Carrying Capacity: How Many Squirrels Can an Oak Forest Support?

Name ______Date ______Pd______

Carrying Capacity: How Many Squirrels Can an Oak Forest Support?

Objective:

To develop an understanding of the concept of carrying capacity in relation to a particular ecosystem

Background:

An ecosystem can be as small as a drop of water or as large as the entire Earth. The productivity of an ecosystem limits its carrying capacity, that is, the mass of living organisms that the ecosystem can support. The carrying capacity can be applied to any life form and to any part of the biosphere, such as the number of squirrels that can be supported by an oak forest.

Ecologists use the term carrying capacity to define the maximum population of a particular species that a given area of habitat can support over a given period of time. The ecological principles that govern a habitat’s carrying capacity are the same for all species. A sustainable supply of resources-including nutrients, energy, and living space-defines the carrying capacity for a particular population in a particular environmental system.

Acorns, produced by oak trees, are a favorite food for squirrels, as well as for deer, jays, quail, crows, woodpeckers, raccoons, rabbits, and foxes. In areas with mild winters, acorns may be available for 8 months of the year and constitute about 80-90% of the diet of squirrel. Acorns are higher in fat and easily-digested carbohydrates than other food sources, such as leaves, twigs, small green plants, and fungi.

In this activity, you will create a model of an oak forest and estimate the number of squirrels that can be supported by the forest.

PROCEDURE:

A. Use the acorn production chart to create a graph to show diameter of tree vs. acorn production for all 5 types of trees. (Use Excel)

Paste your graph here:

Use your graph to answer the following questions:

1. If you wanted to have the fewest trees possible, but highest total yield of acorns what type of Oak trees would you want in the forest? Explain.

2. Does a larger diameter trunk always mean greater acorn production? Explain. Provide evidence from the graph.

B. Use the scale model of the oak forest below:

Figure out the total annual average kilograms of acorns in the forest for your type of Oak tree.

(Black Oak, Chestnut Oak, Northern Red Oak, Scarlet Oak, White Oak)

Average Kilograms of Acorns:

C. Calculate the food energy in one average annual acorn crop. One kilogram of acorns produces approximately 4,500 kcal of food energy.

D. It takes about 137 kcal each day to support an average-sized gray squirrel (weight 0.5 kg). Calculate how many squirrels this forest can support for one year (365 days).

E. Report your group data to the class data table- up front

F. Create an Excel Graph from class data of the various tree species vs. squirrel carrying capacity. Then answer the follow up questions

Post Lab questions:

1.  Define carrying capacity? What factors affect it?

2.  Use the class data graph to determine which Oak tree species achieved the greatest carrying capacity.

3.  Would it be fair to predict that the carrying capacity is actually less than what you calculated? Explain why.

4.  Is the carrying capacity greater with many small trees or a few larger ones?

5.  As much as 25% to 50% of the diet of the black bear, raccoon, white-tailed deer, and wild turkey is made up of acorns. What would happen to the carrying capacity of your plot if any of these animals were present?

6.  Assume the population of squirrels in the forest has been stable for some time. A fire in the nearby hills occurs and the squirrels from that area move into your forest. Describe what will happen to the population of squirrels. Sketch a graph of time versus the number of squirrels. Indicate on the graph when the fire occurred.

7.  Suppose that hawks catch and eat the squirrels that live in this forest. How would you calculate the carrying capacity of hawks for this forest?

8.  Can you think of anything with this lab that might lead to inaccurate results?

9.  5. If there are ______kcal of energy in one 0.5 kg gray squirrel, then what is the approximate percent of transfer of energy from the acorn crop to squirrel?

6.

1.  8. What is another problem with the accuracy of this lab?

2.  9. Write one food chain for this forest. Is this food chain fairly typical?