Species concepts Biological Species (Dobzhansky, 1935 and Mayr, 1942 ). Under this concept, species is a group (or population) of individuals who can naturally interbreed with each other, but are reproductively isolated from other similar groups. This is the most widely accepted concept and greater consensus, at least among zoologists. To assume a species as biological evolutionary implications assume a population that is reproductively isolated and therefore constitutes a separate evolutionary lineage and that is reinforced by a series of barriers can be geographic or biological. The biological species is free to follow their own course in response to genetic and environmental influences processes that cause evolutionary change.The connotation of the concept does not apply to fossil organisms, but the best thing you can do in this case is whether morphological gaps between specimens are as large or larger than those between living species that are reproductively isolated. This concept has limitations as to organisms that reproduce asexually (by apomixis: type of parthenogenesis) some species of rotifers (microscopic organisms), mollusks, arthropods, vertebrates (fish and some lizards of the genus Cnemidophorus Aspidoscelis and Reeder 2002) and some vascular plants . There are also many cases in which hybridization occurs and remain fertile offspring as independent units and evolutionary genetics. This occurs mainly in vascular plants where hybridization is common. To get an idea what if the biological species concept was applied to these cases, we must indicate that each individual should be considered as separate biological species.Evolutionary species (Wiley, 1978). is a lineage (a sequence ancestrodescendiente) of populations or organisms that maintain their identity from other lineages and who have their own historical and evolutionary trends. This concept differs in that the current genetic isolation rather than the potential, is the criterion for the recognition of it. And consider that, given the existence of geographical or biological barriers, gene flow between them is so low that a genetic divergence (cladogenesis) is produced. The evolutionary species concept takes into account that evolution can be reticulated cladogenetic. This means that populations that initially separated, and they began to diverge genetically, come back together thus truncating the isolation and producing hybrids from which emerges a new population that can be recognized as a separate unit.The evolutionary design also have opposed him several objections: 1) is applicable only to monotypic species, so all geographic isolation should be treated as a distinct species, 2) there is no empirical criteria that allow us to observe trends in the fossil record, 3) the evolving definition is not practical in the demarcation of chronospecies. Morphological species. Under this concept, each species is distinguishable from its allies by its morphology. The morphological species concept has been widely criticized. First, the morphological definition ignores behavioral and ecological properties. Secondly, morphological characters do not always allow a species to recognize the one hand, there are many different species, especially among the protozoa, which, however, are morphologically very similar.Species are called cryptic or sibling species “(Mayr, 1948), and secondly, there are many morphological types within a single species, due to individual genetic variation (polymorphic species) or the fact that they belong to different biological categories, as age or gender. Phylogenetic species (of Cracraft, 1989). This concept recognizes as kind to any group of organisms in which all organisms share a unique derived or apomorphic character (not present in their ancestors or relatives). If this concept was used carefully, though local populations located near each other would be considered different species because each population may have unique molecular-genetic variants.Species ecological (Van Valen, 1976). Under this concept, species is a lineage (or a closely related set of lineages) which occupies an adaptive zone minimally different in its distribution of those belonging to other lineages, and also develops independently of all lineages outside its established biogeographical distribution. In this concept, the concept of niche and competitive exclusion are important to explain how populations can be targeted to specific environments and result in genetic differences and geographical factors based on highly organic.