Résumé
A remarkable feature of tropical rainforests is their high biological diversity, particularly regarding trees. However, opinions are divided regarding the types of mechanisms involved in maintaining such a great diversity, especially in terms of number of tree species. The theory of ecological niches and the neutral theory of biodiversity are thus frequently cited. Niche theory is based on the existence of differences among species resulting from selective trade-offs (between resource utilization ability, survival, reproduction). The neutral theory is based on the equivalence of individuals and species according to these same criteria. Both views, however, raise a paradox because in the mean time species are not ecologically equivalent and observed selective trade-offs are often imperfect under natural conditions.Some authors have proposed an explanation for this paradox by showing that net selective trade-offs, according to a large number of axes, could make species appear similar when compared on a limited number of axes. They suggest that characterizing and quantifying intraspecific demographic variations, including interindividual and temporal variability, give a key to interpreting the coexistence of species that is more realistic that the neutral theory and niche theory.The aim of this thesis was to better understand the tree community dynamics observed since 1990 in Uppangala, a permanent study site in a natural rainforest of the Western Ghats of South India. The non-stationary dynamics observed over this period raised questions about the processes involved in the dynamics. In addition, the rich dataset describing the demography of this community has made it a perfect candidate to discuss the various theories proposed to explain tree species coexistence.These objectives have motivated the implementation of statistical models underexploited or rarely used in plant ecology but still more suitable than conventional approaches to structure the variability of demographic processes. Several methodological peculiarities were thus central to this work. (I) We used hierarchical models and interpreted them further than usual to structure tree growth variability, (II) we used the growth model decomposition of variability to predict mortality, (III) we used tree size as a timeline in a joint modeling of tree growth and survival and (IV) we studied emerging properties of these models at the community level through simulations of the dynamics including deterministic and stochastic components.We have shown the existence of strong individual variability of growth and mortality risk. The use of models to structure these differences showed that they were partly explained by measured environmental variables and partly attributed to latent factors (ie d. unobserved or unobservable). This allowed us (I) to assess how to characterize the variability of species growth strategies, (II) to discuss how to define the classic compromise life history used to describe species shade tolerance, (III) to improve the prediction of mortality risk (IV) to interpret in a more realistic way the observed dynamics and (V) to propose a conceptual model of how individual variations may be involved in species coexistence, based on the concept of the individual ecological niche.