Transcript Patterns of Evolution

Patterns of Evolution
1.
2.
3.
Objectives:
Compare and contrast different patterns of evolution
Describe how adaptive radiation occurs
Explain the difference between divergent and convergent
evolution
Natural Selection
•
1.
Leads to predictable outcomes…
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
species
2) 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 longspurred orchid
Plenary
1.
2.
3.
4.
What is adaptive radiation?
Explain what divergent evolution means.
Explain what convergent evolution means.
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.