Species Concepts and the Definition of "Species"
1) Biological species concept: Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups (Mayr, 1940).
Biological species concept: A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature (Mayr, 1982).
Biological species concept: Species are the members in aggregate of a group of populations that breed or potentially interbreed with each other under natural conditions (Futuyma, 1986)
2) Cladistic species concept: A species is a set of organisms (an evolutionary lineage) between two branch points or between one branch point and an extinction event or a modern population (Ridley 1993).
3) Cohesion species concept: A species is the most inclusive group of organisms having the potential for genetic and/or demographic exchangeability. (Templeton, 1989)
4)Competition species concept: Species are the most extensive units in the natural economy such that reproductive competition occurs among their parts (Ghiselin, 1974).
5) Ecological species concept: A species is a set of organisms exploiting (or adapted to) a single niche (Ridley 1993).
Ecological species concept: A species is either 1) a lineage which occupies an adaptive zone minimally different from that of any other lineage in its range, and which evolves separately from all lineages outside its range, or 2) a closely-related set of lineages which occupy an adaptive zone minimally different from that of any other lineage in their range and which evolve separately from all other lineages outside their range (translation of Van Valen, 1975).
Ecological species concept: A species is a lineage or a closely related set of lineages, which occupies an adaptive zone minimally different from that of any other lineage in its range and which evolves separately from all lineages outside its range (Van Valen, 1976).
6) Evolutionary species concept: A species is a lineage (an ancestral-descendant sequence of populations) evolving separately from others and with its own unitary evolutionary roles and tendencies (Simpson, 1961).
Evolutionary species concept: A species is a single lineage of ancestor-descendant populations which maintain its identity from other such lineages and which has it own evolutionary tendencies and historical fate (Wiley, 1981).
Evolutionary species concept: A species is a population or group of populations that shares a common evolutionary fate through time (Templeton, 1989).
7) Isolation species concept: Species are systems of populations: the gene exchange between these systems is limited or prevented by a reproductive isolating mechanism or perhaps by a combination of several such mechanisms. (as defined by Dobzhansky 1970; in Templeton, 1989)
8) Phenetic species concept: A species is a set of organisms that look similar to each other and distinct from other sets (Ridley, 1993).
9) Phylogenetic species concept: A species is the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent (Cracraft 1983).
Phylogenetic species concept: A species is an irreducible (basal) cluster of organisms, diagnosably distinct from other such clusters, and within which there is a parental pattern of ancestry and descent (Cracraft 1989).
10) Recognition species concept: A species is the most inclusive population of individual biparental organisms which share a common fertilization system. (as defined by Paterson, 1985; in Templeton, 1989).
11) Typological species concept: A species is a group of organisms conforming to a common morphological plan, emphasizing the species as an essentially static, non-variable assemblage. According to this concept the observed diversity of the universe reflects the existence of a limited number of underlying "universals" or types (eidos of Plato). Individuals do not stand in any special relation to each other, being merely expressions of the same type. Variation is the result of imperfect manifestations of the idea implicit in each species (Mayr 1969; Lincoln et al. 1982).
Additional Terms Associated with "Species"
Agamospecies: A species of uniparental (asexual) organisms (Simpson, 1961).
Morphospecies: established by morphological similarity regardless of other considerations; a.k.a. "morphological species" (Simpson, 1961).
Paleospecies: temporally successive species in a single lineage; a species which is represented in more than one geological time horizon; a.k.a. "chronospecies", "successional species" or "allochronic species" (Simpson, 1961; Wiley 1981).
