Essentials of Ecology

(Kiana) #1

60 CHAPTER 3 Ecosystems: What Are They and How Do They Work?


Energy Flow and Nutrient Cycling


Sustain Ecosystems and


the Biosphere


Ecosystems and the biosphere are sustained through
a combination of one-way energy flow from the sun
through these systems and nutrient cycling of key mate-

rials within them—two important natural services that
are components of the earth’s natural capital.
These two scientific principles of sustainabil-
ity arise from the structure and function of
natural ecosystems (Figure 3-12), the law of
conservation of matter (Concept 2-3, p. 39),
and the two laws of thermodynamics (Con-
cepts 2-4A and 2-4B, p. 40).

Active Figure 3-12 Natural
capital: the main structural components of an
ecosystem (energy, chemicals, and organisms).
Nutrient cycling and the flow of energy—first
from the sun, then through organisms, and
finally into the environment as low-quality heat—
link these components. See an animation based
on this figure at CengageNOW.

Abiotic chemicals
(carbon dioxide,
oxygen, nitrogen,
minerals)

Decomposers
(bacteria, fungi)

Consumers
(herbivores,
carnivores)

Solar
energy

Heat

Heat

Heat

Heat Heat

Producers
(plants)

Detritus feeders

Long-horned
beetle holes

Time progression Powder broken down by
decomposers into plant
nutrients in soil

Bark beetle
engraving

Carpenter
ant galleries Termite and
carpenter
ant work Dry rot
fungus

Wood
reduced
to powder

Mushroom

Figure 3-11 Various de- Decomposers
tritivores and decomposers
(mostly fungi and bacteria)
can “feed on” or digest
parts of a log and eventu-
ally convert its complex
organic chemicals into
simpler inorganic nutrients
that can be taken up by
producers.
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