1. Patterns of Evolution

2. Looking for Patterns
We’ve examined homologous and vestigial structures
We’ve examined genetic drift and the founder effect
Can we recognize larger patterns of evolution for new species?

3. Before we start…
Niche - The role or function of an organism or species in an ecosystem

4. Adaptive Radiation
Adaptive Radiation: Relatively fast evolution of one species into a number of distinct but related species
Each new species fills a previously empty ecological niche

5. Example: Darwin’s Finches
One species millions of years ago
It has evolved into 13 separate species
Assume an initial medium-sized, medium-beaked species in South America
Competition on the mainland (S. America) probably drove stabilizing selection of these traits

6. Example: Darwin’s Finches
On the island, there was much less competition from other birds
Their only competition was from each other
The islands already had insects and plant species, but relatively few predators
When the finches arrived, they found new food sources to exploit

7. Example: Darwin’s Finches
A finch with a larger beak would not face competition from the medium-beaked birds, and could exploit the new food source
A finch that could eat insects would not face competition from a finch that ate nuts
We now know of
7 seed-eating species
6 insect-eating species

8. Example: African Rift Lakes
Another powerful example of adaptive radiation
Several lakes that are isolated from each other
Each lake has hundreds of unique species, all descended from a very few
Each species fills a unique niche, feeding on something different

9. Example: African Rift Lakes
Lake Malawi, for example, has over one thousand species of African cichlids (fish), all descended from a few initial species
The Toronto Zoo: recreation of Lake Victoria

10. Adaptive Radiation Review
Start with one, or a few, species in a new environment
This species adapts to the new environment by filling different niches
By filling different niches, each new species has less competition for resources
Leads to many new species evolving

11. Ecological Roles
There are so many different roles to fill in any ecosystem
Consumers and producers, for example
Each role must be filled by one or more species

12. Example: Herbivores
Herbivores come in a huge variety of shapes and sizes
Natural selection has directed their evolution into many different species

13. Divergent Evolution
Divergent Evolution: the large-scale evolution of a group into many different species

14. Example: Rodents
Rodents are the largest group of mammals, many of them found here in Ontario
They all descended from a common ancestor
They underwent adaptive radiation in order to fill different ecological roles
Rodents provide an excellent example of divergent evolution

15. Red Squirrels and Flying Squirrels
For example:
Red squirrels: active during the day
Flying squirrels: similar niche, but active at night

16. Porcupines and Beavers
Porcupines climb trees to eat bark and twigs
Beavers cut down trees to eat bark and twigs

17. Outcomes of Divergent Evolution
Competition between species is minimized as new species fill unique ecological niches
New species continue to evolve until most available resources are used

18. Analogous Features Remember: Analogous features?
What causes analogous features to evolve?

19. Convergent Evolution
Convergent Evolution: occurs when two different species evolve to fill similar ecological niches
distantly related species develop similar traits in order to do so

20. Convergent Evolution
Why would a species fill a similar niche as another?
Wouldn’t this mean they’re now competing with each other?
The best examples of convergent evolution occur in different geographic regions

21. Convergent Evolution in Plants
Cacti: evolved in South American deserts
Euphorbia: evolved in African and Asian deserts
- Both have evolved features to deal with desert conditions

22. Why are they Convergent?
Although they look similar and fill similar niches, there are differences:
Cacti: spikes evolved spikes from leaves
Euphorbia: evolved spikes from the stem

23. Example: Sharks and Dolphins
Both have evolved similar features, and fill similar niches (high speed carnivores)
Sharks evolved from primitive fish
Dolphins evolved from land mammals

24. Convergent Evolution and Analogous Features
What’s the difference?
Convergent evolution leads to analogous features

25. Outcomes of Convergent Evolution
Natural Selection favours the evolution of similar traits in similar environments
While some features will converge in function, each species will retain other features that indicate their distinct evolutionary past

26. Co-evolution
Co-evolution: A process in which a species evolves in response to the evolution of another species

27. Co-evolution
Plants evolve hard shells to prevent animals from eating their seeds
Herbivores evolve more powerful jaws and beaks to break the shells
This is known as an evolutionary arms race

28. Example: Coconut Crab

29. Effects of Co-evolution
One species may become dependent on the other
So a threat to one species can also be a threat to the other

30. Co-evolution and Symbiotic Relationships
Coevolution can be best seen in symbiotic relationships
Darwin’s Orchid and the Madagascan Hawk Moth
Each has become so dependent on the other – for food and for pollination – that extinction of one would mean extinction for the other

31. Honeyguides

32. Convergent, Divergent or Co-evolution?!

33. Convergent, Divergent or Co-evolution?!

34. Convergent, Divergent or Co-evolution?!

35. Convergent, Divergent or Co-evolution?!

36. Convergent, Divergent or Co-evolution?!

37. Convergent, Divergent or Co-evolution?!

38. Homework
PG. 345 #1,2,7