Concept:
An ecosystem consists of a community of living things interacting with each other and the environment. Most ecosystems derive their energy directly or indirectly from the sun. Food chains and food webs represent the feeding patterns of the members of an ecosystem.

Materials:

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

Procedure:

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

Variation:
Have one link in the chain drop the yarn indicating its death due to pesticide consumption. Students should hypothesize what happens to the other ends of that yarn. For example, the field mouse could have eaten some poisoned bait. The plant it eats would possibly go unchecked. The snake that normally would eat the mouse has to find another source of food, since it eats live prey. Also, if the snake eats a live contaminated mouse, it will accumulate the same poison in its system, thereby affecting the hawk that 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, such as finding owl pellets which are a good source of food chain information. Pellets can be purchased commercially and dissected to reveal what the owl has eaten.
  
• Other signs of food chains are insect marks on plants such as chewed leaves or aphid colonies. Buy a praying mantis or lady bugs to place on the plants to rid them of insects.
  
• Sing the song, "I Know an Old Lady Who Swallowed a Fly" and discuss with students if the song represents a true food chain. If they decide it doesn't, ask them how it could be changed to be more scientifically accurate.

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