FOOD CHAINS and FOOD WEBS

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

ENERGY IN FOOD CHAINS ProducerPrimary consumer2 o consumer 10% 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 units 100 units 10 units 1 unit 100 units 10 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 [1 o ] consumers that eat producers c. THIRD TROPHIC LEVEL – carnivores or secondary [2 o ] 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 [3 o ] consumers that eat other carnivores

2. FOOD WEB - a series of interconnected food chains

HAWK WEASEL BOBCAT MOUSE GRASSHOPPER FROG SEEDS GRASS VOLE FALLEN LEAVES We will use this simpler food web to answer a series of questions

HAWK WEASEL BOBCAT MOUSE GRASSHOPPER FROG SEEDS GRASS VOLE FALLEN LEAVES Identify an autotroph Identify a primary consumer produces its own food eats a producer

HAWK WEASEL BOBCAT MOUSE GRASSHOPPER FROG SEEDS GRASS VOLE FALLEN LEAVES Identify a secondary consumer a carnivore that eats herbivores producer 1 o consumer 2 o consumer Identify a tertiary consumer a carnivore that eats other carnivores 3 o consumer 1o1o Consumer

Identify an organism at the fourth trophic level [show how it is at this level] HAWK WEASEL BOBCAT MOUSE GRASSHOPPER FROG SEEDS GRASS VOLE FALLEN LEAVES

HAWK WEASEL BOBCAT 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 WEASEL BOBCAT 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 voles voles now eat more grass voles eat more grass less grass for grasshoppers to eat fewer grasshoppers as they leave area as less food Over a longer time  less food means some voles leave fewer voles means less food for bobcat bobcats now eat more frogs fewer frogs means weasels eat more grasshoppers  fewer grasshoppers

HAWK WEASEL BOBCAT 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 & mice Less 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 voles If more voles, more food for bobcats  more bobcats

HAWK WEASEL BOBCAT 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 grass Less grass for grasshoppers & mice Fewer grasshoppers & mice, less food for hawks  fewer hawks Overall, less food for hawks  fewer hawks

HAWK WEASEL BOBCAT 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