Search results for "Mathematic"
showing 10 items of 24974 documents
Berry characterisation of cv shiraz according to position on the rachis
2016
In this study, characterisation of the physical and compositional parameters of berries located in different positions on the rachis of Shiraz/R99 bunches was done. Berries were divided according to position on the rachis (apical, median and basal) and berry weight, resulting in four berry weight classes, averaging 0.86 g, 1.29 g, 1.74 g and 2.26 g and 0.74, 1.18, 1.59 and 2.09 cm3, respectively. The berries were analysed individually. The fresh weight of the berries comprised approximately 4% seeds, 20% skin and 76% flesh. Different percentage distributions were found for each class of berry weight and according to position on the rachis. From the top to the bottom rachis position, an incr…
An Algebraic Derivation of Chao’s Estimator of the Number of Species in a Community Highlights the Condition Allowing Chao to Deliver Centered Estima…
2014
Anne Chao proposed a very popular, nonparametric estimator of the species richness of a community, on the basis of a limited size sampling of this community. This expression was originally derived on a statistical basis as a lower-bound estimate of the number of missing species in the sample and provides accordingly a minimal threshold for the estimation of the total species richness of the community. Hereafter, we propose an alternative, algebraic derivation of Chao’s estimator, demonstrating thereby that Chao’s formulation may also provide centered estimates (and not only a lower bound threshold), provided that the sampled communities satisfy a specific type of SAD (species abundance dist…
Limits and targets for a regional sustainability assessment: an interdisciplinary exploration of the threshold concept
2008
Part 5. Regional and local evaluation-18 ; International audience; Some encompassing terminology is required in order to accommodate different conceptual approaches in the three pillars of sustainability. So, this chapter provides a literature review exploring the threshold concept. In environmental research – especially in ecology – thresholds are often associated with limits which have certain system-inherent processes. In social and economic disciplines, if the notion of limit or critical limit is present, the concept of targets is often more appropriate which are linked to political objectives and social acceptability. The concept of threshold is accommodated within the general framewor…
An ecological multi-Level theory of competition for resources used to analyse density-dependence effects in fruit production
2014
International audience; Lescourret and Génard (2003) developed a multi-level theory of competition for resources applied to fruit production, considering that any collection of unit parts (cells or seeds in a fruit, fruits in an infructescence or in a tree...) can form a population and the population is subject to competition, whatever the level of organization. The principles of the theory are that the mass of each unit decreases when the number of units in the population increases and that the total mass of the population increases as the number of units increases until it reaches a maximum, after which it decreases. A three-parameter model based on that theory was used to analyse the lev…
Estimation of local extinction rates when species detectability covaries with extinction probability: is it a problem ?
2006
Estimating the rate of change of the composition of communities is of direct interest to address many fundamental and applied questions in ecology. One methodological problem is that it is hard to detect all the species present in a community. Nichols et al. presented an estimator of the local extinction rate that takes into account species probability of detection, but little information is available on its performance. However, they predicted that if a covariance between species detection probability and local extinction rate exists in a community, the estimator of local extinction rate complement would be positively biased. Here, we show, using simulations over a wide range of parameters…
Statistical modelling and RCS detrending methods provide similar estimates of long-term trend in radial growth of common beech in north-eastern France
2011
International audience; Dendrochronological methods have greatly contributed to the documentation of past long-term trends in forest growth. These methods primarily focus on the high-frequency signals of tree ring chronologies. They require the removal of the ageing trend in tree growth, known as 'standardisation' or 'detrending', as a prerequisite to the estimation of such trends. Because the approach is sequential, it may however absorb part of the low-frequency historical signal. In this study, we investigate the effect of a sequential and a simultaneous estimation of the ageing trend on the chronology of growth. We formerly developed a method to estimate historical changes in growth, in…
Comparative study of the efficiency of buffer zones and harvest discarding on gene flow containment in oilseed rape. A modelling approach
2009
International audience; Oilseed rape (OSR) genes can escape fields in space via pollen and seeds and in time via volunteers resulting from seeds lost before or during oilseed rape harvests. Previous simulation studies and field observations showed that co-existence at the landscape level of contrasting OSR varieties such as genetically modified (GM) and non-GM varieties require costly measures that are difficult to implement, such as isolation distances between OSR fields and stringent volunteer control in all fields and road margins. In the present study, two local strategies, non-GM buffer zones aroundGMfields and discarding the harvest of boundary plants of non-GM fields, were tested in …
Sustainable production of fennel and dill by intercropping
2008
Intercropping is claimed to be one of the most significant cropping techniques in sustainable agriculture, and much research and many reviews attribute to its utilization a number of environmental benefits, from promoting land biodiversity to diversifying agricultural outcome. In this sense, intercropping is thought to be a useful means of minimizing the risks of agricultural production in many environments, including those typical of under-developed or marginal areas. In order to validate this hypothesis in a representative area of the semiarid Mediterranean environment, we evaluated the possibility of growing dill and fennel, both belonging to the family Apiaceae, in temporary intercroppi…
Priorities for research in soil ecology
2017
The ecological interactions that occur in and with soil are of consequence in many ecosystems on the planet. These interactions provide numerous essential ecosystem services, and the sustainable management of soils has attracted increasing scientific and public attention. Although soil ecology emerged as an independent field of research many decades ago, and we have gained important insights into the functioning of soils, there still are fundamental aspects that need to be better understood to ensure that the ecosystem services that soils provide are not lost and that soils can be used in a sustainable way. In this perspectives paper, we highlight some of the major knowledge gaps that shoul…
Let’s make Pulvigera great again: re-circumscription of a misunderstood group of Orthotrichaceae that diversified in North America
2020
Abstract Orthotrichum lyellii was described in 1878 based on the crisped leaves with plane margins on its elongated and branched stems, and on the presence of brood-bodies. In Europe, these characters remain constant, but in North America several similar forms lacking propagules have been described either at the specific or infraspecific level. These were all reduced to synonyms of O. lyellii. In 2015, Orthotrichum was divided, and O. lyellii was transferred to Pulvigera, a genus thus far considered to be monospecific. In this study, the variability of P. lyellii is analysed in an integrative taxonomic framework. Morphological studies on > 200 specimens, including the nomenclatural t…