Studying predator-prey relationships

Often when discussing extinction with students, I hear the idea that animals become endangered because of their natural predators.  And certainly when we look at footage of just how expertly adapted animals are to hunt their prey, it’s easy to think of predators as having a role to play in extinctions.

However, in natural ecosystems, predators and their prey exist in an equilibrium, with both populations going up and down at times.  To understand this, students did a simulation of tigers and deer living in a forest.

The deer were represented by yellow lentils, and the tigers were represented by a card square.  Their forest habitat was represented by an area of the table top.

Kamachi surveys a thriving deer population
Kamachi surveys a thriving deer population

Girls then had to throw their tiger into the forest.  If the tiger caught at least three deer (i.e. if the cardboard landed on 3 lentils) then the tiger could survive and reproduce, thereby increasing the tiger population, and the game would continue with more tigers.  If the tiger failed to catch three deer, then he or she would die, and a new tiger would enter the forest next year, and the deer population would continue to grow.

Recording the numbers of deer caught by the tigers.
Recording the numbers of deer caught by the tigers.
Selcia, Vaishnavi and Usharani work on the simulation
Selcia, Vaishnavi and Usharani work on the simulation

Girls continued this for several “generations” and observed how the populations of tiger and deer changed and held each other to a certain equilibrium.  The following lesson, they plotted data in a graph and were able to see the pattern more clearly.

Afsana's graph shows how tiger and deer populations oscillate around an equilibrium
Afsana’s graph shows how tiger and deer populations oscillate around an equilibrium (deer are plotted in green, and tigers in blue).

This activity was challenging for the girls, but helped them to perceive how a natural ecosystem can be balanced and successful.

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