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 Services Do Ecosystem Provide?
•Ecosystems provide people with a variety of goods and services.
•The rapidly expanding human population has greatly modified Earth’s
ecosystems to increase their ability to provide some of the goods and
services it needs, particularly food, fresh water, timber, fiber, and fuel.
•The most important driver of alterations in ecosystems and the services they
provide has been changes in land use as natural ecosystem have been
converted to other, more intensive uses.
•The modifications of ecosystems to benefit human beings in one way has
often resulted in the degradation of other services.
56.5 What Options Exist to Manage Ecosystems Sustainably?
•Often the total economic value of a sustainably managed ecosystem is higher
than that of an intensively exploited ecosystem (e.g. land for clear cutting).
•A major barrier to achieving these greater long-term benefits is that many
ecosystem services are considered “public goods” that have no market value.
•More sustainable use of fresh water can be achieved by charging the full cost
of providing the water, by developing methods to use water more efficiently
in agriculture and by altering the allocation of water rights so that the
incentives favour conservation.