Variation
What is variation in a population?
Differences in traits among individuals.
What does “overproduction” mean?
Organisms produce more offspring than can survive.
Name one limited resource organisms compete for.
Food, water, space, mates, shelter, sunlight.
What does “fitness” mean in biology?
Ability to survive and reproduce.
Who evolves—individuals or populations?
Populations.
Why is variation important for natural selection?
It increases the chance that some individuals survive when the environment changes.
Why do organisms overproduce offspring?
Because many will die due to competition.
What happens when resources are limited?
Competition increases
Which bird is most “fit”?
A) Strongest
B) Fastest
C) One that produces the most offspring
C) One that produces the most offspring
Why don’t individuals evolve?
Their DNA does not change.
Which of the following is an example of variation?
A) All birds having the same beak
B) Birds having different beak shapes
C) All birds having the same color
D) All birds eating the same food
B) Birds having different beak shapes
How does overproduction lead to natural selection?
More offspring = more competition = only the fittest survive.
Why can’t all offspring survive?
Resources are limited.
Why does the environment determine fitness?
Traits are only beneficial if they match the environment.
After pollution, dark moths survive more than light ones. What happens next?
More dark moths will be born in the population.
TRUE or FALSE: Variation is always caused by the environment.
FALSE – variation is inherited (comes from DNA).
Which group demonstrates overproduction?
A) 2 turtle eggs
B) 5 wolf pups
C) 500 salmon eggs
C) 500 salmon eggs
A drought reduces food supply. Which individuals survive?
Those best adapted to obtaining food.
A population of fish changes color over generations. Why?
The color that survives predators best is passed on more.
A graph shows trait A increasing. What does this mean?
Trait A gives higher fitness in that environment.
A population of beetles shows three color variations: green, brown, and yellow. Birds eat the beetles more easily on light-colored sand dunes. After a wildfire, the dunes turn black. Predict EXACTLY how the frequency of each color will change over 5 generations AND explain WHY.
Green ↓↓↓, Yellow ↓↓↓ (easy targets), Brown ↑↑↑ (best camouflage → highest survival → highest reproductive success).
A frog lays 600 eggs. Only 40 survive to adulthood.
Explain how overproduction, variation, and competition ALL interact to determine which 40 survive.
Overproduction forces many offspring to compete; variation means not all froglets have equal traits; competition ensures only froglets with advantageous traits survive to adulthood.
A drought causes both food and shelter to decrease. Two traits help survival:
Trait A: Better food-finding ability
Trait B: Better heat tolerance
Which trait becomes more common FIRST and why?
Trait B increases first because temperature stress affects survival immediately, while food advantage matters later. Limited shelter increases heat exposure, so heat tolerance provides immediate selective advantage
Two competing traits in a fish population:
Trait X increases speed but reduces energy storage.
Trait Y increases energy storage but slows the fish down.
During a predator-filled season, Trait X increases.
During a famine, Trait Y increases. Explain why each trait becomes more fit under different environmental pressures.
Fitness depends on environment; predators select fast fish (Trait X), famine selects fish that survive with low food (Trait Y). Different pressures change which trait gives higher reproductive success.
A scientist studies a lizard population over 20 generations. She finds:
The average leg length increased
The average sprint speed increased
The population moved to more open habitats
Explain how environmental change AND differential reproductive success caused all three results.
Open habitats favor longer-legged, faster lizards. Those with these traits escape predators more effectively and reproduce more. Over many generations, these traits accumulate, shifting both average traits and the population’s habitat use.