Résumé
The complexity of natural systems is often cited as one of the main reasons for difficulties in understanding their inter-relationships and to developing ways to manage natural areas. This complexity arises from (1) the great diversity of entities and interrelationships comprised by biological systems, (2) the intricate dynamics and webs of interactions among these entities, and (3) their distribution patterns in both space and time (Solbrig, 1991). All these indicate that natural systems are not static but rather are constantly evolving and changing, as evidenced by the highly elaborate dynamics of the life cycle of species, and of energy and nutrient flows which are exchanged among and within entities. Explaining the complexity of natural systems certainly presents biology with one of its greatest challenges in that answers to questions of complexity should provide keys for sustainable conservation and management of biological diversity, control of environmental pollution and pathogens, and providing better food for human populations in both the developed and developing nations. Fundamentally, a better knowledge of biological complexity in space and time is essential to the promotion of sustainable development for future generations. The complexity of natural systems means that they are more than the simple sum of their constituent parts. They display a non-linear dynamical behaviour and an hierarchical organisation, and are also capable of self-organisation. Adopting integrative scientific approaches to analysis is a prerequisite to understanding this complexity and finding appropriate solutions. To address these issues, an international symposium on "Integrative Biology and Complexity in Natural Systems" was held on 27-29 May, 2002 at UNESCO Headquarters, Paris. Organised within the framework of the IUBS's Towards an Integrative Biology (TAIB) Programme, and co-sponsored by UNESCO, the CNRS and the Ministry of Education and Research France (ACI Ecologie Quantitative), this conference was a far-reaching effort to address integrative approaches to complexity, scaling issues and stochastic phenomena in natural systems. Bringing together an international group of leading scientists, the meeting was concerned with: (1) clarifying of the concept of integrative biology as an approach to studying complexity; (2) discussing conceptual integrative tools, focusing on modelling and scaling at different hierarchical levels, and on models based upon metabolic, ecological and/or evolutionary processes; (3) reviewing examples from epidemiology and host-parasite and predator-prey relationships, where useful solutions have recently been provided for a number of complex biological questions concerning biodiversity and the interactions between and within species; and (4) considering the temporal dimension in dealing with the complexity of natural systems at the short- (biological time), medium- (seasonal variation), and the long- (geological time) terms. The symposium began with a presentation by Marvalee Wake (University of California at Berkeley, USA) on the promise of integrative biology. She first defined the state-of-the-art for the conference theme explaining that traditionally, biologists are trained, and departments and institutes organised, in a manner characterised by specific approaches and techniques, typically working at a specific level of organisation in the biological hierarchy and/or organisms, and investigating model organisms or one/very few species. Conversely, integrative biology deals with integration across all levels of biological organisation, from molecules to the biosphere and diversity across taxa. In so doing, it provides both a philosophy and a mechanism for facilitating science and exchanges at the interfaces of "horizontally" arrayed disciplines, in both research and training. Thus, an important mark of integrative biology is that it changes our personal view of the natural world revealing new, perplexing, findings not expected on the too common basis of accepted dogma and feelings. Receiving its charge from that introduction, the meeting continued with more than 30 different presentations organised into 4 main sections.