Evolution Notes Part II

Natural Selection Stabilizing selection Directional selection Natural selection has three modes of action: Stabilizing selection Directional selection 3. Disruptive selection

1. Stabilizing Selection Favors the average, acts against the extremes. Number of Individuals Size of individuals Small Large

2. Directional Selection Favors one of the two extremes. Number of Individuals Size of individuals Small Large

3. Disruptive Selection Favors both extremes, acts against the average. Number of Individuals Size of individuals Small Large

How do new species evolve? Speciation-the formation of new species In order for new species to form, there must first be reproductive isolation among parts of a population.

Isolating Mechanisms Geographic Isolation Behavioral Isolation Temporal Isolation

Geographic Isolation Populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water.

Behavioral Isolation Populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding.

Temporal Isolation Two populations reproduce at different times.

Adaptive Radiation Emergence of numerous species from a common ancestor introduced to new and diverse environments.

Coevolution Evolutionary change resulting from the interaction between two different species. Example: Pollinators and Flowering plants

Biodiversity The sum total of different species in a given area.

Extinction

Interpretations of Speciation Two theories: 1. Gradualist Model (Neo-Darwinian): Slow changes in species over time. 2. Punctuated Equilibrium: Evolution occurs in spurts of relatively rapid change.