LEARNING OBJECTIVES
To conserve and manage our biological resources wisely, we must understand the basic concepts of energy, energy flow in ecosystems, and biological production. After reading this chapter, you should understand:
• That energy flow determines the upper limit on the production of biological resources.
• How the first and second laws of thermodynamics affect energy and production.
• That energy flow is one way through the ecosystem.
• That a basic quality of life is its ability to create order from energy on a local scale.
• What determines the efficiency of biological production.
Summary
• The study of energy flow is important in determining limits on food supply and on the production of all biological resources, such as wood and fiber.
• In every ecosystem, energy flow provides a foundation for life and thus imposes a limit on the abundance and richness of life. The amount of energy available to each trophic level in a food chain depends not only on the strength of the energy source but also on the efficiency with which the energy is transferred along the food chain.
• Energy is fixed by autotrophs—organisms that make their own food from energy and small inorganic compounds. The initial energy comes from two sources: light (mainly sunlight) and small sulfur compounds. Plants, algae, and some bacteria are autotrophs.
• Only autotrophs can make their own food; all other organisms are heterotrophs, which must feed on other organisms.
• Biological production is the production of new organic matter, which we measure as change in biomass, change in stored energy, or change in stored carbon. Another way to think about biological production is that it is the change in biomass over time.
• Gross production is production measured before any utilization. Net production is the amount stored (not used) at the end of some time period. Respiration uses stored energy, so net production equals gross production minus respiration.
• The laws of thermodynamics connect life to order in the universe. The second law of thermodynamics tells us that order always decreases when any real process occurs in the universe. However, life is more ordered than its environment. The ability to create order is the essence of what we get from our food.
• Energy efficiency is the ratio of output to input, or the amount of useful work obtained from some amount of available energy. Trophic-level efficiency is the ratio of production of one trophic level to the production of the next lower trophic level. This efficiency is never very high, often only about 1%.