Why might an ecologist use a food chain for one study and a food web for another?

It depends on the area of his interest. Behind our consciousness, humans and other living things participate in a natural systematic transformation of energy from one to another through the intake of food. This is presented by the food web. A food web is a network of food chains. Therefore, if the ecologist wants to focus on a more specific relationship, he would look at the food chain. If he wants to look at the bigger picture to study the extent of the ecosystem, he would study the food web.