Chapter 4, Problem 1RQ

To determine

The reason for more often use of term food web instead of the food chain for species in a community.

Answer to Problem 1RQ

In the food chain, each level consists of single species whereas in food web several species occupy a single level. That is the reason that food web is commonly used in place of the food chain.

Explanation of Solution

Pictorial representation: Fig.1 represents a food web. Fig.2 represents food chain.

Fig.1: Food web

Fig.2: Food chain.

In an ecosystem, plants are primary producer which perform photosynthesis. Herbivorous animals feed on plants and they are called primary consumers. Carnivorous feed on herbivorous animals and called secondary consumers. Top carnivores feed on secondary consumers so they are called tertiary consumers.

(i) Food chain: Food chain is sequence based upon the feeding habits of organism living in a community. The basic sequence is from producers to tertiary consumers. For example, plants are producers, a grasshopper used to feed on plants, the grasshopper is consumed by a frog and frog is further consumed by a snake. In this way, the food chain continues.

(ii) Food web: In a food web, each level is occupied by several species. The consumer not only feeds on only one kind of prey, they usually feed on several kinds of prey. For example, a grasshopper, a butterfly and fruit fly feed on plants. These insects can be consumed by a frog. The frog can be consumed by a snake or an eagle.

Food web is more appropriate instead of the food chain because in food chain each species occupy only one level, but in reality, each level is occupied by several species.