VOCABULARY
A group of the same type of organism living in the same area.
Population
A population has more births than deaths. What happens to its size?
The population increases.
True or False: Organisms need energy to reproduce. explain
True. Reproduction requires a lot of energy, and without it populations can decrease due to a lack of energy storage molecules.
Moon jellies eat zooplankton.
Which population is the resource population?
Zooplankton
Why might an ecologist use a sample instead of counting every moon jelly in the ocean?
It would be extremely difficult or impossible to count every individual, so scientists can collect evidence from a smaller portion of the population.
A population that eats organisms from another population.
Consumer population
A population has approximately the same number of births and deaths over time. What happens to the population?
The population remains stable.
How does an organism in a consumer population get energy storage molecules?
By eating organisms in its resource population.
Leatherback sea turtles eat moon jellies. If the leatherback sea turtle population increases, what will most likely happen to moon jelly deaths?
Moon jelly deaths will increase.
Scientists take a sample of only 10 fish from one tiny area of a huge lake. They use those 10 fish to make a claim about every fish in the lake.
What is the biggest problem with their evidence?
The sample may not accurately represent the entire population.
These are molecules organisms can use to release the energy they need to survive and reproduce.
Energy storage molecules
A population begins with 500 organisms. During the year, 75 organisms are born and 40 organisms die. What is the new population size?
535 organisms
500 + 75 - 40 = 535
A rabbit population has access to much more food than before.
Predict what will most likely happen to the number of rabbit births.
The number of births will increase.
More food provides more energy storage molecules, which means more energy is available for reproduction.
The zooplankton population increases dramatically.
Predict what will most likely happen to the moon jelly population.
The moon jelly population will likely increase.
More zooplankton means more energy storage molecules are available to moon jellies. This can increase reproduction and births.
Furbils and stingwings both eat weebugs.
What relationship exists between the furbils and stingwings?
They compete because both populations use weebugs as a resource.
Scientists cannot count every organism in a huge population, so they study a smaller group that represents the whole population.
Sample
(Daily Double) A mouse population has 120 births and 120 deaths during one year.
A student says, “The population didn’t change, so nothing happened in the population.”
Explain why the student is wrong.
Organisms were still being born and dying. The population remained stable because the number of births and deaths were equal.
The population of insects eaten by frogs suddenly decreases. No other part of the ecosystem changes.
Predict what will happen to frog reproduction.
Frog reproduction will likely decrease.
Frogs have fewer resource organisms available, so they have access to fewer energy storage molecules.
Lynx eat roe deer.
The lynx population suddenly decreases.
Predict what happens to:
A. Roe deer deaths
B. Roe deer population size
A. Roe deer deaths decrease.
B. The roe deer population increases.
Fewer lynx means fewer roe deer are eaten. This decreases roe deer deaths and can cause births to become greater than deaths.
Furbils and stingwings both eat weebugs.
The furbil population decreases.
What should happen to the weebug population first?
The weebug population should increase because fewer furbils are eating them.
Two different populations need the same limited resource. What type of interaction is occurring?
Competition
Scientists observe that a population is increasing, but the number of births has not changed.
What must have happened to the number of deaths?
Deaths decreased.
If births remained the same while deaths decreased, births would become greater than deaths and the population would increase.
Complete the cause-and-effect chain:
Resource population increases → __________ → __________ → Consumer population increases
Resource population increases → More energy storage molecules become available → Consumer reproduction/births increase → Consumer population increases
Consider this food chain:
Plants → Grasshoppers → Frogs
The grasshopper population suddenly decreases.
Predict what happens to BOTH the plant population and the frog population.
The plant population increases because fewer grasshoppers are eating the plants.
The frog population decreases because fewer grasshoppers are available as a resource.
(Daily Double)
Furbils and stingwings do not eat each other. However, both populations eat weebugs.
The furbil population decreases dramatically.
Explain how this could eventually cause the stingwing population to increase.
Furbils decrease → Fewer weebugs are eaten → Weebug population increases → More energy storage molecules are available to stingwings → Stingwing reproduction increases → Stingwing population increases.