Conceito de espécie

Species Concepts
(http://science.jrank.org/pages/48776/Species-Concepts.html#ixzz14obeN9ac)
by Richard G. Harrison

Character-based Definitions, History-based Species Concepts, Isolation and Cohesion Species Concepts

Species are fundamental units of biological diversity; beyond general agreement on this simple fact, there exists little consensus among evolutionary biologists and systematists about how the term “species” should be defined. Recent reviews have listed as many as 20 different species concepts, but many of these are subtle variations on a number of common themes. Here, the most frequently cited or discussed concepts and definitions (see Vignette on Seven Species Concepts) are organized according to a set of defining criteria. A number of possible contrasts can serve as organizing principles for a taxonomy of species concepts. For example, definitions of species may rely entirely on examining patterns of character variation, without considering the evolutionary history or processes that have led to those patterns. Emphasis may be placed on making species concepts clearly operational, or universal, or both, so that they will be useful for practicing taxonomists and will apply to groups of lineages regardless of whether those are sexual or asexual, whether they consist of a single interconnected population or of many disjunct (allopatric) populations, or whether they represent fossil or living taxa. Alternatively, the motivation for choosing a species concept may derive from a particular model of the evolutionary process, or from an understanding of the forces that are responsible for maintaining similarity or difference among extant populations or groups of populations. It may be deemed more important to imbue species concepts with theoretical significance so that they are consistent with a history of descent with modification, or so that they are appropriate units for studying the evolution of reproductive/genetic isolation. According