Primary productivity is the rate of photosynthesis for the ecosystem during a specified interval. Net primary productivity is the rate of energy storage in plant tissues in excess of the rate of respiration by the plants themselves. B. Major Pathways of Energy Flow 1. Energy flows into ecosystems from the sun. In detrital food webs it flows mainly from plants through decomposers and detritivores.
Energy leaves ecosystems through heat losses generated by metabolism.
C. Ecological Pyramids 1. Trophic structure can be diagrammed as a pyramid in which producers form a base for successive tiers of consumers above them. A pyramid of biomass makes provision for differences in size of organisms by using the weight of the members in each trophic level. A pyramid of energy reflects the trophic structure most accurately because it is based on energy losses at each level. An Overview A. Biogeochemical cycles influence the availability of essential elements in ecosystems.