Patterns of Evolution

Objectives:1. Compare and contrast different patterns of evolution2. Describe how adaptive radiation occurs3. Explain the difference between divergent and

convergent evolution

Natural Selection

• Leads to predictable outcomes…1. Closely related species share many

homologous structures yet these structures serve different functions.

2. Vestigial features may have at one time serve a function in ancestors

3. Remote islands are inhabited by unique species that have descended from a founder population isolated from their original species

But how did these species evolve???

There are 4 patterns that the evolutionary process may follow…

1. Adaptive radiation

2. Divergent evolution

3. Convergent evolution

4. Coevolution

Adaptive Radiation• A single species

evolves into a number of other species.

• These species are distinct from one another but are closely related.

• Each species is specialized for a different environment (fills a different niche).

Niche: How an organism lives and interacts with its environment.

Darwin’s Finches

• Many finches evolved from a single seed eating ground finch.

• Initially finches arriving to Galapagos would have to compete with each other for food.

• Finches with different shaped beaks could exploit different food sources.

• As finches exploited new food sources they most likely exploited new habitats where their food was more plentiful.

• Their different habitats may have selected for more different traits.

• In adaptive radiation, an initial species evolves into a variety of new species that differ in varied ways from the original species.

Divergent Evolution

• A large scale evolution of a group of species into many different species.

Ex: Adaptive radiation• Leads to two outcomes:1) Reduces competition between different

species2) New species evolve and exploit different

niches as competition within species increase because of limited resources.

New species evolve from a common ancestor.• Populations move into different environments• Differences accumulate as these populations

adapt to the conditions • Gene flow may be blocked (reproductive

isolation)

Convergent Evolution• The evolution of similar traits in distantly

related species.

• Two different species living in similar environments under similar selective pressures will evolve similar traits that allow them to occupy similar niches

Example• Two groups of plants

Cacti – deserts of S. America

Euphorbia – deserts of S. Africa

- Both have adaptations to dry conditions and spines.

Cacti have spines that evolved from leaves.

Euphorbia have spines that evolved from stem tissue.

Both serve a protective function.

Co evolution

• One species evolves in response to evolution of another species.

Ex: Some plants have evolved to produce seeds with hard shells .

Some mammals that eat seeds have coevolved to have powerful jaws and teeth to chew through these hard shells.

Hawk Moth and Madagascar long-spurred orchid

Plenary

1. What is adaptive radiation?

2. Explain what divergent evolution means.

3. Explain what convergent evolution means.

4. Explain why one species would have to evolve as a result of another species evolving. What pattern of evolution is this?

5. Give an example to illustrate adaptive radiation, divergent evolution, convergent evolution and co evolution.