Joe Morlan 940429 10:%:00 SPECIES. Unfortunately, the concept of what constitutes a +quot;

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Joe Morlan 94-04-29 10:%:00 SPECIES... Unfortunately, the concept of what constitutes a "species" is still a matter of considerable debate among systematists. There are three basic species concepts, 1) morphological, 2) biological, and 3) phylogenetic. The morphological species concept defines a species as an individual which conforms to a described "type." This concept has been almost entirely abandoned except that it forms a basis for the phylogenetic species concept. The biological species concept, says that a species is "a population of interbreeding individuals, which is reproductively isolated from other such populations." Note that it is the population and not the individual which constitutes a biological species, unlike the morphological species concept where the individual type is the species. Note that complete reproductive isolation is not required, only some measurable degree of reproductive incompatibility. Occasional hybrids between biological species do not change their status as species under this concept. The phylogenetic species concept says the a species is any population which possesses a unique set of derived characters. This is very similar to the morphological species concept, except that it emphasizes that a species is a population and not an individual. Which concept one uses, depends to some extent on the type of organism one is studying. The biological species concept works well with natural populations of sexually reproducing vertebrates, but is not very good at diagnosing plants and is quite meaningles when applied to asexually reproducing taxa. For those types the phylogenetic species concept can be quite useful. If one were to apply the phylogenetic species concept (PSC) to breeds of dogs, each breed would probably constitute a valid phylogenetic species. But most vertebrate zoologists follow the biological species concept (BSC). The domestic dog does not exist in a native wild state anywhere in the world, so any hybridization experiments must be based on the results of captive breeding. Biological species cannot be diagnosed reliably on the results of captive breeding experiments because the way animals behave in captivity is usually drastically different from their behavior under natural conditions. In general dogs prefer to breed with other dogs, than with wolves or coyotes. Although there may be occasional hybrids in the wild between wolves and coyotes, they are still separate biological species (semispecies) because such hybrids are rare. If hybridization were to occur frequently, then wolf and coyote would soon merge into one huge intermediate population. Since that hasn't happened and since wolves and coyotes have ranges which broadly overlap each other, they are considered biological species (as well as phylogenetic species). Domestic varieties of dog are merely the consequence of selective breeding and a wonderful example of how selection and isolation can cause evolution and even speciation. E.g. it may be physically impossible for a chihuahua to mate with a Russian Wolfhound. If these were wild animals, they might be regarded as "reproductively isolated" and thus biological species. However, in this case, there are many intermediate sizes which do interbreed with each other, so these size extremes would still be regarded as part of the same species.


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