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Species Concepts and Reproductive Isolating Barriers

Author(s): Tadzia GrandPré, PhD, Nancy Moreno, PhD, and Lisa Marie Meffert, PhD

Other Species Concepts

Alternatives to the biological species concept establish different criteria for the definition and identification of species. One alternative is the phylogenetic species concept, which defines species as discreet, irreducible groups of organisms that are "diagnosably different" from other groups and share a common ancestor. Subtle variations of this idea have been proposed, such as the genealogical species concept that defines a species as a group whose members are more closely related to one another than to any organism outside the group. Together, these concepts highlight the role of evolutionary history and genetic divergence in the process of speciation. Phylogenetic relationships are often inferred through the use of quantitative methods. For example, current molecular techniques now permit the direct comparison of genetic information to create groupings or to assign individuals to specific species groups. Before the advent and wide use of DNA, and other sequencing information, phylogenetic relationships were inferred from morphology, geographical distribution, and other characteristics related to phenotype.

While the phylogenetic species concepts are concerned with the identification of historically related groups, a number of alternative species concepts emphasize the origins of the discreet groups seen in nature. For example, the ecological species concept defines species as a group of organisms that has adapted to a particular niche in an environment and evolves independently from all groups outside of its range. Thus, species are identified by the use of a common set of environmental resources. In contrast, the recognition species concept defines a species as a group of "biparental organisms that share a common fertilization system." According to this species concept, species are identified as a group of organisms that only recognize other members of the group as potential mates.

These, and other species concepts, have been proposed to address some of the limitations of the biological species concept. For example, both the ecological and phenotypic species concepts are used to define species in groups that reproduce asexually, for which the biological species concept is not useful.