1.11: Food Chains and Food Webs

Food Chains In order to understand how one organism can affect other organisms, ecologists use the idea of food chains and food webs Food Chain – a feeding order in which each kind of organism eats the one below it Sarah

Example of a Food Chain Grass Mouse Snake Fox Wolf Producer/ Autotrophs Primary Consumer Secondary Consumer Tertiary Consumer Quaternary Consumer Sarah Herbivore Carnivores Top Carnivore (not eaten by any other organism)

Trophic Levels Scientists also use another naming method to classify where organisms are on food chains called trophic levels Trophic Level – a way of categorizing living things according to how they gain their energy Sarah

Example of a Food Chain 1st Trophic Level 2nd Trophic Level 3rd Trophic Level 4th Trophic Level 5th Trophic Level Grass Mouse Snake Fox Wolf Sarah Producer/ Autotrophs Primary Consumer Secondary Consumer Tertiary Consumer Quaternary Consumer Top Carnivore (not eaten by any other organism) Herbivore Carnivores

Some Things to Keep In Mind… The producer/autotroph is always at the 1st trophic level, the primary consumer is always at the 2nd trophic level, the secondary consumer is always at the 3rd trophic level, and so on. The primary consumer eat autotrophs, secondary consumers eat the primary consumers, and so on. Sarah

Some Things to Keep In Mind… Producer = Autotroph (something that can produce its own food from sunlight or basic nutrients) Consumer = Heterotroph (something that has to get its food by eating other organisms) Sarah

Label the Following Food Chains! secondary consumer 3rd trophic level secondary consumer 3rd trophic level fox wolf primary consumer primary consumer 2nd trophic level 2nd trophic level deer rabbit Sarah producer/ autotroph 1st trophic level producer/ autotroph 1st trophic level grass shrub

Any Changes at One Level Affect All Other Levels of a Food Chain Hypothesize! If the number of deer suddenly goes down, then: 1) The number of wolves will go down because they will have no food 2) There will be more shrubs, since no deer are available to eat them wolf deer Sarah shrub

Food Webs In any one ecosystem, there can be many types of producers, primary consumers, secondary consumers, etc. Any individual organism is involved in many food chains. Food Web – two or more food chains inter-connected Sarah

A Food Web fox wolf deer grasshopper rabbit Sarah grass grass shrub

Time to Think! True or False: There are 3 food chains in the food web False: There are many food chains in the food web Which animal is the top carnivore in this food web? The wolf Which organisms are the primary consumers? Grasshopper, rabbit, deer On the web, which organism is on the 3rd trophic level in most of the food chains, but on the 4th trophic level on one of the food chains? The wolf (it consumes the fox in one of the food chains) Sarah

One Last Thing… Decomposers (organisms that break down and feed on dead organisms) are usually not included on food chain diagrams Some organisms that are omnivores (eat both plants and animals) might be on a different trophic level depending on what food chain you are looking at Sarah

Case Study: The Cane Toad Cane Toad was introduced to Australia in 1935 from Hawaii to combat the Cane Beetle population that was destroying their Sugar Cane crops. Toads could not reach the beetles which live high up on the sugar cane They started to eat everything small enough to fit in their mouths Sarah

Case Study: The Cane Toad There is no natural predator for the toad in Australia They poison anything that tries to eat them The introduction of a species to control another species is called biological control. In every single case the outcome is never one we expect Cane Toad Sarah

Homework! Read Pg. 34-35 Do questions #1-7 (Pg. 39) Sarah