All food chains in a community constitute a food web. A food web is simply the total set of feeding relationship amongst and between the species composing a biotic community. These relationships may achieve considerable complexity. With many food chains and cross connecting links, there is greater opportunity for the prey and predator population in an ecosystem to adjust to the changes.
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The producer-consumer arrangement is one kind of structure known as trophic structure (trophic = food) and each food (nutritional) level in the food chain is called trophic level or energy level. The first trophic level in an ecosystem is occupied by the plants-producers (green plant-primary producers), because they utilize solar energy which is transformed to chemical form during photosynthesis. The energy stored in food or green plants is consumed by the plant eaters (herbivores) which make the second trophic level. Herbivores are also called primary consumers. Primary consumers in turn are eaten by carnivores (also known as secondary consumers) which occupy third trophic level. Secondary consumers (Primary carnivores) may be eaten by other carnivores (secondary or top carnivores) which are known as tertiary consumers and occupy fourth trophic level. Decomposer occupy fifth trophic level in an ecosystem.