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Pacific islands are long-settled by mankind, dating back several hundreds to thousands of years ago since discovery by islanders traveling by boat. Amongst these islands are atoll islands, which are small coral islands that lie at a low elevation and are usually part of a ring-like coral reef formation. Past and present islanders collect water from rainwater catchments and groundwater wells, with rainwater used primarily for drinking water and groundwater used as a supplement for wash water. Unfortunately, this region can experience severe drought, over-wash events during strong tropical storms, and typhoons, all of which threaten the freshwater supply for these islands. Due to rising concerns over climate change, there is interest in studying the water security of these especially vulnerable land forms. This thesis evaluates the reliability of the water supplies on four atoll islands in Yap, Micronesia by modeling the reliability of the two main sources. To first analyze rainwater catchment performance, Ifalik Island is evaluated using data collected on the island in 2015 by a collaborative research field team and a water balance model. Second, the results are used to develop design curves as a tool for rainwater catchment design and improvement. The fresh groundwater source is also modeled for each of the four islands to test the effects of varying climate conditions on the shallow, freshwater lens. Rainwater catchment systems on Ifalik Island are evaluated for their performance using a mass balance model that quantifies water storage through time. Performance is quantified primarily by reliability, which is a term to represent the percentage of days a rainwater catchment supplies sufficient water to the users. Based on the data from the Ifalik field survey, ii the average household rainwater catchment system on Ifalik uses a 16.5 square meter guttered roof with a 2,000 liter storage tank and serves seven individuals at 12 liters per capita per day. As a result of a rainwater catchment system sensitivity analyses based on the average rainwater catchment conditions, the most important factors in performance are effective roof area size, water demand, and gutter-downspout efficiency. Further analyses using the mass balance model found that the performance of each individual catchment is sufficient to provide water to the community during conditions similar to the severe drought year of 1997-1998, as well as projected rainfall conditions for the next 30 years. Therefore, analyses suggest Ifalik Island has sufficient rainwater catchment performance to provide water for the community. However, to introduce a conservative measure for water security, it is recommended that the catchment area be extended to the full size of the roof area. This would thereby increase the storage supply for the community by 25 cubic meters on the day of lowest supply under the 1997-1998 severe drought conditions.

Suite à la soutenance de thèse effectuée en juillet 2018 à l’Université de Massey, le manuscrit de Martin Thibault, intitulé « Le bulbul à ventre rouge (Pycnonotus cafer): dynamique d’invasion et impacts écologiques d’un oiseau introduit en Nouvelle Calédonie. Invasive alien species are a major cause of biodiversity loss globally, especially on islands where high species richness and levels of endemism accentuate their impacts. Various international institutions have constructed lists of the most harmful invasive species to help environment managers at both global and local scales to prioritize their efforts. The red-vented bulbul (Pycnonotus cafer) is a passerine bird species considered among the three worst invasive birds on the planet. This species is currently spreading over the tropical archipelago of New Caledonia, one of the 36 world biodiversity hotspots. This dissertation presents the findings of a PhD study conducted in New Caledonia with two objectives: 1) to describe this introduced population, and 2) to evaluate the threats from its dispersal using both existing knowledge and new in-situ and ex-situ data and a variety of analysis techniques. From the literature, I identified three key impacts explaining the species’ status: i) damage to agricultural crops, ii) noxious seed dispersal, and iii) competition with other avifauna. I estimated the local population size (approx. 140,000 individuals), its habitat use (inhabited areas), its density along an urbanization gradient (30-120 ind/km2), and I produced lists of consumed plant and animal species and identified a colour preference in the foraging strategy of the red-vented bulbul. Exploration of each impact category revealed i) substantial losses on fruit production (18% of tomato production), ii) impact on the abundance of nine native bird species that may be driving a spatial reassembly of the community, and iii) a short distance dispersal (77-92 m) that could promote the dispersal of introduced plant species at the expense of endemic species. Finally, through modelling, I estimated the climatic niche of the species at a global scale and identified that most island territories as suitable for the establishment of this invasive bird species. Regardless of whether the red-vented bulbul deserves its status as “world worst” species, quantitative impact assessments in its alien range such as the studies presented here are needed to prevent the dispersal and harmful impacts of this species on human activities and sensitive ecosystems. Implications for management are discussed.

Le chat haret est l’un des prédateurs invasifs les plus dommageables pour la biodiversité insulaire. Sa présence est associée à une perte de biodiversité sur l’ensemble des îles sur lesquelles il est établi, et où il constitue une menace pour de nombreuses espèces de vertébrés souvent endémiques et menacés. En Nouvelle-Calédoniedes populations de chats harets sont présentes dans tous les milieux et habitats et l’étude de son écologie et de ses impacts sur la faune ont fait l’objet de ce travail de thèse. L’analyse du régime alimentaire sur 14 sites d’études représentatifs des 4 habitats majeurs a révélé un régime très diversifié et une forte prédation sur les vertébrés natifs et notamment sur le groupe des scinques, des roussettes et des pétrels. Parmi les 44 espèces de vertébrés retrouvées dans le régime alimentaire de ce prédateur invasif, la plupart sont endémiques et 20 sont listées comme menacées sur la liste rouge mondiale de l’UICN. Le suivi des déplacements d’une dizaine d’individus équipés de colliers GPS au niveau d’une presqu’île de la côte ouest abritant une importante colonie d’oiseaux marins, a permis de mettre en évidence de grands domaines vitaux pour les mâles, des domaines vitaux petits pour les femelles et des patrons de déplacements importants liés aux différentes étapes du cycle reproducteur des oiseaux marins. Ces éléments, couplés aux analyses de régime alimentaire suggèrent une prédation à la fois sur les adultes reproducteurs mais également sur les jeunes oiseaux proches de l’envol, et ceci à une large échelle géographique puisque certains des chats harets concernés avaient le coeur de leur domaine vital situé à plus de 3km de la colonie. Une opération expérimentale de contrôle d’une population de chats harets a été conduite sur cette presqu’île et a montré une faible durabilité des effets de la suppression des individus sur les densités observées et une rapide recolonisation du site. Les résultats de ce travail plaident pour la mise en place de mesures de limitation des impacts occasionnés et permettent en particulier de cibler les habitats de maquis et forêt humide comme prioritaires en matière de limitation des abondances. Ces travaux nous éclairent également sur l’emprise spatiale et l’intensité des futures mesures de contrôle à conduire dans le contexte d’îles de grande superficie et fortement envahies.