Species-habitats relationships : from theory to applied issues

The loss of biodiversity is largely acknowledged by the scientific community but also by the public and politicians. Most research on biodiversity loss is focused on climate change effects, and neglects the main factor of biodiversity loss: habitat destruction. The aim of this thesis is to study species-habitats relationships with a particular focus on the different components of these relationships. In a first part, the thesis deals with the history and the evolution of the concept of habitat in ecology. Particularly, it highlights a complex construction of this concept. For instance, the analysis shows a dichotomy around the definition of the concept of habitat with on one hand, a species-centered approach and on the other hand, a community-centered approach. These definitions are still used nowadays by the different actors of conservation, from scientists to politicians, but with different degrees of importance. Then, through the prism of landscape ecology, the thesis is interested in spatial scale issues via a study of arthropods species distribution in French landscapes. Results show that the spatial scales of species responses to landscapes measures are highly variable. This result holds true whatever the representation of landscape used in the analysis. However, theory would predict some consistencies in spatial scales of response, for example in relation to ecological traits of species. Hence, the spatial scale of relationship between a species and its landscape, which is considered as the scale of perception and interaction of the species with its environment, seems difficult to characterize using usual methodology developed in landscape ecology. Species-habitats relationships can be quantified using specialization measurement. In the next part of the thesis, we try to understand how specialist species are spread along a continuous gradient of habitat and in particular, the role of heterogeneous environments in driving observed patterns of specialization. In this theoretical context, the hypothesis of complementation, which states that particular species need some environmental heterogeneity to strive, cannot be verified. Even if some species prefer heterogeneous landscape, they cannot be classified as specialists. These species seems to be generalists that are excluded from more homogeneous landscape due to competition rather than real specialists that are more often found in these landscapes. These results shed a new light on rules of assemblage of species communities, particularly along a continuous gradient of habitat.Finally, in a last part, the importance of the concept of habitat in conservation public policies is studied. An evaluation of the “habitat” part of the European Habitats Directive is proposed. Different criteria, related to the application, construction, legitimacy and outcomes of the directive were used to evaluate the policy. Through some concrete examples and an extensive literature analysis, this work allows identifying important knowledge gaps in the directive that imped evaluation criteria. Results show a discrepancy between scientific aspects and their application in the directive, questioning the opportunity to use the habitat level to answer to conservation issues. To conclude, this thesis, focused on the concept of habitat, allows identifying important theoretical and applied knowledge gaps that imped a better understanding of species-habitats relationships. This work offers new perspectives and challenges the way we usually think, as scientists, these relationships.