The%20last%20portion%20of%20community%20ecology%20deals%20with%20the%20structure%20of%20communities%20and%20how%20the%20ideas%20presented%20before%20end%20up%20determining%20that%20structure.

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The last portion of community ecology deals with
the structure of communities and how the ideas
presented before end up determining that
structure. The Basic Question About
Structure Are species in communities
interdependent? There were two opposing
views a) If they are - the Clements view of
structure -species as components in a
superorganism -implication boundaries of
species distributions should be closely
linked
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b) If not - the Gleason view of structure
-individualistic species -populations as
independent units come together and
interact -implication boundaries are
independently determined An eminent
ecologist names Robert Whittaker sorted out the
disagreement by studying the structure of forests
in the Smoky Mountains of Tennessee, the Siskyou
Mountains of Oregon, and the Santa Catalina
Mountains of California. Here are the
hypothetical structures and what he found
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individualistic view
superorganism view
observed pattern
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Neither view is completely right. There is
clearly interdependence among species 1) Every
organism except those that feed them- selves
by photosynthesis depends on other living
organisms for food. 2) Many species depend on
others for places to live or the conditions
in those places. Examples Alligator
wallows provide homes for a diversity of
species (frogs, turtles, etc.) in the southern
U.S. Worms condition our garden soil,
adding nutrients and changing the texture.
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However, rarely is that dependence absolute.
Species can usually function separately, and the
individualistic view is the widely accepted one.
Only species that are obligate mutualists need
the partner species to be present. What, then,
determines the structure of a community? Ecosystem
Ecology There are two basic views one based on
energetics (which youve seen in the trophic
pyramids of numbers and biomass), the other based
on materials.
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Materials (carbon, nitrogen, water, phosphorus)
cycle within (and sometimes beyond the boundaries
of) ecosystems. Where did the idea of recycling
come from? It came from the way materials move in
ecosystems. They are recycled. Since the cycles
involve both living and non-living phases, they
are called biogeochemical cycles.
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The water (or hydrologic) cycle
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1. Much more water evaporates from the surfaces
of the oceans than from the land and by
transpiration from plants. 2. Water returns
to earth in precipitation. 3. Water returns to
the oceans by flow in rivers, movement of
groundwater, and by run off from snowfall and
glacial melting. 4. Sufficient rainfall occurs
over land due to the movement of air masses
(currents) inland. Our rainfall comes from
either Gulf of Mexico or Pacific waters,
depending on recent movements.
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the carbon cycle
plant animal respiration
CO2 in air
assimilation by plants
decomposition respiration
In addition to these pools, there are pools of
fossil fuels and in carbonate-containing rocks.
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1. The pools of carbon in carbonate
(CO3)-containing rocks and in the form of
fossil fuels (oil, natural gas, and coal)
represent by far the largest amount of carbon
in the system. 2. Carbon enters the living
portion of the system in photosynthesis.
Plants (most, anyway) initially make a 5-C
sugar using solar energy, water, and carbon
dioxide. 3. Carbon moves among living things as
one kind eats another. Most of the carbon
ends up used in metabolism, and is released
again as CO2 in respiration (accompanied by
waste heat).
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4. Some is still in tissues when the organism
dies. It is used by bacteria in
decomposition. Bacterial metabolism also
releases CO2 and waste heat.
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The nitrogen cycle
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1. The nitrogen cycle is the most complicated
one. It involves more different kinds of
organisms. 2. Nitrogen enters the living
components of the system by fixation
(symbiotic and free-living bacteria) and from
reactions in the atmosphere during lightning
storms (a minor component). 3. Nitrogen fixers
produce either ammonia (NH4) or nitrate
(NO3-). Either ion can be taken up by plants.
Plants use the nitrogen in making amino acids
to make proteins and in making nucleic acids
to make DNA and RNA.
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4. The waste materials of nitrogen metabolism
(urea, uric acid, ammonia) become a source of
food for groups of bacteria. These groups
of bacteria include Nitrifying bacteria -
convert ammonia to nitrite (NO2-). This
oxidation provides their source of
energy. Other nitrifying bacteria - oxidize NO2-
to nitrate (NO3-). Plants can take this
up. Denitrifying bacteria - convert nitrate
back into atmospheric nitrogen (N2). The
entire cycle can begin again.
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The phosphorus cycle
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1. Phosphorus is a key component of bone and of
nucleic acids (DNA, RNA). 2. Very little
phosphorus is in a form available to
organisms in the environment. Only
orthophosphate (H2PO4-) and phosphate (PO4-)
are directly used. 3. Most forms of phosphorus
are insoluble, sink to the bottom if water
bodies, and are slowly incorporated into
rock. Therefore, this is an open cycle. A lot
of phosphorus is lost into unavailable pools
(rock) for literally millions of years. 4.
Phosphorus is restored to the active portion of
the system by the slow weathering of rock.
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5. Since phosphorus is only available in limited
amounts naturally, artificial introduction
has dramatic impact. Phosphates in detergents
used to wash clothes were a key factor in the
eutrophication of Lake Erie. Algae thrived
in the nutrient enriched waters, algal blooms
occurred. The algae used up essentially all
the oxygen dissolved in the water, and fish
died out for lack of oxygen.
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When we alter ecosystems, for example by
clearcutting forest land, we dramatically impact
these nutrient cycles. Suddenly, water runs off
more rapidly and carries with it much larger
amounts of nitrogen and phosphorus. Not only is
the future of the forest affected, but so are
downstream waters that are made more
eutrophic. Your text discusses zoned reserves
that are designed to protect conservation areas
by preventing ecosystem disruption not only
within the preserve, but also in buffer zones
around them.