1. Food Webs and Energy Pyramids

2. Food chains
Food chain- the pathway of energy transfer through trophic levels
The arrow points in the direction of energy flow…it points at the “eater”.
grass → rabbit → hawk
alga → shrimp → small fish → larger fish → man

4. Food Webs
Food web – multiple food chains put together for an entire ecosystem
Oceanic food chains are longer, with more trophic levels than terrestrial (land-based) food chains
This explains the complexity of food webs (why there are so many arrows everywhere!)

6. Niche All organisms have specific roles in an ecosystem
Niche- the role of an organism in an ecosystem (The organism’s “job”)
Producers- make their own food (autotroph)
Consumers- take in food (heterotroph)
Herbivores- eat plants
Carnivores- eat animals
Omnivores- eat both
Decomposers- break down decaying matter/recycle nutrients
Scavengers-eat dead/dying organisms

7. Energy Pyramid
Trophic level- one of the steps in a food chain or energy pyramid
Why is the shape of a pyramid used to illustrate energy in a food chain?
What happens to energy as we move from one trophic level to the next?
Energy decreases (only 10% gets passed on) with each trophic level. The decrease in energy causes a decrease in the number of organisms at the next trophic level. The number of primary consumers for example is much smaller than the number of producers.

8. Energy Pyramid
90% of energy is lost from each trophic level to the next. (10% is passed on.)
How is energy unavailable to the next trophic level?
Metabolism, growth/repair, heat, waste, parts not consumed…

10. Energy Transfer Trace the flow of energy through the energy pyramid:
Sun’s energy is trapped by photosynthesis (producers)
Herbivores/primary consumers graze on the plants and use some (10%) of the plants’ energy
Primary consumers use this energy to perform life functions such as growth, repair, metabolism
Carnivores, or secondary consumers, eat primary consumers
But only about 10% of the energy stored in the herbivore is available to the carnivore…the other 90% is “lost” as body heat, waste, or cannot be eaten by the carnivore
As energy moves up the pyramid to higher trophic levels, only 10% energy from the previous level’s energy remains

11. Biomass Biomass- the total mass of organisms in a trophic level
Pyramid of Biomass:
Energy is stored in the bonds of molecules
Biomass can be used as a measure of energy
Biomass (energy) decreases with distance from the base producers
Used by scientists to try to measure the amount of energy in a population
Biomass decreases with each trophic level