Search results for "diversity"

Diversité fonctionnelle au sein des communautés de plantes adventices : effet de la rotation et du type de culture

2012

During this internship I investigated the effects of habitats i.e. field margin or the core of the field, and of crop sequences weed taxonomic and functional diversity in arable fields. We selected 75 fields from a database of flora surveys that have been conducted since 2005 in the area of Fénay. In the 75 fieds, the flora was sampled four consecutive years. The indices of Shannon-Weaver, Simpson and Pielou and species richness were selected for taxonomic study, while Rao's quadratic entropy and the community weighted mean (CWM) of the traits in the community were used for the functional study. Four functional traits were selected for the analyses. Our results showed that all studied facto…

Le travail agricole à façon : des tribulations à la régulation

2018

International audience; La prestation de service agricole constitue un marché en pleine expansion qui doit son succès aux indéniables intérêts qu’elle offre aux entreprises agricoles, petites ou grandes. Derrière la généralisation de ces pratiques, se cachent néanmoins une mutation profonde des modes d’exploitation ainsi que des phénomènes de fraudes appelant de nouveaux outils de régulation

A paleontological viewpoint on the "6th mass exinction".

2020

Adaptation des communautés microbiennes aux polluants chimiques

2013

L’Homme au travers des activités industrielles, agricoles,…, qu’il développe, exerce une pression de plus en plus prégnante sur l’environnement et sur les organismes qui y vivent. La pression anthropique est quasi-généralisée à la surface du globe terrestre. Elle se caractérise par le relargage et la dispersion de nombreux polluants organiques et métalliques, conduisant des scientifiques à proposer que l’humanité était entrée, depuis la révolution industrielle, dans l’anthropocène, une nouvelle époque géologique. Les sols arables qui nourrissent l’humanité ne sont pas indemnes de contaminations. Ils sont fréquemment exposés aux intrants chimiques et organiques employés dans les itinéraires …

Analyse de sensibilité des modèles de connectivité écologique

2021

Le succès des mesures de conservation de la biodiversité basées sur le maintien de la connectivité écologique dépend de la qualité de la modélisation spatiale des mouvements des espèces. Le calcul de chemins de moindre coût est censé identifier les trajets qui minimisent les coûts de déplacement à travers la matrice paysagère. Il apporte deux types d’information : (i) la localisation spatiale des chemins de moindre coût et (ii) le coût accumulé le long de ces chemins, aussi appelé distance-coût. Cette modélisation spatiale nécessite qu’un coût soit attribué à chaque type d’occupation du sol, constituant alors un scénario de coût. L’influence de ces scénarios sur la localisation des chemins …

Baselines and French Forests

2022

International audience

Multifunctionality: refocusing a spreading, loose and fashionable concept for looking at sustainability?

2008

International audience; The notion of agriculture's Multifunctionality (MF) emerged in the 1980s. It then followed two trajectories since the 1990s: a conflicting period linked to its use in the international trade negotiations on the one hand, a spreading in terms of meaning, use and geographically on the other hand. Specific meanings appeared in connection with policy making, at national or international levels, or through the involvement of new disciplines. Yet, very few authors discuss the implication of the chosen meaning on their findings. To explore and take advantage of using this word and to deliver it from its controversial use in international trade negotiations, it is absolutely…

Biodiversity and characterization of arbuscular mycorrhizal fungi at the molecular level

1994

Biodiversity within a biological group provides the basis for distinguishing members into genera and species according to taxonomic criteria, and between individuals within a species depending on more detailed differences at the genetic level. Diversity between species occurs after a genetic barrier has been created either by a geographic or genetic impedance of gene flow. Divergence can continue by nucleotide substitutions and by mutations in a broader sense (deletions, translocations, duplications), and resulting diversity can be evaluated at the molecular level and used as a phylogenetic character. Diversity at the subspecies level is a function of both mutation rates and gene flow betwe…

Decreasing Phanerozoic extinction intensity as a consequence of Earth surface oxygenation and metazoan ecophysiology

2021

The decline in background extinction rates of marine animals through geologic time is an established but unexplained feature of the Phanerozoic fossil record. There is also growing consensus that the ocean and atmosphere did not become oxygenated to near-modern levels until the mid-Paleozoic, coinciding with the onset of generally lower extinction rates. Physiological theory provides us with a possible causal link between these two observations-predicting that the synergistic impacts of oxygen and temperature on aerobic respiration would have made marine animals more vulnerable to ocean warming events during periods of limited surface oxygenation. Here, we evaluate the hypothesis that chang…

Biological nitrogen fixation for the 21st century

1998

The biodiversity of nitrogen-fixing organisms is huge. Taxonomic and phylogenetic research is needed to structure this diversity, to facilitate communication among scientists, and to increase our understanding of the evolution and biology of diazotrophs. Molecular tools for taxonomic and biodiversity studies of diazotrophic rhizobia, frankiae, cyanobacteria and bacilli are presented in sections 2 to 5. Sections 6 to 9 focus on problems with genus and species assignment.