FOOD CHAINS and FOOD WEBS

FOOD CHAINSAre designed to show the direction that energy flows from producers to top carnivores, in a simplified single pathway.

ENERGY IN FOOD CHAINSENERGY IN FOOD CHAINS

Producer Primary consumer 2o consumer10% 10%

90% 90%

energy used to live

energy passed to consumer

10% Rule: only 10% of the energy in an organism is passed on to the next trophic level

1000 units100 units

10 units

1 unit 100 units10 units

FOOD WEBS & TROPHIC LEVELS

1. TROPHIC LEVEL - the place in a food chain that an organism feeds

a. FIRST TROPHIC LEVEL - producers or autotrophs that feed themselves

b. SECOND TROPHIC LEVEL - herbivores or primary [1o] consumers that eat producers

c. THIRD TROPHIC LEVEL – carnivores or secondary [2o] consumers that eat herbivores

*Any organisms found at the second trophic level or higher are considered to be heterotrophs i.e. they do not produce their own food

d. FOURTH TROPHIC LEVEL – carnivore or tertiary [3o] consumers that eat other carnivores

2. FOOD WEB - a series of interconnected food chains

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

We will use this simpler food web to answer a series of questions

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

Identify an autotroph

Identify a primary consumer

produces its own food

eats a producer

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

Identify a secondary consumer a carnivore that eats herbivores

producer

1o consumer

2o consumer

Identify a tertiary consumer a carnivore that eats other carnivores

3o consumer

1o Consumer

Identify an organism at the fourth trophic level [show how it is at this level]

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

Identify a decomposer something that eats dead things

Identify an omnivore something that eats both plants & animals

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

Explain, what would be the effect on grasshoppers if fewer leaves

fewer fallen leaves means less food for volesvoles now eat more grassvoles eat more grassless grass for grasshoppers to eat

fewer grasshoppers as they leave area as less food

Over a longer time

less food means some voles leavefewer voles means less food for bobcatbobcats now eat more frogsfewer frogs means weasels eat more grasshoppers fewer grasshoppers

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

Explain what would be the effect on bobcats if fewer grasshoppers

Fewer grasshoppers means less grass & seeds being eaten and less food for frog, weasels & miceLess food for frogs means frogs leave

If fewer frogs, less food for bobcats fewer bobcats

Over a longer time

If more grass, more food for volesIf more voles, more food for bobcats more bobcats

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

Explain what would be the effect on hawk if fewer bobcats.

Fewer bobcats means more voles and frogs

more frogs means more grasshoppers eaten

Fewer grasshoppers means less food for mice & weasels [although weasels can eat frogs]

Over a longer time

More voles eat more grassLess grass for grasshoppers & mice

Fewer grasshoppers & mice, less food for hawks fewer hawksOverall, less food for hawks fewer hawks

HAWK

WEASELBOBCAT

MOUSE

GRASSHOPPER

FROG

SEEDS GRASS

VOLE

FALLEN LEAVES

Explain what would be the effect on voles if fewer hawks

Fewer hawks means more weasels and more mice

More mice & weasels eat more grasshoppers

So now fewer grasshoppers so they eat less grass

Now more grass, so more food for voles more voles

References

•Investigating Science – Pearson• A. Dercho