, we show that risk rationing has important policy implications. Specifically, land titling will be only partially effective because it does not enhance producers' willingness to offer up the collateral needed to secure loans under moral hazard constraints. Efforts to enhance agricultural investment and the working of agricultural credit markets must step beyond land titling and also deal with risk.
A Cost Approach to Economic Analysis Under State‐Contingent Production Uncertainty
Authors: Chavas Jean-Paul 
Published: April 2008

AbstractThis article explores the economics of input decision under production uncertainty. The article develops a methodology to specify and estimate cost‐minimizing input decisions under a state‐contingent technology. The analysis is applied to time series data on U.S. agriculture. It finds strong empirical evidence that expected output alone does not provide an appropriate representation of production uncertainty. The results provide empirical support for an output‐cubical technology. This indicates that anex postanalysis of stochastic technology appears appropriate. The analysis also provides evidence that the cost of facing production risk has declined in U.S. agriculture over the last few decades.
Avocado Pests and Avocado Trade
Authors: Peterson Everett B. , Orden David 
Published: April 2008

AbstractThis article evaluates the effects of a November 2004 phytosanitary rule that removed seasonal and geographic restrictions on the importation of fresh Hass avocados from approved orchards in Mexico to the United States. With the remaining systems approach compliance measures in place, pest risks do not substantially increase and U.S. net welfare rises by $77 million. Removal of remaining compliance measures may lead to lower net welfare gains depending on which measures are eliminated and the estimated probabilities of pest infestations.
Proportion of Non-Zero Normal Means: Universal Oracle Equivalences and Uniformly Consistent Estimators
Authors: Jin Jiashun 
Published: April 2008

SummarySince James and Stein's seminal work, the problem of estimating n normal means has received plenty of enthusiasm in the statistics community. Recently, driven by the fast expansion of the field of large-scale multiple testing, there has been a resurgence of research interest in the n normal means problem. The new interest, however, is more or less concentrated on testing n normal means: to determine simultaneously which means are 0 and which are not. In this setting, the proportion of the non-zero means plays a key role. Motivated by examples in genomics and astronomy, we are particularly interested in estimating the proportion of non-zero means, i.e. given n independent normal random variables with individual means Xj∼N(μj,1), j=1,…,n, to estimate the proportion ɛn=(1/n) #{j:μj /= 0}. We propose a general approach to construct the universal oracle equivalence of the proportion. The construction is based on the underlying characteristic function. The oracle equivalence reduces the problem of estimating the proportion to the problem of estimating the oracle, which is relatively easier to handle. In fact, the oracle equivalence naturally yields a family of estimators for the proportion, which are consistent under mild conditions, uniformly across a wide class of parameters. The approach compares favourably with recent works by Meinshausen and Rice, and Genovese and Wasserman. In particular, the consistency is proved for an unprecedentedly broad class of situations; the class is almost the largest that can be hoped for without further constraints on the model. We also discuss various extensions of the approach, report results on simulation experiments and make connections between the approach and several recent procedures in large-scale multiple testing, including the false discovery rate approach and the local false discovery rate approach.
A Semiparametric Approach to Canonical Analysis
Authors: Xia Yingcun 
Published: April 2008

SummaryClassical canonical correlation analysis is one of the fundamental tools in statistics to investigate the linear association between two sets of variables. We propose a method, called semiparametric canonical analysis, to generalize canonical correlation analysis to incorporate the important non-linear association. Semiparametric canonical analysis is easy to implement and interpret. Statistical properties are proved. A consistent estimation method is developed. Selection of significant semiparametric canonical analysis components is discussed. Simulations suggest that the methods proposed have satisfactory performance in finite samples. One environmental data set and one data set in social science are investigated, in which non-linear canonical associations are observed and interpreted.
A Wavelet- or Lifting-Scheme-Based Imputation Method
Authors: Heaton T. J. , Silverman B. W. 
Published: April 2008

SummaryThe paper proposes a new approach to imputation using the expected sparse representation of a surface in a wavelet or lifting scheme basis. Our method incorporates a Bayesian mixture prior for these wavelet coefficients into a Gibbs sampler to generate a complete posterior distribution for the variable of interest. Intuitively, the estimator operates by borrowing strength from those observed neighbouring values to impute at the unobserved sites. We demonstrate the strong performance of our estimator in both one- and two-dimensional imputation problems where we also compare its application with the standard imputation techniques of kriging and thin plate splines.
On Casting Random-Effects Models in a Survival Framework
Authors: Pilla Ramani S. , Kim Yongdai , Lee Hakbae 
Published: April 2008

SummaryLogistic random-effects models are often employed in the analysis of correlated binary data. However, fitting these models is challenging, since the marginal distribution of the response variables is analytically intractable. Often, the random effects are treated as missing data for constructing traditional data augmentation algorithms. We create a novel alternative data augmentation scheme that simplifies the likelihood-based inference for logistic random-effects models. We cast the random-effects model in a ‘survival framework’, where each binary response is the censoring indicator for a survival time that is treated as additional missing data. Under this augmentation framework, the conditional expectations are free of unknown regression parameters. Such a construction has a particular advantage that, in the case of discrete covariates, the score equations for regression parameters have analytical solutions. Consequently, one does not need to resort to a search algorithm in estimating the regression parameters. We further create a parameter expansion scheme for logistic random-effects models under this survival data augmentation framework. The proposed data augmentation is illustrated when the random-effects distribution follows a multivariate Gaussian and multivariate t-distribution. The performance of the method is assessed through simulation studies and a real data analysis.
Thick melanoma: the problem continues
Authors: Tejera‐Vaquerizo A , Mendiola‐Fernández M , Fernández‐Orland A , Herrera‐Ceballos E 
Published: April 2008

AbstractBackground  The incidence of melanoma and its associated mortality has stabilized over the recent years, due in part to efforts directed at better prevention and detection of these lesions. We analysed the trends in the distribution of melanomas, mainly according to their thickness.Methods  Data from the Dermatology Service of ‘Virgen de la Victoria’ University Hospital in Malaga (Spain) showed a total of 459 cases of melanoma between 1990 and 2005, both inclusive. The lesions were stratified according to year of diagnosis (1990–96 and 1997–2005), sex, age (0–49, ≥ 50), thickness (0–0.99, 1.00–1.99, and ≥ 2 mm) and the histological subtype [lentigo maligna melanoma (LMM), superficial spreading melanoma (SSM), nodular melanoma (NM) and acral lentiginous melanoma (ALM)]. Particular attention was given to the distribution of the groups according to thickness.Results  The number of new cases rose by 92% between the two study periods (1990–1996 and 1997–2005). However, the number of new cases of thick melanoma remained almost constant over the two periods, being associated with persons over 50 years of age (65.1% vs. 64.3%), with men having half the cases (48.4% vs. 47%). The proportion of nodular melanomas within the group of thick melanomas was high in both periods (36.5% and 39.3%, respectively).Conclusions  This study shows that despite the large increase in new melanomas, the diagnosis of thick melanomas has remained constant, mainly in persons over the age 50 years, with a relative increase in men. New strategies and education programmes are, therefore, required for the early detection of this type of tumour to reduce its incidence in these patients.
The efficacy of topical 0.2% hyaluronic acid gel on recurrent oral ulcers: comparison between recurrent aphthous ulcers and the oral ulcers of Behçet's disease
Authors: Lee JH , Jung JY , Bang D 
Published: April 2008

AbstractBackground  Hyaluronic acid (HA) is a primary component of the extracellular matrix, and the efficacy of HA on oral ulcers is rarely reported.Objective  To observe the efficacy and safety of the topical application of 0.2% HA gel on recurrent oral ulcers and to compare its effects in patients with recurrent aphthous ulcers (RAU) and the oral ulcers of Behçet's disease (BD)Materials and methods  Thirty‐three outpatients with recurrent oral ulcers were included in the study (17 patients: BD, 16 patients: RAU). The patients used topical 0.2% HA gel twice daily for 2 weeks. The subjective parameters of patients [number of ulcers, healing period, visual analogue scale (VAS) for pain] were investigated and objective assessments (number of ulcers, maximal area of ulcer and inflammatory signs) were inspected by a physician.Results  A subjective reduction in the number of ulcers was observed in 72.7% of the patients. A decrease in the ulcer healing period was observed in 72.7% of the patients; 75.8% experienced improvement in VAS for pain. Objective inspection of the ulcers showed a reduction of numbers in 57.6% of the patients, and 78.8% of the ulcers showed a decrease in area. Among the inflammatory signs, swelling and local heat were significantly improved after treatment. No significant differences were found between the BD group and RAU group in subjective and objective parameters, except for inflammatory signs. No side‐effects were observed.Conclusions  The topical application of 0.2% HA gel seems to be an effective and safe therapy in patients with recurrent oral ulcers; the study supports the use of HA in BD with oral ulcers.
Is there an easier way to autograft skin in chronic leg ulcers? ‘Minced micrografts’, a new technique
Authors: Boggio P , Tiberio R , Gattoni M , Colombo E , Leigheb G 
Published: April 2008

AbstractBackground  Chronic venous leg ulcers represent an urgent and increasing problem for public health. The use of skin autografts results in a greater therapeutic success in healing chronic ulcers.Objective  A simple method of skin autografting that could permit a wider use of skin grafts in outpatients is needed. A new technique allowing skin autografting in a simple one‐step process, without complex surgical procedures or expensive technical supplies, is presented.Methods  A small, full‐thickness skin specimen taken from the patient is finely minced and spread on his leg ulcer bed allowing to cover a surface many times wider than the sample itself.Results  This method induces faster re‐epithelization of chronic leg ulcers that failed to heal despite good conservative local therapy and give the possibility to repair very large ulcers with small fragments of skin. A clinical case is shown as an example out of 20 ulcers we recently treated.Conclusion  Our preliminary report shows that this technique results in a greater therapeutic success (18 of 20 cases) in healing chronic leg ulcers, a common pathology that often affects outpatients treated for very long periods at home or in the Dermatologist's office. In our experience, this new and successful reparative possibility makes ‘mince grafting’ a recommendable procedure.