Résumé
In the theoretical debate on the evolution of species which structures the “neutralist theory” and the “niche theory”, the study of biodiversity has provided numerous examples supporting the niche theory, with a distribution of similar species between Habitats which are differentiated by their abiotic characteristics which define the environment within its wider context. The environment is understood to be the living space of species, whether distributed according to terrestrial biomes or smaller systems such as the gastrointestinal tract of a vertebrate and its associated microorganisms. The heterogeneity of abiotic parameters constituting a mosaic of niches has been integrated as an important factor of evolution and speciation. In this analysis of biodiversity, the various abiotic factors constituted essential determinants regarding the diversity to which species must adapt. This vision can lead to undervalue the importance of interactions between organisms which themselves do not only live in the richness of the ecosystem, but also according to adaptive responses to its components. Research conducted on these biotic interactions, which initially focused on understanding speciation phenomena and their role in the evolutionary dynamics that led to current diversity remains relatively unknown. It is important to decipher the effects of complex relationships between species to understand the dynamic structuring of their communities according to physical environments, whilst studying networks of functional associations in relation to the environment.
Associations between species, on a multi-scale level and at the level of interactions, including those discussed here, are, for a plant, associated with a cohort of partners (pollinators, dispersers, herbivores, symbionts or even a vertebrate such as man, along with microorganisms and parasites), determine the capacity of the ‘host’ partner to persist in its environment thanks to the benefits provided by the association, or rather to its resistance to exploitation attempts by symbionts (competition, predation, parasitism). However, the symbiosis between species, “living together”, is not an exclusive game between partners in a closet space, it comes within a wider environmental context to which each of the partners involved in the association must adapt, consequently modifying its environment and therefore that of other organisms living in it. This adaptive game, a permanent maintaining or breaking up of associations, gives an image of the resulting biodiversity dynamics. Within this conceptual framework, coviability between species, regardless of the level at which we study it, should be perceived according to a range of interactions between species, also encompassing the environment and the changes it undergoes. In the current Anthropocene era, the action of man on his environment may directly or indirectly affect such biotic associations and sometimes result in a cascade of ecological disturbances which are not predictable in terms of their outcome or magnitude.
Biodiversity should not be seen as an assembly of species which are decreasing in alarming numbers but should instead be included in the evolutionary dynamic mechanism in motion, linking past events, genetic diversity and coadaptation within a context of global change.