Evolution and Ecology Study Guide

Charles Darwin traveled on the HMS Beagle and observed

• Different species in different environments  

• Fossils  

• Adaptations of organisms  

• Galápagos finches with different beaks  

Darwin’s Main Idea 

Species change over time through natural selection

Alfred Russel Wallace 

Also known for developing a theory of evolution through natural selection independently of Darwin

Natural Selection

Organisms with traits that help them survive and reproduce are more likely to pass those traits to offspring

Requirements for Natural Selection 

1. Variation exists  

2. Traits are inherited  

3. Some individuals survive/reproduce more  

Effects on Genetic Diversity 

Can increase or decrease diversity depending on the type of selection.  

Directional Selection 

One extreme trait is favored

Stabilizing Selection 

Average trait is favored

Disruptive Selection 

Both extremes are favored

Polymorphism 

When two or more forms of a trait exist in a population. 

Genetic Drift 

Random changes in allele frequencies

Effects of Genetic Drift 

• Decreases genetic diversity  

• Can lead to allele fixation  

Founder Effect 

A small group starts a new population with different allele frequencies

Hardy-Weinberg Equilibrium 

A population that is NOT evolving

Conditions required for Hardy-Weinberg Equilibrium 

• No mutations  

• Random mating  

• No natural selection  

• Large population  

• No migration/gene flow

Genotype Frequencies formula

Frequency = number with genotype ÷ total population 

Allele Frequencies Equation

p + q = 1

p = dominant

q = recessive

Hardy-Weinberg Equation 

p² + 2pq + q² = 1

Used to determine if a population is evolving

Allele Fixation 

When one allele reaches frequency of 100%

Predation 

One organism kills/eats another

Parasitism 

One benefits, one harmed

Mutualism 

Both benefit

Competition 

Species compete for resources

Commensalism 

One benefits, other unaffected

Keystone Species 

A species with a major effect on ecosystem stability

Trophic Cascade 

Changes at one trophic level affect others

Ecosystem Engineer 

Organism physically changes environment

Biological Species Concept 

Species can interbreed and produce fertile offspring. Different species are reproductively isolated. 

Allopatric Speciation 

Separated by geographic barrier

Sympatric Speciation 

Occurs in same area

Peripatric Speciation 

Small isolated population forms new species

Pre-Zygotic Barriers 

Prevent mating/fertilization

Post-Zygotic Barriers 

Fertilization occurs, but offspring are weak/sterile

Ecological Niches 

Role of organism in environment

Fundamental Niche 

Where organism COULD live

Realized Niche 

Where organism ACTUALLY lives

Competitive Exclusion 

Two species cannot occupy same niche forever

Niche Partitioning 

Species divide resources to reduce competition

Exponential Growth 

N(t) + 1 = N(t) + rN(t)

N(t) = current population

r = growth rate

N(t) + 1 = next generation population

• J-shaped curve

Logistic Growth 

N(t) = N1 + rN1 (k - N1/k)

K = carrying capacity

N1 = starting population

• S-shaped curve

Density-Dependent Factors 

Depend on population size

• Ex. Disease, Competition, Predation  

Density-Independent Factors 

Affect populations regardless of size

• Ex. Fires, Floods, Hurricanes

Producer 

Makes own food

Primary Consumer 

Eats producers

Secondary Consumer 

Eats primary consumers

Tertiary Consumer 

Top predator

Energy Transfer 

Only about 10% of energy moves to next trophic level. 

Biomagnification 

Toxins build up at higher trophic levels

Highest toxin levels

Top predators