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.
