Variation
A group of wolves in Canada have thicker fur than the wolves found in Rocky Mountains. What is the variation in this scenario?
Thick fur and not thick fur
What is selection pressure?
Something in an environment that affects which traits help organisms survive and reproduce
What is an adaptation?
a trait that helps an organism survive and reproduce in its environment
What does "survival of the fittest" mean?
The organisms best suited to their environment are more likely to survive and reproduce
A drought causes a decrease in plant population. The table below shows the number of plants before and after the drought. Predict the number of plants in year 6 if the trend continues.
Year Plant Population
1 800
2 750
3 700
4 650
5 600
The population is decreasing by 50 each year, so the prediction for year 6 is 600 - 50 = 550.)
Give an example of a variation that can't be seen (like eye color).
Bacteria that is resistant to hand sanitizer
In a forest, hawks eat the brightest colored mice more often. What is the selection pressure in this example?
Predation (the hawk)
True or False: All traits are adaptations. Explain your reasoning
False. Only traits that improve survival and reproduction in a specific environment are adaptations.
In a population of insects, some are green and some are brown. Birds eat the green ones more often. Which are more likely to survive? Use survival of the fittest in your answer.
The brown insects - they blend in better, so they are less likely to get eaten. They will survive and reproduce with offspring having the same adaptation.
Based on the table below, what would you predict the bird population will be in year 6?
Year Population Size
1 500
2 510
3 520
4 530
5 540
The population increases by about 10 each year, so in Year 6, we would predict the population will be 550.
What is trait variation and why is it important?
Differences in traits within a population; it helps with survival and adaptation
A sudden drought causes most shallow-rooted plants to die. What trait is now favored, and what is the selection pressure?
Deep roots are favored; drought is the selection pressure
Some bacteria have become resistant to hand sanitizer. Why is this considered an adaptation?
The resistance helps them survive
In a population of rabbits, the fastest rabbits escape predators more often.
Over time, what will happen to the speed trait in the population?
The trait for speed will likely increase over generations, as faster rabbits survive and reproduce.
A species of birds shows an increase in average beak size over 6 generations due to increased seed size. Predict what you think the missing beak size would be.
Generation Average Beak Size (mm)
1 10
2 11
3
4 19
5 27
12-18 mm because the trend of beak size goes up
Give an example of how two individuals of the same species can have different traits. (you can not use rats, hawksbeard, or juncos)
Example: Rock mice that are tan and black but the same species
Farmers spray a pesticide that kills 90% of insects. Over time, more insects are resistant. What caused the population to change?
The pesticide acted as a selection pressure favoring resistant insects.
Scenario: Owls have large eyes and silent flight. How are these adaptations?
Large eyes help them see in the dark, and silent flight helps them sneak up on prey
Why does reproduction matter when talking about survival of the fittest?
Survival alone is not enough. The "fittest" also have to pass their traits to the next generation.
Here’s the data for the frequency of a genetic trait in a population over 4 generations. Predict the frequency of this trait in generation 5.
Generation Trait Frequency
1 25%
2 36%
3 38%
4 42%
Answer: A reasonable number over 42%
Imagine a population with no trait variation. What would happen if the environment changed suddenly?
The entire population could be wiped out - no individuals would have traits that could survive
You are studying fish in a stream. Some have spots that blend in with the pebbles, others do not. Birds eat the unspotted ones more often.
What is the selection pressure, and which variation is likely to increase over time?
Bird predation is the selection pressure; fish with spots are more likely to survive and reproduce.
Some fish that live in dark caves are blind. Why is losing eyesight considered an adaption in this case?
Because eyesight is unnecessary in total darkness, and not developing eyes saves energy.
A drought causes plants with shallow roots to die. Some plants with deep roots survive and produce seeds.
What does this show about survival of the fittest?
The drought selected for deep-rooted plants — they were the “fittest” for the new environment.
The table below shows the number of large and small-beaked birds in a population across several generations. What could be inferred about the population?
Generation Large Beaks Small Beaks
1 200 100
2 231 94
3 256 71
4 287 46
5 303 25
The population of birds with larger beaks is increasing, possibly because larger beaks are more suited for accessing food sources, making the larger-beaked birds more fit.