Biological Species Concept

1. Biological Species Concept
How We Define Species

2. Objectives
• Define Biological Species Concept
• Name the eight barriers that define a species
• Categorize the barriers as either geographic or
reproductive
• Categorize the barriers as either prezygotic or
postzygotic
• Remember and understand the basis for each of
the categories
• Provide examples for each of those barriers

3. Biological Species Concept
• The biological species concept
emphasizes reproductive isolation through
prezygotic and postzygotic barriers that
can result in separating the gene pools of
different populations.

4. Vocabulary
• Geographic Isolation – • Reproductive Isolation
Refers to being separated – Refers to being
by space. separated by not being
able to reproduce.

5. Vocabulary Cont.
• Prezygotic (Before • Postzygotic (After
fertilization) – Refers fertilization) – Refers
to a time before the to a time after the
sperm and egg fuse. sperm and egg have
fused.
← Before this point After this point →

6. Table 1 – Barriers between Species
Barriers
Prezygotic 1. Habitat Isolation
2. Temporal Isolation
3. Behavioral Isolation
4. Mechanical Isolation
5. Gametic Isolation
Postzygotic 6. Reduced Hybrid Viability
7. Reduced Hybrid Fertility
8. Hybrid Breakdown

7. 1. Habitat Isolation
• Same as Geographic Isolation

8. 2. Temporal Isolation
• Mate at different times

9. 3. Behavioral Isolation
• Different courtship rituals (mating signals)

10. 4. Mechanical Isolation
• Physically can’t mate

11. Mechanical Isolation Cont.
• More mechanical isolation

12. 5. Gametic Isolation
• When sperm can’t fertilize the egg

13. 6. Reduced Hybrid Viability
• When hybrids can’t develop
This salamander is frail
and underdeveloped.

14. 7. Reduced Hybrid Fertility
• When the hybrids develop but can’t reproduce
Horse + Donkey =
Mule
(The mule is sterile; it
can’t reproduce)

15. 8. Hybrid Breakdown
• When hybrids reproduce but their offspring can’t
Hybrid A + B = C
C can’t reproduce
Hybrid: A C B

16. Table 2 – Classification of Barriers in Relation
to Zygote Formation
Classification Prezygotic Postzygotic
Pre-mating Pre- Post-fertiliztion
fertilization
Barriers Habitat Mechanical Reduced Hybrid Viability
Isolation Isolation
Temporal Gametic Reduced Hybrid Fertility
Isolation Isolation
Behavioral Hybrid Breakdown
Isolation

17. Check Your Understanding
• What is one example of a POST-mating
but PRE-zygotic barrier?

18. Answer
Classification Prezygotic Postzygotic
Pre-mating Pre- Post-fertiliztion
fertilization
Barriers Habitat Mechanical Reduced Hybrid Viability
Isolation Isolation
Temporal Gametic Reduced Hybrid Fertility
Isolation Isolation
Behavioral Hybrid Breakdown
Isolation

19. Table 3 – Classification of Barriers in Relation
to Isolation Type
Classification Isolation
Geographic Reproductive
Barriers Habitat Isolation Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown

20. Check Your Understanding
• Out of 8 barriers, how many are
geographic?

21. Answer
Classification Isolation
Geographic Reproductive
Barriers Habitat Isolation Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown

22. Table 4.1 – Making Sense of the Barriers
Classification Don’t meet Do meet Do meet Do meet
Don’t have sex Do have sex Do have sex
Don’t Do fertilize
fertilize
Offspring have
issues
Barriers Habitat Temporal Gametic Reduced
Isolation Isolation Isolation Hybrid Viability
Behavioral Reduced
Isolation Hybrid Fertility
Mechanical Hybrid
Isolation Breakdown

23. Check Your Understanding
• What were the four bolded
classifications?

24. Answer
Classification Don’t meet Do meet Do meet Do meet
Don’t have sex Do have sex Do have sex
Don’t Do fertilize
fertilize
Offspring have
issues
Barriers Habitat Temporal Gametic Reduced
Isolation Isolation Isolation Hybrid Viability
Behavioral Reduced
Isolation Hybrid Fertility
Mechanical Hybrid
Isolation Breakdown

25. Table 4.2 – Making Sense of the Barriers
(Translated)
Classification Don’t meet Do meet Do meet Do meet
Don’t have sex Do have sex Do have sex
Don’t Do fertilize
fertilize
Offspring have
issues
Barriers Location Timing Sperm and Don’t grow
egg can’t
fertilize
Behavior Can’t
reproduce
Physical Children can’t
reproduce

26. Check Your Understanding
• What was the pattern for Barriers in each
column?

27. Answer
1 3 1 3
Classification Don’t meet Do meet Do meet Do meet
Don’t have sex Do have sex Do have sex
Don’t Do fertilize
fertilize
Offspring have
issues
Barriers Location Timing Sperm and Don’t grow
egg can’t
fertilize
Behavior Can’t
reproduce
Physical Children can’t
reproduce

28. Summary
• You have just been introduced to the
Biological Species Concept.
• You also learned about the 8 barriers
between species.
• Now that you have the basics, read Ch.
24, Overview and Concept 24.1