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Chapter 9: Ecology Lesson 9.3: Relationships and Interactions in an Ecosystem Lesson Objectives Vocabulary

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Chapter 9: Ecology Lesson 9.3: Relationships and Interactions in an Ecosystem Lesson Objectives Vocabulary Chapter 9: Ecology Lesson 9.3: Relationships and Interactions in an Ecosystem Why are pyramids important in ecology? The classic example of a pyramid is shown here. But the pyramid structure can also represent the decrease in a measured substance from the lowest level on up. In ecology, pyramids model the use of energy from the producers through the ecosystem. What is the source of energy for almost all ecosystems? The Sun supports most of Earth's ecosystems. Plants create chemical energy from abiotic factors that include solar energy. Chemosynthesizing bacteria create usable chemical energy from unusable chemical energy. The food energy created by producers is passed to consumers, scavengers, and decomposers, thus it passes through the food chain. What does it mean to be interdependent? Organisms are not independent, they are interdependent. Species cannot live alone. All life needs other life to survive, many live in communities with other organisms. All species rely on other species in some way for their survival. They may rely on other species for food, shelter or to help them reproduce. Species are not independent, they are interdependent. Lesson Objectives • Describe how energy flows through ecosystems. • Explain how food chains and webs model feeding relationships. • Identify trophic levels in a food chain or web. • Define community as the term is used in ecology. • Describe interdependent relationship like predation and competition and their effects on population size. • Explain why interspecific competition leads to extinction or greater specialization. • Compare and contrast mutualism, commensalism, and parasitism. Vocabulary • biological interactions • intraspecific competition • carnivore • keystone species • chemoautotroph • mutualism • commensalism • omnivore • consumer (heterotroph) • parasitism • decomposer • photoautotroph • detritivore • predation • detritus • producer (autotroph) • food chain • saprotroph • food web • scavenger • herbivore • specialization • interdependent • trophic level • interspecific competition 301 Introduction When it comes to energy, ecosystems are not closed. They need constant inputs of energy. Most ecosystems get energy from sunlight. A small minority get energy from chemical compounds. Unlike energy, matter is not constantly added to ecosystems. Instead, it is recycled. Water and elements such as carbon, oxygen, phosphorus, nitrogen and hydrogen are constantly recycled. All biomes have populations of interacting species. Species interact in the same basic ways in all biomes. For example, all biomes have some species that prey on others for food. Species also compete with one another for living spaces, mates, habitats, and food resources. The focus of study of species interactions is the community. Symbiosis is a close relationship between two species in which at least one species benefits. For the other species, the relationship may be positive, negative, or neutral. There are three basic types of symbiosis: mutualism, commensalism, and parasitism. Community Relationships: How Energy Flows Through Ecosystems Energy enters ecosystems in the form of sunlight or chemical compounds. Some organisms, like producers (autotrophs) use this energy to make food (usable energy). Other organisms (consumers, heterotrophs) get energy by eating the producers. They pass some of the energy on to other consumers when they are eaten. In this way, energy flows from one living thing to another. All living things need energy. They need it to power the processes of life. For example, it takes energy to grow. It also takes energy to produce offspring. In fact, it takes energy just to stay alive. Remember that energy cannot be created or destroyed (first law of thermodynamics). It can only change form. Energy changes form as it moves through ecosystems. Producers (Autotrophs) Producers are organisms that produce food for themselves and other organisms. They use energy and simple inorganic molecules to make organic compounds. The stability of producers is vital to ecosystems because all organisms need organic molecules. Producers are also called autotrophs. There are two basic types of autotrophs: photoautotrophs and chemoautotrophs. 1. Photoautotrophs use energy from sunlight to make food by photosynthesis. They include plants, algae, and certain bacteria (see Figure 9.15, on next page). 2. Chemoautotrophs use energy from chemical compounds to make food by chemosynthesis. They include some bacteria and also Archaea. Archaea are microorganisms that resemble bacteria. The energy of the sun is first captured by producers, organisms that can make their own food. Many producers make their own food through the process of photosynthesis. The "food" the producers make is the sugar, glucose. Producers make food for the rest of the ecosystem. As energy is not recycled, energy must consistently be captured by producers. This energy is then passed on to the organisms that eat the producers, and then to the organisms that eat those organisms, and so on. Recall that the only required ingredients needed for photosynthesis are sunlight, carbon dioxide (CO2), and water (H2O). From these simple inorganic ingredients, photosynthetic organisms produce the carbohydrate glucose (C6 H12 O6), and other complex organic compounds. Essentially, these producers are changing the energy from the sunlight into a usable form of energy. They are also making the oxygen that we breathe. Oxygen is a waste product of photosynthesis. The survival of every ecosystem is dependent on the producers. Without producers capturing the energy from the sun and turning it into glucose, an ecosystem could not exist. On land, plants are the dominant producers. Phytoplanktons, tiny photosynthetic organisms, are the most common producers in the oceans and lakes. Algae, which is the green layer you might see floating on a pond, are an example of phytoplankton. 302 There are also bacteria that use chemical processes to produce food. They get their energy from sources other than the sun, but they are still called producers. This process is known as chemosynthesis, and is common in ecosystems without sunlight, such as certain marine ecosystems. Figure 9.15: Different types of photoautotrophs are important in different ecosystems. Consumers (Heterotrophs) Consumers are organisms that depend on other organisms for food. They take in organic molecules by essentially ‘‘eating” other living things. They include all animals and fungi. (Fungi don’t really ‘‘eat”; they absorb nutrients from other organisms.) They also include many bacteria and even a few plants, such as the pitcher plant in Figure 9.16. Consumers are also called heterotrophs. Heterotrophs are classified by what they eat: • Herbivores consume producers such as plants or algae. They are a necessary link between producers and other consumers. Examples include deer, rabbits, and mice. • Carnivores consume animals. Examples include lions, polar bears, hawks, frogs, salmon, and spiders. Carnivores that are unable to digest plants and must eat only animals are called obligate carnivores. Other carnivores can digest plants but do not commonly eat them. • Omnivores consume both plants and animals. They include humans, pigs, brown bears, gulls, crows, and some species of fish. Figure 9.16: Pitcher Plant. Virtually all plants are producers. This pitcher plant is an exception. It consumes insects. It traps them in a sticky substance in its flower. 303 Decomposers The organisms that obtain their energy from other organisms are called consumers. All animals are consumers, and they eat other organisms. Fungi and many protists and bacteria are also consumers. But, whereas animals eat other organisms, fungi, protists, and bacteria "consume" organisms through different methods, they are known as decomposers. When organisms die, they leave behind energy and matter in their remains. Decomposers break down the remains and other wastes and release simple inorganic molecules back to the environment. Producers can then use the molecules to make new organic compounds. The stability of decomposers is essential to every ecosystem. Decomposers are classified by the type of organic matter they break down: • Scavengers consume the soft tissues of dead animals. Examples of scavengers include vultures, raccoons, and blowflies. • Detritivores consume detritus—the dead leaves, animal feces, and other organic debris that collects on the soil or at the bottom of a body of water. On land, detritivores include earthworms, millipedes, and dung beetles (see Figure 9.17). In water, detritivores include ‘‘bottom feeders” such as sea cucumbers and catfish. • Saprotrophs are the final step in decomposition. They feed on any remaining organic matter that is left after other decomposers do their work. Saprotrophs include fungi and single-celled protozoa. Fungi are the only organisms that can decompose wood. Figure 9.17: Dung Beetle. This dung beetle is rolling a ball of feces to its nest to feed its young. Decomposers and Stability Decomposers (Figure 9.18) get nutrients and energy by breaking down dead organisms and animal wastes. Through this process, decomposers release nutrients, such as carbon and nitrogen, back into the environment. These nutrients are recycled back into the ecosystem so that the producers can use them. They are passed to other organisms when they are eaten or consumed. Many of these nutrients are recycled back into the soil, so they can be taken up by the roots of plants. The stability of an ecosystem depends on the
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