Food Chain, Webs, and Pyramids

H. Biology

Relationship of Organisms• Organisms are resources /

“food” for other organisms• Food is energy which

allows the survival and reproduction of populations

• Food chains and food webs show how energy is transferred from one organism to another

Energy Roles• The sun is the original source of all energy!• Producers: “Harness” energy from the sun– Ex. plants

• Consumers: Organisms that eat something else– Ex. animals

• Decomposers: return energy to the environment– Ex. fungus, bacteria

Vocab You Need to Know!• Producer - usually a green plant that produces its own food by

photosynthesis• First-order Consumer - the organism that eats the producer• Second-order Consumer - the organism that eats or derives

nutrients from the first-order consumer • Herbivore - a plant eater• Carnivore - an organism that obtains nutrients from the blood or

flesh of an animal• Omnivore - an organism which eats both plant and animal matter• Scavenger - an consumer that eats dead animals (e.g. crab)• Detritivore - a consumer that obtains its nutrients from detritus• Decomposer - an organism such as bacteria and fungi that breaks

down dead organisms and their wastes

Trophic StructureEcosystems divided into trophic levels (feeding

levels)Primary producers—autotrophs (mostly

photosynthetic but can be chemosynthetic)Primary consumers—herbivoresSecondary consumers—carnivores that eat

herbivoresTertiary consumers—carnivores that eat other

carnivoresDetrivores/Decomposers—consumers that eat

dead or decaying matter

Ecosystems

Producers• Plants harness energy from the sun through

photosynthesis• Producers are the base of every food chain– Meaning they are the source of food for all other

animals

Consumers• 4 Types of Consumers:– Herbivore: Eat only plants

• Ex. Cows, horses

– Carnivore: Eat only meat• Ex. Polar bear

– Omnivore: Eat plants and animals• Ex. Humans, grizzly bears

– Scavenger: Carnivores that feed on bodies of dead organisms• Ex. Vultures

Decomposer• Decomposers break down waste and dead organisms

and return the raw materials to the environment– Ex. Bacteria, fungi

Energy Flow through Biological Systems

Which Way Will the Energy Flow Go?!

Grass ------ Cow ------ Human

Plant ------ Mouse ------ Snake

Food Chain• Food Chain – series of

organisms showing feeding relationships. – almost always begins

with a green plant (producer) which is eaten by an animal (consumer).

– The arrow means 'is eaten by', and points to the animal doing the eating!

– This shows the flow of matter and energy along the food chain.

– There are no decomposers in a food chain.

Food Web• Food Web is a network of interrelated food chains in a

given area– Includes decomposers

Toxins in the Environment• In some cases, harmful

substances persist for long periods in an ecosystem

• One reason toxins are harmful is that they become more concentrated in successive trophic levels

• In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower

Zooplankton0.123 ppm

Phytoplankton0.025 ppm

Lake trout4.83 ppm

Smelt1.04 ppm

Herringgull eggs124 ppm

Con

cent

ratio

n of

PC

Bs

BiomagnificationWhat happens as levels of toxins (like DDT and mercury) as they move up trophic levels?

• Toxin INCREASES in concentration from one link in a food chain to another– B/c they’re insoluble

Energy Pyramid

• 2nd Law of Thermodynamics: 100% of the energy from one organism is NOT transferred to the next – Most of the energy (90%) is lost to the

environment / used by the organism to carry out its life processes or it is lost to the environment

• Energy Pyramid shows the amounts of energy that moves from one level to the next

Sample Energy Pyramid

Only 10% is passed on from one level to the next…the rest is LOST (usually as heat)

What happens as

levels of toxins (like DDT) move up trophic

levels?

Pyramid of Net Productivity:

~10% of energy at each level converted

to new biomass

CALLED 10% rule (trophic efficiency)

LOTS OF BIOMASS HERE