VPE 511: Environment and Environmental Hygiene (2+1)

Introduction

FOOD CHAIN

• The transfer of food energy from the source in plants through a series of organisms with repeated stages of eating and being eaten is known as the food chain. A food chain always starts with plant life and ends with an animal. Animals that eat only plants are called herbivores. Animals that eat other animals are called carnivores. For example, a simple food chain links the plant, the insect (that eat plant), and the frog (that eat the insect), and the snake (that eat the frog) and the eagle (that eat the snake).

• Why there are more herbivores than carnivores?
  • When a herbivore eats, only a fraction of the energy (that it gets from the plant food) becomes new body mass; the rest of the energy is lost as waste or used up ( by the herbivore as it moves). Likewise, when a carnivore eats another animal, only a portion of the energy from the animal food is stored in its tissues. In other words, organisms along a food chain pass on much less energy (in the form of body mass) than they receive.
• The further along the food chain you go, the less food ( and hence energy) remains available.
• The above pyramid-shaped food chain shows many trees & shrubs providing food and energy to giraffes. Note that as we go up, there are fewer giraffes than trees & shrubs and even fewer lions than giraffes.
• Most food chains have no more than four or five links. This is because the animals at the end of the chain would not get enough food (and hence energy ) to stay alive.
• Most animals are part of more than one food chain and eat more than one kind of food in order to meet their food and energy requirements.
• A change in the size of one population in a food chain will affect other populations. This interdependence of the populations within a food chain helps to maintain the balance of plant and animal populations within a community. For example, when there are too many giraffes; there will be insufficient trees and shrubs for all of them to eat. Many giraffes will starve and die. Less giraffe means less reproduction, less food is available for the lions to eat and some lions will starvae to death. When there are fewer lions, the giraffe population will increase.