Chapter 24 Flashcards
Allopatric speciation
Gene flow is interrupted or reduced when a population is divided into geographical subpopulations
Sympatric speciation
Speciation takes place in geographically overlapping population. Gene flow is reduced by factors other than geographic speciation
How does allopatric speciation occur?
subpopulations evolve independently through mutation, natural selection, and genetic drift
Types of Allopatric speciation
- Definition of barriers depends on the organism
- When individuals colonize new areas
- Reproductive isolation
How can reproductive isolation arise?
a by-product of genetic divergence
Microevolution
consists of changes in allele frequency in a population over time
Macroevolution
broad patterns of evolutionary changes above the species level
Speciation
process in which one species splits into two or more species
Speciation is the focal point of evolutionary theory and…
forms a conceptual bridge between micro and macro evolution
Species
Latin for “kind” or “appearance”
Hybrids
the offspring of crosses between members of different species
Biological species concept defines species as…
a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring
Aspects of biological species concept
- Gene flow between populations holds a species together genetically
- Reproductive isolation
Reproductive isolaltion
biological factors (barriers) that impede two species from producing viable, fertile offspring
Types of reproductive isolation
- Prezygotic barriers
2. Postzygotic barriers
Prezygotic barriers
“before the zygote” -block fertilization
Types of prezygotic barriers
- Habitat isolation
- Temporal isolation
- Behavioral isolation
Habitat isolation
breed in different places in the same range
- not isolated by obvious barrier; rarely encounter each other
Temporal isolation
breed during different times of the day, different seasons, or years
Behavioral isolation
courtship rituals and other behaviors enable mate recognition and prevent breeding
After Mating Attempt, Prior to Fertilization
- Mechanical isolation
2. Gametic isolation
Mechanical isolation
mating attempted, but morphological differences prevent completion
Gametic isolation
sperm of one species may not be able to fertilize the eggs of another species
Postzygotic barriers
“after the zygote” -contributes to reproductive isolation after formation of hybrid zygote
Types of postzygotic barriers
- Reduced hybrid viability
- Reduced hybrid fertility
- Hybrid breakdown
Reduced hybrid viability
genes of different parent species interact in ways that impair development and survival
Reduced hybrid fertility
hybrid survives, but is steril
Hybrid breakdown
first generationviable and fertile, but when mate with each other or either parent species, offspring are feeble or sterile
Limitations to Biological Species Concept
- cannot be bapplied to fossils
- cannot be applied to asexual organisms
- emphasizes absence of gene flow, but gene flow can occur between distinct species
Morphological species concept
defines species by strucural features
What does the morphological species apply to
- sexual and asexual species
2. fossils
What does morphological species concept rely on?
subjective criteria (debatable)
Examples of subjective criteria
Monarch and Viceroy
Ecological species concept
defines species in terms of its ecological niche
Niche
species “role” in environment defined as the set of conditions in which a viable populaiton can be maintained
What does niche apply to?
sexual and asexual species
What does niche emphasize?
the role of disruptive selection
