David Claessen is a lecturer at the ENS and director of CERES (training centre on the environment and society). His research focuses on the eco-evolutionary dynamics of ecosystems and socio-ecosystems. He lectures on two main themes: the theory of ecological evolution, and the study of interdisciplinarity between environment and society. Although these two axes are distinct, he often emphasizes their complementarity in complex systems. As a seasoned ecologist, he works with his data for the sustainable improvement of society by lecturing on the themes of sustainable and ecological development.