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 high-quality 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 * Nitrogen• Carbon * Phosphorus• Oxygen * 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

– 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