Search results for "competition"
showing 10 items of 1409 documents
Fragmentation des habitats et interactions hôtes-parasites
2021
Habitat fragmentation is one of the main threats to global biodiversity and despite an abundant literature on the impact of fragmentation on species abundance and diversity, the consequences of this global change in terms of ecological and evolutionary processes remain poorly understood. Beyond their direct contribution to biodiversity, as species-rich category of organisms, parasites could be involved in biodiversity change as key actors of ecological and evolutionary processes. The present work aims to understand the effect of forest fragmentation on host-parasite interactions. It is based on a large sampling carried out in the Lesser Antilles and in French Guiana, and allowing the obtent…
No performance reduction at the present northern edge of Ambrosia artemisiifolia L. invasion range
2014
Plant populations at range edges may exhibit reduction of performances and fitness. In the case of biological invasions, such a reduction could be associated with a slowing down of the spread and explain the non-naturalization of a species outside its present invasion range. Common ragweed (Ambrosia artemisiifolia L.) is an ideal model to investigate such processes, since it is invasive in France but not naturalized in northern countries, such as Belgium and the Netherlands. In this study, we test if the performances of ragweed populations vary among different invasion zones. Three populations were selected in each of four invasion zones in Western Europe: 1) French invasion area; 2) northe…
Common ragweed growth under different level of competition
2013
Common ragweed (Ambrosia artemisiifolia L.) is colonizing various habitats. From mid-May to September 2012, the growth and development of different plants was monitored in four different habitats. Main development stages were observed and a final aerial biomass was measured. The number of ragweed plants surviving competition and management practices was lower in the plots with alfalfa than in the other plots. The number of ragweed plants reaching the male-flowering stage was significantly higher in the spontaneous vegetation and the “sown wildflowers”. Nevertheless, it was never observed a strong enough competition in any of the plots to avoid the flowering stage. We can extrapolate that in…
Effets de la fertilisation azotée et du choix des espèces/variétés cultivées sur l’assemblage des communautés. Comment les optimiser pour favoriser l…
2018
National audience; La nécessaire diminution de l’usage des herbicides et des engrais minéraux dans les systèmes de culture pourrait entraîner le développement d’une flore adventice résiduelle et une compétition accrue pour les ressources, notamment azotées, entre cultures et adventices. L’objectif de cette thèse est d’analyser dans quelle mesure optimiser les techniques de fertilisation azotée et le choix des espèces/variétés cultivées pourrait fournir un levier pour piloter les communautés végétales, afin de favoriser la régulation biologique des adventices par compétition pour l’azote, et ainsi réduire l’usage des herbicides. Un premier volet vise à compléter et paramétrer le modèle FLORS…
Can obligatory omnivore carabids be useful for the biocontrol of weeds?
2017
National audience; Many thousands of carabid individuals exist in farm fields, in communities of carnivore and opportunistic (e.g. granivores) and obligate omnivore guilds. As carabids can eat a substantial amount of weed seeds they are considered as credible biocontrol agents for the regulation of weeds in arable fields. Some studies have suggested that “granivores” are more important biocontrol agents than obligate omnivorous species. Yet, in some instances, obligate omnivores are very abundant and appear to drive the predation of weeds leading some authors to question whether specialist natural enemies are better. Moreover, niche complementarity, facilitation and interference (i.e. intra…
Maize-based low-input cropping systems can provide effective weed control while ensuring crop productivity
2016
Conventional Maize Monoculture (MMConv) is now questioned for environmental reasons. During a five-year field experiment, yield and weed pressure of MMConv was compared to three low-input Cropping Systems (CS) : MMLI, a Low-Input Maize Monoculture; MMCT, a Conservation Tillage Maize Monoculture; Maize-MSW, Maize rotated with Soyabean and Wheat, all designed to reduce water pollution. In 2014 and 2015, weed-free zones were established on all CS. Weed biomass was higher in MMCT, especially for spring grasses and perennials. MMConv (11.3±1.1 T ha-1) and MMLI (10.6±2.3 T ha-1) had higher grain yields than MMCT (8.2±1.9 T ha-1). Finally, concerning yields observed in weed-free zones, MMCT yields…
Approches de la nuisibilité du bleuet en colza d'hiver
2016
Infestation of oilseed rape fields by cornflower is more and more frequent, which could become harmful. In contrast, cornflower produces nectar that is a resource for pollinators and probably crop pest predators and parasitoides. In order to get benefit of this resource, it is necessary to determine a balanced equilibrium between the services and the weediness of cornflower in spite of destroying it. We describe here bispecific competition trials against oilseed rape in small experimental plots. Experimental conditions led to too high or too small plant densities to estimate a threshold of competition. Results provide relevant information on self-concurrence among cornflower plants and on i…
Contextualization of archaeological information using augmented photospheres, viewed with head-mounted displays.
2019
Photospheres, or 360°
Sensory methodology developed for the investigation of sciaccarello wine concept
2004
<p style="text-align: justify;">The aim of the present work was to underline the existence of a sensory space relevant to Sciaccarello wines. Twenty-eight wines were selected for viticultural and enological characteristics, using 1/2 Sciaccarello/Non- Sciaccarello ratio. Sensory analyses (orthonasal then overall perceptions) were performed with a panel composed of seventeen judges. All of the judges were experienced in Sciaccarello wines knowledge. Statistical treatment by PCA was first carried out to display the consensus between the assessors. ANOVA was performed to discriminate accurate and inaccurate examples of Sciaccarello wines. This study demonstrated the existence of the sens…
Taking action or thinking about it? : State orientation and rumination are correlated in athletes
2019
Athletic performance in competitive sports relies heavily on the ability to cope effectively with stressful situations. In contrast, some athletes report that their thoughts revolve around the future or past and not around the actual demands during competitions. In those specific stressful situations, the lack of focus like an unintended fixation on repetitive cognitions can have fatal consequences with regard to the performance. Especially when competitors are close in their athletic capabilities, differences in effectively coping with stress and mental stability may decide about winning and losing. One established factor of performing effectively under pressure is the individual tendency …