A food web is a natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. It is a simplified illustration of the various methods of feeding that link an ecosystem into a unified system of exchange. A food web consists of all the food chains in a single ecosystem. Each living thing in an ecosystem is part of multiple food chains, and each food chain is one possible path that energy and nutrients may take as they move through the ecosystem. All of the interconnected and overlapping food chains in an ecosystem make up a food web. The linkages in a food web illustrate the feeding pathways, such as where heterotrophs obtain organic matter by feeding on autotrophs and other heterotrophs. There are different kinds of feeding relations that can be roughly divided into herbivory, carnivory, scavenging, and parasitism. Food webs are complex networks that exhibit similar structural properties and mathematical laws that have been used to describe other complex systems, such as small world and scale-free properties. The fundamental purpose of food webs is to describe feeding relationships among species in a community. Food webs serve as a framework to help ecologists understand the interactions between species in an ecosystem.