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1 Standards Preview Life Sciences Standard Set 3. Life Sciences 3. Living organisms depend on one another and on their environment for survival. As a basis for understanding this concept: 3.c. Students know many plants depend on animals for pollination and seed dispersal, and animals depend on plants for food and shelter. 3.b. Students know that in any particular environment, some kinds of plants and animals survive well, some survive less well, and some cannot survive at all. by Catherine Quirin Genre Comprehension Skill Text Features Science Content Nonfiction Cause and Effect Captions Diagrams Glossary How Living Things Survive Scott Foresman Science 4.5 ì<(sk$m)=cdffee< +^-Ä-U-Ä-U ISBN

2 Vocabulary adaptation community competition pollination population seed dispersal Plants and Animals in Ecosystems Picture Credits Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). 2 (BL) Zig Leszcynski/Animals Animals/Earth Scenes, (B) Tony Craddock/Photo Researchers, Inc.; 4 (BL) Michael & Patricia Fogden/Corbis; 6 (BL) Tim Fitzharris/Minden Pictures, (B) Tom Lazar/Animals Animals/Earth Scenes; 7 (BR) Michael Quinton/Minden Pictures, (B) Bosque Del Apache/Visuals Unlimited; 8 (BL) Steve Maslowski/Visuals Unlimited, (BR) Robert and Jean Pollock/Visuals Unlimited; 12 (BL) Mark Chappell/Animals Animals/Earth Scenes, (B) Gerald and Buff Corsi/Visuals Unlimited. by Catherine Quirin ISBN: Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois V

3 How do living things survive? Have you ever seen a squirrel scurrying through the trees? You may have seen just one squirrel, but you can be sure there are more nearby. All of those squirrels make up a population. A population is all of the same kind of living things that live in one place. A community is made up of all the different populations living in that place. Some populations work together to find food, travel, and protect each other from predators. Populations also must live with limited resources. This causes competition. Competition occurs when two or more living things must use the same limited resources. In Southern California s Mojave Desert, sidewinder snakes hunt rodents. Many sidewinder snakes compete for the same rodents. Different Kinds of Competition Plants compete for resources too. A lot of seedlings may sprout close to each other. But very few will become adult plants. There is not enough space for all of them. The taller plants will do better than the shorter ones. They can get more sunlight, which means they can make more food. Competition may also occur between different populations in a community. Sidewinder snakes are not the only desert animals that eat the Mojave Desert s small rodents. Barn owls and bobcats prey on the rodents as well. These predators must all compete for the same populations of rodents. This owl competes with the sidewinder snake for mice. This sidewinder snake must compete for food. 2 3

4 Animals Sharing Cactus wrens and desert bats both eat insects. The wrens hunt during the day, while the bats hunt at night. This reduces competition. It helps the wrens and bats share resources. The yucca moth and Joshua tree share resources through symbiosis. The moth helps the Joshua tree grow new seeds through pollination, which you will read about later. It lays its eggs in the tree s seedpods. The moth larvae eat the seeds when they hatch. The moth helps the tree grow. In return, its young get food. Symbiosis sometimes helps one organism while hurting the other. The one that is helped is called a parasite. The one that is hurt is called a host. Spider mites are a parasite. They take nutrients from the leaves of trees. Eating Different Foods As you know, animals are consumers. They eat other organisms to survive. Some animals reduce competition by eating more than one kind of food. Quails in California eat the seeds of grasses, shrubs, trees, and cacti. Golden eagles have been known to eat small animals, reptiles, birds, and fish. Gray foxes prefer small mammals. But they will eat eggs, insects, birds, acorns, and fruit when they are hungry. The less animals have to share the same resources with each other, the better their chances are for survival. Eating both insects and cactus fruit helps the desert bat survive. The yucca moth and Joshua tree live in symbiosis. 4 5

5 Animals and Territory Many animals compete for territory. Territory is the area where an animal lives. Animals get food, water, and space to live from their territory. By claiming and defending territory, animals can more easily get the resources they need. Animals have special ways of protecting their territory from others in their population and from predators in their community. When a predator threatens a killdeer s nest or young, the adult bird pretends to be injured. It hobbles along the ground dragging its wing so that it looks broken. Usually, the predator will follow the bird. Once the killdeer has led the predator away from the nest, it will fly safely away. Sandhill cranes have a different way of protecting their territory. They will stand straight and walk in a way that is like a soldier on parade. When they feel threatened they will also flap and ruffle their feathers, stomp the ground, and make sounds such as snorts or growls. When a sandhill crane is frightened by a nearby predator, it spreads its wings, sticks out its body as if it were about to attack, and walks toward the predator. At other times it will go into a crouch threat, ruffle threat, or charge. These are names scientists use to describe how a sandhill crane behaves when it feels threatened. When their territory is safe again, male and female sandhill cranes give a special call. The female crane makes a noise that sounds like a bugle. Then the male joins. The killdeer to the left is trying to scare away predators. The one below is pretending its wing is broken. The sandhill cranes to the right are making warning calls. The ones below are acting as if they are threatened. 6 7

6 Living Things and Environmental Change Organisms can survive better in some environments than in others. For example, you will not see a sidewinder snake in a rain forest. Organisms must have adaptations for their environments. An adaptation is a trait that helps an organism survive in its environment. White-tailed deer are reddish-brown in summer and fall. In winter, they change to a grayish-brown color. This color almost matches the color of the tree bark in the surrounding forests. It makes the deer difficult to see. These color changes are an adaptation to the environment. It can be hard for living things if the environment changes. One kind of sea bird lives only in the redwood forests of California. When redwoods are cut down, these birds have less space to live in. How Whales Are Adapted Whales are adapted to life underwater. They have a thick layer of fats and oils called blubber. This is an adaptation that helps them keep warm in cold water. Whales are also adapted to eating in the water. Some kinds of whales have plates in their mouths called baleen. When they squeeze seawater out of their mouths, tiny organisms called plankton get trapped in the baleen. Adaptation In the fall, the long-tailed weasel s brown fur matches the log and leaves. In the winter, its white fur matches the snow. As the diagram shows, whale blubber is very thick. It keeps whales warm in cold water. 8 9

7 Plant Adaptations Plants also have adaptations that help them live in their environment. Desert plants have many adaptations that help them survive in a dry climate. Cactus plants have adaptations that allow them to store and conserve, or save, water. For example, they do not have many leaves. The water in leaves evaporates into the air quickly. Without leaves, the cactus plants can save water. Some desert plants have also developed very long roots that can find water deep underground. These cactus plants have adaptations that help them live in dry desert environments. In order to grow seeds, flowering plants must be pollinated. Pollination is the movement of plant pollen from a male part of a flower to a female part. Birds, insects, and bats help pollinate plants. Plants often have sweet smelling or bright flowers. This adaptation helps attract the animals that pollinate plants. When they go to use the plant for food, they also pollinate it. Many plants also change when the weather changes. For example, some plants stop using sunlight to make food when winter arrives. Their leaves turn brown, red, yellow, or purple, and then drop off. Some plants use their roots, stems, seeds, or fruits to store food. By doing this, the plant can survive if the environment changes. Once the environment returns to the way it was, the plant can grow again. Insects such as this butterfly help pollinate plants

8 Animals Need Plants Not all animals get their energy from plants. But all animals need plants to survive. Animals that do not eat plants get their energy from animals that do eat plants. Animals live in places where the plants they eat grow. The kangaroo rat only lives in deserts. It feeds on seeds from grasses, mesquite, and creosote bushes. There is often very little water in the kangaroo rat s environment. The rat makes up for it by getting water from the seeds it eats. Plants use sunlight, water, and carbon dioxide to make their own food. In the process, they release oxygen into the air. Oxygen is important to living things, including people. Living things use it to get energy from the food they eat. People and Animals Using Plants Plants also provide shelter. Many animals hide in plants. Some insects even hide by looking like a part of a plant! In deserts, large bushes and cactus plants give animals such as lizards, snakes, and birds shade and places to live. Birds use twigs, moss, leaves, and other plant parts to build nests. The cactus wren builds its nest from dry grasses. It adds an outer layer of thorny twigs to protect against predators. People depend on plants as well. We use trees for lumber to build homes and furniture. Some plants provide us with tasty fruits and vegetables. Finally, many clothes are made from plant fibers such as cotton. Kangaroo rats eat the seeds of creosote bushes. A gilded flicker bird uses a cactus as its nesting place

9 Animals Help Plants Many plants need animals to survive as well. For example, some plants need animals to help pollinate them. Pollen is made in a flower s stamens. These are the male parts of a plant. For pollination to happen, pollen has to get from the stamens to the pistils. Flowers make a sweet liquid called nectar to lure animals to them. Animals such as bats, bees, butterflies, and birds eat nectar. These animals go from flower to flower trying to find nectar. The colors, smells, and shapes of the flower draw the animals to the nectar within them. Pollen rubs off on the animal s body when it eats the nectar. Then the pollen might stick to the pistil of the plant the animal goes to next. Fertilization When a pollen grain lands on a pistil, it starts growing a thin tube. The tube grows from the pollen down through the pistil. The pollen tube then gets to the egg cells inside the pistil. The pollen releases sperm cells into the tube. These cells combine with the egg cells in a process called fertilization. How does a plant make a pear or an orange? After the flower is fertilized, it changes a lot. The petals and stamens dry up and fall off. Then the fertilized egg changes into a seed. The bottom of the pistil gets bigger and becomes a fruit. The seed or seeds are protected by the fruit. Fertilization Process The bee gets nectar from the flower. It carries pollen from plant to plant. The rose attracts bees for pollination. After fertilization, the petals drop off. Seeds develop and grow into a fruit

10 How Seeds Move Some seeds just sprout where the plant drops them. Scattering seeds, or seed dispersal, can be more difficult. Some plants spread seeds using wind or water, but most need the help of animals. Many fruits not only protect seeds, but also attract animals. When animals eat the fruit, they often leave the seed in a place where it can grow. Birds sometimes scatter seeds by flying away with the fruit before eating it. Some animals, such as mice and other rodents, bury seeds to eat later. The buried seeds might sprout before the rodents have eaten them. Animals may also swallow the seeds when they eat the fruit. If the animal does not digest the seeds, they are part of the animal s waste. Then a new plant can grow from the undigested seed. When the bird flies away with the fruit, it will help the plant scatter its seeds. This dandelion is scattering its seeds into the wind. This is a type of seed dispersal

11 More Ways of Carrying Seeds Animals can even carry seeds they do not eat. Some seeds are in prickly pods called burs. Burs can get stuck in an animal s fur. Eventually the seed will drop to the ground and grow into a new plant. Other seeds may be carried by the wind or the water. Milkweed seeds have tufts of silky hairs at their tops. The hairs act like little parachutes, carrying the seeds on the wind until they drop somewhere else. Mango seeds can be carried by the ocean until they wash up on shore and sprout. You may be wondering why plants need adaptations for seed dispersal. Suppose all the seeds of an evergreen tree fell to the ground right under the tree. Many new trees might sprout up. But the new trees would have to compete with the parent tree and the other seedlings for water and nutrients. The parent tree s roots would get more of water and nutrients from the soil than the new trees could. It would also get more sunlight than the new trees could. The new trees would be unable to grow. As you can see, seeds are much more likely to grow if animals, wind, or water carry them to other places. The young tree is able to grow because it is away from the parent tree. Burs can stick to a dog s fur. When they drop off, they might grow into a new plant

12 Glossary adaptation a trait that helps an organism survive in its environment What did you learn? 1. What adaptations do cactus plants have for their environment? 2. How do insects, birds, and bats help plants survive? community competition pollination population seed dispersal all of the different populations in one place two or more living things using the same limited resources the movement of pollen from a male part of a flower to a female part all of the same kind of living things that live in one place the process of scattering plant seeds 3. In what ways do animals depend on plants? 4. Using information from the librarymedia center or other sources, choose one plant and one animal that live in the same place. Then write a report about the adaptations they have for surviving in that place. 5. Cause and Effect What could cause a decrease in the population of cactus wrens in an area? What effect might fewer cactus wrens have? 20