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Ch. 37.14 - 37.23:
Ecosystem Structure and Dynamics
37.14 Energy flow and chemical cycling
• In an ecosystem,
– energy flow moves through the components
of an ecosystem and
– Chemical/Matter cycling is the transfer of
materials within the ecosystem.
37.15 Primary production sets the energy budget
• The amount of solar energy converted to
chemical energy (in organic compounds)
by an ecosystem’s producers for a given
area and during a given time period is
called primary production.
• Ecologists call the amount, or mass, of
living organic material in an ecosystem the
biomass.
Different ecosystems vary in their primary
production and contribution to the total
production of the biosphere.
Open ocean
Estuary
Algal beds and coral reefs
Desert and semidesert scrub
Tundra
Temperate grassland
Cultivated land
Boreal forest (taiga)
Savanna
Temperate deciduous forest
Tropical rain forest
0
500
1,000 1,500 2,000 2,500
Average net primary production (g/m2/yr)
Data from R.H. Whittaker, Communities and Ecosystems, second edition, New York: Macmillan (1975).
37.16 Energy supply limits the length of food chains
• A caterpillar represents a
primary consumer.
• Of the organic compounds a
caterpillar ingests, about
– 50% is eliminated in feces,
– 35% is used in cellular
respiration, and
– 15% is converted to caterpillar
biomass.
37.16 Energy supply limits the length of food chains
•A pyramid of production illustrates the
cumulative loss of energy with each transfer in
a food chain.
•Only about 10% of the energy stored at each
trophic level is available to the next level.
37.16 Energy supply limits the length of food chains
• The amount of energy available to top-level
consumers is small compared with that
available to lower-level consumers.
– Only a tiny fraction of the energy stored by
photosynthesis flows through a food chain all the
way to a tertiary consumer.
– This explains why top-level consumers such as
lions and hawks require so much geographic
territory.
37.17 CONNECTION: A pyramid of production
explains the ecological cost of meat
• When humans eat
– grain or fruit, we are primary consumers,
– beef or other meat from herbivores, we are
secondary consumers, and
– fish like trout or salmon, we are tertiary or
quaternary consumers.
37.18 Chemicals are cycled between organic
matter and abiotic reservoirs
• In addition to energy from the sun, life also
depends on the recycling of chemicals.
• Biogeochemical cycles include
– biotic components,
– abiotic components, and
– abiotic reservoirs, where chemicals accumulate or
are stockpiled outside of living organisms.
Figure 37.19
CO2 in atmosphere
5
Burning
3
Photosynthesis
Cellular respiration
1
Higher-level
consumers
Wood
and fossil
fuels
Plants, algae,
cyanobacteria
Primary
consumers
2
Decomposition
Wastes; death
Decomposers
(soil microbes)
4
Detritus
Plant litter;
death
abiotic reservoir:
 CO2 in atmosphere
enter food chain:
 photosynthesis =
building carbon
based molecules
recycle:
 decaying organic
material
return to abiotic:
 respiration
 combustion
Increased burning of
wood and fossil fuels
(coal and petroleum) is
raising the level of CO2
in the atmosphere.
37.19 The carbon cycle
abiotic reservoir:
 rocks, minerals, soil
enter food chain:
 erosion releases
soluble phosphate
 uptake by plants
recycle:
 decomposing bacteria
& fungi
return to abiotic:
 loss to ocean
sediment
37.20 The Phosphorus Cycle
abiotic reservoir:
 N in atmosphere
enter food chain:
 nitrogen fixation by
soil & aquatic bacteria
recycle:
 decomposing &
nitrifying bacteria
return to abiotic:
 denitrifying bacteria
http://www.npr.
org/templates/s
tory/story.php?
storyId=13043
7080
37.21 The Nitrogen Cycle
37.22 CONNECTION: A rapid inflow of nutrients degrades aquatic
ecosystems
Over time, standing water
ecosystems gradually
accumulate excess nutrients
and primary production
increases in a process known as
eutrophication.
– depletes oxygen levels and
– decreases species diversity.
NPR: It’s All About Carbon
• http://www.npr.org/2007/05/01/9943298/episode1-its-all-about-carbon
• http://www.npr.org/templates/story/story.php?story
Id=11027169
• http://www.npr.org/templates/story/story.php?story
Id=11366031&ps=rs
• http://www.npr.org/templates/story/story.php?story
Id=11662978&ps=rs
• http://www.npr.org/templates/story/story.php?story
Id=12099564&ps=rs