FOOD WEBS POWERED BY THE SUN
AFTER GEORGE SHOWED US the video of the whales making bubble nets, and Tom built the whale’s food chain, the kids cleared the dinner table. Then they moved into the living room of the summer house while we adults washed the dishes.
A while later, I wander out to see what the children are doing. They’ve set up a card table in the middle of the room and are gathered around it. But I see that, instead of playing cards or Monopoly, all four are writing stuff on pieces of paper.
“What are you doing?” I look over Julie’s shoulder.
“We’re all making our own food chains,” Julie answers, without looking up from her work. “We each picked an animal we like. Now we’re figuring out where they fit in a food chain. I chose the polar bear because I think they’re really beautiful. See, here’s the chain I’ve built.”
She hands me her paper, on which she’s drawn a chain with four links. In the links are pictures of a polar bear, a seal, some shrimp and krill, and some phytoplankton.
Phytoplankton can take carbon out of the air, using energy from the sun.
“How did you know that seals eat shrimps and krill?” I ask her.
“Looked it up on Google,” she answers. “But do people hunt polar bears, Gramps?” “Yes,” I reply, “but mostly the native peoples who live way up north. And they’re only allowed to kill a few each year.”
“You mean like the Eskimos?” Haley looks up from her drawing.
“That’s right. Actually those people in the far north are called the Inuit,” I explain. “They eat the meat from bears they kill, and use the skins to make warm clothing and boots.”
Julie takes her paper back. “I’ll add a link above the polar bear.” She draws a small link with a hunter inside. “It’s a little link because only a few people kill only a few polar bears. I’m glad, because polar bears are one of my favorite animals—especially the babies!”
“Good. A few people do eat a few polar bears. What about the other end of your chain? When Tom was doing the food chain for the whale, what did the phytoplankton grow on?”
“Carbon!” she shouts. “Gas Guy told us about how phytoplankton can take carbon out of carbon dioxide gas, using energy from the sun. Sun power!”
She pauses and goes on. “So those plants grow by using the carbon. Then the krill eat the sea plants, and the seals eat the krill, and my polar bear eats the seal!”
The Polar Bear Food Chain
“Good thinking!” I congratulate Julie and move on to Haley, who wants me to look at her drawing. “I picked the fox,” she says, “because a fox is really smart. Foxes eat mice and ducks and rabbits, so I put the duck in the next link down. Now I’m working on the third link.”
“Okay, so what do ducks eat?” I ask her.
“Ducks eat grass and weeds and small fish and things like that.” She sketches grass and weeds into her third link. Then she adds another link at the bottom and pauses, looking doubtful.
“So what do grasses eat?” I ask gently.
Haley chews thoughtfully on the end of her pencil. “Grass doesn’t have a mouth, so it can’t eat like animals do,” she murmurs quietly. She glances over at Julie’s chain and gets an idea.
“When Tom made the whale food chain, he showed us that thing called photosynthesis, where plants take carbon out of the air using the sun’s heat. And that’s how all those sea plants live. So maybe grass grows the same way, by using that carbon.”
“Exactly right!” I clap my hands. “That’s really good thinking!”
George is working on the opposite side of the table. “I picked an eagle,” he says proudly, as I peek at his paper. “The eagle is our national symbol!”
“That’s true,” I answer with a smile. “Where does it fit in your food chain?”
“Pretty much at the top, like the whale and the polar bear—except that people do kill a few eagles, even though it’s illegal.”
“So what do the eagles eat?” I continue as with the other kids.
George moves his paper over so that I can see it.
The Eagle Food Chain
“Eagles eat lots of different things,” he says, “so I did a chain with two different branches. This is the one with fish. See?”
He points to the picture. “My fish chain starts with people, of course. Then comes my eagle, which feeds on fish like trout and salmon. These big fish eat little fish, which eat krill. The krill eat plankton, which grow by taking carbon out of the air and water.”
Then he shows me how his duck branch also starts with humans, linking to the eagle, which eats the duck, which eats water plants, which also grow by using photosynthesis.
“Nice!” I say, as George finishes filling in his links. “So animals that eat lots of different things are part of several food chains.”
Animals that eat lots of different things belong to lots of food chains.
“Right,” George replies. “Eagles also sometimes eat rabbits and mice and things, so I could build food chains with those animals in them, too.”
Tom has been listening to George. “Same thing with my striped bass,” he says. “It eats lots of things, including a kind of herring called an alewife, and crabs, and sea worms. I’m building my first chain just using the herring.”
I see that Tom also has people in the top link of his chain. Then come seals, and in the third link is his striped bass. But Tom has made the fourth link bigger, to fit in lots of different things that bass eat—herring, crabs, sea worms, even krill.
The Striped Bass Food Chain
He has highlighted herring in yellow and shows in the next link that herring eat zooplankton, shrimp, small fish, and fish eggs. In that link shrimp is highlighted, and the link below that contains different things shrimp eat—zooplankton, seaweed, and baby clams. Zooplankton is colored here, and the next-to-last link shows that zooplankton eat phytoplankton.
Finally, in the bottom link, Tom has written CO2 for carbon—food for the phytoplankton plant. And beside that last link he’s drawn the sun, to show how energy from the sun makes photosynthesis happen.
“Wow!” I say. Tom’s food chain for the striped bass is the biggest one yet. “It looks like in most links there’s more than one animal or plant.”
Tom looks up and nods. “That’s right,” he says, “and I could have done the same thing in the top two links, with us people and with the seals. People eat lots of different plants and animals, and seals eat more than just bass. So it gets pretty complicated, showing all the links in all those food chains.”
For a few minutes I just watch while the four of them continue to work on their food chains. Then I have an idea.
“I wonder if there’s a way you could link all your food chains together?’
George straightens up from his drawing and looks at me curiously. “How do you mean, link them together?” he asks. “You mean, like, find out if our chains have the same animals or plants in them?”
He leans over to look at Haley’s chain. “Like both Haley and I have the duck in our chains?”
“Right,” I answer. “So your chain could link up with Haley’s at the duck. Have you ever played Scrabble? It’s kind of like that, but instead of building a new word on a letter of the earlier word, you’re using a whole word—duck—to connect one chain with another.”
Tom and Julie have been listening carefully. Now Julie looks over at Tom’s chain. “Shrimp!” she says quickly. “Tom, you and I can connect our chains with shrimp.”
Tom is walking around the table now, looking at all the chains. “So Julie can link with me through the shrimp, and I can link with George’s eagle, and George can link with Haley’s duck. Everybody can link up with everybody else! Let’s try it! But we’ll need a bigger piece of paper.”
He trots over to the desk in the living room and finds some tape. Using pieces of tape, he joins four pieces of paper together to make one big sheet. Then he draws three lines across the sheet so it’s divided into four long rows.
Julie gets the idea suddenly. “It’s like a puzzle!” she exclaims, bouncing up and down. “And Haley’s grass is pretty much the same as the phytoplankton in my chain. They both eat carbon.”
Julie’s phytoplankton is a plant, like Haley’s grass.
Haley has an idea, too.
“Hey Tom,” she says, grabbing his arm. “We can help you. I’ll cut up my chain and give you the pieces, so you don’t have to draw the whole thing again. George and Julie can do the same thing. Then you can just connect them up with the animals they share. It’ll be teamwork—just like with the whales and their bubble nets.”
“Good idea, but it might be too complicated,” Tom replies. He thinks for a minute.
“Let’s take the animals at the top of our food chains and put them in this top row.” He points to the top part of the big sheet. “See, Julie—you cut out your polar bear and put it there, and I put my person there, and George his eagle, and we could put the whale there, too. Then in the second row we’d put the animals that come next in our food chains, like my bass, Julie’s seal, George’s trout, and your duck.”
George likes that idea. “Works for me,” he says, smiling. “Let’s get going.”
AN HOUR HAS PASSED. I’ve been in the kitchen, talking with the other adults. When I return to the living room, Julie and Haley are on the couch playing a card game, but Tom and George are still hunched over the card table, finishing the giant food chain.
They’ve cut up their individual chains and pasted in the pictures of animals and plants on different levels of the big poster. In the first row, at the top of the food chain, are the whale, the person, the polar bear, and the eagle. Below each of those dominant animals are examples of what they eat. In the bottom row are lots of different kinds of phytoplankton (other plants), and next to them is the sun.
Tom opens the laptop and checks to make sure that shrimp eat zooplankton.
A food web constructed from the whale, polar bear, striped bass, and eagle food chains.
“Yikes,” I say. “That got pretty complicated.”
“Yup,” George murmurs, looking up at me with a tired smile. “The hard thing is, everything is kind of connected to everything else. Like, the man in the top row doesn’t just eat the seal right below him in his chain. He also eats the striped bass and the trout.” He points to two other examples from the second row.
“That’s right.” Tom nods. “And the striped bass in the second row eats pretty much everything in the third row.”
“We thought of drawing lines to connect all the animals to whatever they eat,” George adds, “but we realized there would be too many lines, and it would be a mess.”
Tom sits back in his chair. “If we did that, it wouldn’t look like chains any more. I think it would look more like a spider web.”
“That’s actually what scientists call it when you link together several food chains,” I offer. “The four of you have built a pretty detailed food web.”
“The four of you have built a pretty detailed food web.”
“The thing is, it could go on and on,” Tom observes, yawning and putting down his pencil. He points to the person at the top of the food web. “People all over the world eat so many different kinds of food—we could never make a picture that includes everything.”
“That’s a really important point,” I answer. Tom looks wiped out from all his work on the giant web, so I go behind him and give his shoulders and neck a little massage.
“All living things are connected to one another.” I sweep my hand across the food web. “That means we depend on all these other living things, because we’re at the top of the food web.”
I look around at all of them. “Which of the living things in your web do you think we depend on the most?”
Haley and Julie have been listening in. Now they put aside their cards and come over to the table. “I’d say the most important animals are the ones we eat,” Julie suggests. “Like, for instance, the fish.” She points at the bass and the trout.
Tom and George have a different idea. “We eat a lot of plants, like lettuce and carrots and potatoes and peas and all sorts of other vegetables,” says George. “And think of all the fruits, too.”
“Right,” Tom agrees, “and look at all the other animals that eat plants.” He gestures at the food web picture. “If you count phytoplankton as plants, then pretty much everything depends on plants.” He points to the phytoplankton in the bottom row of the food web.
Phytoplankton absorb carbon by photosynthesis and provide energy for the rest of the food web.
Julie’s eyes light up. “I see! Everything near the top of the food web needs what’s down near the bottom.”
“Good point!” I exclaim. “Food gives us and other animals the energy we need to live on and grow. So the energy comes from the plants at the bottom of the food web, which are eaten by the small animals, which carry the energy up to us big animals!”
Tom looks at me steadily, thinking hard. Then he picks up his pencil and draws a big arrow along the left side of the paper, from the bottom of the web pointing up to the top.
“There,” he sighs. “Energy flowing from plants to us through all those other animals.” He tosses his pencil onto the drawing.
George points to the big sun at the bottom of the paper. “The other thing is photosynthesis, like Tom was telling us,” he says. “Plants are the only things that can take carbon out of the air and use it to grow.”
“If plants are so important, what do they need to grow well?” I ask.
“I know!” says Julie, the Water Woman. “They need the water that comes from the water cycle!”
Haley looks at the sun in the picture. “And they need the sun, for energy to help them grow,” she says timidly.
Tom nods wearily. “That’s right” he says, “but not too much sun or they’ll burn up. Not too much and not too little. Just right!”
“Plants on land also need the right stuff in the dirt where they grow,” George notes. “That’s why we use fertilizer in our garden—to make our vegetables grow better and faster.”
I point again to the phytoplankton at the bottom of the food web. “What about these sea plants?” I ask. “What do they need?”
Tom is rolling up the big chart. He plans to use it in science class once school starts next month. “They live in water, so they’ve got that,” he says, thinking aloud. “They have the sun, when it’s shining on the ocean. And probably the temperature of the water makes a difference. It can’t be too hot or too cold, like with plants on land.”
He finds a rubber band in the desk and slips it over the rolled sheet. “I wonder if there’s other stuff in the sea water that helps sea plants grow … like fertilizer in the dirt?”
“That would make a good science project,” I suggest. “Don’t forget that phytoplankton produce about half of all the oxygen in our atmosphere, plus feeding the animals that feed us. So they’re super important, and we need to make sure they stay healthy.”
“Don’t forget that phytoplankton produce about half the oxygen in our atmosphere.”
Tom’s mouth opens in a huge yawn. “Too much to think about tonight, Gramps” he says. “See you tomorrow!”