Chapter 56: Ecosystem and Global Ecology
56.2 How Does Energy Flow Through the Global Ecosystem?
Solar energy drives ecosystem processes
Solar energy enters ecosystems by way of plants and other photosynthetic organisms.
Only about 5 percent of the solar energy that arrives on Earth is captured by photosynthesis;
remaining energy is either radiated back into the atmosphere as heat or taken up by the
evaporation of water.
Gross primary productivity (GDP) is the rate at which energy is incorporated into the bodies of
The accumulated energy is called gross primary production.
Primary producer use some of this accumulated energy for their own metabolism; the rest is
stored in their bodies or used for their growth and reproduction.
The energy available to organisms that eat primary producer, called net primary production
(NPP), is gross primary production minus the energy expended by the primary producers during
Only the energy of an organism’s net production is available to other organisms that consume it.
The geographic distribution of the energy assimilated by primary producers reflects the
distribution of land masses, temperature, and moisture on Earth.
Production in aquatic ecosystems in limited by light, which decreases rapidly with depth; by
nutrients, which sink and must be replaced by upwelling of water; and by temperature.
Human activities modify flows of energy
Some human activities decrease net global primary productivity (e.g. conversion of forests).
56.4 What Services Do Ecosystem Pro