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