Examples
Grass--grasshopper--frog--snake--Hawk
Grass--Rabbit--Fox--Wolf
Grass--Goat--Man
organisms by putting arrows and make a food chain.
Name the producer and consumers in the above food chain.
Try to guess what does the arrows marked by you indicate?
Identify at least four other food chains in your surroundings. Name
the producers and different levels of consumers in those food chains.
While identifying different food chains in your surroundings you will
find that most of the food chains are quite short and they rarely consists
of not more than four steps. You will also notice that as we move from
producer to consumers (primary, secondary & tertiary) in a food chain the
numbers of organisms at each level decreases.
What type of relationships exist among the biotic components? In an ecosystem the energy rich food passes from producers to consumers stepwise, with respect to their (food) relationships
Why do most of the food chains consist of four steps?
Why do the number of organisms get decreased as we move form producer to different level of consumers?
To get answers for the above question we have to recall some of the things which have been discussed in the earlier classes. In chapter 7 “Different Ecosystems” of class 8th it was mentioned that all organisms in an ecosystem derive energy from food to live and sunlight is the main source of the energy. Food chain shows that how the energy is passed from one organism to another. At each transfer a large proportion (80 to 90 percent) of energy is dissipated as heat produced during the process of respiration and other reactions. After three steps in a food chain, very little energy is still available for top carnivores to use.
Within the biosphere there are a number of major ecosystems. The terrestrial ecosystems are determined largely by the variations in climatic conditions between the Poles and Equator. In a similar way, if you climb a mountain such as Kilimanjaro in Equatorial Africa or Himalayan mountains in our country. You quickly go through a comparable system of ecosystems.