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Readings 13
Pgs. 605-633 (refer to Figure 16.7)
-a species is the smallest evolutionary independent unit
-evolutionary independence occurs when mutation, selection, gene flow, and drift operate on
populations separately
-speciation is caused by lack of gene flow
-there are three important species concepts, which all agree that species are evolutionary
independent units that are isolated by lack of gene flow
-each concept employs a different criterion for determining that independence is in effect
-the morphospecies concept involves people naming species based on morphological
similarities and differences (widely applicable concept)
-morphospecies can be identified in species that are extinct or living and in species that
reproduce sexually or asexually
-the disadvantage of the morphospecies concept is that when it is not applied carefully,
species definitions can be arbitrary
-cryptic species }µo]}vZZÀÀÇo]u]((vÁvZ}ZZv[
be distinguished
-cryptic species are considered the same based on morphological similarity
-under the biological species concept, the criterion for identifying evolutionary independence
is reproductive isolation
-the advantage of the BSC is that reproductive isolation confirms the lack of gene flow in
speciation
-Z]ÀvP}(Z^]Z]]Z}µvÇ}µo]}vZ}v[
overlap may or may not be reproductively isolated
-the biological species concept can never be tested in fossil forms and is irrelevant to asexual
populations
-the phylogenetic species concept (also known as the genealogical species concept) focuses
on a criterion for identifying species called monophyly
-under the PSC, species are identified by estimating the phylogeny of closely related
populations and finding the smallest monophyletic groups
-the rationale behind the phylogenetic species concept is that traits can only distinguish
populations on a phylogeny if the populations have been isolated in terms of gene and
diverged genetically and possibly morphologically as well
-populations within species have shared derived traits that distinguish them from populations
of other species
-this concept can be applied to any type of organism because species are named on the basis of
difference in traits used to estimate phylogeny
-speciation has been hypothesized to be a three stage process involving (1) isolating
populations (2) divergence in traits (3) reproductive isolation
-the final phase was hypothesized to occur when these diverged populations came back into
physical contact, which is referred to as secondary contact
-gene flow tends to homogenize gene frequencies and reduce the differentiation of populations
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Document Summary

A species is the smallest evolutionary independent unit. Evolutionary independence occurs when mutation, selection, gene flow, and drift operate on populations separately. Speciation is caused by lack of gene flow. There are three important species concepts, which all agree that species are evolutionary independent units that are isolated by lack of gene flow. Each concept employs a different criterion for determining that independence is in effect. The morphospecies concept involves people naming species based on morphological similarities and differences (widely applicable concept) Morphospecies can be identified in species that are extinct or living and in species that reproduce sexually or asexually. The disadvantage of the morphospecies concept is that when it is not applied carefully, species definitions can be arbitrary. Cryptic species are considered the same based on morphological similarity. Under the biological species concept, the criterion for identifying evolutionary independence is reproductive isolation.

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