Food Webs and Energy Pyramids

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

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!)

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

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.

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…

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

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