Unit 2, Part 3 NotesFood Chains, Food Webs, and

the Transfer of Energy

Autotrophs

• A groups of organisms that can use the energy in sunlight to convert water and carbon dioxide into Glucose (food)

• Autotrophs are also called Producers because they produce all of the food that heterotrophs use

• Without autotrophs, there would be no life on this planet

• Ex. Plants and Algae

Autotrophs

Autotrophs• Chemotrophs

– Autotrophs that get their energy from inorganic substances, such as salt

– Live deep down in the ocean where there is no sunlight. Some bacteria use the sulphur to get energy and then use this to perform photosynthesis

– Ex. Bacteria and Deep Sea Worms

Heterotrophs

• Organisms that do not make their own food

• Another term for Heterotroph is consumer because they consume other organisms in order to live

• Ex. Rabbits, Deer, Mushrooms

Heterotrophs

Heterotrophs

• Consumers– 1. Scavengers/Detritivores – feed on the

tissue of dead organisms (both plans and animals)

• Ex. – Vultures, Crows, and Shrimp

Heterotrophs

• Consumers– 2. Herbivores – eat ONLY plants

• Ex. – Cows, Elephants, Giraffes

Heterotrophs

• Consumers– 3. Carnivores – eat ONLY meat

• Ex. – Lions, Tigers, Sharks

Heterotrophs

• Consumers– 4. Omnivores – eat BOTH plants and

animals • Ex. – Bears and Humans

Heterotrophs

• Consumers– 5. Decomposers – absorb any dead material

and break it down into simple nutrients or fertilizers they do this by excreting an enzyme like substance, dissolving and absorbing the nutrients.

• Ex. – Bacteria and Mushrooms

Transfer of Energy

• When a zebra eats the grass, it does not obtain all of the energy the grass has (much of it is not eaten)

• When a lion eats a zebra, it does not get all of the energy from the zebra (much of it is lost as heat)

Transfer of Energy

• The two (2) previous examples of energy transfer show that no organism EVER receives all of the energy from the organism they just ate

• Only approximately 10% of the energy stored in the organic matter of one trophic level is used by the next level for growth.

• This is called the 10% law• The rest goes into heat, cellular

respiration and waste products

When a bird eats a caterpillar, how much energy is available for the bird?

Trophic Levels

• Energy moves from one organism to another when it is eaten

• Each step in this transfer of energy is know as a trophic level– The main trophic levels are producers,

consumers, and decomposers

Food Chains• The energy flow from one trophic level to the

other is know as a food chain• A food chain is simple and direct• It involves one organism at each trophic level

– Primary Consumers – eat autotrophs (producers)– Secondary Consumers – eat the primary consumers– Tertiary Consumers – eat the secondary consumers– Decomposers – bacteria and fungi that break down

dead organisms and recycle the material back into the environment

Food Chain

Food Web

• Most organisms eat more the JUST one organism

• When more organism are involved it is know as a FOOD WEB

• Food webs are more complex and involve lots of organisms

Food Web

Food Web

• Notice that the direction the arrow points the arrow points in the direction of the energy transfer, NOT “what ate what”

Food Web

Biomass

• The total mass of the organic matter at each trophic level is called biomass

• This is always measured as dry weight because water has no useable energy.

• Biomass is often used as another term for potential energy – energy that is to be eaten and used.

• The transfer of energy from one level to another is very inefficient (10% Law)

Productivity• Productivity: is the Rate at which

the biomass accumulates. It is usually written as grams per square metre of land per year

• A rainforest will produce 1000-3500g dry matter per m2 per year

• A dessert will produce from 10 up to 250g per m2 per year

Energy transfer

Ecological Pyramid

• Which level has the most energy?• Which level has the most organisms?• Which level has the least organisms?• Which level has the least energy?• Which level has the most biomass?

Ecological Pyramids - Biomass

• An ecological pyramid shows the relationship between consumers and producers at different trophic levels in an ecosystem

• Shows the relative amounts of dry matter contained at each trophic level

• The Pyramid shows which level has the most dry matter for a given unit of time

• This can be inverted

These can be inverted• In some ecosystems the pyramid can

look different. For example a simple marine system where:

• Phytoplankton grow and reproduce really quickly and then are eaten by the zoo plankton just as quickly.

• They never develop a large population size for a given period of time.

• Their rate of production, however is higher than the zooplankton that eat them or else the system would fail.

• Biomass of some aquatic systems

Pyramid of Energy

• Similar to the biomass pyramid • Shows the amount of energy

transferred to each level in a given area over a time period

• This can not be inverted.• The energy amounts at the bottom

must be more than the energy in the levels above. Why?

Ecological Pyramid of Energy

Ecological Pyramid of Energy

Pyramid of Numbers

• This is when each box of the pyramid shows the numbers of individuals present in that level.

• These can be inverted• For example: If you have 3-4 rose

bushes only but hundreds of insects feeding off them.

Biomass versus Numbers Pyramids

Symbiosis

• A close and permanent association between organisms of different species– Commensalism – a relationship in which one

organism benefits and the other is not affected• Example: Barnacles on a whale

– Mutualism – a relationship in which both organisms benefit from each other

• Example: Birds eating pest off a rhino’s back

– Parasitism – A relationship in which one organism benefits and the other is harmed

• Example: Ticks on a dog

Ecological Succession

• A change in the community in which new populations of organisms gradually replace existing ones

– 1. Primary Succession – occurs in an area where there is no existing communities and for some reason (s) a new community of organisms move into the area

Ecological Succession

• A change in the community in which new populations of organisms gradually replace existing ones

– 2. Secondary Succession – occurs in an area where an existing community is partially damaged

Ecological Succession

• A change in the community in which new populations of organisms gradually replace existing ones

– 3. Climax Community – a community that is stable and has a great diversity of organisms