Food Chains, Food Webs, and Ecological Pyramids • A food chain is the simplest path that energy takes through an ecosystem. • Energy enters from the sun. • Each level in the transfer of energy is a trophic level. • Organisms at each level use energy in cellular respiration and heat loss and store the rest. The 1st Trophic Level • Consists of primary producers (autotrophs). • Primary producers include land plants and phytoplankton in aquatic environments. 2nd Trophic Level • Consists of primary consumers (heterotrophs) • Primary consumers that eat green plants are herbivores. • Examples: grasshoppers, rabbits, zooplankton The 3rd and Any Higher Trophic Level • Consists of consumers. • Carnivores and omnivores • Examples: Humans, wolves, frogs, and minnows Food Chains • Arrows represent the flow of energy …Not Who Eats Who. Food Web • A food web represents may interconnected food chains describing various paths that energy takes through an ecosystem. Ecological Pyramids • Models that show how energy flows through ecosystems. • Pyramids can show the relative amounts of energy, biomass, or numbers of organisms at each trophic level in an ecosystem. • The base of the pyramid represents producers. • Each step up represents a different level of consumer. • The number of trophic levels in the pyramid is determined by the number of organisms in the chain or web. Energy pyramids compare energy used by producers and other organisms on trophic levels. • Between each tier of an energy pyramid, up to 90 percent of the energy is lost into the atmosphere as heat. • Only 10 percent of the energy at each tier is energy energy transferred lost transferred from one trophic level to the next. Other pyramid models illustrate an ecosystem’s biomass and distribution of organisms. • Biomass is a measure of the total dry mass of organisms in a given area. Biomass pyramid tertiary consumers 75 g/m2 150g/m2 secondary consumers primary consumers producers producers 675g/m2 2000g/m2 • Even though a biomass pyramid shows the total mass of organisms at each level, it doesn’t necessarily represent the amount of energy available at each level. • For example, the skeleton and beak of a bird will contribute to the biomass but aren’t available for energy. • A pyramid of numbers shows the numbers of individual organisms at each trophic level in an ecosystem. tertiary consumers 5 secondary consumers 5000 primary consumers 500,000 producers producers 5,000,000 • A vast number of producers are required to support even a few top level consumers.