Food Chains & Energy Flow

Food Chains & Energy Flow

Food Chains vs. Food Webs • Food chains show the path of food from a producer to the final consumer • Food webs consist of interconnected food chains

Food Chain

Food Web

Trophic Levels • Primary consumers: (herbivores) feed directly on producers • Secondary consumers: (carnivores) feed on primary consumers • Tertiary consumers: feed on carnivores

Aquatic Ecosystems

Terrestrial Ecosystems

Food Chains • Which are more numerous in an ecosystem: producers or consumers? • Producers are always more numerous than consumers, why?

Energy Loss • Of the energy that an organism consumes, only a small fraction (ecological efficiency of about 10%) is transferred to the next trophic level

Where does that energy go? • Most of the energy is lost as heat That’s hot. Drop it like it’s HOOOTT

“Rules” of Energy Pyramids • Not everything in the lower levels gets eaten • Not everything that is eaten is digested • Energy is always being lost as heat

House Analogy • Just like how much of the energy used to heat a house is wasted, much of the energy used by organisms is wasted

Efficiency Example • Cars are only about 25% efficient • Only 25% of the total energy in gasoline is used to make cars move • What happens to the other 75%???

Energy Efficiency • Why is it more energy efficient to eat grains directly, rather than the meat of grain-eating animals? 15 lbs. of feed 1 lb. of beef

Energy Efficiency • Why is it more energy efficient to eat grains directly, rather than the meat of grain-eating animals? 6 lbs. of feed 1 lb. of pork

Energy Efficiency • Why is it more energy efficient to eat grains directly, rather than the meat of grain-eating animals? 5 lbs. of feed 1 lb. of chicken

Energy Efficiency • Why is it more energy efficient to eat grains directly, rather than the meat of grain-eating animals? 2 lbs. of feed 1 lb. of fish

Summary Question • Why do food chains rarely have more than 4 or 5 trophic levels?

Primary Productivity • Gross primary productivity (GPP): the rate at which an ecosystem's producers convert solar energy into chemical energy as biomass • Net primary productivity (NPP): the rate at which energy for use by consumers is stored in new biomass • NPP = GPP – [rate producers use biomass]

Net Primary Productivity

The Food Chain RAP • From the SUN ENERGY flows • Captured by plants this energy goes • CHLOROPHYLLand WATER plus CO2 • Used in PHOTOSYNTHESIS to manufacture food • Plants get energy right from the sun • Making sugar for their food, a food chain has begun • Plants are PRODUCERS, the first link in the chain • Animals eat these plants for energy is obtained

The Food Chain RAP • Some can’t make food these are CONSUMERS • They search for edibles this is no rumor • An animal like a mouse is the second shackle • It’ll eat only plants but animals it won’t tackle

The Food Chain RAP • REFRAIN • OH OH OH PLEASE DON’T EAT ME! • OH OH OH PLEASE JUST LET ME BE • OH OH OH I’LL BE REAL GOOD • OH OH OH JUST DON’T MAKE ME FOOD

The Food Chain RAP • Our mouse will nibble, on a plant as a treat • Mice don’t make food, only plants do this feat • Now this second link involves such a critter • Whose diet is plant material for lunch and dinner • The next animal could include a snake • Snakes are PREDATORS that sit and lie and wait • They’ll sit and stare with a watchful eye • Until a mouse comes passing by…

The Food Chain RAP • Now you gotta be quick you can’t be lazy • or this food chain will drive you crazy • You gotta be speedy you gotta be faster • to move too slow would be disaster • The snake had to act to stay alive • And that’s a fact it ain’t no jive • The snake will find food, and to its own dismay • Soon it too will become the PREY

The Food Chain RAP • So the snake just feasted on the mouse • The snake better be careful he better look out • Up in the air up in the sky • A hungry hawk is soaring by

The Food Chain RAP • On the snake the hawk will swoop • After it eats the hawk will poop • Who will clean up all this mess? • Here come the DECOMPOSERS at their best • If you’re a hawk you’ll eat a snake • A snake eats a mouse to stay in shape • A mouse eats some seeds and some grain • Put it together you have a FOOD CHAIN

Food Chains & Energy Flow