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 Martin E. Lee Genre Comprehension Skill Text Features Science Content Nonfiction Cause and Effect Captions Diagrams Call Outs Glossary How Living Things Survive Scott Foresman Science 4.5 ì<(sk$m)=cdffdh< +^-Ä-U-Ä-U ISBN 0-328-23553-9
Vocabulary adaptation community competition pollination population seed dispersal Interactions 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. by Martin E. Lee Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson. ISBN: 0-328-23553-9 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 60025. 1 2 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06
What determines survival? Competition All of the owls that live in an area make up a population. A population is all of the same kind of living things that live in one place. All of the different populations in that place make up a community. Animal populations may hunt together, travel together, and protect each other. But their environment might not have enough resources. Competition happens when living things must use the same limited resources. Owls compete for food, shelter, and places to hunt. Mice compete for food and shelter from owls. Plants also compete to stay alive. Many seedlings may sprout close together. But only a few grow into mature plants. This is because there is not enough space for all of them. Taller plants get more sunlight than shorter plants do. This allows them to make more of their own food through photosynthesis. Their shorter neighbors in the shade may not be able to survive. Different populations in a community might compete. Snakes, owls, and mice all share an area. The owls and snakes must compete for the same population of mice. This mistletoe competes with other plants by taking resources from the tree. Owls compete with other animals for food sources such as mice. 2 3
Sharing Resources Both owls and hawks feed on the same kind of prey. Hawks do their hunting by day. Owls hunt at night. This reduces competition between hawks and owls. Symbiosis is two living things needing each other to live. One kind of symbiosis is with lichens. Lichens are fungi and algae. Algae supply food for the fungi. Fungi give algae water and protect them from sunlight. Symbiosis between living things can sometimes help one while it hurts the other. The organism that is helped is called a parasite. The one that is hurt is called the host. The mistletoe on page 3 is a parasite. The tree is a host. A Varied Diet Animals eat other living things to get the energy they need. Some animals compete by eating different kinds of food. Black bears eat in this way. They eat whatever they can find at different times of the year. Black bears eat grasses and meadow plants in the spring. All summer they claw into logs and stumps for insects. They eat pine cones, acorns, berries, and nuts in late summer and fall. They also eat fish. Bears will even eat trash left out by humans if they can get at it. Black bears sleep for much of the winter. In the spring they eat young plants and grasses. California s black bears hunt for salmon in the late summer. 4 5
Claiming and Defending Territory Many animals compete for territory. Territory is an area where an animal finds its food and water. It provides space for living and raising young. Territory helps animals get the resources they need. Animals do many things to claim and defend their territory. Male crickets sing loudly and fight each other for territory. Male butterflies defend where they perch. Mammals, including male bighorn sheep, elk, and deer, will crash their horns or antlers together to compete for territory. This also helps them attract mates. Skunks spray a smelly substance on animals that get too close. The bad smell works! Birds also have many behaviors for claiming or defending their territory. They may strut or sing. Or they will spread their wings wide. This makes them look threatening. The avocet is a shore bird. Avocets work together to protect their nesting areas. They make loud noises and rush away from the nest. Such behavior may distract predators. This red-winged blackbird is singing and spreading his wings wide to defend his territory. An avocet spreads its wings as wide as possible. This scares away predators. Plants Compete for Resources The desert has many creosote plants. Creosote plants seem to claim territory that other plants cannot survive in. Their wide, shallow root system helps them soak up water quickly. They soak up so much water that other plants cannot grow! 6 7
How do environmental changes affect living things? An adaptation is a trait that helps an organism survive in its environment. Color change is an adaptation. In spring, the feathers of birds called white-tailed ptarmigan are gray or brown. They blend in with plants. In winter, these birds have white feathers. They are able to blend in with snow and ice. A change in the environment can cause problems for living things. Many birds migrate to California salt marshes. But people have drained or built over most of these marshes. This has reduced space for migrating birds. This makes it harder for birds to survive. A ptarmigan s feathers change colors with the seasons. This makes it harder to see. Blubber is a thick layer of fats and oils under a whale s skin. This adaptation keeps whales warm in cold water. Whales Adaptations Flippers, smooth skin, and a tail fluke are adaptations that help whales swim. Whales are adapted to life underwater. Along with the adaptations shown in the picture, whales also have a special way to feed. They push seawater out of their mouths through plates called baleen. Baleen is like a filter. It traps tiny living things called plankton. Plankton are the whale s main food. One of the largest animals in the world survives by eating tiny sea life! 8 9
How Plants Survive Plants also have adaptations that help them survive. Pine trees have thin waxy leaves, also called needles. Pine needles do not lose much water. Some plants leaves or thorns are poisonous. This protects them from animals that would eat them. Pollination is the movement of plant pollen from a male part of a flower to a female part. Birds, bats, and insects help flowers pollinate. They move the pollen as they feed on the plants. Bright flowers and sweet smells are helpful adaptations for plants. They attract the animals that pollinate. Skunk cabbage grows in shade in moist forests. Its large leaves help it take in light. These plants bright colors are an adaptation. So are their thick leaves and stems. Plants often change as the weather changes. In winter, many plants stop using sunlight to make food. Their leaves turn brown and drop off. Some plants can store food in their roots, stems, seeds, or fruits. These adaptations allow the plant to survive winter. When spring returns, they can grow again. Plants compete for sunlight, water, nutrients, and living space. In a group of the same kind of plant, some plants will get more nutrients than others. This helps them grow taller. Taller plants will get more sunlight. This helps them make more food. 10 11
How do animals depend on plants? Food and Other Substances Animals would starve without plants. Some animals do not eat plants. But they get energy by eating animals that eat plants. Animals live where they can find the plants they eat. Monarch butterfly caterpillars eat only milkweed plants. Many caterpillars spend the winter in parts of California. Milkweed is easy to find in those areas. Milkweed plants contain a chemical. The chemical enters the monarch s body as it eats. This chemical tastes bad or even poisons other animals. But it protects the butterfly. Other animals learn not to eat the butterfly. Some animals get other things they need by eating plants too. Some desert animals survive by getting water from plants. Oxygen You have read that plants use energy from sunlight. They use the energy with water and carbon dioxide to make their own food. Plants also make oxygen when they make food. They release the oxygen into the air. This oxygen is important to all living things. People and other living things must have oxygen. Oxygen helps living things get energy from the food they eat. This sheep would starve if the grass died out. It depends on grass for energy. This monarch butterfly caterpillar gets its food from milkweed plants. 12 13
Shelter and Materials Animals also use plants for shelter. Some insects stay protected by looking like part of a plant. Many animals in tropical rain forests live in the trees their whole lives. This helps them stay safe. Fish and other water animals stay away from danger by hiding in plants. Large bushes and cactus plants in the desert give shade and shelter for snakes, lizards, and birds. Other animals use plants to build shelters of their own. Most birds build their nests from plant matter such as leaves, twigs, and moss. Beavers build dams and homes from trees and branches. Plants and People People depend on plants for all kinds of materials. Trees provide us with wood for buildings and furniture. The paper this book is printed on was made from plant fibers. The clothes you are wearing might be made from plants too! Many kinds of cloth are woven from plant fibers such as cotton. Other fibers, such as silk and wool, come from animals. But it takes plants to feed those animals. Wool comes from sheep that ate grass and other plants. The silkworms that spin silk fibers eat the leaves of mulberry trees. Everywhere you look, you will see something that came from a plant. This hummingbird uses plant fibers, moss, lichens, and spiderwebs to build its nest. Plant Fibers Yarn and linen cloth are made from the flax plant. Cotton cloth is made from cotton plants. 14 15
How do plants depend on animals? Pollen on the Move Pollen is made in stamens. Stamens are male parts of flowers. Pollen has to get to the pistils for pollination to happen. Pistils are the female parts. Some plants need help from animals in order to pollinate. Flowers make a sweet liquid called nectar. Bats, bees, butterflies, and birds eat nectar. They move from flower to flower in search of it. They are drawn by the flowers colors, smells, and shapes. Pollen rubs onto the animal s body as it eats the nectar. It may then stick to the pistil of the next plant the animal visits. Bees carry pollen back to their hives. From Fertilization to Food Suppose a pollen grain lands on a pistil. It may cause a thin tube to start growing down through the pistil. Soon the tube reaches the pistil s egg cells. Then sperm cells from the pollen move down the tube. There they combine with the egg cells. This is called fertilization. A flower goes through many changes after fertilization. The petals and stamens dry up and fall off. The fertilized egg soon develops into a seed. The bottom part of the pistil grows larger and becomes a fruit. The fruit protects the seed or seeds. Many animals eat these fruits. This flower has a pistil and stamens. The yellow part at the end of each stamen is pollen. This bat helps certain plants pollinate. 16 17
Seeds on the Move Some plants scatter their seeds by spreading them in the wind. Others spread them on moving water. Many plants rely on animals to help. Scattering seeds is called seed dispersal. Fruits protect seeds and attract hungry animals. Animals eat the fruit and leave the seeds behind. This often happens in a place where a seed can sprout. An animal may swallow plant seeds with the fruit it eats. The seeds may pass through its body without being digested. The seeds leave the animal s body with its other wastes. Those dropped seeds may sprout into new plants that grow far from the parent plant. Chipmunks, mice, and squirrels bury seeds to use later. But some seeds sprout before they are dug up. Seed Dispersal Some seeds are inside prickly pods called burs. Burs have tiny hooks that catch on an animal s fur. The animal carries the seed away when it moves. Eventually the bur will drop to the ground. The seeds in it may then grow into new plants. Seed dispersal helps plants in many ways. Think of a cherry tree. Many new cherry trees might sprout if they fell near the adult tree. But the tree and the seeds would compete for water, soil, nutrients, and sunlight, and the tree would get more of those things. The tiny, crowded seedlings would not be able to grow. Seeds have a better chance to grow if animals, wind, or water carry them away from their parent plant. The seeds stored by chipmunks can sprout before the chipmunks eat them. The seeds from this dandelion float in the wind like parachutes. Ocean currents might carry this coconut seed many kilometers. 18 19
Glossary adaptation a trait that helps an organism survive in its environment What did you learn? 1. How are populations and communities related? 2. How do algae and fungi help each other live? community competition pollination population 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 3. How do male bighorn sheep, elk, and deer compete for territory and attract mates? 4. Use information from different sources to write a report that answers this question: What adaptations do black bears have for staying alive? 5. Cause and Effect What has caused California s salt marshes to change? What has been an effect of this? seed dispersal the process of scattering plant seeds 20