PREDATOR PREY WORKSHEET

Name ______

How do Predator and Prey Populations Change?

The sizes of predator and prey populations can change with the seasons. Biologists sometimes need to know the sizes of certain predator and prey populations. They can sample the population by trapping and/or counting the animals. The results of samplings change as the populations change.

The James Hyde farm has not had people living on it since June of 1974. An interstate highway was put through the middle of the farm. Now there are only 100 acres of land left on this farm. In April of 1982, two biologists wanted to find out how the fox and rabbit populations were changing on the abandoned farm. They counted rabbits by trapping and releasing them. They counted foxes by looking for them with field glasses because the foxes would not go near the traps. The biologists trapped and released 23 rabbits and saw two foxes.

I.Sampling a Population

  1. Put 92 brown beans and 8 white beans into the paper bag. Assume brown beans are rabbits and white beans are foxes. These beans will represent the numbers in the actual population of rabbits and foxes.
  2. Shake the beans in the bag. Pick a bean without looking. Put a tally mark in the table in the correct column.
  3. Return the bean to the bag. Repeat the previous step, returning the bean each time after you record the results in the table. Pick a total of 25 beans (25% of the population). Total your results in the table.

Date / Rabbits (brown beans / Foxes (white beans)
April 1982 / Tallies / Total / Tallies / Total
  1. Recording Changes in Populations
  1. Examine the table below. It explains how to change your numbers of beans to show how the rabbit and fox populations changed at later dates.

Population Changes

Sampling Date / Rabbit Population / Fox Population
October 1982 / Remove 10 rabbits. Winter was harsh and food was low. Many rabbits died. / Add 2 foxes. Foxes ate pheasants. Fox numbers increased.
October 1983 / Add 15 rabbits. Food was plentiful. More rabbits moved into the area. / Add 2 foxes. Foxes had larger litters than usual.
April 1984 / Remove 8 rabbits. Many rabbits died from disease. / Remove 3 foxes. Food was low. Some foxes left the area.
October 1984 / Add 12 rabbits. Spring came early. Rabbits could breed earlier. / Remove 4 foxes. Rabbis were fewer from disease. Foxes decreased.
April 1985 / No change. / Add 8 foxes. Food was plentiful. Foxes moved into the area.
October 1985 / Remove 14 rabbits. Hunters killed pheasants. Foxes ate more rabbits. / Remove 2 foxes. Hunters shot some foxes.
  1. Using the table of population changes and the sampling method from the first section, sample the populations of rabbits ad foxes twice a year (nine times) to fill in the data below.
  2. Compare the dates in the two tables. For each date in the sampling data table, sample 25 times. Make marks to fill in the totals of rabbits and foxes.
  3. When you come to a date in the Population Changes table that indicates a change in population size, follow the directions as to adding or removing beans from the bag.

Date / Rabbits (brown beans / Foxes (white beans)
April 1982 (transfer data) / Tallies / Total / Tallies / Total
October 1982
April 1983
October 1983
April 1984
October 1984
April 1985
October 1985
April 1986
October 1986

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PREDATOR PREY WORKSHEET

IV.Questions

  1. How did your first sampling (April 1982) compare with those of the two biologists in April 1982? ______
  2. What are limiting factors? ______
  3. Give three factors that caused a decrease in the rabbit population.

a. ______b. ______c. ______

  1. Give two factors that caused an increase in the rabbit population.

a. ______b. ______c. ______

  1. Give three factors that caused a decrease in the fox population.

a. ______b. ______c. ______

  1. Give three factors that caused an increase in the fox population.

a. ______b. ______c. ______

  1. Which limiting factors are density independent factors? ______
  2. Which limiting factors are density dependent factors? ______
  3. How would the presence of pheasants affect the fox population? ______
  4. What will happen to the rabbits when there is a decrease in the pheasant population? Why? ______
  5. Predict what would happen to the rabbit population if the foxes disappeared. ______

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