Search results for "Margin"
showing 10 items of 715 documents
From glacial refugia to hydrological microrefugia: Factors and processes driving the persistence of the climate relict tree Zelkova sicula
2021
Abstract With only two tiny populations, the climate relict Zelkova sicula (Sicily, Italy) is one of the rarest trees in the world. It also represents the most marginal member of genus Zelkova that was widespread in the broadleaved forests thriving in warm–temperate climates throughout Eurasia until the Last Glacial Age. Occurring at the westernmost range of the genus under typical Mediterranean climate, the micro‐topographic settings have always appeared crucial for the survival of this relict. However, the factors and processes actually involved in its persistence in the current refugia, as well as the response of similar relict trees in arid environments, are poorly understood worldwide.…
Empirical Bayes improves assessments of diversity and similarity when overdispersion prevails in taxonomic counts with no covariates
2019
Abstract The assessment of diversity and similarity is relevant in monitoring the status of ecosystems. The respective indicators are based on the taxonomic composition of biological communities of interest, currently estimated through the proportions computed from sampling multivariate counts. In this work we present a novel method to estimate the taxonomic composition able to work even with a single sample and no covariates, when data are affected by overdispersion. The presence of overdispersion in taxonomic counts may be the result of significant environmental factors which are often unobservable but influence communities. Following the empirical Bayes approach, we combine a Bayesian mo…
Efficient estimation of generalized linear latent variable models.
2019
Generalized linear latent variable models (GLLVM) are popular tools for modeling multivariate, correlated responses. Such data are often encountered, for instance, in ecological studies, where presence-absences, counts, or biomass of interacting species are collected from a set of sites. Until very recently, the main challenge in fitting GLLVMs has been the lack of computationally efficient estimation methods. For likelihood based estimation, several closed form approximations for the marginal likelihood of GLLVMs have been proposed, but their efficient implementations have been lacking in the literature. To fill this gap, we show in this paper how to obtain computationally convenient estim…
Permanent genetic resources added to molecular ecology resources database 1 April 2010 - 31 May 2010
2010
Correspondance: Molecular Ecology Resources Primer Development Consortium, E-mail: editorial.office@molecol.com; International audience; This article documents the addition of 396 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Anthocidaris crassispina, Aphis glycines, Argyrosomus regius, Astrocaryum sciophilum, Dasypus novemcinctus, Delomys sublineatus, Dermatemys mawii, Fundulus heteroclitus,Homalaspis plana, Jumellea rossii, Khaya senegalensis, Mugil cephalus, Neoceratitis cyanescens, Phalacrocorax aristotelis, Phytophthora infestans, Piper cordulatum, Pterocarpus indicus, Rana dalmatina, Rosa pulverulenta, Saxifraga …
Gene flow relates to evolutionary divergence among populations at the range margin
2020
Background Morphological differentiation between populations resulting from local adaptations to environmental conditions is likely to be more pronounced in populations with increasing genetic isolation. In a previous study a positive clinal variation in body size was observed in isolated Roesel’s bush-cricket, Metrioptera roeselii, populations, but were absent from populations within a continuous distribution at the same latitudinal range. This observational study inferred that there was a phenotypic effect of gene flow on climate-induced selection in this species. Methods To disentangle genetic versus environmental drivers of population differences in morphology, we measured the size of …
Effects of traditional coppice practices and microsite conditions on tree health in a European beech forest at its southernmost range
2016
Abstract: European beech (Fagus sylvatica) grows at the southern limit of its range in the mountain-Mediterranean vegetation belt up to the timberline. The southernmost beech forests of Sicily (southern Italy) show peculiar ecological, structural and silvicultural characteristics, growing in fragmented and isolated stands near the timberline and in topographically marginal unfavorable habitats. Past silvicultural practices increased the heterogeneity of stand structure at these sites. We compared stand structural characteristics and tree health in coppice-cut and control beech stands with respect to the local topographic gradient (bottom, slope and ridge) and canopy cover (clearing/border v…
Variational Approximations for Generalized Linear Latent Variable Models
2017
Generalized linear latent variable models (GLLVMs) are a powerful class of models for understanding the relationships among multiple, correlated responses. Estimation, however, presents a major challenge, as the marginal likelihood does not possess a closed form for nonnormal responses. We propose a variational approximation (VA) method for estimating GLLVMs. For the common cases of binary, ordinal, and overdispersed count data, we derive fully closed-form approximations to the marginal log-likelihood function in each case. Compared to other methods such as the expectation-maximization algorithm, estimation using VA is fast and straightforward to implement. Predictions of the latent variabl…
Variations spatiales et temporelles des communautés adventices des cultures annuelles en France
2007
Although arable weed species are particularly well adapted to habitats characterised by high levels of disturbance(ploughing, harvest), the degree and rate at which agro-ecosytems have been transformed in the last 50 years in Europe(use of chemicals, changes in crop rotations) has led to profound changes in the composition and diversity of arable weedcommunities. This thesis provides an update on the composition and diversity of weed communities that can be foundacross the main crop types and regions of France. It also addresses two objectives i) applying (community) ecologytheories for the analysis and interpretation of spatial and temporal variations in weed communities and ii) using the …
Which traits allow weed species to persist in grass margin strips ?
2017
EASPEGESTADINRA; Sown-grass margin strips, historically established to limit pesticide drift and soil erosion, are now also promoted for enhancing floral diversity and associated ecosystem services. To better understand weed community assembly in grass margin strips, we performed floral surveys in 75 sown-grass margin strips in two regions in France and characterized each species using information from trait databases. We hypothesized that traits of dominant species would differ between newly sown-grass margin strips and older strips. Weed species were separated into functional groups based on their traits using multiple correspondence analysis and hierarchical ascendant classification. Fun…
A Fractional-Order Control Approach to Ramp Tracking with Memory-Efficient Implementation
2020
We investigate the fractional-order (FO) control of arbitrary order LTI systems. We show that, for ramp tracking or input disturbance rejection, it is advantageous to include an FO integrator to the open-loop if we have to increase the order of integration further than one. With the lower phase-loss of the FO integrator it is easier to guarantee a desired phase margin. Furthermore the flat phase response around the crossover-frequency (iso-damping property) can be achieved for a wider frequency range such that the closed-loop is more robust wrt. amplitude and phase margins. The drawback of the FO approach is the increased implementation effort and the algebraic decay, which slows down the t…