  Community ecology consists of models of interacting species, forming an ecological “community,” in which each species is treated as a unit. The appropriate definition of “community” has been widely debated among ecologists and philosophers; what is being given here is an interactive  definition.[33]  Alternative options include defining community by mere geographical association of species at one extreme, or by requiring a good deal of structure in the interactions at the other, making the community analogous to an organism. The interactive definition given above is attractive for two reasons: (a) mere association leaves little of theoretical or practical interest to study, while requiring some specified elevated levels of interaction introduces an unnecessary arbitrariness in a definition of community; and (b) the former would make any association of species a  community[34]  whereas the latter would typically introduce so much structure that virtually no association would constitute a community.