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
• 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 photosynthetic organisms.
• 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
• 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 their metabolism.
• 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 Service