Section: Application Domains
Experimentation in ecology
Mathematics and simulations show that substrate dependent models of competition and density-dependent models have radically different predictions in terms of extinction of species. A substrate dependent model is likely to be a reasonably good model for the case of low densities of biomass, the density-dependent model being a good one for high densities. The mathematical treatment on realistic parameters predicts outcomes which are to be tested. In connection with micro-biologists (among whose J.J. Godon, INRA-LBE) and ecologists (in particular R. Arditi, INAPG), we are currently working on this subject.
In September 2006, we started experiments in five chemostats performing nitrification within the framework of the PhD thesis of Maxime Dumont realized at the LBE. Maxime's thesis aims at studying intra vs inter-specific relationships within different species in a complex (i.e. natural) ecosystem. The nitrification process has been chosen because it is a well known biological process. On the one hand it is simple enough for molecular techniques to give a quite clear view of major species (the natural diversity of this process is known to be limited : only 5 or 6 major species are commonly detected within such a process). On the other hand, it is a natural process and not a reconstituted (artificial) ecosystem. In addition, it is of great interest because of its fundamental role within the nitrogen bio-geochemical cycle. The phenomenological observations together with molecular data that have been obtained are now going to be used as inputs of dynamical systems - in conjunction with nonlinear observers - in order to link functional and population diversity concepts. The first results obtained recently allowed us to propose a new procedure for identifying the functional group of unknown micro-organisms within the nitrification process. Perspectives of the work include the refinement of macroscopic models that have been obtained in order to better understand the role on diversity of inter vs intra-competition in such complex bio-systems. In order to extend these results to more complex ecosystems (and in particular to study the role of the space on the ecosystem functioning), experiments on reconstituted ecosystems isolated from soils are conducted simultaneously with colleagues from INRA in Dijon within the framework of another PhD thesis.