Main Article Content
Direct and indirect biotic interactions driving community structure, can be positive, increasing the fitness of both partners, or negative, increasing the fitness of only one of the participant to the interaction. Moreover, both partners may produce an integration among them, thus giving rise to an association defined as symbiosis, with parasitism and mutualism as the two extremes of a symbiotic continuum. In the past, negative interactions have been considered more widespread within communities and responsible for most of their structures. By contrast, cooperative interactions have mainly approached with a descriptive aspect. Both parasitism and mutualism can evolve from a commensal interaction depending from the ecological context and have a different role in promoting evolution. In turn commensalism can evolve from epibiosis, a widespread phenomenon in marine benthic environment where the high spatial competition promotes the overgrowth of organisms. Therefore, epibiosis is the starting point for further evolution of different kind of interactions leading to an increasing of biodiversity.