explain CONCEPT OF SPECIES
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Answers
Species are groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups.
The biological species concept has been prevalent in the evolutionary literature for the last several decades and is emphasized in many college-level biology courses. It is probably the species concept most familiar to biologists in diverse fields, such as conservation biology, forestry, fisheries, and wildlife management. Species defined by the biological species concept have also been championed as units of conservation.
Theodosius Dobzhansky, a prominent evolutionary geneticist and an important contributor to the modern evolutionary synthesis, characterized the concept of a biological species as a system of populations. The gene exchange between these systems (species) is limited or prevented by reproductive isolating mechanisms, such as species-specific breeding behaviors, hybrid sterility, and gametic incompatibility. Thus, under the biological species concept, species are simultaneously a reproductive community, a gene pool, and a genetic system.
The study of reproductive isolating mechanisms is central to the biological species concept because these mechanisms provide barriers to gene flow that define the boundaries of the reproductive community and gene pool, and preserve the integrity of the genetic system of the species. In practice, however, isolating mechanisms are rarely studied and species are usually diagnosed by differences in phenotypic (morphological) features.
Despite the long historical acceptance of the biological species concept, it has become controversial because a growing number of evolutionary biologists have found the biological species concept unworkable in a wide variety of situations. Critics of the biological species concept come from the fields of both botany and zoology. A fundamental drawback to this concept is that it is exclusively defined in terms of sexual reproduction.
Asexual taxa are obviously excluded from this concept, but it is also true that many species capable of sexual reproduction cannot be easily accommodated within the framework of the biological species concept. From the viewpoint of population genetics, species capable of self-fertilization (e.g., parasitic tapeworms and some plants) and those with mandatory sibling mating are more similar to asexual than to sexually outcrossingspecies[20]. Species that freely hybridize (open mating systems) with one or more other species yet maintain their evolutionary identity as species also provide a serious challenge to the validity of the biological species concept. Groups of freely hybridizing species are known from plants, insects, and vertebrates.
Another important limitation of the biological species concept concerns speciation. The most widely accepted model of speciation is the allopatric model. Generally speaking, the allopatric model entails the geographic subdivision of a single population followed by the differentiation of the isolated subpopulations into new species. Historically, the notion of a correlation between geographic subdivision of populations and speciation grew out of the observation that the closest relatives tend to occupy separate but contiguous geographic areas. Thus, in allopatric speciation lineage independence is achieved when two or more lineages are geographically disjunct. Therefore, isolating mechanisms which are fundamental to the biological species concept have very little, if anything, to do with the process of speciation because the populations undergoing speciation are geographically disjunct from one another. Hence, the evolutionary forces responsible for allopatric speciation have nothing to do with the isolating mechanisms that are a fundamental aspect of the biological species concept. A species concept that fundamentally fails to illuminate the process of speciation cannot provide the intellectual framework for the identification of units of biodiversity. Because it is impossible to study gene flow and reproductive behavior of species known only from fossil remains, the biological species concept cannot be applied to the thousands of species known only from their fossils.
In summary, the major limitations of the biological species concept are that it is irrelevant to allopatric speciation and is inapplicable to: (1) fossil species; (2) organisms reproducing asexually or with extensive self-fertilization; and (3) sexual organisms with open mating systems (species that freely hybridize). On the other hand, the biological species concept is intuitively appealing to people because Homo sapiens fits in the narrow range of sexual reproduction that is the domain of the biological species concept
Answer:
Species is the basic unit of classification. Species is a Latin meaning 'kind' or 'appearance'.