1. Speciation
Chapter 14
March 2014

2. Defining Species

3. 14.1 The origin of species is the source of biological diversity
Microevolution is the change in the gene pool of a population from one generation to the next
Speciation is the process by which one species splits into 2 or more species
Every time speciation occurs, the diversity of life increases
The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago

4. 14.2 There are several ways to define a species
The Biological Species Concept defines a species as
Group of populations
Whose members have the potential to interbreed in nature
Produce fertile offspring
Therefore, members of a species are similar because they reproduce with each other

5. 14.2 There are several ways to define a species
Reproductive Isolation
Prevents members of different species from mating with each other
Prevents gene flow btwn species and
Maintains separate species
Therefore, species are distinct from each other because they do not share the same gene pool

6. 14.2 There are several ways to define a species
The Morphological Species Concept
Classifies organisms based on observable physical traits
Can be applied to
Asexual organisms
Fossils
However there is some subjectivity in declining which traits to use

7. 14.2 There are several ways to define a species
The Ecological Species Concept
Defines a species by its ecological role and
Focuses on unique adaptations to particular roles in a biological community
For example, 2 species may be similar in appearance but distinguishable based on:
What they eat
Where they live

8. 14.3 Reproductive barriers keep species separate
Serve to isolate the gene pools of species and
Prevent interbreeding
Depending on whether they function before or after zygotes form, reproductive barriers are categorized as
Prezygotic
Postzygotic

9. 5 types of Prezygotic Barriers Prevent Mating or Fertilization btwn Species
1. Habitat Isolation – 2 species live in the same general area but not in the same kind of place
2. Temporal Isolation – 2 species breed at different times (seasons, times of day, years)
3. Behavioral Isolation – little or no mate recognition btwn females and males of different species
4. Mechanical Isolation – female and male sex organs are not compatible
5. Gametic Isolation – female and male gametes are not compatible

10. 3 Types of Postzygotic Barriers Operate After Hybrid Zygotes Have Formed
1. Reduced Hybrid Viability – most hybrid offspring don’t survive
2. Reduced Hybrid Fertility – hybrid offspring are vigorous but sterile
3. Hybrid Breakdown
The 1st generation hybrids are viable and fertile but
The offspring of the hybrids are feeble or sterile

11. Mechanisms of Speciation

12. 14.4 In Allopatric Speciation, Geographic Isolation Leads to Speciation
In Allopatric Speciation, populations of the same species are geographically separated, isolating their gene pools
A Gene Pool is the total collection of genes in a population at any one time
Isolated populations will no longer share changes in allele frequencies caused by
Natural Selection
Genetic Drift
And/or Mutation
Gene flow btwn populations is initially prevented by a geographic barrier. For example:
The Grand Canyon and Colorado River separate 2 species of antelope squirrels
And the Isthmus of Panama separates 15 pairs of snapping shrimp

13. 14.6 Sympatric Speciation takes place without Geographic Isolation
Sympatric Speciation occurs when a new species arises within the same geographic area as a parent species
How can reproductive isolation develop when members of sympatric populations remain in contact with each other?
Gene flow btwn populations may be reduced by
Polyploidy
Habitat Differentiation
Or Sexual Selection
Polyploidy = more than regular number of chromosomes (usually double)

14. 14.6 Sympatric Speciation takes place without Geographic Isolation
Many plant species have evolved by Polyploidy, in which cells have more than 2 complete sets of chromosomes
Sympatric Speciation can result from polyploidy
Within a species (by self-fertilization) or
Btwn 2 species (by hybridization)

15. 14.8 Isolated islands are often Showcases of Speciation
The evolution of many diverse species from a common ancestor is Adaptive Radiation
The Galapagos Archipelago
Located 900 km west of Ecuador
One of the world’s great showcases of adaptive radiation
Has many species of plants and animals found nowhere else in the world