Isolation Leading to Speciation…
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Isolation Leading to Speciation…
Speciation - formation of two species from one species because of divergent natural selection
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Difference between Geographic and Reproductive Isolation
Geographic• Physically separated for long
periods of time• Physical barrier• Volcano/earthquake• Wind/water
Reproductive• Mutation and natural
selection• Divergent evolution• Change enough to not be
able to interbreed
Can take hundreds of years… if the species is quickly reproducing. Otherwise, it takes tens of thousands to
millions of years!
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Geographic Isolation
…can lead to reproductive isolation, divergence of gene pools and speciation.
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Convergent evolution
• Organisms have similar adaptations to similar environments, e.g. whales and sharks, bats and birds
These two succulent plant genera, Euphorbiaand Astrophytum, are only distantlyrelated, but have independently convergedon a very similar body form.
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Convergent evolution
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Convergent evolution
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Divergent Evolution
• Organisms are related but have different adaptations to different environments
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Divergent EvolutionOr Adaptive Radiation
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Darwin’s Finches
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Divergent
Convergent
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Coevolution
• Refers to complex interactions that involve evolutionary adaptations between 2 species
• E.g. Acacia tree and leafcutter ants, flowering plants and their pollinators
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Evolution and Adaptation
• Co-Evolution–Populations of two different species
interacting over a long period of time
–Changes in the gene pool of of one species changes the gene pool of another species
• Predator-Prey Relationships• Plant defense mechanisms
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Extinction: Lights Out
• Extinction occurs when the population cannot adapt to changing environmental conditions.
The golden toad of Costa Rica’s Monteverde cloud forest has become extinct because of changes in climate.
Figure 4-11
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Extinction: Lights Out
• 99.9 % of all species that ever existed are now extinct
Figure 4-11
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Fig. 4-12, p. 93
Tertiary
Bar width represents relative number of living speciesEra Period
Species and families experiencing
mass extinctionMillions ofyears ago
Ordovician: 50% of animal families, including many trilobites.
Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites.
500
345
Cambrian
Ordovician
Silurian
Devonian
Extinction
Extinction
Pale
ozoi
cM
esoz
oic
Cen
ozoi
c
Triassic: 35% of animal families, including many reptiles and marine mollusks.
Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.Carboniferous
Permian
Current extinction crisis causedby human activities. Many speciesare expected to become extinctwithin the next 50–100 years.Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.
Extinction
Extinction
Triassic
Jurassic
Cretaceous
250
180
65Extinction
ExtinctionQuaternary Today
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Extinction• Background extinction
–Normal extinction of various species as a result of changes in local environmental conditions
• Mass extinction– extinction resulting from
catastrophic, wide-spread event in which large groups of existing species are wiped out
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Period of Recovery Following Extinction
Adaptive radiation -Process in which numerous new
species evolve to fill vacant and new ecological niches in changed environments