Chapter 4.3: How Species Form

1. Chapter 4.3: How Species Form Pages 136 - 142

2. What is a species? • Biological species consists of populations that interbreed and produce fertile offspring • Species are reproductively isolated from other species • Biological species that are geographically isolated cannot interbreed

3. What is a species? • - Lions and tigers are a different species. • - Lions are savannah cats • Tigers are jungle cats • These species are separated by biological barriers (different behaviors, habitats) and geographic barriers.

4. Female Lion + Male Tiger = Liger It's pretty much my favorite animal. It's like a lion and a tiger mixed... bred for its skills in magic. - Napoleon Dynamite (2004)

5. Male Lion + Female Tiger = Tigon

6. Forming a new species • Speciation: the formation of a new species • Two pathways can lead to the formation of a new species. • Transformation • Divergence

7. Forming a new species • Transformation –new species gradually develop • result of mutation and adaptation to changing environmental conditions • old species is gradually replaced • does not result in increased biodiversity

8. Evolution of mammoths – the ancestral mammoth slowly evolved into the steppe mammoth than slowly evolved into the woolly mammoth that lived up to 10 000 yrs ago.

9. Forming a new species • Divergence – one or more species arise from a parent species that continues to exist • Results in increased biodiversity • The small hoofed Hyracothermium is thought to be the ancestor of modern horses, tapirs, and rhinoceroses.

11. Forming a New Species

12. Conditions for Speciation • For speciation to occur, populations must be prevented from interbreeding • If isolation occurs for long enough, changes accumulate in the population • Significant changes may prevent reproductive compatibility • Types of separation • Geographical Barriers • Biological Barriers

13. Geographical Barriers • Geographical barriers prevent interbreeding because populations are physically separated • a peninsula becoming an island • Canyons can separate populations • Powerful storms can transport animals (birds) to islands • The geographic isolation does not have to occur indefinitely, just long enough for speciation to occur.

14. The Kaibab squirrel (Sciurusabertikaibabensis, left) became geographically isolated from the common ancestor with its closest relative, the Abert squirrel (Sciurusabertiaberti, right) in the North Rim of the Grand Canyon about 10,000 years ago. Since then, several distinguishing features, such as the black belly and forelimbs have gradually evolved Speciation Animation

15. Biological Barriers • Behaviour is a biological barrier that keep populations separate • Courtship songs of birds; some bird calls are similar (if they shared a recent common ancestor) but are different enough to provide a biological barrier to reproduction.

16. Biological Barriers • Temporal barriers – species breed during different seasons • Similar organisms use different habitats; two species of garter snake – one lives near water, the other lives in open areas.

17. Adaptive radiation • Adaptive radiation : the diversification of a common ancestral species into a variety of species all of which are differently adapted • Finches in the Galapagos • The fruit fly Drosophila of the Hawaiian Islands

19. The Pace of Evolution • Gradualism • evolution/speciation proceeds by small, cumulative steps over long periods of time • Punctuated Equilibrium • evolution takes place in rapid bursts, separated by long periods of stability

21. The Theory of Evolution by Natural Selection: • Life forms have developed from ancestral forms. • All living things are related to one another by varying degrees through common ancestry. • All living things on Earth have a common origin (share a common ancestor) • The mechanism by which populations change is natural selection

22. The process of natural section: • Random heritable genetic mutations (variations) exist within populations • Some mutations result in a survival advantage • Organisms with an advantage are more likely to pass on the trait to offspring • The frequency (occurrence) of the mutation increases in the population; the population as a whole starts to change.