1. Lecture #2 Speciation
Unit 6: Evolution

2. These are all members of a single species.
Macroevolution
What is a Species?
9/14/2018
These are all members of a single species.
G. Podgorski, Biol. 1010

3. There is only one extant (existing) human species.
Macroevolution
What is a Species?
9/14/2018
There is only one extant (existing) human species.
G. Podgorski, Biol. 1010

4. Macroevolution
Determining What Is and What Isn’t a Distinct Species Can Have Economic Consequences
9/14/2018
Northern spotted owl (left) and barred owl (right).
G. Podgorski, Biol. 1010

5. What exactly IS a species?
Species - a group of organisms that
look alike and are capable of
producing fertile offspring in nature.

6. About 2 million species have been described.
Macroevolution
9/14/2018
How Many Species Are There?
We don’t know.
About 2 million species have been described.
Estimates of existing species number range from 4 million to 100 million (with million being a more commonly considered upper estimate).
G. Podgorski, Biol. 1010

7. Question: How do new species arise?
Speciation – The process whereby a population achieves reproduction isolation and results in the formation of new species.

8. The key to speciation is reproductive isolation of populations.
Macroevolution
9/14/2018
The key to speciation is reproductive isolation of populations.
Geographic isolation is an example of a reproductive isolating mechanism.
G. Podgorski, Biol. 1010

9. Other ways to achieve reproductive isolation
(different habits within an overlapping range)

10. Isolation is not enough however!
Populations of the same species that live in different locations will only evolve in different directions if they are exposed to slightly different selective pressures.

11. As isolated populations of the same species become more different over time, they may eventually be unable to breed with one another. The two populations are then considered to be different species.

12. Harris’ antelope squirrel White-tailed antelope squirrel
Macroevolution
9/14/2018
Example I
Harris’ antelope squirrel
White-tailed antelope squirrel
Two species of ground squirrel are believed to have descended from a common ancestral population that was separated by formation of the Grand Canyon.
G. Podgorski, Biol. 1010

13. Example II Darwin’s Finches
Darwin hypothesized that the Galápagos finches had descended from a common ancestor. These ‘founders’ were probably blown over from the South American mainland in a storm.
The ancestral finch was a ground-dwelling, seed-eating finch.

14. There are now 13 species of finch living on the Galapagos Islands.

15. Darwin’s Finches are an example of
Adaptive Radiation.
Adaptive Radiation - The diversification
of several new species from a recent
ancestral source.
‘Recent’ meaning in the last 100,000 years in the case of Darwin’s finches.

16. Darwin proposed that natural selection shaped the beaks of different bird populations as they became adapted to eat different foods.

17. Take 2 minutes to summarize what you have learned regarding what is necessarily in order for a new species to arise. Give an example of speciation as well.

18. Three Types of Evolution
Divergent Evolution
Convergent Evolution
Parallel Evolution

19. 1. Divergent evolution - speciation in which
sub- populations of a species split to form 2
or more new species
When species have undergone divergent evolution, there is a common ancestral form.
Example: Darwin’s Finches

20. Another example
Eohippus (common ancestor to all the rest) gave rise to several species of horse, all of which are currently extinct except for modern day Equus.

21. similar environmental pressures.
Convergent
Evolution
The independent
evolution of similar
structures among
distantly related
species due to
similar environmental
pressures.
Example: body plan of shark & dolphin

22. Convergent Evolution

23. Example - Marsupials vs Placental Mammals.
Parallel Evolution - the independent evolution of similar traits, starting from a similar ancestral condition.
Example - Marsupials vs Placental Mammals.
Parallel Evolution is similar to convergent evolution in that similar features evolve in two species independently. They differ in the fact that two species are DISTANTLY related in convergent evolution. (Ex: dolphins vs. sharks)

24. Examples of parallel evolution
Marsupials and placental mammals most recently shared a common ancestor million years ago, yet these similar features appeared in each of the distant relatives!

25. Is this an example of Convergent, Parallel or Divergent Evolution?
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

26. Take 2 minutes to summarize what you have learned about the three types of evolution that can occur.

27. At what rate does evolution occur?
Gradualism - the model of evolution in which gradual change over a long period of time leads to species formation. For decades, gradualism was the model of evolution that most biologists agreed on.

28. Some biologists in recent times suggested a different theory; in which successful species remain UNCHANGED for long periods of time. (‘If its not broke, don’t fix it!’)
They hypothesize that major environmental changes in the past have caused evolution to occur in spurts.

29. Punctuated Equilibrium – The model of evolution in which periods of rapid change in species are separated by periods of little to no change.

30. Extinction and Evolution
Rapid bursts of evolution tend to follow in the
wake of extinctions.
Extinction - when a species disappear
permanently.
Best estimates from the fossil record indicate
that greater than 99% of species that have ever
existed are now extinct.

31. Why does extinction occur?
If the environment changes beyond the capacity of a species to survive that change, extinction is inevitable.

32. According to the fossil record, a large
percentage of the organisms on Earth
suddenly became extinct 440 million years ago.
This was the first of five major mass extinction’s that have occurred on Earth.
Mass extinction - the death of all members
of many different species, usually caused by
an ecological disaster.
Ex of natural events that may trigger extinction
Volcanic eruption, climate change, Meteor crashing in to the earth.

33. After each of the 5 mass extinctions, species that
are better suited to the new conditions may
replace those that became extinct.
There is always a burst of evolution following a mass extinction as the survivors recolonize the habitats unoccupied due the mass extinction.
There are many resources available and little competition, so populations grow readily.

34. Example
The extinction of the dinosaurs was followed by the ‘rise of mammals’.
out/videos#what-killed-the-dinosaurs

35. Is the 6th mass extinction happening now?
Humans are currently accelerating the rate
of extinction!
The leading cause of species extinction today is habitat loss. Much of this is due to human activity. We are disrupting many of the earth’s ecosystems (ex: logging, mining, farming, housing development).
This displaces many species and leads to extinction.

36. Are We Now Causing a Mass Extinction?
Macroevolution
9/14/2018
Are We Now Causing a Mass Extinction?
G. Podgorski, Biol. 1010

37. Take 2 minutes to summarize what you have learned regarding the rate at which evolution occurs and the relationship between extinction and evolution.