[In search of universal patterns in community organization: the concept of neutrality paved the way to a new approach].

The recent renewal of interest in community structure was strongly stimulated by the concept of neutrality, a new view on the problem of species coexistence. In contrast to traditional approach claiming that species competing for common resources should occupy different ecological niches, the neutrality concept assumes that species can coexist if they are ecologically identical, i.e., they have similar specific (per individual) rate of population growth, probability of extinction and the rate of colonization of free space. The analysis of recent literature, full of contradictory opinions on the ideas of neutrality and niche, can be resulted in form of following questions: (1) What do we suggest when we say that "species coexist"? (2) How can we explain the usual pattern of species relative abundances in a community, the so-called "hollow curve" (the distribution of numbers of species arranged in classes of abundance)? (3) Do rare species have some advantages in comparison with abundant species? (4) Can the mechanisms implied by neutrality concept and traditional niche approach work simultaneously in the same community? Trying to answer these questions we should: (1) refuse the demand of indefinite coexistence of species although this condition was considered as necessary in classical mathematical models of competition; (2) accept that community structure depends not only on ecological processes (species dispersal, competition and others) but also on the evolutionary ones (speciation) that determine the pool of species; (3) accept that rare species have some advantages as compared with the most abundant species; (4) accept that in any real community species can coexist either occupying the different niches or approaching ecological similarity. Despite considerable progress achieved in understanding of general principles of community organization, we still don't know how to answer the question "Why are there so many kinds of animals?" that was posed by Hutchinson 50 years ago.