3-3 Energy in Ecosystems

Concept to Understand

As energy flows through

ecosystems in food chains and

webs, the amount of chemical

energy available to organisms at

each succeeding feeding level

decreases.

Fig. 3-8, p. 46

Trophic Levels

At each level energy is transferred to the

next but some energy is “lost” in the form

of heat

Energy Flow in Ecosystems

Food chain

Sequence of organisms, each

of which serves as a source of

food for the next

Food web

Network of

interconnected food

chains

More complex than a food

chain

Usable Energy by Trophic Level

Energy flow follows the second law of

thermodynamics, which is……

2nd Law of Thermodynamics: Energy

cannot be created or destroyed, but

changed.

But as energy is changed, some

energy is lost in the form of heat.

Usable Energy by Trophic Level

Biomass – dry weight of all organic

matter in plants and animals in an

ecosystem.

Biomass

decreases with

increasing

trophic level

Fig. 3-10, p. 47

Ecological efficiency – typically 10%

(10% rule)

Two Kinds of Primary ProductivityGross primary productivity (GPP) – The rate at which

ecosystems producers convert solar energy into chemical energy in the form of biomass

So the amount of solar energy converted into cellskilocalories/square

meter/year

Two Kinds of Primary ProductivityNet primary productivity (NPP) – is what energy is left over

for the consumers in the ecosystem.

GPP minus the energy the producer need to survive

Two Kinds of Primary ProductivityPlanet’s NPP limits number of consumers

Humans use, waste, or destroy 10-55% of earth’s total potential NPP

Human population is less than 1% of total biomass of earth’s consumers

Temperate forest

Aquatic Ecosystems

Open ocean

Continental shelf

Lakes and streams

Estuaries

Terrestrial Ecosystems

Extreme desert

Desert scrub

Tundra (arctic and alpine)

Temperate grassland

Woodland and shrubland

Agricultural land

Savanna

Northern coniferous forest (taiga)

Swamps and marshes

Tropical rain forest

Fig. 3-11, p. 48

Average net primary productivity (kcal/m2/yr)

800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600