Destruction des habitats | EPFL Graph Search

vignette|Les 5 grandes causes de régression de la biodiversité selon l'ONU et la Convention mondiale sur la biodiversité.Les flèches à double sens évoquent les relations d'exacerbations qui peuvent exister entre chacune de ses causes et les autres. vignette|Déforestation au Guatemala. La notion de destruction des habitats ou perte des habitats englobe tout phénomène par lequel des habitats nécessaires à la vie d'espèces, disparaissent ou se détériorent rapidement. La perte des habitats ou leur dégradation (notamment leur fragmentation) peuvent être causées par des perturbations naturelles (incendies, inondations, maladies, séismes, activité volcanique) ou des perturbations anthropiques. Destruction des habitats et biodiversité Les principales causes évoquées à l'origine de la perte de la biodiversité sont les modifications des habitats par l'homme (perte et dégradation des habitats dues à la déforestation, l'agriculture intensive, les routes, l'urbanisation, les explo

Beyond the patch: on landscape-explicit metapopulation dynamics

Jonathan Giezendanner

Climate change threatens biodiversity and species distribution all over the world at unprecedented rates. Human induced changes to landscape structure and habitat are redefining the relation between species and their environment. Understanding, characterizing and modeling the relation between complex landscape features and geographical species presence, the subject of this thesis, have thus gained paramount importance in order to make informed decisions on near- and far-term management strategies for species and landscape protection. The present thesis pays particular attention to the understanding of how mountain landscapes, described as heterogeneous habitat matrices, govern the presence of a species in space and time. To this end, throughout this thesis a metapopulation model is considered, a spatially-explicit model based on the balance between colonization and extinction events in areas of different suitability. The classical patch-based modelling approach is extended here in various ways in order to incorporate landscape-explicit information about the habitat matrix. A first theoretical study is performed on geometric, realistic, and real landscapes which highlights how different levels of connectivity, the degree to which different areas of similar habitat are actually linked together in the landscape (say, derived from geomorphic structures, such as valleys and peaks or emerging structures shaped by fluvial erosion and tectonic uplift) impact the dynamic of mountain species under climate change. A second, applied, study investigates how different landscape descriptors derived from Earth Observation data can be used in order to dynamically model the spatial, landscape-explicit, presence of two carabid species (Pterostichus flavofemoratus and Carabus depressus) in the Gran Paradiso National Park. In a final study, the consistency of the metapopulation model is investigated when considering different resolutions of the landscape matrix, i.e. different levels of coarse-graining. This last part is fundamental to the understanding of how conclusions drawn from local studies can be made general and extrapolated to larger regions. Overall, this thesis bridges the fields of population and landscape ecology, focusing on modelling metapopulation dynamics in complex landscapes seen as the substrate for ecological interactions. The result from the three studies show that metapopulation ecology can profit from the insights of landscape ecology. The combination of the two fields can be a useful tool in furthering the understanding and monitoring of mountain species.

EPFL2020

Effects of drought on the effectiveness of Phalaris arundinacea and Impatiens glandulifera in building up soil aggregates – a microcosm approach

Thomas George McMullin

Near natural floodplain ecosystems are not only stressed by frequent inundations over a year but also by periodical droughts in summer due to their reduced water retention capacity. To maintain floodplain habitats as biodiversity hotspots, a stable soil structure is required. Soil ecosystem engineers (EEs) such as plants and earthworms, who are known to build up soil macro-aggregates, have to tolerate rough conditions while they colonize these habitats. EEs¿ effectiveness on soil aggregation under periodical drought conditions has never been investigated so far. To simulate different drought intensities, a microcosm approach under controlled conditions will be set up. Soil sediments, plants and earthworms will be collected in a restored floodplain river section and incubated 8 weeks at 15°C under different soil moisture conditions. Plant resistance to drought will be assessed through leaf water potential and transpiration monitoring as well as through innovative measurements of plant resistance to embolism. This approach will help to increase the understanding of how EEs behave under periodical stress conditions.

2017

Relationships between key functional traits of the waterlily Nuphar lutea and wetland nutrient content

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

Beyond the patch: on landscape-explicit metapopulation dynamics

Jonathan Giezendanner

EPFL2020