A food web is made up of inter-connected food chains. More often, the range of food is sufficiently great for a consumer, i.e., the consumers have several alternative sources of food. For instance, a plant species may be fed by several herbivores which are in turn preyed on by several predators. In other words, a complex feeding relationship that may exist between different animals and plant species in a functioning ecosystem is regarded as a food web.
From the above figure, you will see that a grasshopper is preyed on by several consumers, i.e., a hawk can either form its food chain by eating a lizard or weaverbird; both prey on grasshoppers.
A food chain only shows one possible pathway through which energy (food) flows in an ecosystem. It is usually linear ( a straight line) in nature, while a food web shows all the possible pathways, through which energy can flow, in an interconnected manner.
Plants and animals all need food in order to grow. Because plants are green, they make food from water and the gas (carbon dioxide) and every thing that breathes out.
Sunlight supplies the energy which green leaves use to re-group the atoms in water and carbon dioxide to turn them into sugar. In plants, sugar is turned into starch, fats, oils and proteins.
Animals eat this ready-made food. Some of them eat plants; they are called herbivores. Others eat other animals; they are called carnivores.
Animals called scavengers eat dead plants and animals. Decaying plants and animals are broken down into food products, which can be used again by green plants to make proteins.
The illustration below shows the food eaten by some of the herbivores, carnivores, and scavengers which live in freshwater. This is often called a ‘food web’