ABSTRACT
Ecology studies the relationships between living organisms (individuals)—vegetal or animal-and the environment in which they live. The biosphere in which we live is made up of the whole set of terrestrial, marine, and aerial ecosystems. A scientist who endeavors to explain the relationships and the interactions within an ecosystem must often be in contact with colleagues more specialized in other fields like chemistry, genetics, oceanography, geography, hydrology, ethology, and climatic sciences. Considering the complexity of this multidisciplinary study, modeling is a fundamental tool to understand ecosystems. A good modeling practice is to design a model with a precise goal in mind; a modeler expects that his model outputs (results) will help understanding the real system under study. The model final objective also helps selecting the model simplifying assumptions and the level of realism, taking into account the limits of our knowledge and the limits of our modeling techniques. Even if we had precise descriptions and observations, estimating future trends will always be considered very risky. Considering the lack of biological data, we see in Begon et al. (1990) that many ecologists focus on the following levels of organization: individuals, populations of individuals, and ecosystems.
