1. Patterns and processes of Evolution
Section 19.2

2. Why do some organisms live but others die?
Some changes occur within a species
Others can be over much larger scales
When changes occur in clades greater than a single species they are referred to as Macroevolutionary patterns
Creation of species through speciation
Disappearance through extinction
Emergence of large clades – dinosaurs, mammals – examples of macro evolutionary patterns

3. Classification of fossils
Fossils can be classified into clades
Either clades only containing extinct organisms
Or clades also containing living organisms
Cladograms illustrate how closely related organisms are
Relation does not mean direct ancestor

4. Why do species go extinct?
They fail to adapt to a changing environment
Some clades appear more susceptible to extinction than others - why?
The rate of speciation within a clade must equal to or greater than the rate of extinction for a clade to continue to survive over the long term
Reptillia is an example of a highly successful clade
Living organisms continue to adapt and thrive
Most species in clade dinosauria are extinct, but birds survived because they adapted to the new environment

5. What drives extinction of a species?
Two types of extinction
Extinction due to Natural selection – always occurring (background extinction)
Extinction due to a mass Extinction
A mass extinction is when a many species become extinct over a short period of time.
Entire ecosystems vanish, food webs collapse…
Earth has experiences many of these throughout it’s history

6. What causes mass extinctions?

7. Is there a good side to a mass extinction?
Yes, there can be. It creates many new opportunities for survivors to adapt and speciate
Recovery takes about 5 – 10 million years

8. Does evolution always occur at the same rate?
No!
Some organisms change consistently through time – gradualism
Some organisms do not really change over time, until something happens to upset their equilibrium – ‘punctuated equilibrium’.
It has been proposed that most new species are produced during this period of rapid change

9. Why does evolution occur at different rates?
Rapid evolution may occur if a small population gets separated from the main populations
Small population will evolve faster as there are fewer individuals to spread change to
Migration to a new environment
Eg. Galapagos Islands
Mass extinctions create many new ecological niches
Organisms that survive will fluorish

10. Macroevolution There are two main types of macroevolution
Adaptive Radiation
One ancestral species (or small group) evolves to produce a number of different species that live in different ways
Can be caused by migration, extinctions
Species can also evolve a new feature allowing them to take advantage of the environment
Example – dinosaurs and mammals
Mammals were around during dinosaurs but were not successful
After dinosaur extinction, an adaptive radiation of mammals began.
Convergent Evolution
Unrelated organisms in different places but similar environments evolve similar features
Emus, Rheas and Ostriches

11. What is Coevolution?
The process by which two species evolve in response to changes in each other over time
Often they become so intertwined that neither can live without the other
If one has an evolutionary change so will the other
Examples
Specific flowers and pollinators
Plants and herbivores
Plants produce poisons to stop themselves being eaten
But insects resistant to the poisons will flourish
Often these insects use the poisons to their advantage

12. Key Points
Macro-evolutionary patterns are changes that affect many species of entire clades
Examples – speciation and extinction
Earth has experienced a number of mass extinctions
Evolution can occur at different rates
Gradualism vs punctuated equilibrium
Paleontologists have identified patterns of macroevolution
Adaptive radiation and convergent evolution