Abondance (écologie) | EPFL Graph Search

thumb|upright=1.2|On estime que la Tourte voyageuse, maintenant disparue, était l’un des oiseaux les plus abondants au monde avec une population se situant entre 3 et 5 milliards d’individus. Ici un individu naturalisé du Boston Museum of Science. thumb|upright=1.2|Le Travailleur à bec rouge revendique maintenant le statut d’espèce aviaire la plus abondante au monde avec une population d’environ 1,5 milliard d’individus. thumb|upright=1.2|Les activités humaines peuvent avoir un impact important sur l’abondance de nombreuses espèces vivantes. Les coupes forestières en sont un exemple. En éliminant le couvert forestier sur de vastes surfaces, cette activité modifie profondément l’abondance, non seulement des espèces végétales, mais de toutes les communautés animales qui en dépendent. En écologie, l’abondance d’un organisme est le nombre total de cet organisme ou le nombre d’organismes par unité d’espace. La seconde définition réfère à la densité de la population de l’organisme. L’abo

Analysis of labelled compounds by mass spectroscopy in the presence of heavy isotopes at natural abundance: the NAIC program

A program is described, which allows the intensity contributions from naturally occurring heavy isotopes to be eliminated from the mass spectrometric ions of an artificially labelled compound. This allows the accurate measurement of the isotopomer distribution of the compound and hence its percentage isotopic abundance. In the case of radioactively labelled compounds the specific radioactivity can then be derived from the abundance data. The program utilizes a graphical user interface based upon the C++ Builder 6.0 environment and VCL library.

2009

Responses of permanent grasslands to drought during the plant growing season: combining agronomic, functional and ecophysiological approaches

Amarante Vitra

Extreme summer drought events are predicted to increase in intensity and frequency within the current century. The resulting water scarcity could dramatically impact human activities related to agriculture, due to the strong relationship between precipitations and plant biomass production. However, little is known about the interactions between timing of drought and vegetation dynamics along the growing season. In Switzerland, were grasslands are at the core of the agriculture, droughts could have severe economical consequences. Thus, farmers should be provided with insights on how to adapt and optimize their management to the changing climate. In order to further our understanding on the response of grasslands to different timing of drought and its interaction with other factors such as management intensity, productivity or soil characteristics, we developed the GRASSALT project -which was the context of this PhD- as a joint venture between AGROSCOPE, EPFL and WSL, with the aim to investigate this challenge through a multidisciplinary perspective at the crossroad between applied and fundamental research. The setup of a realistic drought experiment in three semi-natural grasslands in the Swiss Jura Mountains (even though this thesis is focusing mainly on two) where 70% of the precipitations were removed during two months at two different (during the peak of vegetation growing season vs after this peak later in the season) and two management intensities were applied, enabled us to investigate how grassland communities responded to drought at different timings and sites and investigate its interacted with management. To perform this investigation we adopted a combined agronomic, functional and ecophysiological approach that leads us to analyse the effect of drought from the plant community level to the physiological level and to the analysis of the aboveground-belowground interaction. The main findings of this thesis were the following: (i) a drought event occurring later in the growing season leads to stronger reduction in aboveground productivity than a drought event occurring during the peak of growing season. (ii) The decrease in aboveground productivity is mediated by an intraspecific variability in the functional traits of the most abundant plant species. (iii) the effect of drought is more deleterious under higher mowing intensity. (iv)The effect of drought on plant aboveground and belowground productivity is dependent on soil types and modulated through the effects on microbial communities in response to climate. Altogether the presented work has shown that timing of drought plays a big role on the impact of drought on the productivity of grasslands per se or by interacting with otherfactorsand that this requires further in-depth studies to offer efficient management strategies to farmers.

EPFL2019

The role of mixing in controlling resource availability and phytoplankton community composition

Bieito Fernandez Castro, Emilio Marañón

We investigate the role of mixing, through its effect on nutrient and light availability, as a driver of phytoplankton community composition in the context of Margalef’s mandala. Data on microstructure turbulence, irradiance, new nitrogen supply and phytoplankton composition were collected at 102 stations in three contrasting marine environments: the Galician coastal upwelling system of the northwest Iberian Peninsula, the northwestern Mediterranean, and the tropical and subtropical Atlantic, Pacific and Indian oceans. Photosynthetic pigments concentration and microscopic analysis allowed us to investigate the contribution of diatoms, dinoflagellates, pico- and nanoeukaryotes, and cyanobacteria to the phytoplankton community. Simple linear regression was used to assess the role of environmental factors on community composition, and environmental overlap among different phytoplankton groups was computed using nonparametric kernel density functions. Mixing and new nitrogen supply played an important role in controlling the phytoplankton community structure. At lower values of mixing and new nitrogen supply cyanobacteria dominated, pico- and nanoeukaryotes were dominant across a wide range of environmental conditions, and finally enhanced new nitrogen supply was favourable for diatoms and dinoflagellates. Dinoflagellates were prevalent at intermediate mixing levels, whereas diatoms spread across a wider range of mixing conditions. Occasional instances of enhanced diatom biomass were found under low mixing, associated with the high abundance of Hemiaulus hauckii co-occurring with high N2 fixation in subtropical regions, and with the formation of thin layers in the Galician coastal upwelling. Our results verify the Margalef’s mandala for the whole phytoplankton community, emphasizing the need to consider nutrient supply, rather than nutrient concentration, as an indicator of nutrient availability.

2019