Sitting in a circle version:
Sit at the carpet in a circle. (Standing can work too for older students.)
Hand each student a card with a living thing on it. Students hang it around their neck to display their living thing for everyone to see. Each student tells the class what living thing they are.
Hand a ball of yarn to a student who has a plant on their label. Tape the end of the yarn to the carpet securely with duct tape in front of them.
After class discussion, pass the yarn ball to a student that has a living thing that would eat the plant. Make a line of wool stretching between them, then tape the yarn strand to the floor in front of the new living thing.
Continue, connecting more living things together.
Once you get to the top of the food chain (top predator like cougar), it can be connected to a living thing that might grow out of its body after it dies e.g. mushrooms. Or, after a top predator, you can also move back down the food chain to something that is eaten by the predator. The order does not really matter, but just connect all the living things to something else by who eats who.
To help determine who has not yet been included in the food chain, students can remove their card from around their neck and place it on their tape piece on the floor in front of them.
A criss-crossing web of connections is made, forming a 'Food web'. (A food web is many connected food chains.)
Depending on the age of the students and how long they can sit, living things can be linked many times.
For younger students, include each student once, then discuss how there are many more connections.
This activity is similar to: https://betterlesson.com/lesson/640194/the-food-web (see the Explore/Explain section). This lesson also includes the sun and talks about transfer of energy through the food chains.
Tabletop version:
Give student groups a stack of index cards with a living thing named on each.
Students lay the cards on a table, then use lengths of wool to connect the living things that eat each other.
Students could add their own living things to their food web.
Compare the food webs that each group made.
As a class, discuss how complicated a food web is, and how living things depend on each other. If one living thing is removed, through habitat change or human interference, other living things are affected.