January 24, 2014 – Biology
What is a species? Chp. 24
• Formally defined: biological species concept (group of individuals which can interbreed)
• Eastern bluebird (Manitoba and east) and western bluebird. They have become hybrids
because of the reduction of the physical divide between the east and west. Geographical
separation has dwindled affecting hybrids.
• How does speciation occur?
o Biological species concept highlights the importance of reproductive isolation
Biological factors (barriers) that impede two species from producing
viable, fertile offspring
Hybrids are the offspring of crosses between different species.
Big figure in chapter 24 (24.3b) about what factors keep them apart.
(Habitat isolation: terrestrial vs aquatic) (Temporal isolation: one mates in
the spring another in the fall) (Behavioral isolation: The blue pigment
comes from fish – indicates to the female that the male will be able to
provide for the young) (Mechanical isolation: physically they cannot mate)
(Gamete isolation: Mating can occur but the sperm and eggs don’t
recognize each other)
o Reduced hybrid viability: genes of the different parent species may interact and
impair the hybrid’s development (very feeble) Changing conditions affected by
humans create hybrids.
ex: mule and Hinny are sterile. between a horse and a donkey: Female
donkey + Male horse: Hinny, Male donkey + Female Horse: Mule
Lion and Tiger
Grizzly bear and Polar bear
o Hybrid breakdown (mostly plants)
F 1 robust and fertile species
F 2 weak and sterile
o Prezygotic and Postzygotic barriers.
• Allopatric speciation: interruption of gene flow via geographic separation
o Definition of barrier is linked to the ability of a population to disperse
o Separate populations may evolve independently via natural selection and/or
genetic drift, ultimately leading to reproductive isolation.