Chapter 6

Ecology and Evolution

Case Study: Inadvertent Evolution

• Bighorn Sheep: Ovis canadensis; have the ability to balance on steep ledges

• Males can weigh 180 lbs; their horns are collected as trophies, which caused populations to reduce by 90%

• This hunting has taken the largest, strongest males out of the population

• How do you think the population has changed?

Humans Affect Evolution

• Global warming• Hunting• Fishing• Pollution• Deforestation• How do these affect populations of

organisms?

Chapter 6.1: What is Evolution

• Evolution: Change in a population overtime• Change can be large or small– Examples: • bighorn sheep horn size decreases over time• Whales lost their back legs over time (still have a pelvis)

• Evolution occurs on a genetic level• Genes control physical traits that are either

good or bad for a specific environment

Evolution is Genetic

• Genes are made of DNA – DNA codes for specific proteins

• A gene can have two or more forms (alleles) for a given trait

• Genotype: the genetic make-up of an individual

• Phenotype: the physical traits of an individual

Descent with Modification

• Charles Darwin hypothesized that offspring (descendants) change from their parents over many generations

• This occurs because of natural selection: the environment dictates evolution based on certain traits (adaptations)

• POPULATIONS evolve; individuals do NOT – DNA does not change in an organism, DNA is selected for or against

Chapter 6.2: Mechanisms of Evolution

• There are four key influences of evolution:– Mutation– Natural Selection– Genetic Drift– Gene Flow

• Mutation is the raw material for evolution• A change in DNA CAN change an entire gene,

but sometimes it has no affect

Genetic Differences

• Organisms differ genetically in each species• Differences are due to:– Mutations– Recombination

• Recombination: rearrangement of alleles between parent and offspring (occurs in Meiosis I)

Natural Selection

• The process of natural selection INCREASES alleles that are advantageous

• These alleles are then selected for in one of three ways:– Directional selection: one extreme is favored– Stabilizing selection: intermediates are favored– Disruptive selection: both extremes are favored

Genetic Drift is Random

• Genetic drift: a mechanism that can cause allele frequencies to change

• CHANCE events affect genetic drift• Usually, only small populations are affected

over a short period of time• Example:– A wildflower population is severely altered when a

moose crushes 40% of it

Gene Flow

• Gene flow: alleles move from one population to another

• Gene flow usually occurs because of emigration and immigration

• This can introduce new alleles into a population, but it can also take alleles out of a population

Chapter 6.3: Adaptive Evolution

• Adaptations: characteristics of an organism that INCREASES its ability to survive and reproduce in a particular environment– Example: white fur on a polar bear, beak size for

finches, trunk on an elephant, etc• Adaptations result directly from genes• Natural selection directly causes adaptive

evolution

Adaptive Evolution can be Quick

• Depending on the organism and it’s generation time, adaptations can drive evolution quickly

• Bacteria populations can develop antibiotic resistance in a matter of days

• Insects can become immune to insecticides in a matter of weeks to months

Adaptations are NOT Perfect

• Just because an adaptation occurs, does not mean it’s a perfect match for the environment

• This is sometimes caused by gene flow, but not always

• Most likely, the environment surrounding the organism is constantly changing, so the organisms need to constantly adapt

Chapter 6.4: Evolutionary History of Life

• The diversity of life has resulted in speciation• Adaptations to different environments has

developed new species• Species: a group of organisms with similar

characteristics that HAVE the ability to interbreed

• Speciation usually occurs when two populations are cut off from each other

Mass Extinction &Adaptive Radiation

• In earth’s history, there have been a few instances of mass extinction of life

• Because of extinctions, large holes were left in particular habitats and niches that needed to be filled

• Adaptive Radiation: a group of organisms forms many different species to fill empty habitats and niches

Chapter 6.5: Ecology & Evolution

• Ecology and evolution are completely intertwined

• Different ecological interactions can shape evolutionary patterns through adaptations– Predator/prey interactions– Red queen hypothesis– Competition

Ecology & Evolution

• Evolution can also alter ecological interactions– Predator/prey interactions– Red queen hypothesis– Competition

• Adaptive radiation can affect the physical environments, affecting other species as well

• As populations adapt, they can also change their own environment, causing other populations to adapt as well

Case Study: Revisited

• Humans inadvertently caused bignorn sheep to adapt to being hunted (smaller average horn size)

• How else have humans affected evolution?– Antibiotic resistance in bacteria– Fish size– Fox fur color