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 D left off here 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: Coevolution Convergent Evolution Divergent Evolution

Patterns of Evolution Coevolution: Two or more species change together! Examples: Predator/Prey Plant and pollinator

Patterns of Evolution Convergent: Two dissimilar species becoming structurally similar Environment selects for similar phenotype (but ancestors were different) Convergent evolution is the independent evolution of similar features in species of different lineages. Convergent evolution creates analogous structures that have similar form or function, but that were not present in the last common ancestor of those groups

Patterns of Evolution Divergent: Two similar species become dissimilar in response to environment

Evolution Speciation and Reproductive Isolation 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 Reproductive Isolation Temporal Isolation Behavioral Isolation Populations separated by geographical barriers like water, canyons, and mountains Populations separated by behaviors like mating calls, physical traits, mating dances Populations separated by time like nocturnal, diurnal, months, years

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 2 ways in which evolution of species can occur Scientists think that species with a shorter evolution evolved mostly by punctuated equilibrium, and those with a longer evolution evolved mostly by gradualism. Gradual - stable rate of change Punctuated- instant change

Critical Questions: How does reproductive isolation affect speciation? How does geographic isolation affect speciation?