3 Types of Interactions

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1 CHAPTER 18 3 Types of Interactions SECTION Interactions of Living Things BEFORE YOU READ After you read this section, you should be able to answer these questions: What determines an area s carrying capacity? Why does competition occur? How do organisms avoid being eaten? What are three kinds of symbiotic relationships? National Science Education Standards LS 3a, 3c, 4b, 4d How Does the Environment Control Population Sizes? Most living things have more offspring than will survive. A female frog, for example, may lay hundreds of eggs in a small pond. If all of the eggs became frogs, the pond would soon become very crowded. There would not be enough food for the frogs or other organisms in the pond. But in nature, this usually does not happen. The biotic and abiotic factors in the pond control the frog population so that it does not get too large. Populations cannot grow without stopping because the environment has only a certain amount of food, water, space, and other resources. A resource that keeps a population from growing forever is called a limiting factor. Food is often a limiting factor in an ecosystem. All plants need sunlight. In this forest, sunlight may be a limiting factor. Not all plants can get the same amount of light. STUDY TIP Make a List As you read this section, write down any questions you may have. Work with a partner to find the answers to your questions. STANDARDS CHECK LS 4d The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem. Word Help: resource anything that can be used to take care of a need 1. Define What is a limiting factor? Interactive Textbook 301 Interactions of Living Things

2 What Is Carrying Capacity? The largest number of organisms that can live in an environment is called the carrying capacity. When a population grows beyond the carrying capacity, limiting factors will cause some individuals to leave the area or to die. As individuals die or leave, the population decreases. The carrying capacity of an area can change if the amount of the limiting factor changes. For example, the carrying capacity of an area will be higher in seasons when more food is available. 2. Explain Why can the carrying capacity of an area change? How Do Organisms Interact in an Ecosystem? Populations are made of individuals of the same species. Communities are made of different populations that interact. There are four main ways that individuals and populations affect one another in an ecosystem: in competition, as predator and prey, through symbiosis, and coevolution. 3. List What are four ways that organisms in an ecosystem interact? Interactive Textbook 302 Interactions of Living Things

3 Why Do Organisms Compete? Competition happens when more than one individual or population tries to use the same resource. There may not be enough resources, such as food, water, shelter, or sunlight, for all the organisms in an environment. When one individual or population uses a resource, there is less for others to use. Competition can happen between organisms in the same population. For example, in Yellowstone National Park, elk compete with one another for the same plants. In the winter, when there are not many plants, competition is much higher. Some elk will die because there is not enough food. In spring, when many plants grow, there is more food for the elk, and competition is lower. Competition can also happen between populations. In a forest, different types of trees compete to grow in the same area. All of the plant populations must compete for the same resources: sunlight, space, water, and nutrients. Critical Thinking 4. Predict In a prairie ecosystem, which two of the following organisms most likely compete for the same food source: elk, coyotes, prairie dogs, vultures? How Do Predators and Prey Interact? Another way organisms interact is when one organism eats another to get energy. The organism that is eaten is called the prey. The organism that eats the prey is called the predator. When a bird eats a worm, for example, the bird is the predator, and the worm is the prey. PREDATORS Predators have traits or skills that help them catch and kill their prey. Different types of predators have different skills and traits. For example, a cheetah uses its speed to catch prey. On the other hand, tigers have colors that let them blend with the environment so that prey cannot see them easily. 5. Identify What are two traits different predators may have to help them catch prey? Interactive Textbook 303 Interactions of Living Things

4 Say It Discuss In small groups, talk about other animals that escape predators in the four ways described in the text. PREY Prey generally have some way to protect themselves from being eaten. Different types of organisms protect themselves in different ways: 1. Run Away When a rabbit is in danger, it runs. Critical Thinking 6. Infer Why do you think it would be difficult for predators to attack animals in a herd? 2. Travel in Groups Some animals, such as musk oxen, travel in herds, or groups. Many fishes, such as anchovies, travel in schools. All the animals in these groups can help one another by watching for predators. When musk oxen sense danger, they move close together to protect their young. 3. Show Warning Colors Some organisms have bright colors that act as a warning. The colors warn predators that the prey might be poisonous. A brightly colored fire salamander, for example, sprays a poison that burns. Interactive Textbook 304 Interactions of Living Things

5 TAKE A LOOK 7. Color A fire salamander has a black body with bright orange or yellow spots. Use colored pencils to give this salamander its warning colors. 4. Use Camouflage Some organisms can hide from predators by blending in with the background. This is called camouflage. A rabbit s natural colors, for example, may help it blend in with dead leaves or shrubs so that it cannot be seen. Some animals may look like twigs, stone, or bark. What Is Symbiosis? Some species have very close interactions with other species. A close association between two or more species is called symbiosis. Each individual in a symbiotic relationship may be helped, hurt, or not affected by another individual. Often, one species lives on or in another species. Most symbiotic relationships can be divided into three types: mutualism, commensalism, and parasitism. MUTUALISM When both individuals in a symbiotic relationship are helped, it is called mutualism. You can see mutualism in the relationship between a bee and a flower. 8. List List the three types of symbiotic relationships. Organism hurt? Organism helped? Example No one both organisms A bee transfers pollen for a flower; a flower provides nectar to a bee. Interactive Textbook 305 Interactions of Living Things

6 In a mutualistic relationship, both species benefit. Critical Thinking 9. Compare How does mutualism differ from commensalism? COMMENSALISM When one individual in a symbiotic relationship is helped but the other is not affected, this is called commensalism. Organism hurt? Organism helped? Example No one one of the organisms A fish called a remora attaches to a shark and eats the shark s leftovers. The remoras get a free meal, but the shark is not harmed. 10. Define In parasitism, is the host helped or hurt? PARASITISM A symbiotic relationship in which one individual is hurt and the other is helped is called parasitism. The organism that is helped is called the parasite. The organism that is hurt is called the host. Organism hurt? Organism helped? Example Host parasite A flea is a parasite on a dog. Interactive Textbook 306 Interactions of Living Things

7 TAKE A LOOK 11. Infer How do you think the caterpillar helps the wasps? This tomato hornworm is being parasitized by young wasps. Their cocoons are on the caterpillar s back. What Is Coevolution? Relationships between organisms change over time. Interactions can even be one reason that organisms change. When a long-term change happens in two species because of their close interactions, the change is called coevolution. One example of coevolution can be seen in some flowers and the organisms that pollinate them. A pollinator is an organism, such as a bird, insect, or bat, that carries pollen from one flower to another. Flowers need to attract pollinators to help them reproduce. Different flowers have evolved different ways to attract pollinators. Some use colors or odors. Others use nectar as a food reward for the pollinator. Some plants can use a variety of pollinators. Others have coevolved with certain pollinators. For example, the bat in the picture below has a long sticky tongue. It uses its tongue to get nectar from deep inside the flower. Only an organism with a way to reach the nectar could be a pollinator for this flower.. Say It Investigate With a partner, look up the meaning of the suffix co-. Discuss how the meaning of this suffix can help you remember what coevolution means. Think of some other words that have co-. Interactive Textbook 307 Interactions of Living Things

8 Section 3 Review NSES LS 3a, 3c, 4b, 4d SECTION VOCABULARY carrying capacity the largest population that an environment can support at any given time coevolution the evolution of two species that is due to mutual influence, often in a way that makes the relationship more beneficial to both species commensalism a relationship between two organisms in which one organism benefits and the other is unaffected mutualism a relationship between two species in which both species benefit parasitism a relationship between two species in which one species, the parasite, benefits from the other species, the host, which is harmed predator an organism that kills and eats all or part of another organism prey an organism that is killed and eaten by another organism symbiosis a relationship in which two different organisms live in close association with each other 1. Identify What are two resources for which organisms are likely to compete? 2. Explain What happens to a population when it grows larger than its carrying capacity? 3. Infer Do you think the carrying capacity is the same for all species in an ecosystem? Explain your answer. 4. Summarize Complete the chart below to describe the different kinds of symbiotic relationships. Example organisms Type of symbiosis Organism(s) helped Organism(s) hurt Flea and dog host (dog) Bee and flower mutualism Remora and shark none 5. Apply Concepts The flowers of many plants provide a food reward, such as nectar, to pollinators. Some plants, however, attract pollinators but provide no reward. What type of symbiosis best describes this relationship? Explain your answer. Interactive Textbook 308 Interactions of Living Things

9 Life Science Answer Key continued 4. No, only organisms of one species make up a population. There are usually more than one species of bird in an area. SECTION 2 LIVING THINGS NEED ENERGY 1. Producers use energy from sunlight to make their own food. 2. Tigers: carnivores Deer: herbivores Humans: omnivores 3. Decomposers break down dead matter into nutrients for other organisms to use. 4. Labels go on sun, grasses, prairie dog, coyote, vulture, and bacteria, in that order. 5. Most organisms eat more than one type of food. 6. Without producers, consumers would have no food. None of the animals would live. 7. about 90% 8. The middle level deer are herbivores like the prairie dogs. 9. Wolves were at the top of the food chain and controlled the populations of herbivores. Review 1. Producers use energy from the sun to make their own food. Producers are the base of the food chain. All consumers depend on producers. 2. Grass (Producer) Mouse (Primary consumer) Snake (Secondary consumer) 3. Answers will vary but should include at least one of the organisms from question No, energy is lost as it moves through a food chain. After a few steps in the chain, there isn t enough energy left to support more organisms. TYPES OF INTERACTIONS 1. a resource that keeps a population from growing forever 2. if the amount of the limiting factor changes 3. in competition, as predator and prey, through symbiosis, and coevolution 4. elk and prairie dogs 5. speed, colors that let them blend with the environment 6. Possible answer: It may be difficult for the predator to see individual animals in the group. 7. Any combination of black and orange patches is acceptable. 8. mutualism, commensalism, parasitism 9. In mutualism, both species benefit. In commensalism, only one species benefits. 10. The host is hurt. 11. The wasps can use the caterpillar for food. Review 1. Possible answers: food, water, sunlight, shade, shelter 2. Individuals will die or will have to move to a new area. This will cause the population to decrease. 3. No, some species may use more resources than others. Some species may be more affected than others by a limiting factor. 4. First row, left to right: parasitism, parasite (flea) Second row, left to right: both, none Third row, left to right: commensalism 5. Commensalism; the pollinator is not harmed, but the plant still benefits. Chapter 19 Cycles in Nature SECTION 1 THE CYCLES OF MATTER 1. Water vapor cools and changes into drops of liquid water. The water drops form clouds. 2. Photosynthesis uses carbon dioxide from the air. When the sugars that a plant makes during photosynthesis are broken down, carbon returns to the environment. 3. photosynthesis 4. respiration, combustion, decomposition 5. Animals need to get nitrogen from plants or other animals. Plants get their nitrogen from nitrogen fixation. 6. decomposition 7. They are recycled in the environment or reused by other organisms. Review 1. energy from the sun 2. There should be arrows from air to plants to animals to decomposers to air, and from plants to decomposers. 3. Matter on Earth is limited, so it needs to be used over and over again. 4. Living things are made mostly of water. Water carries nutrients to cells and carries wastes away. Water also helps organisms regulate their body temperatures. Interactive Textbook Answer Key 21 Life Science