Mayden, 1997 - Texas Tech University

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390 A hierarchy of species conceptsIn reality the composite of individual organisms of the species may oftenbe polyphyletic, resulting from multiple crosses between parental, bisexualspecies. These taxa are most often diagnosed by features related to eithermorphology or chromosomes. Often, these species have very restrictedranges. Some authors only recognize them as species if their range includesat least 20 km diameter (Weber, 1981).SynopsisBecause of the limited application of the ASC to asexually reproducingspecies the ASC should serve as a primary concept.19.7.2 Biological Species Concept (BSC)'A biological species is an inclusive Mendelian population; it is integratedby the bonds of sexual reproduction and parentage'.(Dobzhansky, 1970: 354)'...groups of actually or potentially interbreeding natural populationswhich are reproductively isolated from other such groups'.(Mayr, 1940)'A species is a group of interbreeding natural populations that isreproductively isolated from other such groups'. (Mayr and Ashlock,1991)SynonymsGSC, Isolation Species Concept (Paterson, 1993), Second Species Concept(Mayr, 1957), Speciationist Species Concept (Blackwelder, 1967),DiscussionThis concept has been reviewed by its strongest proponent, Mayr, in severalpublications and by several other authors (see Mayden and Wood,1995). As recently espoused by Mayr and Ashlock (1991: 26-27) and Mayr(1997), species consist of reproductive communities wherein there is bothan ecological and genetic unit. Individuals of a species seek and recognizeone another for mating and thereby maintain an intercommunicating genepool that, 'regardless of the individuals that constitute it, interacts as a unitwith other species with which it shares its environment'. For Mayr (1997),each biological species is an assemblage of well balanced, harmoniousgenotypes and... indiscriminate interbreeding of individuals, no matterhow different genetically, would lead to an immediate breakdown of theseharmonious genotypes. As a result, there was a high selective premium forthe acquisition of mechanisms, now called isolating mechanisms, thatwould favour breeding with conspecific individuals and inhibit matingwith non-conspecifics. This consideration provides the true meaning ofspecies. The species is a device for the protection of harmonious, well integratedgenotypes. It is this insight on which the biological species concept
The species concepts 391is based'. Central to this concept, and the sole criterion for the reality of aspecies, is thus the idea of reproductive isolation of species from other suchspecies. 'A species is a protected gene pool' that is 'shielded by its owndevices (isolating mechanisms) against unsettling gene flow from othergene pools' (Mayr and Ashlock, 1991). The word interbreeding in the definitionabove 'indicates a propensity; a spatially or chronologically isolatedpopulation, of course, is not interbreeding with other populations but mayhave the propensity to do so when the extrinsic isolation is terminated'(Mayr, 1997). Accordingly, speciation is the process of achieving reproductiveisolation (Mayr, 1963: 502; 1970: 288).The BSC specifically excludes uniparental species even though they areknown to exist, and some have relegated diversity of this type to pseudospecies(Dobzhansky, 1970). The concept also is viewed as being anoperational definition in that 'taxa of the species category can be delimitedagainst each other by operationally defined criteria, for example, interbreedingversus non-interbreeding of populations' (Mayr and Ashlock,1991: 27). This concept is relational because'A is a species in relation to Band C because it is reproductively isolated from them'. Finally, it is a nondimensionalconcept that 'has its primary significance with respect tosympatric and synchronic populations..., and these are precisely the situationswhere the application of the concept poses the fewest difficulties.The more distant two populations are in space and time, the more difficultit becomes to test their species status in relation to each other but the morebiologically irrelevant this status becomes'.At least ten elements of this concept are viewed by Mayden and Wood(1995) as counter-productive toward discovering and understanding biodiversity.The BSC has received substantial criticism in recent years forissues dealing with: (1) the absence of a lineage perspective; (2) its nondimensionality;(3) erroneous operational qualities as a definition; (4) itsexclusion of non-sexually reproducing organisms; (5) indiscriminate useof a reproductive isolation criterion; (6) confusion of isolating mechanismswith isolating effects; (7) implicit reliance upon group selection; (8) its relationalnature; (9) its teleological overtones; and (10) its employment as atypological concept, no different from the frequently criticized morphologicalspecies concept.SynopsisThe nature of the unfavourable attributes inherent in the BSC preclude itfrom being considered a primary species concept.19.7.3 Cladistic Species Concept (CISC)' ...that set of organisms between two speciation events, or betweenone speciation event and one extinction event, or that are descendedfrom a speciation event'. (Ridley, 1989)
Page 1 and 2: 19A hierarchy of species concepts:t
Page 3 and 4: Methodology 383functions into a con
Page 5 and 6: Concepts. definitions, groups, cate
Page 7 and 8: The twin meanings ofspecies 387niza
Page 9: The species concepts 389tinct speci
Page 13 and 14: The species concepts 393DiscussionT
Page 15 and 16: The species concepts 395other linea
Page 17 and 18: The species concepts 397organisms t
Page 19 and 20: SynonymsBSC (Grant, 1981), PhSC, MS
Page 21 and 22: The species concepts 401in time'. H
Page 23 and 24: The species concepts 403allopatric
Page 25 and 26: 19.7.17 Phylogenetic Species Concep
Page 27 and 28: The species concepts 407magnitude,
Page 29 and 30: The species concepts 409recognition
Page 31 and 32: The species concepts 411However, in
Page 33 and 34: Discussion 413diversity was left to
Page 35 and 36: Discussion 415standing issue of con
Page 37 and 38: Hierarchy of concepts: species in t
Page 39 and 40: Hierarchy of concepts: species in t
Page 41 and 42: R~erenc~ 421There are extraordinary
Page 43 and 44: References 423Kornet, D.J. and McAl

Mayden, 1997 - Texas Tech University

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