Espèce clé de voûte

Résumé

Une espèce clé de voûte est « une espèce qui a un effet important et disproportionné par rapport à son abondance » sur la stabilité et la diversité spécifique d'une communauté. La caractère clé de voûte d'une espèce n'est pas intrinsèque. En effet, le rôle d'une espèce au sein d'une communauté dépend des conditions biotiques et abiotiques du milieu dans lequel elle se trouve. Ce concept a été introduit pour la première fois par R. T. Paine dans son article « A note on trophic Complexity and Community stability », publié en 1969. Cet article fait suite à des expériences qu'il a menées, en 1963, sur des communautés de zones rocheuses intertidales dont la diversité spécifique et la structure du réseau trophique sont maintenues grâce à la présence de prédateurs dominants qui jouent le rôle espèces clé de voûte. Le terme « clé de voûte » est une métaphore. En effet, ces espèces joueraient un rôle analogue à la clé de voûte, pierre placée au sommet d'un

Source officielle

https://fr.wikipedia.org/wiki/Esp%C3%A8ce_cl%C3%A9_de_vo%C3%BBte

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The students will learn the fundamentals in ecology with the goal to perceive the environment beyond its physical and chemical characteristics. Starting from basic concepts, they will acquire mechanistic understanding of biodiversity, ecosystem functioning and global change.

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Analysis of loads, water quality and certain biological production on the Kis-Balaton Water Protection System

Elise Kaiser

Wetlands are important ecosystems: they are habitats for many key species and act as natural regulators of the environment. They filter water and remove pollutants with the help of plants. Constructed wetlands are artificial wetlands built to treat mainly wastewaters. These artificial ecosystems can also be used for freshwater treatment, such as river water. The Kis-Balaton Water Protection System (KBWPS) is one of them and the main goal of the system is to treat the River Zala water before its entrance in the Lake Balaton. The two mains objectives are to avoid the eutrophication of the Lake Balaton and improve the wetland ecosystems. It is a vast constructed wetland of 71 km2, situated at Southern part of Lake Balaton, in Hungary. The goal of this thesis was to analyze the loads, water quality and biological production of the KBWPS. Interpretation of three different sets of data and field work was carried out. The first set was about inflow and outflow data, from which the removal rates of different nutrients on a long time period were computed. The second data series contained regular water quality monitoring data along the flow path and the goal was to study the inner processes happening in the KBWPS. The last data set was collected on the field and included basic water properties and some biological and physico-chemical measurements, such as primary production or tecton analysis. It allowed to differentiate the water types of the system and their properties and to better understand the inner processes, particularly the biological characteristics of the system. The interpretation of the data series gave background to understand the processes occurring within the system and it helped to characterize the actual different water groups. It drew the main lines for possible more detailed analysis. This work was partly connected to a project aiming at the development of a monitoring system that serves a better management of the KBWPS. Several conclusions can be drawn from the results found in this thesis: • General conclusions on the system, which could apply to other systems of the same type. • Specific conclusions about the operation of the system, which would refer to this system only. • Some management and monitoring suggestions for the future system.

2013

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Little attention has been paid to how aquatic habitat characteristics affect the traits of plant species. Nuphar lutea (L.) Sm. is a keystone species distributed across temperate regions of Europe, northwest Africa and western Asia. Its apparently low phenotypic variability compared to other aquatic plants led us to test whether the species exhibited significant phenotypic variability and whether trait values correlated to environmental parameters. The hypotheses were that (1) the environmental variation within our set of wetlands (both water and sediment characteristics) led to significant variation among four sets of traits related respectively to growth, reproduction, defence and storage and (2) that nutrient limitation (nitrogen and especially phosphorus) should affect plant traits towards a higher investment in storage and defence and a lower investment in growth and reproduction, thereby negatively affecting the success of N. lutea. To test these hypotheses, 11 populations of N. lutea were sampled in wetlands differing in physicochemical characteristics and spread along three rivers. A total of 15 traits, grouped into four sets (growth, reproduction, storage and defence), were measured during the growing season. Most N. lutea traits were related to the environmental characteristics of wetlands. The growth and reproduction traits were mostly positively related to habitat resource conditions, whereas the defence traits were positively correlated with both ammonium concentration and temperature, outlining possible anoxic stress (habitat adversity). Nitrogen or phosphorus limitation led to the variation of only a few traits: the rhizome starch content was higher in phosphorus-limited wetlands, while the rhizome length and volume, and the number of flowers were higher in nitrogen-limited wetlands.

2019

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Mitigating the variability of hydrogen production in mixed culture through bioaugmentation with exogenous pure strains

Nicolas Bernet, Simon Marius Jean Poirier

Process stability is a key operational issue when operating dark fermentation with mixed microbial cultures for hydrogen production. This study aimed at mitigating the instability of hydrogen production by separately adding exogenous pure strains suspected to have key roles in fermentative cultures. Among them, Clostridium acetobutylicum, Clostridium pasteurianum and Lactobacillus bulgaris which became predominant within the mixed culture strongly reduced the spectrum of produced metabolites and H-2 production variability. Interestingly, Escherichia coli and Cupriavidus necator, which remained in minor abundance, maintained a high and stable H-2 production while lowering the metabolic variability. 16S rRNA revealed that this could correlate to a simplification of the microbial diversity and the non-emergence of spore-forming competitors such as Sporolactobacillus sp. These results illustrate the potential beneficial role of minor OTUs as keystone species on H-2-producing complex ecosystem and support the possibility of using them to engineer the ecosystem and maintain high and stable performances. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2020

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Analysis of loads, water quality and certain biological production on the Kis-Balaton Water Protection System

Elise Kaiser

2013