1. Modes of Speciation

2. Modes of speciation
There are different modes that can lead to the formation of new species: Sympatric and Allopatric speciation

3. Sympatric speciation
A single population divides suddenly into two reproductively isolated groups within the same geographical area. Plants are best example – due to changes in chromosome number (polyploidy) doubling of chromosome number during cell division. These plants can no longer breed with the plants around them.

4. Sympatric speciation
Many plants are able to reproduce both sexually and asexually. If an individual plant has a mutation that prevents successful sexual reproduction, it may be
able to reproduce asexually.

5. Allopatric speciation
New species are formed once populations are physically separated. Once separated, they can no longer exchange genetic information. Over generations the two population become less and less alike. Any mutations that arise in one population are not shared with the other population. Different environments lead to different forms of natural selection.

6. Allopatric speciation

9. Pace of speciation
Phyletic gradualism Change is very slow but steady within a lineage before or after a divergence (splitting of a line of descent) Could explain the lack of transitional species, because the changes are subtle

10. Pace of speciation
Punctuated equilibrium Speciation occurs rapidly during periods of stasis (limited change)
This could also explain the lack of transitional species, because the changes are significant

11. Is speciation smooth or jerky?
Gradualism model Punctuated equilibrium model

12. Homework
Answer questions: # 20,21,22,and 24 on page 365 # 27,28, and 30 on page 370 # 2,3,4,7,8,11 and 13 on page 373