EcologyThe Food Web

13.4 Food Chains And Food Webs

A food web shows a complex network of feeding relationships. • An organism may have multiple feeding relationships in an

ecosystem.• A food web emphasizes complicated feeding relationships

and energy flow in an ecosystem.

How many trophic levels are present in this food web?

Ecology - 13.4Food Webs

• The Anatomy of the Arrow• - In a food web, the arrow is always pointing to the animal

that is doing the “eating”.• - The arrow is signifying the energy flow from the

organism that is being consumed, to the organism that is receiving that energy through the action of consumption.

Ecology - 13.4Food Webs

Which organism, if removed, would impact this food web the most?

Ecology - 13.4Food Webs

Now, introduce the lion. How might the food web energy flow change with the presence of the lion?

Ecology -13.4Food Webs

• - At every every link in the food web, energy is going to be stored in the organism (i.e eating, growth, bodily repair, reproduction).

• - At every link some energy will be dissipated into the environment (i.e. heat, waste product)

• 3-2-1 Exit Ticket

• List 3 things about this arrow that makes it important in a food web.

• List tell me 2 facts about this food chain.

• Give me 1 real life connection you made with the lesson.

Ecology – 13.5Cycling of Matter

Law of Conservation of Matter:

-Matter can neither be created nor destroyed; however it can change form.

-Matter may change form many times, but the amount of matter will always remain constant.

Ecology - 13.5Cycling of Matter

The Hydrologic Cycle (water cycle):

-Circular pathway of water on the planet, stretching from the atmosphere to the surface, underneath the ground, then back up into the atmosphere again.

-

Ecology - 13.5Cycling of Matter

Biogeochemical Cycle:

*Elements essential for life also cycle through ecosystems.

- A biogeochemical cycle is the movement of a particular chemical through the biological and geological parts of an ecosystem.

- The main processes involved in the oxygen cycle are photosynthesis and respiration.

Ecology - 13.5Cycling of Matter

The Oxygen Cycle:

-Oxygen cycles indirectly through an ecosystem by the cycling of other nutrients.

-Organisms need oxygen to perform cellular respiration.

- Plants release oxygen as a waste product during photosynthesis.

-Humans and other organisms will take in the oxygen, and in turn release carbon dioxide back into the atmosphere.

-Oxygen Cycle Clip

oxygen

respiration

Carbon dioxide

photosynthesis

fossil fuels

photosynthesis

carbon dioxidedissolved in water

decompositionof organisms

respiration

carbondioxidein air

photosynthesis

combustionrespiration

Ecology - 13.5Cycling of Matter

Carbon is the building block of life.– The carbon cycle moves carbon from the atmosphere,

through the food web, and returns to the atmosphere.– Carbon is emitted by the burning of fossil fuels.– Some carbon is stored for long periods of time in areas

called carbon sinks.

13.5 Cycling of Matter

nitrogen inatmosphere

animals

denitrifyingbacteria

nitrifyingbacteria

nitrifyingbacteria

ammonium

ammonification

decomposers

plant

nitrogen-fixingbacteria in soil

nitrogen-fixingbacteria in

roots

nitrates

nitrites

• The nitrogen cycle mostly takes place underground.– Some bacteria convert gaseous nitrogen into ammonia

through a process called nitrogen fixation.– Some nitrogen-fixing bacteria live in

nodules on theroots of plants;others livefreely inthe soil.

13.5 Cycling of Matter

– Ammonia released into the soil is transformed into ammonium.

nitrogen inatmosphere

animals

denitrifyingbacteria

nitrifyingbacteria

nitrifyingbacteria

ammonium

ammonification

decomposers

plant

nitrogen-fixingbacteria in soil

nitrogen-fixingbacteria in

roots

nitrates

nitrites

– Nitrifying bacteria change the ammonium into nitrate.– Nitrogen moves through the food

web and returnsto the soil duringdecomposition.

13.5 Cycling of Matter

geologic upliftingrain

weathering ofphosphate from rocks

runoff

sedimentationforms new rocks

leaching

phosphate in solutionanimals

plants

decomposers

phosphatein soil

The phosphorus cycle takes place at and below ground level.

– Phosphate is released by the weathering of rocks. – Phosphorus moves through the food web and returns to

the soil duringdecomposition.

– Phosphorus leaches into groundwater from the soil and is locked in sediments.

– Both mining and agriculture add phosphorus into the environment.

Ecology – 13.6Pyramid Models An energy pyramid shows the distribution of energy among trophic levels.

energy transferredenergylost

An energy pyramid shows the distribution of energy among trophic levels.

Energy pyramids compare energy used by producers and other organisms on trophic levels.

• Between each tier of an energy pyramid, up to 90 percent of the energy is lost into the atmosphere as heat.

• Only 10 percent of the energy at each tier is transferred from one trophic level to the next.

Other pyramid models illustrate an ecosystem’s biomass and distribution of organisms.

Biomass is a measure of the total dry mass of organisms in a given area.

tertiaryconsumers

secondaryconsumers

primaryconsumers

producers

75 g/m2

150g/m2

675g/m2

2000g/m2producers 2000g/m2

A pyramid of numbers shows the numbers of individual organisms at each trophic level in an ecosystem.

tertiaryconsumers

secondaryconsumers

primaryconsumers

producers

5

5000

500,000

5,000,0005,000,000producers

• A vast number of producers are required to support even a few top level consumers.