ABSTRACT
Energy captured in the primary production of photosynthates and transferred to other trophic levels-herbivores, predators, and decomposers—is generally considered an inefficient process because most of the energy is dissipated along the way. The transfers of energy through biological systems and the cycling of minerals from soil through plants and back to the soil constantly change in rate and magnitude. Herbivores divert portions of plant nutrients into animal food chains. Grazing animals alter the pathways, change the rates of nutrient release by decomposition, and reposition nutrients in the pasture. Grazing animals return a large proportion of the consumed plant nutrients to the soil. Nitrogen, which is the largest component of air and tends to return to its relatively inert gaseous state in the atmosphere, is an ideal example of nutrient cycling. Detailed analysis of mineral reserves describes the system organization and provides a base for the study of mineral flow through the system, the system physiology.
