Transcript Outcomes of evolution

Outcomes of Evolution
Outcomes of Natural Selection
• Most quantitative traits resemble bell
curve for phenotypes
Natural Selection can alter variation in a
population in 3 ways:
1) Stabilizing Selection
• Favors individuals with the average
phenotype of the trait (average form
have the highest fitness)
Example of Stabilizing Selection
2) Directional Selection
• Environmental conditions favor
individuals of one extreme phenotype
Example of Directional Selection
3) Disruptive Selection
• Environmental conditions favor individuals of
both extremes of the phenotype.
• Can lead to creation of a new species
Example of Disruptive Selection
Patterns of Evolution
Ways species change to adapt to their
habitats:
o Coevolution
o Convergent Evolution
o Divergent Evolution
Patterns of Evolution
Coevolution: Two or more species change together!
Examples:
1) Predator/Prey
2) Plant and pollinator
Patterns of Evolution
Convergent: Two dissimilar species becoming
structurally similar
Environment selects for similar phenotype (but
ancestors were different)
Patterns of Evolution
Divergent: Two similar species become
dissimilar in response to environment
Creating a New Species
Evolution
Speciation and Reproductive Isolation
Species:
• A group of similar organisms that can
breed to produce fertile offspring
Liger - not fertile
Speciation:
• Creating a new species
• 1 species evolves into 2 different species
How Speciation Occurs
• When a group in a population are separated
and can no longer reproduce a new species
is formed
Ways to create a new species: how are
species separated?
Isolation
Geographical
Isolation
Populations
separated by
geographical
barriers like
water, canyons,
and mountains
Reproductive
Isolation
Temporal
Isolation
Populations separated
by time like
nocturnal, diurnal,
months, years
Behavioral
Isolation
Populations separated
by behaviors like
mating calls, physical
traits, mating dances
Geographic Isolation
• Habitat becomes divided
• No mating because one species gets separated by a
barrier (earthquake, river, etc)
• Over time, can lead to two different species.
Behavioral Isolation
• No mating
• One does not desire the courtship behavior of
the other one
• Over time, can lead to two different species
Temporal Isolation
• No mating
• One reproduces at different times of day, month,
year
• Over time, can lead to two different species.
Rates of Speciation
Gradual - stable rate of change
Punctuated- instant change
Critical Questions:
• How does reproductive isolation affect
speciation?
• How does geographic isolation affect
speciation?