Balance in a food web Lesson 30 of the world course of Mova's primary school: 17 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: the lesson at school .
0 When an animal eats, most of the energy in its food is used up for moving, keeping warm and living, and only a small part (about a tenth) is built into its body and can pass on to whoever eats it. 1 So each step of a food chain has much less energy than the one below: there must be far more grass than zebras, and far more zebras than lions, which is why big predators are always rare. 2 In a food web everything is connected, so a change to one living thing spreads: when wolves disappeared from Yellowstone Park, deer grew so many that they ate the young trees by the rivers; when wolves came back, the trees grew again. 3 Sea otters eat sea urchins, and sea urchins eat kelp seaweed; where otters were hunted away, the urchins multiplied and ate whole kelp forests, and all the fish living in the kelp lost their home. 4 To guess what happens when one living thing disappears, follow the arrows: what it ate will grow in number, what ate it will go hungry and must switch food, shrink or move away. 5 Only about a tenth of the energy at one step of a food chain passes on to the next step. 6 Most of the energy an animal eats is used for moving, growing, keeping warm and staying alive. 7 Because energy is lost at each step, there are always far fewer predators than plant-eaters. 8 Food chains rarely have more than four or five steps, because too little energy is left at the top. 9 If a predator disappears, its prey usually increases in number. 10 If prey animals increase too much, they can eat too many plants and harm the whole habitat. 11 If a prey animal disappears, the predators that ate it must find other food, move away or decline. 12 An animal that eats many kinds of food survives the loss of one food more easily than an animal that eats only one. 13 Predators help keep a habitat healthy by stopping plant-eaters from growing too many. 14 In Yellowstone Park, returning wolves reduced the number of deer and the riverside trees grew back. 15 Sea otters protect kelp forests by eating the sea urchins that eat kelp. 16 A field of crops can feed many more people directly than through feeding animals for meat. ← previous Classifying unusual animalsnext → The skeleton and muscles↑ back to World This page in Markdown → https://md.mova.elamur.ai/free/en/corpora/school/world/30-balance-in-food-webs/