Natural Selection Flashcards
What is Evolution?
Just means change over time
Natural Selection is one mechanism for it
What is needed for Natural Selection?
Pre-Existing Variation
Pressure - not everyone is successful
Differential success
Some survive, some don’t
Heritability
Some code accounts for different
traits & different successPre-Existing Variation
Within a species, individuals differ slightly in terms of their outwardly visible traits or Chemistry
Ex. In a population of mice, some have light fur, medium brown fur, or dark fur
Selective Pressure
Organisms must contend with challenges, like finding food, mates, avoiding predators, or evading thermal stress, or bad weather
Ex. Mice need to go out & forage for food, but they need to avoid being eaten by birds of prey
Law of Tolerance
Differential Success
Not all organisms will be successful & live to reproduce… related to trait variation
Ex. Some colours of coat provide better camouflage
Better camouflage = not getting
by predators, so the survivors live to
reproduce
Heritability
Traits can be passed from parents to offspring
Ex. Genes (DNA) codes to Colour
What is Adaption?
Any feature of Characteristic of an organism that helps for make that species more successful in their environment or their role in it (niche)
How does Natural Selection work?
It “picks” Beneficial traits from the already existing variations, these traits increase in the population
It also selects against harmful traits,
Those decrease in the population
What are the two types of Selective pressures?
Abiotic
Biotic
Abiotic pressures
What are Density Independent factors?
Non-Living
Weather (temp, precipitation)
What conditions are tolerable
Density Independent factors will:
affect organisms the same way
regardless of how many organisms
there are
Eg. Hurricanes
Biotic pressures
What are Density Dependent factors?
Living stuff, (relationships)
Competition
Fight for limited resources
Interference Competition
Direct physical interaction
Exploitative Competition
Indirect (no touching)
Predator - prey interactions
Prey adapt to avoid predators
Predators adapt to catch/kill prey
Symiosis
Mutualism
Everybody wins
Commensalism
One benefits, une unharmed
Parasitism
One benefits, one is harmed
Density Dependent is when:
Intensity of the pressure changes
with the number of organisms
How are Variations formed?
DNA must be copied, mistakes called mutations can occur. Mutations can possibly produce different proteins and therefore different traits
If the new trait is beneficial, it gets
selected for
If it’s bad, it’s gets selected against
How do Nucleotide/Amino Acid sequences help in analysing how closely related organisms are?
How similar the sequences
=
How closely related the organisms are
