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