Isolation Leading to Speciation…

Speciation - formation of two species from one species because of divergent natural selection

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!

Geographic Isolation

…can lead to reproductive isolation, divergence of gene pools and speciation.

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.

Convergent evolution

Convergent evolution

Divergent Evolution

• Organisms are related but have different adaptations to different environments

Divergent EvolutionOr Adaptive Radiation

Darwin’s Finches

Divergent

Convergent

Coevolution

• Refers to complex interactions that involve evolutionary adaptations between 2 species

• E.g. Acacia tree and leafcutter ants, flowering plants and their pollinators

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

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

Extinction: Lights Out

• 99.9 % of all species that ever existed are now extinct

Figure 4-11

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

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

Period of Recovery Following Extinction

Adaptive radiation -Process in which numerous new

species evolve to fill vacant and new ecological niches in changed environments