A food pyramid is a diagram that represents the structure of a food chain, showing the number of organisms — or the total biomass, or the energy — at each trophic level, from producers at the base up through herbivores to top carnivores. Because energy is lost at each transfer, the pyramid typically narrows sharply toward the top: it takes many plants to support a few herbivores, and fewer still carnivores. (The term is also used, quite differently, for the nutritional food guide pyramid that illustrates recommended proportions of food groups in the diet.) In ecology teaching, the pyramid makes visible why top predators are rare and why contaminants such as mercury concentrate up the chain — a process called biomagnification — with implications for the safety of foods like large predatory fish.