why do food chains only have 4-5 levels
Food web In a pyramid of numbers, the number of consumers at each level decreases significantly, so that a single top consumer, (e.g., a polar bear or a human), will be supported by a much larger number of separate producers. There is usually a maximum of four or five links in a food chain, although food chains in aquatic ecosystems are more often longer than those on land. Eventually, all the energy in a food chain is dispersed as heat.[4]
Staple food Just 15 crop plants provide 90 percent of the world's food energy intake (exclusive of meat), with rice, maize, and wheat comprising two-thirds of human food consumption. The three are the staples of about 80 percent of the world population,[8] and rice feeds almost half of humanity.