SPECIES DEFINITION

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SPECIES DEFINITION
Groups of actually or potentially interbreeding
populations that are reproductively isolated
from other such groups (Ernst Mayr-- evolutionary
biologist) share a common gene pool--
genetically related populations- we should
expect variation within species members of
different species don't mate-- don't share genes
(keeps species distinct)
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SPECIES FORMATION

• GEOGRAPHIC ISOLATION
• continuous geography with interbreeding
• geographic separation
• divergent evolution
• geographic overlap without interbreeding

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GEOGRAPHIC ISOLATION
continuous geography with interbreeding
geographic separation
divergent evolution (different environments)

geographic overlap without interbreeding
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EVIDENCE

• Environments vary with geography
• Genetic composition varies with geography
• Geographic barriers are dynamic

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Environments vary with geography
January Precipitation
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Genetic composition varies with geography
PINUS CONTORTA
Pinus contorta latifolia
Pinus contorta contorta
AK coast
provenance tests assess genetic basis
Pinus contorta murrayana
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Geographic barriers are dynamic
present
21,000 years ago
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ARCTIC OCEAN
ALASKA
NE SIBERIA
Bering Strait
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ISOLATING MECHANISMS
geographic overlap without interbreeding
What prevents interbreeding?
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ISOLATING MECHANISMS

• ecological separation
• temporal separation
• mechanical separation
• pollination incompatibility
• hybrid inviability
• hybrid sterility

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Ecological separation
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Temporal separation
May
June
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Temporal separation
Pinus sabiniana
Pinus coulteri
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Mechanical separation
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Pollination incompatibility
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hybrid inviability
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hybrid sterility
donkey
horse
mule
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hybrid sterility
meiosis
DONKEY
HORSE
MULE
meiosis
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