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species concepts

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BIOL 1602
Rebecca Jubis

Chapter 16- Mechanisms of Speciation 16.1- Species Concepts • Species is the smallest evolutionarily independent unit • Evolutionary independence occurs when mutation, selection, gene flow, and drift operate on populations separately • Evolution consists of changes in allele frequencies, and species form a boundary for the spread of alleles o As a result, different species follow different evolutionary trajectories o The essence of speciation is lack of gene flow • Species consist of interbreeding populations that evolve independently of other populations • The three most important “species concepts”: o Morphospecies Concept o Biological Species Concept o Phylogenetic Species Concept  Each of the three agrees that species are evolutionarily independent units that are isolated by lack of gene flow, but each employs a different criterion for the determining that independence is actually in effect The Morphospecies Concept • In traditional cultures, people name species based on morphological similarities and differences • In biology, careful analyses of phenotypic differences are the basis of identifying morphospecies • Morphospecies can be identified in species that are extinct or living, and in species that reproduce sexually or asexually • Fossil species that differed in color or the anatomy of soft tissues cannot be distinguished • Neither can populations that are similar in morphology but were strongly divergent in traits like songs, temperature, or drought tolerance, habitat use, or courtship displays o Species like these are called cryptic species  Species that are indistinguishable morphologically, but divergent in songs, calls, odor, or other traits The Biological Species Concept • Under this concept, criterion for identifying evolutionary independence is reproductive isolation • If populations of organisms do not hybridize regularly in nature, or if they fail to produce fer
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