Another name for plant eaters is herbivore. Carnivores eat herbivores. Omnivores eat both herbivores and carnivores. Man is an omnivore. Energy flow in an ecosystem is one way.
Much energy is lost in the form of heat.
The higher the trophic level, the less energy is available to the consumer. Decomposers are an essential part of this model, also. Their primary function is to cycle nutrients. They are responsible for the breaking down of organisms into organic compounds which are added to the nutrient reservoir which contains, among others, the limited nutrient, phosphorus. Biomass, or living weight, is formed by a process of production.