chapter 6 ecology and evolution. case study: inadvertent evolution bighorn sheep: ovis canadensis;...
TRANSCRIPT
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