Transcript Chapter 4: Ecosystem Structure and Function

Chapter 4: Ecosystem Structure
and Function
Ecosystems
• Study of how organisms interact with
each other and with the biotic EVR
Organism -> species-> population ->
community -> ecosystem
Each species has a range of tolerance –
physical/chemical EVR, biotic/abiotic
factors
Ecosystems
Purpose of an organism – to reproduce
successfully, ensure offspring
reproduce successfully with genetic
variation as the lowest energy cost
Adaptations –
chemical/physical/behavioral
changes to increase survival rates
The earth can be divided into layers:
• Atmosphere:
–Trophosphere – goes up 11
miles, greenhouse contains
ozone
– Stratosphere – ozone layer, filter
out harmful UV rays
• Hydrosphere: all the ice, H2O, and
H2O vapor
• Lithosphere: the land
(crust/mantle)
What sustains life on earth?
• The one-way flow of highquality energy
• The cycling of matter or
nutrients
• Gravity
– Allows the planet to hold onto its
atmosphere
– Causes the downward movement of
nutrients
How does the sun sustain
life on earth?
• Supplies light energy needed for
photosynthesis
• Warms the earth
• Drives the weather systems that
distribute heat and fresh water
Principles of Ecosystem Functioning
• Ecosystems run on solar
energy.
• Nutrients are recycled in an
ecosystem.
• Ecosystems cannot support
large numbers of top
consumers
– the amount of energy is limited
– energy is lost as heat AND is used to keep
consumers alive so the amount of energy
available decreases as we move up the food chain
Ecosystem Structure: the living
components of an ecosystem
The roles of organisms in an
ecosystem:
• Producer (autotrophs): make food;
plants, algae
• Consumer (heterotrophs): eat other
organisms
• Decomposer: eat dead organic
matter; bacteria and fungi
Role of organisms
Classes of Consumers
Herbivore – primary consumer – eats
plants
Carnivores – secondary – meat eaters;
eat herbivores
Tertiary – feed on carnivores
Omnivores – eat plants/animals
Role of Organisms
Scavengers – feed on dead organisms
(vultures, flies, crows, lobsters)
Detritus feeders – organisms that extract
nutrients from fragments of dead
organisms into more simple organic waste
(termites, earthworms, crabs)
Decomposers – organisms that digest parts
of the dead organisms into simplest
chemicals (bacteria, fungi)
Ecosystem Function
#1. Energy flow in an
ecosystem is represented by
a food web.
The amount of energy available to
the organisms at each trophic
level decreases as one moves
up the food chain since …
• energy is lost as heat and
• organisms use energy to sustain
themselves
• Remember the laws of energy?
Because the amount of energy
decreases at each successive
trophic level, the number of
organisms also decreases
Only approximately 10% of the energy
is transferred to the next trophic
level.
So, are there more producers or
consumers on Earth?
Energy and biomass pyramids
The amount of energy available in
an ecosystem depends on the type of
vegetation the area can support.
This is measured as an area’s net
primary productivity (NPP).
The higher the NPP, the greater the
diversity of animals in that
ecosystem.
The net primary productivity of biomes
Ecosystem Function (con’t)
#2. Nutrients are recycled
within an ecosystem.
• Water
• Carbon
• Oxygen
* Nitrogen
* Phosphorus
* Sulfur
Water Cycle
• condensation of water vapor in the
air leads to precipitation
• evaporation returns water vapor to
the atmosphere
• infiltration of rainwater replenishes
groundwater supplies
• surface runoff of rainwater
replenishes surface water supplies
Carbon Cycle
• CO2 is taken up by plants during
photosynthesis
• CO2 is released by organisms
during respiration and
decomposition; fires, volcanoes
• CO2 is also released by autos and
industries
• carbon, present in all organic
molecules, moves through the food
chain as one organism eats another
Carbon Cycle
Sinks:
- Lithosphere – limestone (largest
reservoir)
- hydrosphere – ocean (2nd largest)
- Atmosphere – in form of CO2
- biosphere – wood, plants, dead
animals
Oxygen Cycle
• Essential for animals during
respiration, released by plants
• Cycles much like the carbon cycle
• What is threatening this cycle?
Forest deforestation, ocean
pollution, etc
Nitrogen Cycle
• 78% of the volume of trophosphere
• Most complex cycle
• N2 gas can’t be used ‘as is’ – it must be ‘fixed’ so that
organisms can use it
• Steps to the cycle: b/c of complexity, no certain order
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N Fixation – occurs in plant, by bacteria
Ammonification
Nitrification
Assimilation
Denitrification
• N2 gas is modified by “nitrogen-fixing” bacteria in legumes
into ammonia (NH3) – NITROGEN FIXATION – aids in
production of sugars/starches
• Bacteria turn wastes and detritus into ammonia –
AMMONIFICATION – released into atm
• NH3 is converted into nitrite (NO2-) which is then used to
produce nitrate (NO3-) - NITRIFICATION
Nitrogen cycle (con’t)
• Plant roots take up the ammonia and
nitrate ions and converts it into
amino acids, proteins, DNA/RNA =
Assimilation
• other bacteria convert nitrite (NO2-)
into N2 gas - DENITRIFICATION
• nitrogen, present in proteins, moves
through the food chain as one
organism eats another
Phosphorus Cycle
• phosphorus is released as rocks erode
and plants assimilate this
• Very slow process
• phosphorus passes from one organism
to another in the food chain
• decomposers release phosphorus
during decomposition
• Mined for production of fertilizer. Mined
in Tampa, FL
Sulfur Cycle
• sulfur is released as rocks erode and
plants assimilate this
• Mostly found under ground like
phosphorus
• H2S is released by decomposers and
during volcanic eruptions; some H2S in
soil is converted into sulfur by aerobic
bacteria and plants assimilate this
• 99% of all sulfur in the atm is due to man
• SO2 gas is released by industries; SO2
then reacts with water to form H2SO4
which falls to the earth as acid rain