The sequence of the transfer of food energy from one organism to another in an ecological community. A food chain begins with a producer , usually a green plant or alga that creates its own food through photosynthesis. In the typical predatory food chain, producers are eaten by primary consumers (herbivores) which are eaten by secondary consumers (carnivores), some of which may in turn be eaten by tertiary consumers (the top carnivore in the chain). &diamf3; Many species of animals in an ecological community feed on both plants and animals and thus play multiple roles in the chain. Parasites feed on living tissues, generally without killing their hosts, and may themselves be hosts to smaller parasites. In addition, organisms that die without being eaten are consumed by detritivores, some of which serve as prey for other consumers. The complex system of interrelated food chains in an environment is known as a food web.