Two conceptual approaches which offer promise for improved understanding of biological invasions are conceptualizing the invasion process as a series of distinct stages and explicitly incorporating human actions into analyses. This study explores the utility of these approaches for understanding the invasion of Trifolium (true clover) species in New Zealand. From the published literature, I collected a range of Trifolium species attributes, including aspects of global transport and use by humans, opportunistic association with humans in New Zealand, native range attributes, habitat characteristics, and biological traits. I also searched historical records to estimate the extent to which each species had been planted in New Zealand, a search facilitated by the enormous importance of Trifolium in New Zealand’s pastoral agriculture system. Regression analysis and structural equation modelling were then used to relate these variables to success at each invasion stage. Fifty-four of the 228 species in the genus Trifolium were intentionally introduced to New Zealand. Species introduced for commercial agriculture were characterised by a large number of economic uses and presence in Britain, while species introduced for horticulture or experimental agriculture were characterised by a large native range area. Nine of these 54 intentionally introduced species subsequently naturalised in New Zealand. The species that successfully naturalised were those that had been planted extensively by humans and that were well-matched to the New Zealand climate. A further 16 species (from the pool of 174 species that were never intentionally introduced) arrived and naturalised in New Zealand without any recorded intentional aid of humans. Several attributes appeared to assist species in unintentional introduction-naturalisation, including a good match to the New Zealand climate, a large native range area, presence in human-influenced habitats, a widespread distribution in Britain, and self-pollination capability. The 25 total naturalised species varied greatly in their current distributions and in the rates at which they had spread to achieve those distributions. Species that had spread quickly and are currently more widespread had been frequent contaminants in the pasture seed supply and have a long flowering period in New Zealand. Other biological traits and native range attributes played supporting roles in the spread process. Attributes facilitating success clearly varied among invasion stages. Humans played a dominant role at all stages of this invasion, although biological traits had increasing importance as a species moved through the invasion sequence. My findings suggest that incorporation of human actions and the stage-based framework provide valuable insight into the invasion process. I discuss potential avenues by which these approaches might be integrated into predictive invasion models.

Cette thèse présente les trois approches : analytique, expérimentale et numérique développées pour étudier le comportement d'une hydrolienne à membrane ondulante. Cette technologie, portée par l'entreprise EEL Energy, est basée sur les déformations périodiques d'une structure flexible pré-contrainte. Des convertisseurs d'énergie, positionnés de part et d'autre du système, sont actionnés par le mouvement d'ondulation.Analytiquement, la membrane est représentée par un modèle linéaire de poutre à une dimension et l'écoulement par un fluide potentiel 3D. L'action du fluide sur la membrane est évaluée par la théorie des corps élancés. L'énergie est dissipée de façon continue sur la longueur de la membrane. Expérimentalement, un prototype à l'échelle 1/20ième a été développé, des micro-vérins permettent de simuler l'énergie produite. Les essais avec le prototype1/20ième ont permis de valider le concept d'hydrolienne à membrane ondulante et le mode de récupération d'énergie. Un modèle numérique 2D éléments finis a été mis au point. Chaque élément constitutif de la membrane y est reproduit, la dissipation d'énergie est réalisée par des éléments dissipatifs mais la loi d'amortissement est limitée à un amortissement linéaire en vitesse.La comparaison des résultats issus de ces trois modèles a permis de valider leur bonne capacité à reproduire le comportement de la membrane sans conversion d'énergie. La dissipation d'énergie appliquée avec le modèle analytique se distingue clairement des deux autres modèles de part sa localisation mais aussi par la loi d'amortissement utilisée. Les autres modèles sont cohérents entre eux et si on ne parvient pas à corréler les résultats de puissance dissipée, le comportement du système et la répartition de la puissance dissipée le long de la membrane sont semblables. Ces trois approches ont permis de mettre en avant les paramètres clés dont dépend le comportement de la membrane et l'étude paramétrique démontre la complémentarité et l'intérêt du développement conjoint des modèles dans un souci industriel d'optimisation du système. Le développement d'un prototype à l'échelle supérieure (1/6ème), devant faire le lien entre les essais en bassin et les essais en mer, a permis de travailler sur les effets d'échelle. Des différences de comportements sont observées entre ces deux prototypes mais elles sont dues en partie à des différences de conditions aux limites et en partie à des effets de confinements très importants. Pour évaluer la tenue sur le long terme du prototype, ses composants (composite, élastomère) ont été caractérisés précisément et des essais de vieillissement accéléré par température ainsi que des essais de fatigue ont été mis en place sur des échantillons de matière. / This manuscript presents three approaches : analytical, experimental and numerical, to study the behavior of a flexible membrane tidal energy convertor. This technology, developed by the EEL Energy company, is based on periodic deformations of a pre-stressed flexible structure. Energy convertors, located on each side of the device, are set into motion by the wave-like motion.In the analytical model, the membrane is represented by a linear beam model at one dimension and the flow by a 3 dimensions potential fluid. The fluid forces are evaluated by the elongated body theory. Energy is dissipated all over the length of the membrane. A 20th scale experimental prototype has been designed with micro-dampers to simulate the power take-off. Trials have allowed to validate the undulating membrane energy convertor concept. A numerical model has been developed. Each element of the device is represented and the energy dissipation is done by dampers element with a damping law linear to damper velocity.Comparison of the three approaches validates their ability to represent the membrane behavior without damping. The energy dissipation applied with the analytical model is clearly different from the two other models because of the location (where the energy is dissipated) and damping law. The two others show a similar behavior and the same order of power take off repartition but value of power take off are underestimated by the numerical model. These three approaches have allowed to put forward key-parameters on which depend the behavior of the membrane and the parametric study highlights the complementarity and the advantage of developing three approaches in parallel to answer industrial optimization problems.To make the link between trials in flume tank and sea trials, a 1/6th prototype has been built. To do so, the change of scale was studied. The behavior of both prototypes is compared and differences could be explained by differences of boundary conditions and confinement effects. To evaluated membrane long-term behavior at sea, a method of aging accelerated by temperature and fatigue tests have been carried out on prototype materials samples immerged in sea water.

Two conceptual approaches which offer promise for improved understanding of biological invasions are conceptualizing the invasion process as a series of distinct stages and explicitly incorporating human actions into analyses. This study explores the utility of these approaches for understanding the invasion of Trifolium (true clover) species in New Zealand. From the published literature, I collected a range of Trifolium species attributes, including aspects of global transport and use by humans, opportunistic association with humans in New Zealand, native range attributes, habitat characteristics, and biological traits. I also searched historical records to estimate the extent to which each species had been planted in New Zealand, a search facilitated by the enormous importance of Trifolium in New Zealand's pastoral agriculture system. Regression analysis and structural equation modelling were then used to relate these variables to success at each invasion stage. Fifty-four of the 228 species in the genus Trifolium were intentionally introduced to New Zealand. Species introduced for commercial agriculture were characterised by a large number of economic uses and presence in Britain, while species introduced for horticulture or experimental agriculture were characterised by a large native range area. Nine of these 54 intentionally introduced species subsequently naturalised in New Zealand. The species that successfully naturalised were those that had been planted extensively by humans and that were well-matched to the New Zealand climate. A further 16 species (from the pool of 174 species that were never intentionally introduced) arrived and naturalised in New Zealand without any recorded intentional aid of humans. Several attributes appeared to assist species in unintentional introduction-naturalisation, including a good match to the New Zealand climate, a large native range area, presence in human-influenced habitats, a widespread distribution in Britain, and self-pollination capability. The 25 total naturalised species varied greatly in their current distributions and in the rates at which they had spread to achieve those distributions. Species that had spread quickly and are currently more widespread had been frequent contaminants in the pasture seed supply and have a long flowering period in New Zealand. Other biological traits and native range attributes played supporting roles in the spread process. Attributes facilitating success clearly varied among invasion stages. Humans played a dominant role at all stages of this invasion, although biological traits had increasing importance as a species moved through the invasion sequence. My findings suggest that incorporation of human actions and the stage-based framework provide valuable insight into the invasion process. I discuss potential avenues by which these approaches might be integrated into predictive invasion models.