evolutionary ecology

evolution

changes in allele frequencies over time

4 main mechanisms of evolution

• Selection

• Genetic drift

• Gene flow

• Mutation

Selection

Some individuals survive/reproduce better → their traits increase

(a) Natural selection

• based on survival

• example: better camouflage → don’t get eaten

(b) Sexual selection

• based on mating success

• example: peacocks with big tails

types of selection: directional selection

favors ONE extreme

• shifts the average

Example:

• bigger beaks survive drought

types of selection: stabilizing selection

favors the MIDDLE

• removes extremes

• reduces variation

Example:

• medium size is best

types of selection: disruptive selection

favors BOTH extremes

• splits population

Example:

• small + large both good, middle bad

genetic drift

changes due to chance, NOT fitness

founder effect and bottleneck

types of drift: founder effect

• small group starts new population

• not genetically representative

👉 example: isolated island

types of drift: bottleneck

• population drastically reduced

• survivors are random

👉 leads to:

• low genetic diversity

• inbreeding

gene flow

movement of alleles between populations

• migration

• mating between populations

Effect:

• increases genetic variation

• makes populations more similar

mutation

change in DNA

• creates NEW alleles

• ultimate source of variation

Most mutations:

• neutral (no effect)

comparisons!

random: drift, mutation

nonrandom: selection, gene flow

create variation: gene flow, mutation

does not create variation: selection, drift

Hardy-Weinberg

A² + 2Aa + a² = 1

used to predict genotype frequencies

Heterozygosity

measure of genetic variation

Fixation

only one allele remains

three types of natural selection charts