Objective: Understand How Populations Change over Time
Key Words: Resources, Limiting Factors, Carrying Capacity
How Does Deer Population Grow Overtime?
Do Now
• List 2 things you learned about how the a population change over time.
or
• Explain what limiting factors and carrying capacity are. Examples.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Scenario #2
•In 1970 the deer population of an island forest reserve about 518 square kilometers in size
was about 2000 animals. Although the island had excellent vegetation for feeding, the food
supply obviously had limits. Thus the forest management personnel feared that overgrazing
might lead to mass starvation. Since the area was too remote for hunters, the wildlife
service decided to bring in natural predators to control the deer population. It was hoped
that natural predation would keep the deer population from becoming too large and also
increase the deer quality (or health), as predators often eliminate the weaker members of
the herd. In 1971, ten wolves were flown into the island.
a. Make a Hypothesis
•
Predict how the deer population will change over the years.
• Give a rationale of your prediction.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
b. Results of the program.
• The results of this program are shown in the following table.
Data Table
Trials (years)
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
Number of Deer
2,000
2,300
2,500
2,360
2,224
2,094
1,968
1,916
1,952
1,972
10
12
16
22
28
24
21
18
19
19
Number of Wolves
• Graph the deer and wolf populations on the graph below in a graph line. Use one color to
show deer populations and another color to show wolf populations.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Deer and Wolf Populations from 1971 to 1980
c. Conclusion
• Compare your hypothesis to your data graph.
• How did the deer and wolf populations change over time?
• Deer and wolf populations first increased, then decreased, and then became stable.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Deer and Wolf Populations from 1971 to 1980
d. Discussion
1. Once the wolves were introduced, what is the carrying capacity for deer and wolves in the
ecosystem?
• Deer’s carrying capacity is_______. Wolf’s carrying capacity is ________
2. What do you think would have happened to the deer on the island had wolves NOT been
introduced?
• Initially, deer’s population would increase because there would be no predators .
Then, deer’s population would decrease, because deer would have used up all of the
resources and then starve to death.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Deer and Wolf Populations from 1971 to 1980
d. Discussion
3. What limiting factors affect deer population?
• Water, food, shelter, predators, diseases, hunters, and climate.
4. What limiting factors affect wolf population?
• Water, food, shelter, diseases, hunters, and climate.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Deer and Wolf Populations from 1971 to 1980
Less wolves
Deer and wolf
Less deer populations More deer
depend on
each other.
More wolves
d. Discussion
5. How would you describe the relationship between a deer and wolf population sharing an
ecosystem? What patterns do you see in both populations?
• Deer and wolf populations depend on each other.
• Both show the same pattern: increase and decrease, then become stable.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Deer and Wolf Populations from 1971 to 1980
d. Discussion
8. Would you agree or disagree with the following statement. “Predators and prey populations
exist in a balance” Explain.
• Agree, because…
• Or disagree, because…
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Deer and Wolf Populations from 1971 to 1980
d. Discussion
9. In summary, what the advantages of having a population of predators and preys in an
ecosystem.
• It increases biodiversity and makes the ecosystem more stable.
• Predators keep the deer population from becoming too large and prevent mass starvation.
• Predators increase the deer health, as predators often eliminate the weaker members of the
herd.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
Regents Questions
The article below was written in response to an article entitled "Let all predators become
extinct."
Predators Contribute to a Stable Ecosystem
In nature, energy flows in only one direction. Transfer of energy must occur in an ecosystem
because all life needs energy to live, and only certain organisms can change solar energy into
chemical energy.
Producers are eaten by consumers that are, in turn, eaten by other consumers. Stable
ecosystems must contain predators to help control the populations of consumers.
Since ecosystems contain many predators, exterminating predators would require a massive
effort that would wipe out predatory species from barnacles to blue whales. Without the
population control provided by predators, some organisms would soon overpopulate.
1. Draw an energy pyramid that illustrates the information underlined in the second paragraph.
Include three different, specific organisms in the energy pyramid.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
The article below was written in response to an article entitled "Let all predators become extinct."
Predators Contribute to a Stable Ecosystem
In nature, energy flows in only one direction. Transfer of energy must occur in an ecosystem because all life needs energy
to live, and only certain organisms can change solar energy into chemical energy.
Producers are eaten by consumers that are, in turn, eaten by other consumers. Stable ecosystems must contain predators
to help control the populations of consumers.
Since ecosystems contain many predators, exterminating predators would require a massive effort that would wipe out
predatory species from barnacles to blue whales. Without the population control provided by predators, some organisms
would soon overpopulate.
2. Explain the phrase "only certain organisms can change solar energy into chemical energy," in
the underlined portion of the first paragraph. In your answer be sure to identify:
• the type of nutrition carried out by these organisms _______________________________
autotrophic nutrition
photosynthesis
• the process being carried out in this type of nutrition ______________________________
• the organelles present in the cells of these organisms that are directly involved in changing
chloroplasts
solar energy into chemical energy ______________________________________________
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
3. Some people claim that certain carnivores should be destroyed because they kill beneficial
animals. Explain why these carnivores should be protected.
Your answer must include information concerning prey population growth, extinction, and the
importance of carnivores in an ecosystem.
• Carnivores (reduce/enlarge) the prey population, so prey organisms do not over-eat
their food.
• If carnivores were killed, then prey population would (decrease/increase), and
(have/not have) food, so the prey species would become extinct.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
4. Explain why an ecosystem with a variety of predator species might be more stable over a long
period of time than an ecosystem with only one predator species.
• The more variety of predators, the more biodiversity, the more complex the food web
is, the more stable the ecosystem is.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
5. In certain areas of the United States, the populations of wolves and other predators have
decreased. As a result, deer populations in these areas have increased.
Describe one way that an increase in the deer population can be harmful to humans.
•They transmit diseases to humans, i.e. Lyme disease.
•They cause automobile accidents
•They eat crops
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
The graph shows interactions of moose and wolf populations on Isle Royale.
6. What is the relationship between a wolf and a moose?
a. wolf–prey; moose–predator
b. wolf–predator; moose–decomposer
c. wolf–parasite; moose–host
c. wolf–predator; moose–prey
7. State one possible reason for the change in the moose population between 1995 and 1997.
• Diseases, habitat destruction, overhunting, starvation
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
8. Two species of microorganisms were placed in the same culture dish, which included basic
materials necessary for life. The size of each population increased during the first three days.
After one week, the population size of one species began to decline each day. State one possible
reason for this decline.
• Increased competition
• Predator-prey relationship between the two
species of microorganisms.
Objective: How a Predator-Prey Population Changes Over Time
Key Words: Natural Resources, Limiting Factors, Carrying Capacity
DO NOW
• What are the advantages of having a population of predators and preys in an
ecosystem.
• It increases biodiversity and makes the ecosystem more stable.
• Predators keep the deer population from becoming too large and prevent mass starvation.
• Predators increase the deer health, as predators often eliminate the weaker members of the
herd.