Animals spend much of their time looking for and consuming food. Many meat-eating animals obtain their meat by hunting other animals. The hunters are known as predators and the hunted animals are known as prey. Owls, being excellent hunters, eat many different kinds of animals, including rabbits, squirrels, rats, mice, shrews, birds, fish and insects. In this exercise, the owls will be hunting for mice!
Materials:
Masking tape, meter stick, scissors, 400 mice squares and 1 owl rectangle
Procedure:
Each team should cut out 400 mice squares and 1 owl rectangle. Using masking tape, mark off a square approximately 50 cm on a side on your lab table. This square represents Hoot Woods where the mice and owls live.
Distribute three mice in the field and toss the owl once in an effort to catch a mouse (mice). In order to survive, each owl must catch at least three mice in every generation. If it doesn't, it will starve. For every three mice that an owl catches, it produced one offspring. In each generation, the surviving mouse population will double to form the next generation. (For example: if six mice are living in the woods and two are caught by an owl, then four mice will survive. Each of these four mice will produce one offspring, bringing the total of mice in the next generation to eight.) At the beginning of each generation there must be at least three mice and one owl in the woods. If the populations drop below these numbers, new mice and owls will migrate in. For example, if just one mouse survives the first generation, just one offspring will be produced, for a total of two mice and one mouse must migrate in to bring the mice total to three. If all the owls die, one owl must migrate it.
As the number of owls increases, throw the owl square once for each owl.
Remove and count the number of mice caught by each owl at each drop. Keep all the mice from each owl catch in separate stacks and record your data in the chart provided.
Before you proceed - answer the following questions based on these results. Suppose a generation begins with 20 mice and 2 owls. The first owl captures 7 mice and the second owl captures only 2 mice.
What is total number of mice caught?
How many mice are left?
How many mice will the next generation of mice begin with? Explain.
How many offspring does the first owl produce?
What happens to the second owl?
Follow this procedure for 25 generations. Always place mice randomly in the woods.
|
Generation |
# mice at start* |
# owls at start** |
# mice caught |
# owls starved |
# surviving mice + offspring |
# surviving owls + offspring |
|
1 |
3 |
1 |
||||
*There must always be at least three mice at the start; if necessary, have mice migrate in.
**There must always be at least one owl at the start; if necessary, have one owl migrate in.
Plot your data on population size on graph paper. Put the data for owls and mice populations on the same graph. Let the X axis represent the Generation Number.
What is a good title for this graph?
What should the Y axis represent?
How can you distinguish the owls from the mice on your graph?
Follow-Up:
Define the following terms:
Food chain
Population
immigration
predator
prey
carrying capacity
Draw the food chain shown in this exercise. Identify the producer, first-order and second order consumers. (See P. 828 in your text.)
Describe the pattern of the fluctuations in the sizes of the two populations.
By looking only at the graph, can you tell which species is the prey and which is the predator? How can you tell?
Which species attains the greater number of individuals? Why?
How do your results support the Pyramid of Biomass? (See P. 830 in your text.)
What do you think would happen to the mouse population in Hoot Woods if the owls were all hunted to extinction? Explain.
The owl is a member of the Order Strigiformes and is considered a nocturnal bird of prey. What does nocturnal mean? Hawks are members of the Order Falconiformes and are known as raptors. They are diurnal. What does diurnal mean? Select either one of the orders of the birds of prey and describe how they are adapted for this mode of nutrition. * The following sites are excellent sources of information.
http://www.seaworld.org/birds/bird.html
*Why not do both for extra credit?
The two graphs below show density changes of the same prey species. In graph A there are no predators on the prey population. In graph B predators are present. Study the two graphs and then answer the questions.
See graph on your sheets and answer the following questions:.
· What is happening to the prey populations in each graph? Explain.
· Which prey population is more stable and why?
· Using a dotted line, draw in the curve for the predator population in graph B.
· Using a heavy solid line, draw in you prediction of the curve for the prey population in Graph A if predators were introduced at time X.
· Why should most predators be praised, not scorned?
How doth the little crocodile
Improve his shining tail,
And pour the waters of the Nile
On every golden scale!
How cheerfully he seems to grin,
How nearly spreads his claws,
And welcomes little fishes in
With gently smiling jaws.
Lewis Carroll
10. In 1624, the poet John Donne wrote, "No man is an island, entire of itself; every man is a piece of the continent, a part of the main." This is one of the main concepts on ecology. How does this exercise demonstrate this concept?
