FOOD WEBS AND ENERGY FLOW

FOOD WEBS•Do you only eat one thing?

•In the wild, animals may eat more than one thing, so they belong to more than one food chain.

•To get the food they need, small herbivores may eat lots of different plants, and carnivores may eat many different animals.

FOOD WEBSWe can show this by using a food web, which is just a more

complicated version of a food chain.owl fox

rabbits

grass

mice

berriesseeds

BREAKING THE CHAIN

•Organisms living in a habitat depend on each other.

•If one part of a food chain dies out or is greatly reduced, the consumers have to find alternative food, move away, or starve.

•This then affects more consumers in the same way.

•More diversity = more stability

KEYSTONE SPECIES• Some species have a bigger

impact than others

• Species that have strong and/or wide-reaching effects on a community

• Removal of a keystone species can significantly alter the structure of a community.

• Examples:• Otters• Elephants• Oysters in Chesapeake • Beaver• Wolves

TO THINK ABOUT…

•When was the last time you saw a herbivore?

•When was the last time you saw a top carnivore?

ENERGY IN COMMUNITIESAn organismʼs rank in a feeding hierarchy is its trophic level.

Primary producers always occupy the first trophic level of any community.

In general, only about10% of the energy available at any trophic level is passed to the next; most of the rest is lost to the environment as heat.

Pyramid of Energy

10% RULE

•Food chains are not 100% efficient•90% is lost HOW?•Why does this matter?•Energy runs out•Food chains are short•We have fewer carnivores than herbivores

LET’S TRY!

10,000 Joules of energy

NUMBERS AND BIOMASS IN COMMUNITIESA trophic levelʼs biomass is the mass of living tissue it contains.

In general, there are more organisms and greater biomass at lower trophic levels than at higher ones.