Ecological balance and ecosystem health: between functional myths and social consensus.
Résumé
The notions of "ecosystem health" and "ecological balance" as valid concepts of ecology have been heavily promoted by a large numbers of ecologists since long and are still under debate. As a consequence, researchers have to face an increasing demand from managers and conservationists for relevant and (ideally) absolute references about ecosystem "health" and "equilibrium", in order to guide actions in the field of sustainable development and conservation. The aim of this presentation is to question this issue in the light of wildlife population and landscape management. Based on selected examples, we believe that many sustainable stages are possible for a given ecosystem with advantages and disadvantages that are perceived essentially from a human point of view. Furthermore, ecosystems and their components are intrinsically unstable, since evolving at various time scales. Management options should more thoroughly consider portmanteau words such as "equilibrium", "ecosystem health" and some fashioned words as those related to "fragmentation/connectivity" to give them a real sense, and incorporate in applied issues the indispensable temporal and evolutionary dimensions of any living system. We will exemplify this using results obtained from researches carried out in eastern France where landscape/agricultural changes have triggered a cascade of unintended consequences at various scales on small mammal population dynamics, prey-predator relationships and disease transmission. Biodiversity issues, landscape management, small mammal pest control, conservation of protected species, game management, pathogen transmission, are just different point of views on the same system, whose functioning produces desirable ecosystem services or undesirable effects for a given community of stakeholders. Within some limits, it cannot be judged good or bad from a strict ecological point of view. In such anthroposystems, ecosystem health and equilibrium appear to be defined more as the result of a combination of economic constraints and social consensuses among the variety of dynamic equilibriums that the non-human component of the ecosystem can sustainably provide at a given time. A critical challenge for research is certainly to bring out scientific concepts essential for the management of such multi-potential systems, in a context where physical, ecological and darwinian evolution, among which that of human societies, combine and make any static or fixist management irrelevant, including where biodiversity is concerned.