Hasard, déterminisme et édification des communautés écologiques insulaires : le cas des araignées d'Hawaï et des îles de l'océan indien

Cette thèse se place dans le cadre théorique de l'édification des communautés écologiques, un phénomène complexe pouvant s'étudier à de nombreuses échelles et influencé par des facteurs variés. Dans le chapitre 1, je présente l'hypothèse d'une relation entre la dynamique de colonisation et les règles d'assemblage des communautés. Dans le chapitre 2, je propose que les facteurs intrinsèques et géographiques jouent sur l'édification d'une communauté écologique en influant sur les flux d'individus entre la source de colonisateurs et l'endroit où elle s'assemble. Dans le chapitre 3, j'étudie l'influence du contexte régional, géographique et écologique sur les différentes composantes des communautés locales, ces composantes n'étant pas toutes influencées par les mêmes facteurs régionaux. Dans le chapitre 4, je me concentre sur un cas d'étude qui nous met en garde sur l'interprétation de patrons de diversification locale apparente sans prise en compte de la biologie des individus ; je propose aussi que certains facteurs intrinsèques aux lignées puissent empêcher une diversification in situ malgré un contexte écologique potentiellement favorable. L'édification des communautés écologiques est le résultat de nombreux processus agissant dans des paysages qui sont l'expression de contingences historiques et géographiques, ce qui explique en partie pourquoi les questions d'édification des communautés sont parmi des plus débattues de l'écologie scientifique. Seul un examen prudent d'un ensemble de données morphologiques, génétiques, écologiques et comportementales pourra permettre de déterminer dans quel contexte les théories classiques des communautés écologiques seront valables.This thesis belongs to the ecological community edification framework, which is a complex phenomenon that can be studied at various scales and is influenced by numerous factors. After proposing the hypothesis of a link between the colonization dynamics and the assembly rules of a community (chapter 1), I highlight the role of these factors in the ecological community edification. In the chapter 2, I propose that intrinsic and geographical factors can impact on ecological community edification through the persistence of individual flow between the immigration source and the place where the community is built-up. In the chapter 3, I show how the regional, geographical and ecological context could impact on various components of local communities; I also highlight the fact that not all the regional factors impact on the same community components. In the chapter 4, I develop a case study that warns us against the interpretation of so-called local diversification patterns without taking into account the species biology; I also show how some intrinsic factors of some lineages could prevent an in situ diversification despite a potentially favorable ecological context. The edification of ecological communities is the product of numerous processes that acts on landscapes that are the expression of historical and geographical contingencies, which probably partly explains why the topic of community build-up and assembly is one of the most controversial of scientific ecology. Only a careful examination of a combination of morphological, genetic, ecological and behavioral data could allow us to identify in which context the classical theories of ecological communities are valid

Randomness, determinism and edification of insular ecological communities (a case of the Hawaiian and indian ocean spiders)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Living with the dead: when the body count rises, prey stick around

Most terrestrial prey species are assumed to assess predation risk by detecting predators directly rather than using cues of previous attacks on conspecifics. However, such cues might represent valuable information, and prey can be expected to respond to the presence of congeners killed by enemies. Such cues are available in aphid colonies attacked by parasitic wasps because they do not remove parasitized hosts from the colony. Colonies are thus often a mixture of healthy, parasitized, and killed aphids, which corpses ("mummies") stay attached to the plant and can be encountered by live aphids. Aphids exhibit a dispersal polyphenism. Recent studies show that they produce more winged offspring when directly exposed to natural enemies or to alarm pheromone emitted by conspecifics. We hypothesized that aphids perceive the corpses of congeners killed by parasitoids and respond by increasing the production of winged morphs, but we surprisingly found the opposite. We determined the adaptive value of this response by analyzing the foraging behavior of parasitoids in aphid colonies with killed aphids ("mummies"). Parasitoid females responded to the presence of mummies by reducing both their time allocation and parasitism activity in the patch. The strategy of aphids to reduce emigration (i.e., they produce more wingless morphs when mummies are present) is adaptive because the presence of killed congeners reduces parasitoid pressure on colonies. This demonstrates that the remains of individuals killed by natural enemies can still have an ecological relevance in prey populations and that enemy-induced phenotypic plasticity depends on the type of predation cues. Copyright 2009, Oxford University Press.