Cavern Life Lesson 3: The Food Web

Objectives

Students will learn to:

  • Understand the importance of each element in a food web.
  • Realize that without light there can be no life.

Background Information

Due to the isolated nature of a cavern system, food sources are limited. Animals who live in the entrance zone are not permanent inhabitants and leave the cavern to acquire food. Those living in the twilight zone may leave the cavern as well, or they may rely on food sources within the cavern. The animals living in the dark zone must rely completely on food sources already in the cavern, or on those brought in.

Due to lack of light in the dark zone, no plant life can grow. However, bacteria, mold and fungus may grow from organic material. The web begins with small organic materials that may be washed in through underground streams, come from the surface through sinkholes, travel by air currents, or fall off troglophiles. Another source of organic material is from animal droppings and dead animals. Bat guano is an important contributing food source.

It is important to understand that even though light does not reach the dark zone, life would not be able to exist there without food sources that began with light. The organic material that makes its way into the dark zone originated on the surface where there is light. Without light plant life cannot grow. Plants break down to organic material that is brought into the cavern. Animal droppings also are produced from organic material, so again, without light there would be no animal droppings. Without any of these food sources that originate on the surface with light, life in the dark zone (or anywhere else on earth) would not be possible.

In the dark zone, small insects and protozoa feed off the bacteria and fungi that grow from the organic material. Small, water-dwelling animals may eat organic material floating on the water surface. Larger animals then eat the smaller animals. Their droppings provide the nutrients for more bacteria & fungi to grow and the web is then complete.

Since the food supply is limited and does not have much variety, the animals that can sustain life in a cavern are also limited. The balance of nature in the cavern food chain is very fragile, as are the animals that live there. If one element in the web is effected, it causes a chain reaction that eventually effects every living thing in the cavern.

A sample cavern system FOOD WEB is shown here:

FoodWeb

Experiments & Activities

Grades K – 4 “Without Light There is No Life”

Materials

  • two medium-sized jars
  • potting soil
  • two bean seeds
  • medium-sized box

Procedure

Plant a seed in each jar (use the same kind for each). Put one near a window and cover the other with a box that will not allow light in. Water them both at the same time on a regular basis. Over time, see how the seed receiving light grows into a plant and the one under the box does not. Maybe the one under the box will become moldy. This is what happens in a cavern.

Grades K – 4 “Food Web Game”

The game listed under Grades 5 – 8 can also be used for younger grades. It may be useful to explain a simple food chain first using familiar elements such as:
light – grass – cow (hamburger) – person

When doing the cavern food web game, using pictures instead of the names may be more appropriate for younger students.

Grades 5 – 8 “Food Web Game”

Materials

  • large card (3″ x 6″) for each student
  • ball of yarn

Procedure

Write the name of an element of the food web on each card. If you have used up all the names and have cards left over, either repeat some names, or if enough are left over, create a second set and divide students into two groups.

Have students form a circle (or two) and give each a card. (Do not put cards in a logical order.) Starting with an organic material person, have them hold the beginning of the yarn then pass it to the next element of the food web until everyone is included.

Let them see how they are all interconnected to form a “web.”

Choose an element to eliminate from the web. Have that person drop their section of the yarn and step back. The people who had hold of the other sides now have a slack string on one side. They then drop their section and step back. This continues until the last person drops the yarn. This shows how all the elements are dependant on all the others even if not directly, and the importance of maintaining a healthy food web.

You may want to try it several times, each time choosing a different element to eliminate, to show that it doesn’t matter where the problem starts, everyone is still effected.

Grades 9 – 12

Choose a specific cavern animal and do a report listing such information as the category in which it fits, the area of the cavern it is located, the zone it stays in, what it eats, and how it contributes to the cavern community.