Lecture 4: Evolution and Ecology Flashcards
Biology all arises from
process of evolution
Evolution
change in allele frequency in population over time
Gene
basic physical and functional unit of heredity (DNA), specify how to build proteins
Allele
variant or specific form of a gene
Phenotype
observable characteristics of an organism
Ex. size or color
Fitness
organism’s ability to survive and reproduce within its environment
Frequency
relative abundance of an allele in a population or another unit which evolution is being examined
4 mechanisms of evolution
- mutation
- natural selection
- genetic drift
- gene flow
_____ evolve, not ______!
Populations ; individual
Mutation
random introduction of a new allele
rare
usually disadvantageous and dies out
necessary for variability –> provides raw material for evolution
3 types of natural selection
Directional, stabilizing, disruptive
Requirements for natural selection
- population has variation
- differences are genetic (heritable)
- differences influence (individual fitness)
Natural selection
Darwin’s survival of the fittest
When individuals with particular heritable traits consistently leave more offspring than do individuals with other heritable traits
MAIN MECHANISM OF ADAPTIVE EVOLUTION
Disruptive selection:
favorable to both extremes and no intermediate
can cause speciation
What is the main and only mechanism for adaptive evolution?
Natural selection
Directional selection:
favorable to one extreme
Genetic drift
Occurs when chance events determine which alleles are passed to the next generation
Drift is always occurring
Can overwhelm selection
Causes many differences between isolated populations
How can genetic drift overwhelm selection?
Favorable mutations usually starting from rarity may be lost due to drift despite benefits
Can cause unfavorable alleles go to fixation
Stabilizing selection:
favorable to middle/ mean
Why is genetic drift important in small populations?
allele frequencies fluctuate at random
genetic variation of population is reduced
frequency of harmful alleles can increase if they only have mildly deleterious effects
chance events may lead to allele fixation in one population and loss from another population
Gene Flow
Caused by immigration and emigration
From populations with differing allele frequencies
Can limit local adaptation causing homogenization
Adaptive evolution
traits that confer survival or reproductive advantage that tends to increase in frequency over time
can be quite fast
Ingredients needed for Adaptive evolution:
variability in population
heritability of that variability
differential fitness
Adaptations are not perfect due to
environment not static
emigration, immigration
drift and mutation
Evolutionary Constraints
- Lack of generation
- Evolutionary history
- Ecological tradeoffs
How is lack of generation an evolutionary constraint?
If there is no beneficial allele, adaptive evolution at that gene cannot occur
Advantageous alleles arise by chance, not on demand
How is evolutionary history an evolutionary constraint?
Natural selection works on traits that already exist
Organisms have certain characteristics and lack others because of their ancestry
To evolve, each small step generally needs to be beneficial itself
Ex. Dolphins evolved from terrestrial mammals; they have lungs and cannot breathe underwater
How is ecological an evolutionary constraint?
Organisms do many things over their lives
Traits that would make them better at one thing might make them worse at another
Ex. Duck Feet help them swim, but not walk
Evolution and Ecology can do feedback to each other
Constant cycle of change in environment –> change in which traits are beneficial in the environment –> change in population and community –> back to change in the environment
Speciation
Can be caused from disruptive selection
Occurs when populations have accumulated enough differences to stop gene flow
Once reproductive barriers are in place local adaptation can proceed more effectively and create daughter species
Difficult to kick off in the first place
The key to speciation is development of
reproductive barriers –> cease gene flow across populations
Reproductive barriers can be:
behavioral or biological
Diversity
function of speciation and extinction
How many mass extinction events?
5
Diversity is driven by
major environmental changes
Adaptive radiation is a major speciation event that is
group of organisms gives rise to many new species that expand into new habitat or fill new ecological roles
Diversity shows interdependency of ecology by
When some species go, many others follow
Creates huge chances on Earth
What are ways human actions alter the course of evolution?
Pollution
Habitat fragmentation
Overharvesting
Introductions of invasive species
Human actions can alter mechanisms of evolutions
natural selection, genetic drift, gene flow
Not mutation!
Extinction rate today is ___ to ____ higher
100 to 1000
What will become leading cause of extinctions in coming decades?
Climate change
