Geoffrey Gearheart Scripps Institution of Oceanography

FOOD WEBS  Basis of life: the sun  Autotrophes=primary producers  Autotrophes tranform the Sun’s energy + nutrients into organic compounds like carbohydrates (sugars) that can be eaten by herbivores  Herbivores are primary consumers  Each step up the trophic pyramid= one trophic level  Decomposers (like bacteria) transform organic back to inorganic matter Source: rriculum/elem/lesson37.htm

ENERGY FLOWS  Energy flow for each trophic level: when one organism gets eaten by another (one goes up one step in the food web) only 10% of the energy (or body weight) of the one who is eaten is transformed into new “biomass” (weight of living stuff). The rest (90%) is lost as heat (respiration)! Source: nt/energy-flow-diagram.jpeg

NOT EFFICIENT TO BE A PREDATOR! 1,000 Tons 10,000 Tons 100,000 Tons  To produce 1,000 Tons of lion (~6,500 lions) the energy (meat) of 6,500 giraffes is required (a giraffe is 10 times heavier than a lion!), and these giraffes eat 100,000 tons of fodder (leaves, grass). They need 800,000 acres of Savannah to get that amount of food.  Want to fight climate change? Think of how much oil you could save by not eating meat! Source: images/food%20pyrmaid.gif

A SIMPLE FOOD WEB  How many trophic levels?  Decomposers are at the last (highest) level Bacteria-decomposers Insect-Primary consumer Grass-Primary producer Earthworm-decomposers

MARINE FOOD WEBS  Simple ones: polar  less biodiversity example: phytoplankton  krill  whales  Complex ones  coral reefs Example: corals  many herbivores  many carnivores  more links (trophic levels)