The tropical hardwood forests of south Florida persist as well-drained patches of broadleaf forest separated by brackish water swamp, marsh, or pineland. In this dissertation, a functional trait approach was used to understand the structure and dynamics of these communities and their responses to abiotic and biotic variation. Twenty-seven permanent plots (20 x 20 m2) were established across the south Florida landscape, representing four sub-regions: Everglades marsh, Long Pine Key, Upper Keys, and Lower Keys. Community weighted mean trait values for four of six selected traits showed significant inter-sub-regional variation. Out of them, three traits (specific leaf area, tree height, and leaf phosphorus) increased significantly from dry and low productivity Florida Keys in the south to the moist and productive areas on the south Florida mainland, while wood density showed the opposite pattern. Trait variance ratios (T-statistic metrics) was used to explore internal filtering (processes that operate within a community) and external filtering (processes that operate at larger scale than that of the individual population or community) on community structure. Both external and internal filtering in the functional composition of south Florida hardwood hammock forest were important for local communities differing in freshwater accessibility, or that occupy different positions along strong edaphic or climatic gradients. To understand the underlying mechanisms that drive species assembly during forest succession in Florida dry sub-tropical forest, 13 leaf, stem, reproductive, and architectural traits of resident tree species across the successional gradient were measured. Tests of null models showed that younger communities are shaped by environmentally driven processes, while mature communities are shaped by competitively driven processes. The overall trait similarities among species present in North Key Largo tropical dry forest suggest that tree species are specialists on the local environment, and their ability to survive and grow in a stressful environment may be more important than competition for resources at larger scale. Moreover, tree species in these forests may exhibit specialization or trait plasticity in coping with drought by changes in their stomatal morphology or activity, allowing for a balance between gas exchange and water loss in a periodically stressful environment. A significant negative correlation between stomatal density and size, and a positive correlation between leaf δ13C and stomatal density were observed across habitat gradient for one of the dominant hardwood hammock species (Bursera simaruba). Small and densely distributed stomates in tandem seems to represent a strategy that allows hammock species to conserve water under physiological drought. Furthermore, findings from this work also showed both intra- and inter-specific trait variation at regional and local scales influence community assembly patterns in hardwood hammock communities in South Florida.

[pt] O objetivo da dissertação é analisar criticamente o uso do conceito do Antropoceno pela linha crítica de teoria das Relações Internacionais. Isso se faz com um foco específico na origem do conceito em Ciência do Sistema Terrestre (CST), e através de uma discussão geral sobre autoridade científica atribuída à ciência moderna e suas conexões com práticas de world-making, entendidas especificamente como cosmologias científicas, e em relação com mobilização de propostas na política internacional. Nesse sentido, a discussão explora a construção de CST e propõe a formulação do Antropoceno como relacionada com os comprometimentos políticos dessa disciplina – a partir daí, sugere-se o uso da problematização Foucaultiana como forma de análise das soluções políticas ao Antropoceno propostas pela disciplina. A seguir, a dissertação conecta as Ciências do Sistema Terrestre com outros momentos de desenvolvimento da ciência moderna com o âmbito de mover uma discussão geral sobre o poder de uma autoridade científica legitimar formas de política internacional através de práticas de world-making. Com isso, a discussão expande em dois mundos e formulações de política internacional possíveis advindos de distintas interpretações do Antropoceno. Finalmente, no que se refere à literatura de Relações Internacionais, a dissertação avalia como a apropriação do conceito de Antropoceno a partir de CST é realizada, prestando atenção especificamente na chamada por uma mudança na ontologia da disciplina e na relação entendida como desejável entre teoria e prática política presente na literatura, ambos elementos associados à CST. Por último, a noção de problematização é retomada para se analisar as soluções políticas e intelectuais propostas pela literatura Crítica de Relações Internacionais em sua mobilização do Antropoceno. / [en] This dissertation attempts to critically analyze the mobilization of the concept of the Anthropocene by Critical International Relations literature. It does so with a particular focus on the origins of the concept within Earth System Sciences (ESS), and within a more general discussion over the scientific authority of modern science and its connections to practices of world-making - discussed specifically in terms of scientific cosmologies - and propositions over international politics. As such, the discussion explores the construction of ESS and the formulation of the Anthropocene as related to the political commitments of the discipline and proposes the use of the Foucauldian problematization to analyze the political solutions stemming from the discipline. Then, the dissertation connects Earth System Sciences to other scientific endeavors, in a different historical context in order to move a more generalized discussion on the power of scientific authority to inform international politics through world-making practices. With that, the discussion lays out two possible worlds and political implications stemming from interpretations of the Anthropocene. Finally, within IR literature the dissertation assesses how the appropriation of the Anthropocene is conducted, paying particular attention to the call for an ontological shift within the discipline and to the specific relationship between theory and political action present in the literature, both elements connected to ESS. At last, the notion of problematization is brought back in order to analyze the intellectual and political solutions brought forth by Critical IR in their mobilization of the Anthropocene.

Cette thèse est une enquête d'histoire et de philosophie des sciences sur l'hypothèse Gaïa (HG) proposée par Lovelock et Margulis dans les années 1970. L'examen historique de l'élaboration d'HG et de sa très riche réception dans diverses disciplines scientifiques (climatologie, biogéochimie, géochimie, biologie de l'évolution, écologie et sciences de la complexité) et au sein des mouvements environnementalistes nous conduit à montrer qu'une ambiguïté majeure sur le statut d'HG grève la littérature : qu'est-ce qu'HG ? Nous montrons qu'HG a été considérée tantôt comme une hypothèse, tantôt comme une théorie, tantôt comme un programme de recherche, tantôt comme une philosophie de la nature. Chacune de ces lectures est ensuite examinée. Nous proposons une caractérisation épistémologique et historique d'HG montrant qu'HG ne doit pas être interprétée comme une hypothèse devant être confrontée de manière directe aux faits, mais comme une théorie élaborée avec des modèles. Nous clarifions alors le rôle et le statut méthodologique des modèles et théories d'HG ainsi que les concepts et hypothèses fondamentales qui les sous-tendent. La reconnaissance de Gaïa comme un système constitué des vivants et de l'environnement avec lequel ils interagissent a été l'origine de la constitution d'un nouveau programme de recherche: les sciences du système Terre. Nous proposons une histoire et une caractérisation de ce programme, repérons les déplacements philosophiques qu'il a opérés à propos des concepts de vie, d'environnement et de nature puis analysons les liens entre les conceptions que Lovelock a de Gaïa et les prescriptions environnementales qu'il a prononcées au nom de Gaïa. / The Gaia hypothesis (GH) proposed in the 1970's by Lovelock and Margulis is here analyzed from a history and philosophy of science perspective. The historical analysis of GH's elaboration and rich reception across various disciplines (climatology, biogeochemistry, geochemistry, evolutionary biology, ecology and complexity sciences) and within environmentalist movements leads me to argue that a major ambiguity plagues the relevant literatures: what is GH? I show that GH has been considered as a hypothesis, as a theory, as a research program, or as a philosophy of nature. Each of these interpretations is then analyzed. An epistemological and historical characterisation of GH shows that GH should not be interpreted as a hypothesis which ought to be confronted directly to empirical facts, but as a theory elaborated with models. I elucidate the methodological role and status of GH's models and theories before clarifying the concepts and expliciting the fundamental hypotheses underlying these models and theories. The recognition of Gaia as a system constituted of living organisms and the environment with which they internet led to the constitution of a new research program: the Earth system sciences. I offer a history and a characterisation of this research program, specify the philosophical shifts it brought about concepts such as life, the environment and nature and I analyze the relationships between Lovelock's conceptions of Gaia and the environmental prescriptions he pronounced in the name of Gaia.