Essentials of Ecology

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.