Variation & Adaptation
What is Variation?
Differences in traits within a population
After a drought, only plants with deep roots survive. What process is occurring?
Answer: Natural selection
After the 2004 Indian Ocean Tsunami, many coastal fish populations initially dropped but later increased.
Question:
Why could fish populations increase after such a massive disaster?
Reduced human activity (fishing) + fewer predators/competition → faster recovery and population growth
If a flood wipes out plants, what happens first in the food chain?
Herbivores decrease
What is a natural disaster?
A sudden natural event that causes damage to the environment and affects living organisms
Why is variation important after a natural disaster?
Increases chance some individuals survive
Why are traits that help survival during disasters more likely to appear in future generations
Survivors reproduce and pass on advantageous traits
Following the Chernobyl disaster, scientists observed thriving wildlife despite radiation.
Question:
Why did animal populations increase even in a harmful environment?
Absence of humans reduced hunting, habitat destruction, and disturbance allowing populations to grow despite radiation risks
Why do predators decline after a disaster even if they survive initially?
Loss of prey
Name TWO natural disasters that can affect populations.
Any two: earthquakes, floods, droughts, volcanic eruptions, hurricanes, wildfires
A disease spreads after a disaster, but some individuals are unaffected. Why?
Genetic variation gives resistance
Explain how a disaster can both increase AND decrease the effectiveness of natural selection.
Increases it by strongly selecting traits, but decreases it if deaths are random rather than trait-based
After the Mount St. Helens eruption, many plant species disappeared, but some quickly returned.
Question:
What allowed certain plants to recover faster than others?
Adaptations like seed resistance, underground roots, or ability to grow in nutrient-rich ash
A coral reef is destroyed. Name one long-term food chain impact.
Loss of biodiversity / collapse of marine food webs
Why do populations usually decrease immediately after a natural disaster?
Death of organisms + destruction of habitat and resources
Explain why low variation makes a population more vulnerable to extinction after disasters.
Fewer traits = less chance of survival under new conditions
Why might genetic diversity decrease after a disaster, even though natural selection is occurring?
Many individuals die randomly, reducing variation (bottleneck effect)
After Hurricane Maria, researchers found lizards with stronger gripping ability survived better.
Question:
What type of selection occurred, and why?
Directional selection traits that improved survival (strong grip) became more common
Explain how removing one species after a disaster can cause a trophic cascade.
Changes ripple through the food chain, affecting multiple levels
A flood kills both strong and weak individuals randomly in a population.
Question:
Will this event strongly drive natural selection? Explain why or why not.
No because deaths are random, not based on traits. This is a bottleneck effect, not strong natural selection.
A disease spreads rapidly after flooding in a frog population. Most frogs die, but a small number survive due to a genetic resistance. Over time, the population recovers, but scientists notice the frogs are now genetically very similar.
Question:
Explain how variation helped the population survive, but also created a new risk for the future.
Variation allowed resistant individuals to survive, but the population now has low diversity, making it vulnerable to new diseases or environmental changes.
After a severe drought, a population of beetles drastically decreases. The surviving beetles all have thicker outer shells that reduce water loss. Over several generations, nearly all beetles in the population have this trait, but genetic studies show overall genetic diversity has dropped.
Question:
Explain how natural selection and the bottleneck effect worked together and why this could still be dangerous for the population long-term.
Natural selection favored thicker shells, but the bottleneck reduced genetic diversity. This makes the population less adaptable to future changes or new threats.
There was the 2018 Sulawesi earthquake and tsunami incident. Explain how this disaster could lead to long-term evolutionary change in affected species, AND give one reason why it might NOT result in significant evolution.
Explain how this disaster could lead to long-term evolutionary change in affected species, AND give one reason why it might NOT result in significant evolution.
A volcanic eruption covers a forest in ash, killing most plant life. In the following months, insect populations crash, followed by bird populations. However, after a few years, fast-growing plants begin to dominate the area instead of the original forest species.
Question:
Explain how this disaster caused both a collapse and a restructuring of the food chain.
Initial plant death caused a collapse of herbivores and predators. Later, new plant species changed the base of the food chain, leading to a different ecosystem structure.
After a volcanic eruption, a population survives but shows very low genetic variation. Over time, the population begins to increase again.
Question:
Why might this population still be at risk of extinction EVEN AFTER recovering in size? Give TWO reasons.