Births & Deaths
What are the two things that always affect the size of a population?
Births and deaths are always happening.
Name one life process that requires energy (living is NOT an example of a life process).
Life processes like moving, growing, reproducing, breathing, and digesting food.
If there are suddenly more wolves in an area, what will most likely happen to the deer population?
The prey population decreases.
What does it mean if two populations compete in a food web?
They rely on the same resource population for energy.
plankton → shrimp → whales
The plankton population decreases. What happens to the shrimp population?
The shrimp population decreases because there is less food available.
Why is this statement incorrect? “All populations in a food web increase together.” “If one population changes, every population decreases.”
Different populations can increase or decrease depending on food web relationships.
If rabbits in a forest are reproducing faster than they are dying, what happens to the rabbit population?
The population increases.
Use one science vocab word in your answer: how do animals get the energy they need to survive?
From eating their resource population (prey).
If the owl population drops, what will most likely happen to the mouse population?
The prey population increases.
fish → bears
fish → eagles
What are the bears and eagles doing in this food web?
They are competing for the same resource population (fish).
Create a food chain with:
Answers will vary. Example: grass → rabbit → fox
What does a stable population mean?
Births and deaths are equal.
A fish population is shrinking over time. What must be true about births and deaths?
There must be more deaths than births.
Why might a deer population grow if more plants become available?
More food provides more energy for organisms to survive and reproduce.
grass → mice → snakes
The snake population increases. What happens to the mouse population?
The mouse population decreases because more snakes eat more mice.
grass → rabbits → foxes
grass → deer → wolves
If the deer population increases, what will most likely happen to the rabbit population? Explain.
The rabbit population will decrease because the larger deer population will use more grass, leaving less energy available for rabbits.
Create a food web that shows competition between two predators.
Answers will vary.
Example: fish → bears
fish → eagles
Why do predators affect prey populations?
Predators eat prey, increasing deaths in the prey population.
A squirrel population stayed stable for 50 years. What must be true?
The number of births and deaths stayed about the same.
What are energy storage molecules?
Molecules organisms get from food that provide energy.
worms → pigs → tigers
The tiger population increases. What happens to the worm population?
The worm population increases because fewer pigs will eat the worms.
berries → mice → owls
berries → squirrels → hawks
If the squirrel population decreases, what will most likely happen to the mouse population? Explain.
The mouse population will increase because fewer squirrels are competing for berries, leaving more food available for mice.
clams → sea otters → sharks
clams → sea stars
The shark population increases. What happens to the sea star population?
The sea star population increases because fewer sea otters eat clams, leaving more clams for sea stars.
Why do resource populations affect consumer populations?
Consumers rely on resources for energy.
Why is this statement wrong? “Populations always increase because animals reproduce.”
Animals also die, so population size depends on births compared to deaths.
True or False: If a population has less energy available, births may decrease.
True.
frogs → snakes
The snake population decreases. Explain what happens to the frog population AND why.
The frog population increases because fewer frogs are being eaten.
What is an indirect effect in a food web?
An indirect effect happens when a change in one population causes changes in another population that it does not directly interact with.
frogs → ducks → owls
frogs → ducks → raccoons
The raccoon population decreases. Explain what happens to BOTH the duck and frog populations.
Duck population increases because fewer ducks are eaten. Frog population decreases because more ducks eat more frogs.
Explain this chain reaction: A predator decreases → prey increases → prey’s food decreases.
Fewer predators means fewer prey are eaten, so prey increase. The larger prey population eats more of its food source, causing that population to decrease.