Biology HN-Evolution- Day 2

What is evolution?

The change in allele frequencies within a population of organisms over time.

What are the three modes of natural selection?

Stabilizing, directional, and disruptive (diversifying) selection.

What does stabilizing selection favor?

Average (middle) individuals, decreasing variation in the population.

Provide an example of stabilizing selection.

Average-sized lizards are more likely to survive than larger or smaller lizards.

What does directional selection favor?

One of the extreme variations of a trait.

Provide an example of directional selection.

Long-trunked elephants have a selective advantage over those with shorter trunks.

What does disruptive selection favor?

Both extremes of a trait's variation while selecting against average phenotypes.

Provide an example of disruptive selection.

Limpets with white or dark shells are favored in environments with light and dark rocks.

What is speciation?

The evolution of a species when two populations can no longer mate to produce offspring.

What are the two main causes of speciation?

Geographic isolation and reproductive isolation.

Define geographic isolation.

The physical separation of populations, such as by land or water barriers.

Define reproductive isolation.

Formerly interbreeding organisms cannot produce fertile offspring due to various barriers.

What are the types of reproductive isolation?

Behavioral, temporal, and mechanical isolation.

What is gradualism?

A slow and steady change in a population over time.

What is punctuated equilibrium?

Rapid change in a population caused by environmental factors.

What is a species?

Organisms that can reproduce and produce fertile offspring.

Why are ligers and zorses not considered their own species?

They are infertile and cannot produce fertile offspring.

What is a niche?

The role that an organism plays in its ecosystem.

How can geographic isolation lead to speciation?

It separates populations, leading to different evolutionary paths.

What is the selective advantage in stabilizing selection?

Average traits are favored, increasing the likelihood of survival.

What happens to variation in a population under stabilizing selection?

Variation decreases as more individuals exhibit the average trait.

What is the outcome of directional selection on a population's traits?

It reduces variation by favoring one extreme phenotype.

What is the impact of disruptive selection on average phenotypes?

It selects against average phenotypes, potentially leading to speciation.

How does behavioral isolation occur?

Species do not recognize each other's mating rituals.

How does temporal isolation occur?

Species mate at different times, preventing interbreeding.

How does mechanical isolation occur?

Sexual organs of different species are incompatible.

What is an example of a physical barrier that can cause geographic isolation?

A river changing course or a highway being built.

What is the significance of the Grand Canyon in terms of geographic isolation?

It serves as a barrier leading to different species of squirrels on either side.

What is the role of environmental factors in punctuated equilibrium?

They trigger rapid changes in a population.