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Unformatted text preview: n According to today's biological concept of a species, how should lions, tigers, ligers and tigons be classified? A. Lions and tigers should still be classified as a different species, and their offspring should be classified as a third species. B. They should all be classified as the same species. C. They should all be classified as hybrids. D. Lions and tigers should still be classified as different species, and their offspring should be classified as hybrids. Species formation New species are the result of divergence between pre-existing populations. Once organisms have diverged to such an extent that they can no longer interbreed successfully, two species have emerged. A Herring Gull, Larus argentatus (front) and a Lesser Black-backed Gull. Larus fuscus (behind) in Poland: two species with clear differences. The Larus gulls interbreed in a ring around the arctic Ring species consist of a chain of interbreeding populations that surround some physical barrier. Individuals from all adjacent populations can interbreed, with the exception of individuals from Lesser black gull and Herring gull populations which are reproductively isolated from each other. Ring species illustrate that the species concept is not as clear-cut as it is often understood to be. The problem is whether to quantify the whole ring as a single species (despite the fact that not all individuals can interbreed) or to classify each population as a distinct species (despite the fact that it can interbreed with its near neighbours). When a geographic barrier divides a single species into two allopatric populations, natural selection favoring the evolution of reproductive isolation occurs in each population. True False Natural selection doesn't directly favor the evolution of new species. Reproductive isolation generally evolves in allopatry as a by-product of natural selection based on different environmental demands in geographically separated habitats. Originally, the black bear (Ursus americanus) was distributed across North America. The black bear's distributio...
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- Fall '08