Objective: Understand How Populations Change over Time

Objective: Understand How Populations Change over TimeKey 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.

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 TimeKey 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

Number of Wolves 10 12 16 22 28 24 21 18 19 19

• 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.


c. Conclusion• Compare your hypothesis to your data graph.

• How did the deer and wolf populations change over time?

Deer and Wolf Populations from 1971 to 1980

• Deer and wolf populations first increased, then decreased, and then became stable.


d. Discussion1. Once the wolves were introduced, what is the carrying capacity for deer and wolves in the ecosystem?

2. What do you think would have happened to the deer on the island had wolves NOT been introduced?


• Deer’s carrying capacity is_______. Wolf’s carrying capacity is ________

• 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.


d. Discussion3. What limiting factors affect deer population?

4. What limiting factors affect wolf population?


• Water, food, shelter, predators, diseases, hunters, and climate.

• Water, food, shelter, diseases, hunters, and climate.


d. Discussion5. 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.


More wolves

Less wolves

More deerLess deerDeer and wolf

populations depend on each other.

d. Discussion8. Would you agree or disagree with the following statement. “Predators and prey populations exist in a balance” Explain.


• Agree, because…• Or disagree, because…


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.


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.


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 _______________________________

• 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

solar energy into chemical energy ______________________________________________

photosynthesis

autotrophic nutrition

chloroplasts


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.


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.


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


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–decomposerc. 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

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.

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.


Objective: Understand How Populations Change over Time

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