Bottom-up control: Resource supply determines
trophic structure. Bottom-up control is the influence
of producers on the sizes of the trophic levels above
them in a food web.
Top-down control: Predation and grazing by
higher trophic levels on lower trophic levels
ultimately controls ecosystem function.
Biomagnification: Increase in concentration of
the contaminant from one link in a food chain to
another
Question of the Day: What happens to energy as
it is passed from producers to consumers?
Bottom-up
Control
Top-down Control
Biomagnification
Biomagnification
 Populations of many predatory and fish-eating birds in the
United States declined in the 1950s and 60s
 The causes of these population declines were traced to pollution
of aquatic habitats by residues of DDT
 DDT is a pesticide that was used to control crop pests after
World War II
Biomagnification
 The pesticide’s residues resisted degradation and
entered aquatic food chains
 DDT residues accumulated in the fatty tissues of
animals and were concentrated with each step in the
food chain
 The high doses consumed by predatory birds
interfered with their physiology and reproduction,
making their eggshells excessively thin and causing the
deaths of embryos
 Breeding success declined, and populations followed
Biomagnification
 DDT affected wildlife and non-target species
 The peregrine falcon was a sensitive indicator of the
health of the environment
How do chemicals cycle through an
ecosystem?
 Carbon dioxide in the atmosphere
 Carbon dioxide in decaying matter
 Carbon dioxide in fossil fuels underground
 Plants use of carbon during photosynthesis
 Animals obtaining carbon from plants
 Animal respiration and plant respiration
The carbon cycle is closely tied to
the flow of energy through the
biosphere
 Classes of processes cause carbon to cycle through
ecosystems



Photosynthesis and respiration
Ocean-atmosphere exchange
Deposition and burial, Volcanic release
Global Carbon Cycle
Photosynthesis and Respiration
 Photosynthesis and respiration are the main energy
transforming reactions of life
 Photosynthesis is the conversion of light energy to
chemical energy that is stored in glucose or other
organic compounds
 Respiration is the use of oxygen to metabolize organic
compounds and release chemical energy
Photosynthesis and Respiration
 During photosynthesis, carbon gains electrons and is
reduced, this is accompanied by a gain in chemical
energy
 An equivalent amount of energy is released by
respiration, which results in a loss of electrons and a
loss of chemical energy
Photosynthesis and Respiration
 About 85 billion metric tons (1 billion metric tons is a
gigaton) of carbon will enter into these reactions each
year
 There is something like 2,650 gigatons of total carbon
in organic matter
How is carbon extracted from the
atmosphere?
 Carbon is extracted from the atmosphere through
plants in a process called photosynthesis.
What are ways in which carbon is
released into the atmosphere?
 Carbon can be released into the atmosphere by
animal respiration (when animals breathe out),
by plant respiration,
Ocean-atmosphere exchange
 Physical exchanges of carbon dioxide between the
atmosphere and oceans, lakes, and streams
 Carbon dioxide dissolves readily in water
 The oceans contain about 50 times more carbon
dioxide as the atmosphere does
 Carbon dioxide is continuously being exchanged
across the boundary between the oceans and the
atmosphere
Ocean-atmosphere exchange
 Exchange across the air-water boundary links the
carbon cycles of terrestrial and aquatic ecosystems
 The ocean is an important sink for the carbon dioxide
produced by the burning of fossil fuels
Deposition and burial
 In the atmosphere, atmospheric carbon dioxide reacts with
water to form carbonic acid
 Carbonic acid will fall to the earth as rain and reacts with
minerals at the earth’s surface
 Through the process of chemical weathering, carbonic acid
will slowly dissolve these minerals into their
component ions
 These component ions are carried in surface waters like
streams and rivers eventually to the ocean
 Component ions precipitate out as minerals like calcite and
through continued deposition and burial, this
calcite sediment forms limestone
Deposition and burial
 This cycle continues as subduction occurs
 As seafloor carbon is pushed deeper into the earth by
tectonic forces, it heats up, this causes it to melt
 It then can rise back up to the surface, where it is
released as CO2 and returned to the atmosphere.
 This return to the atmosphere can occur through
volcanic eruptions
Human Driven Carbon Flow
 Release of carbon from fossil fuels and land use change
 The rise in atmospheric CO2 leads to increase in global
temperature
 Fossil Fuels were formed millions of years ago from
plant or animal remains that were buried, compressed,
and transformed into oil, coal, or natural gas
 The carbon is said to be "fixed" in place and is
essentially locked out of the natural carbon cycle
Human Driven Carbon Flow
 Humans intervene by burning the fossil fuels
 During combustion of fossil fuels, carbon dioxide and
water molecules are released into the atmosphere
What happens to the carbon in
plants and animals when they die?
 They decay, and the carbon is released back into the
ground. Some of the carbon gets buried far
underground and will become fossil fuels after many
millions of years.
What is one way in which carbon
is released into the atmosphere?
 Carbon can be released into the
atmosphere when humans burn fossil
fuels.