Limiting Factors and an Eagle Population

With unlimited resources and ideal environmental conditions, a population would increase in size indefinitely. This rarely happens, however, because of limiting factors. A limiting factor is anything that keeps a population from growing unchecked for example the amount of available food, climate changes, or habitat changes. Limiting factors may be abiotic or biotic factors. Carrying Capacity is the maximum number of individuals of the same species an ecosystem can hold. If a population goes over carrying capacity, limiting factors should cause it to decrease and drop back to or below carrying capacity. In this investigation, you will simulate a simplified model of the effects of some limiting factors on a bald eagle population and you will determine how carrying capacity for the eagles is affected.

Objectives:

  • Understand what factors can affect population size and growth.
  • Hypothesize how competition affects a bald eagle population.

Materials:

  • LakeGrid• Rulers
  • Male an Female Eagle Pieces• 150 Rice Grains

Procedure:

Scenario A: The lake under “normal” conditions.

► Eagles mate for life.

► Only one pair occupies, defends, and hunts a well-defined territory.

  1. Lay out your lake grid on your table.
  2. Count out 150 grains of rice.

→ The rice represents fish in the lake.

  1. Evenly scatter the rice grains over the lake.

→ Be careful not to lose any “fish” throughout the lab or your data will be off.

  1. To simulate your eagles hunting for fish, hold an eagle approximately 20cm above the lake and drop it on the lake.

→ If the eagle lands on any fish, even a part of a fish, it has captured that fish. (See Figure 2.)

  1. Remove the fish the eagle caught and repeat the procedure with the other eagle.
  2. Remove the fish the female eagle caughtand rescatter the remaining rice to represent the fish swimming around the lake.

→Once a fish has been caught, it cannot be returned to the lake until the next scenario.

  1. Each eagle hunts twice a day. Repeat steps 4, 5 and 6.
  2. Total the number of fish caught by the eagles for all 4 drops on Day 1 and record on Table 1.

→ Each eagle must catch 9 fish in any 3 day period to survive. This means two eagles must catch 18 fish in any 3 day period for both of them to survive. Extra fish may be shared with the other eagle.

  1. Repeat the steps above for days 2-10. Remember that each eagle gets to hunt 2 times each day.
  2. After each day, look back at the previous 3 days and calculate whether one or both eagles have survived following the rules in step 8.

→ If only one survives, continue to hunt with one eagle.

Scenario B:The lake with 2 Ospreys hunting each day.

  1. Rescatter all 150 rice grains (fish) on the lake.
  2. Repeat the procedure from Scenario A, but remove an additional 6 fish from the lake each day and place in a separate pile.

→ These represent the fish the Ospreys would catch.

  1. Record your data under Scenario B in Table 1.

→ Be sure you don’t include the Osprey caught fish with your eagle data.

Scenario C:The lake during drought.

► The water level of the lake has dropped.

► ¼ of the fish population has died.

  1. Rescatter only 112 (or remove 38) rice grains (fish) on the lake.
  2. Repeat the procedure from Scenario A.
  3. Record your data under Scenario C in Table 1.

Scenario D: The lake polluted with phosphates.

► Phosphate pollution has caused algae in the lake to grow out of control.

► The algae decreases the amount of dissolved oxygen in the lake.

► ¾ of the fish population has died.

  1. Rescatter only 38 rice grains (fish) on the lake.
  2. Repeat the procedure from Scenario A.
  3. Record your data under Scenario E in Table 1.

ScenarioE:The eagles have offspring.

► The eagles now have 2 offspring.

► Adults have to catch 2 extra fish to survive.

  1. Rescatter all 150 rice grains (fish) on the lake.
  2. Repeat the procedure from Scenario A.

→ Each eagle must catch 11 fish in any 3 day period to survive, or 22 fish between the 2 of them.

  1. Record your data under Scenario D in Table 1.

Scenario F:The lake during spring when fish are spawning.

  1. Pair up with another group to have a total of 300 rice grain (fish).
  2. Rescatter all 300 rice grains (fish) on the lake.
  3. Repeat the procedure from Scenario A.

→ The two pairs only need to repeat the procedure once for the entire group.

  1. Record your data under Scenario F in Table 1.
  • After collecting all the data and filling in the data table:

1)Return all supplies.

2)Complete a line graph to represent the data in the table.

3)Answer the Analysis questions below in complete sentences.

Analysis:

  1. How does eagle predation affect the fish population over time?
  2. What effect, if any, might a small decrease in the fish population have on the eagle population?
  3. Ospreys and eagles compete for food. What effect, if any, might the competition have on the eagle population?
  4. Explain how a climate change might or might not indirectly affect the eagle population.
  5. What effect, if any, does an increase in the fish population have in the eagle population?
  6. Explain how phosphate pollution in a lake can indirectly affect the eagle population.
  7. How does an increase in the eagle population affect the fish population?

Eagle and Fish Lab

Purpose: To understand how environmental conditions and limiting factors can affect populations.

Hypothesis:

Pre-Lab questions:

1. What is carrying capacity?

2. Give an example of a limiting factor for an eagle population.

Procedure: Follow procedure steps 1-10 for scenarios A-F on the lab handout. Be sure to keep track of the difference in fish for each scenario. Record your data in Table 1.

Eagle and Fish Lab

Purpose: To understand how environmental conditions and limiting factors can affect populations.

Hypothesis:

Pre-Lab questions:

1. What is carrying capacity?

2. Give an example of a limiting factor for an eagle population.

Procedure: Follow procedure steps 1-10 for scenarios A-F on the lab handout. Be sure to keep track of the difference in fish for each scenario. Record your data in Table 1.

Eagle and Fish Lab

Purpose: To understand how environmental conditions and limiting factors can affect populations.

Hypothesis:

Pre-Lab questions:

1. What is carrying capacity?

2. Give an example of a limiting factor for an eagle population.

Procedure: Follow procedure steps 1-10 for scenarios A-F on the lab handout. Be sure to keep track of the difference in fish for each scenario. Record your data in Table 1.