Concept:
An ecosystem consists of a community of living things interacting with eachother and the environment. Most ecosystems derive their energy directly orindirectly from the sun. Food chains and food webs represent the feedingpatterns of the members of an ecosystem.

Materials:

• Name cards of river plants, animals, and sun (enough for yourclass--list included at end of lesson)
  
• Ball of yarn

Procedure:

1. Pass out the name cards to the students. Give the sun the ball ofyarn.
   
2. Review with them that the sun is the source of all energy on theearth. Ask the student portraying the sun to whom he or she would throw theball of yarn to begin the food chain (green plant, or producer). The sunholds on to the end of the yarn and tosses the ball of yarn to a studentwearing the name of the plant. Ask the student why the first step of thechain is a plant.
   
3. Now ask the plant person who would get the ball of yarn next (planteater, or herbivore). Have the plant toss the ball of yarn to a studentwearing the namecard of a plant-eater animal. Be sure the "plant" holdsonto the yarn before tossing the ball.
   
4. The plant eater now looks around for something that eats it, andtosses the yarn to that animal (carnivore or omnivore).
   
5. The game progresses as each member of the food chain takes a turnwhile holding onto the yarn. The sequence stops at the top of the foodchain, a predator that has no enemies, such as a hawk.
   
6. Snip off the yarn and give it back to the sun. Start the sequenceagain. Those who participated before can have another turn, therebyillustrating the growth of a food web. An animal usually has more than onesource of food. For example, a bird can eat seeds and insects; or a hawkcan eat rabbits or snakes. The coyote and oppossum eat nearlyeverything--plants, animals and human foods.

Variation:
Have one link in the chain drop the yarn indicating its death due topesticide consumption. Students should hypothesize what happens to theother ends of that yarn. For example, the field mouse could have eaten somepoisoned bait. The plant it eats would possibly go unchecked. The snakethat normally would eat the mouse has to find another source of food, sinceit eats live prey. Also, if the snake eats a live contaminated mouse, itwill accumulate the same poison in its system, thereby affecting the hawkthat eats the snake.

Extensions:

• Students can make food web/chain mobiles using pictures from magazines,a hanger and string.
  
• Outdoors, students can explore for signs of food chains in nature, suchas finding owl pellets which are a good source of food chain information.Pellets can be purchased commercially and dissected to reveal what the owlhas eaten.
  
• Other signs of food chains are insect marks on plants such as chewedleaves or aphid colonies. Buy a praying mantis or lady bugs to place onthe plants to rid them of insects.
  
• Sing the song, "I Know an Old Lady Who Swallowed a Fly" and discusswith students if the song represents a true food chain. If they decide itdoesn't, ask them how it could be changed to be more scientificallyaccurate.

Riparian Food Chain Links:

Plants:	Herbivores:	Omnivores:
Watercress	Grasshopper	Coyote
Duckweed	Mallard duck	Mouse
Grasses	Rabbit	Oppossum
Algae	Butterfly	Raven
Castor bean	Mourning Dove	Pigeon
Water hyacinth	Snail	Raccoon
Cattail	Red-winged Blackbird

Carnivores:	Detritivores:
Garter snakes	Sow bugs
Red-tailed hawk	Bacteria
Feral cat	Fungi
Dragonfly
Great blue heron