Download Speciation I

Zoology 445
Fall 2006
Speciation I: Handout
I. The Species Concept
1. The Biological Species Concept (BSC) = Species are groups of interbreeding (actual
or potential) natural populations that are reproductively isolated from other groups.
2. The Phylogenetic Species Concept = Species are monophyletic groups of organisms.
3. The Morphospecies Concept = Species defined on the basis of morphological
differences among fossils.
II. Allopatric model of speciation
Sequence of events:
1. Isolation = Physical separation between populations acts as a barrier gene flow.
2. Genetic and ecological divergence of the isolated gene pools.
a. The two gene pools diverge so they have different niches.
3. Secondary contact; Gene pools come into contact. If hybrids have low fitness, selection
favors reproductive isolation (Reinforcement).
AM Jarosz
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a. Note: If hybrids fitness is not lower than fitness of parental gene pools, then
selection will not favor reproductive isolation. The gene pools will coalesce into
a single gene pool (i.e., No speciation).
Two important forms of isolation:
a. Dispersal = A small group of individuals migrate to a new geographically remote location.
b. Vicariance = The range of a species is split into one or more separate gene pools.
a. Long-distance dispersal. Example: Hawaiian Drosophila, an example of long distance
dispersal. (Fig 15.7)
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b. Vicariance
Example 1: Snapping shrimp in the Caribbean Sea and Pacific Ocean. Figure 15.8
Vicariance example 2: Spotted sunfish
\Evolution Zol 445\2006\ Speciation1 Handout.doc
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