AP Bio Unit 7 || Speciation and Extinction

Speciation

The formation of a new species

Two types of speciation

Allopatric speciation and Sympatric speciation

Allopatric speciation

Physical barrier that divides a population, or seperated a small population from the main population. Gene flow is prevented.

Sympatric speciation

New species evolves while inhabiting the same geography as the ancestral species. Often due to genetic mutations, egological differences, or behavioral changes.

Speciation prevents ____ ____.

Gene Flow

Prezygotic barriers

Barriers that prevent mating or fertilization

5 types of prezygotic barriers

1. Habitat isolation

2. Temporal isolation

3. Behavioral isolation

4. Mechanical isolation

5. Gametic isolation

Habitat isolation

Species live in different areas or different habitats within an area

Temporal isolation

Species breeds at different times of day, year, or season

Behavioral isolation

Unique behavioral patterns and rituals seperate species

Mechanical isolation

Reproductive anatomy of a species doesn’t fit with one another

Gametic isolation

Protein on gametes do not allow for sperm and egg to fuse

Postzygotic barriers

prevent a zygote from developing into a viable and fertile adult

3 different types of postzygotic barriers

1. Reduced hybrid viability

2. Reduced hybrid fertility

3. Hybrid breakdown

Reduced hybrid viability

genes of different parent species interact in ways that impair hybrid development or survival

Reduced hybrid fertility

a hybrid can develop into an adult but it is sterile; typically due to differences in the number of chromosomes between parents.

Hybrid breakdown

hybridd of first generation may be fertile, but the second generation is sterile

Stasis

Occurs when no changes happen over a long period of time

microevolution

Small-scale changes within a population over a short time

• Affects allele frequencies

macroevolution

Large-scale evolutionary changes over long periods

• Leads to the formation of a new species

Different speeds of evolution

Punctuated equillibrium and gradualism

Punctuated equillibrium

When evolution occurs rapidly after a long period of stasis

Gradualism

When evolution occurs slowly over hundreds, thousands, or millions of years

Divergent evolution

Groups with the same common ancestor evolve and accumulate differences resulting in the formulation of a new species

Convergent evolution

Two different species develop similar traits despite having different ancestors

Variation in a population

The different combinations of alleles in a population

Less diversity =

Greater risk of extinction

Envitonmental pressures examples:

climate change, human activity, predation, habitat loss, food source adjustments, ect.

Adaptive traits

increases chances of survival

Deleterious traits

Traits that decrease chances of survival

Abiogenesis

Suggests that the first simple life forms developed from organic molecules through natural processes

Organic molecules came to early earth via ___

celestial events; or inorganic molecules sythesized them

Miller and Urey experiment

Tested the hypothesis that the composition of the early earth was ammonia, methane, hydrogen, and water. They found that these organic compounds created the building blocks for macromolecules.

RNA world hypotesis

Proposes that RNA was the first life and was able to self replicate

The endosymbiotic theory

Large prokaryote engulfed small prokaryote- small prokaryote developed functionally into organelles; explains how eukaryotes came to be