Download Community and Ecosystem Ecology . . . After QUIZ 11!!!1!!1!! Energy

4/21/11
. . . After QUIZ 11!!!1!!1!!
Community and Ecosystem
Ecology
by Dr. W.
Energy Flow
• You can divide organisms into three types,
according to the roles they play in an ecosystem
– Producers: carry out photosynthesis. These are the
ultimate sources of all living matter (biomass) and
energy in an ecosystem. EXAMPLES: Most plants;
photosynthetic protists; photosynthetic bacteria.
– Consumers: obtain matter and energy from feeding on
other organisms. EXAMPLES: Most animals; many
non-photosynthetic protists.
– Decomposers: obtain matter and energy from feeding
on dead organisms. EXAMPLES: most fungi, many
bacteria, some protists.
• 1. Draw a graph showing how a typical
population in nature might grow over time.
Include and label the carrying capacity.
• 2. Define niche.
• 3-4. Describe the two main possibilities that
result when two different species share a niche.
• 5. Describe the difference between an r-selected
life history and a K-selected life history. Energy Flow
• You can then look at energy flow through an
ecosystem. – The energy that organisms use is stored as chemical
energy in the form of chemical bonds.
– As organisms feed on each other, etc., energy—in the
form of food—flows through the ecosystem.
– Biomass—living matter—also "flows" through the
ecosystem, as some organisms grow larger by eating
others.
– These pathways can be represented by a diagram called
a food web.
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Energy Flow
• You can define several levels of energy flow, called trophic
levels:
– Primary producters / Primary productivity
– Primary consumers—feed directly on the producers. A.k.a.
herbivores (plant eaters)
– Secondary consumers—feed on the primary consumers
– Tertiary consumers—feed on the secondary consumers
– Quaternary consumers—you guessed it, feed on the tertiary
consumers
A food web diagram
for an open ocean
ecosystem.
• This is a bit of a simplification, because many organisms
occupy several levels at once.
• Also, some ecosystems may have fewer trophic levels than
this, and some may have more.
This diagram
shows typical
organisms on the
various trophic
levels in a prairie
(left) and ocean
(right) ecosystem.
The highest-level consumers in an ecosystem—those that
are not preyed on themselves—are sometimes called
apex predators.
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Imagine taking the amount of biomass (living
matter) of each trophic level and representing it as a
bar. Stack the bars on top of each other, and you get
a diagram called a trophic pyramid.
Pyramid Schemes
• At each trophic level, energy and biomass are lost.
– Not all of the matter an animal eats goes into building
new biomass. In fact, most of it doesn't.
• Why? Metabolism isn't 100% efficient. Some food is lost as
waste. And a lot of energy is lost as heat or used for
“maintenance activities” instead of new growth.
– The ecological efficiency of each trophic level averages
about 10%, although in real life it varies quite a bit.
• Typical beef cattle convert about 6% of their total food intake
into beef; pigs are more efficient at about 14%, and broiler
chickens can do about 21%.
Thus the rule of thumb is that each level of the trophic
pyramid is only one-tenth the size of the level below.
This leads to the
phenomenon of
biological
magnification—
toxins such as
DDT, which
organisms can't
easily break
down or
eliminate,
become more
concentrated at
higher levels of
the pyramid.
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Another toxin that builds up at higher trophic levels is mercury. The
US government currently advises pregnant and nursing women and
young children not to eat shark or swordfish, and to limit their
consumption of tuna— because these fish are high -level
consumers, and are likeliest to contain dangerous levels of mercury.
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