Ecosystems: What They Are
1. Photographs of the earth taken from the moon made it clear as never before that the Earth is a sphere in the void of space like a spaceship on an everlasting journey. "Spaceship Earth" became a popular term and concept. Spaceship Earth is unique among all the planets we know. In addition to its rock base, it has an oxygen-rich atmosphere, an abundance of liquid water, and, most conspicuous, millions of kinds of living things of which we, Homo sapiens, are but one. The layer around the Earth where air (atmosphere), water (hydrosphere), and minerals (lithosphere) interact with living things is called the biosphere. 2. No living organism exists or can exist as an entity unto itself. Each organism is but one member of a particular species. The word "species" refers to the total population of a specific kind of plant, animal, or microbe. But no species is an entity unto itself either. All species depend on air, water, and nutritive elements from the earth's minerals. But plants, animals, and microbes also play important roles in removing pollutants from air and replenishing its oxygen and carbon dioxide, in purifying water, and in recycling mineral elements. Therefore, we can say that plants support animals; animal activities support plants; and all organisms help to support and maintain air, water, and soil quality. 3. Thus, the biosphere consists of a virtually infinite number of mutually dependent and mutually supportive interrelationships among all living organisms, air, water, and minerals. Humans are no less a Part of and no less dependent on these interrelationships than any oth-er species, although we frequently delude ourselves into thinking that we are. Our very term "natural resources" implies that all these things ~ air, water, soil, minerals, grasslands, forests, wildlife - are there simply tor our taking with no prices to be paid for their use, misuse, or pollu-tlQn, and no need to put anything back in return. However, there are Unit Three Ecosystems: What They Are
prices to be paid, and some of the prices, such as potential global warming, depletion of the ozone shield, and loss of tropical forests, may be steeper than we can afford. 4. It should be clear that sustainability of human society as well as sustainability of other species will depend on maintaining the integrity of the biosphere. To do this, we need to know how the biosphere works, how the biosphere functions to support all life. Thus, it is important to examine ecosystems. An ecosystem may be defined as a grouping of various species of plants, animals, and microbes interacting with each other and with their environment. The environment includes temperature, precipitation, amount of moisture, and all other chemical and physical factors to which organisms are exposed. Furthermore, the interrelationships are such that the entire grouping may perpetuate itself, perhaps indefinitely. This definition is a very condensed description of what is observed in nature and can be best understood by considering some examples of ecosystems with which you are probably already familiar. 5. A quick tour across the United States shows deciduous (leaf-shedding) forests in the East, which turn brilliant colors in the fall before the leaves drop; prairies or grasslands in the Central States; deserts with distinctive cacti in the South-west; and coniferous (evergreen) forests in the northern and western Mountain States. Across northern Canada and on the upper slopes of mountains, there are treeless expanses called tundra, and in equatorial regions we find tropical rainforests. These different ecosystems are the result of different climates, that is, different environmental conditions of temperature and rainfall. 6. Looking at these examples more closely, we note that each ecosystem is characterized by a distinctive plant community, which is defined as grouping of particular plants. Each plant community supports a particular array of animals. An array of microbes will be found in each ecosystem, feeding on dead plant and animal material. Each of these examples represents a distinctive grouping of plants, animals, and microbes interacting with one another and with the environment. Thus, each grouping in association with the environment that supports it is an ecosystem. Furthermore, we know that these groupings existed long before humans came on the scene and, if not disturbed by humans, would continue to exist for a very long time and perhaps even indefinitely. That is, ecosystems perpetuate themselves.
7. Major terrestrial ecosystems, such as forest or prairie, are not entirely uniform; each consists of a number of more or less distinct but related ecosystems. Thus, each is also called a biome, a term that refers to a number of closely related ecosystems. Within a biome, an ecosystem may include any more or less distinctive grouping of organisms interacting with each other in a particular environment. For instance, a patch of woods, an open field, a pond, a stream, each may be considered and studied as an ecosystem. While it is convenient to divide the biosphere into biomes and ecosystems for study and discussion, it is important to recognize that they seldom have distinct boundaries, and they are definitely not independent of one another. Rather, one ecosystem tends to blend into next through a transitional region called an ecotone, which is a region that contains many of the species and characteristics of the two adjacent systems. 8. The ecotone between adjacent systems may include unique environments that support distinctive plants and animals as well as those that are common to the adjoining ecosystems. Consider a marshy area, which often occurs between the open water of a lake and dry land. Whether they contain distinctive species or not, ecotones may be studied as ecosystems in their own right. Furthermore, some animal species - migratory birds, for instance, - may inhabit different ecosystems at different times of the year, and what happens in one ecosystem used by the migrators will definitely affect any other ecosystems used during other seasons. For example, losses and fragmentation of forests have disrupted migration lanes_and resulted in drastic declines in the populations of certain North American songbirds. How the loss of all these birds will affect various ecosystems is a question we just cannot answer at this time. 9. Oceans include a variety of environments depending on temperature, water depth, nature of the bottom, and concentrations of nutrients and sediments. Each of these environments, called marine environments, supports a more or less distinctive array of seaweeds, Plankton, fish, shellfish, and other marine organisms. Thus, different areas of oceans — reefs, continental shelves, deep oceans — may be studied as separate ecosystems, even though their interconnections and mterdependencies are obvious. There are conspicuous ecotones be- ween ocean and freshwater systems in the form of estuaries, and be- Unit Three Ecosystems: What They Are
Paragraph 1 earth sphere void of space oxygen-rich atmosphere liquid water layer air hydrosphere lithosphere biosphere Paragraph 2 entity nutritive elements replenish purifying water recycling soil quality paragraph3 interrelationships grasslands forests wildlife global wanning Paragraph 4 precipitation amount of moisture chemical and physical factors perpetuate Paragraph 5 deciduous (leaf-shedding) forests coniferous (evergreen) forests slopes treeless expanses tropical rainforests rainfall Paragraph 6 plant community array of animals in association with Paragraph 7 terrestrial ecosystems biome patch of woods open field pond stream boundaries blend transitional region adjacent systems paragraph8 adjoining ecosystems marshy area lake dry land migration lanes drastic declines Paragraph 9 bottom nutrients sediments reefs continental shelves freshwater systems beaches wetlands rocky coastlines Paragraph 10 movement wind divide EXERCISES I. READING COMPREHENSION 1. What is the main idea of the article? a. No living organism exists or can exist as an entity unto itself. b. Sustainability of human society will depend on maintaining the с The entire biosphere is really one mammoth ecosystem. 2. What is said about the Earth in paragraph 1 ? a. It is a sphere in the void of space. b. It is unique among all the planets, 3. According to paragraph 2, what does the word "species" refer to? a. Air, water, and nutritive elements from the earth's minerals. b. The total population of a specific kind of plant, animal or mi с Plants, animals, and microbes. 4. According to paragraph 3, some prices to be paid for use, misuse, a. potential global warming b. mutually supportive interrelationships among all living organisms 5. In paragraph 4, an ecosystem is defined as: a. temperature, precipitation, amount of moisture, and all other b. a very condensed description of what is observed in nature с a grouping of various species of plants, animals, and microbes interacting with each other and with their environment 6. Which paragraph gives a quick tour across the United States? a. Paragraph 4. b. Paragraph5. 7. How is each ecosystem characterized in paragraph 6? a. By grouping of particular plants. b. By a particular array of animals, 30_________________ Unit Three Ec0systems: What They Are___________________ 31 8. According to paragraph 7, the following may be considered as an a. a patch of woods, an open field b. distinctive grouping of organisms 9. Ecotones may be studied as: a. ecosystems in their own right b. some animal species 10. Different areas of oceans may be studied as: a. conspicuous ecotones between ocean and freshwater systems b. the land in the form of beaches, wet lands and rocky coastlines 11. According to paragraph 10, аИ ecosystems and biomes are inter a. the entire biosphere b. one mammoth ecosystem с the movement of air (wind) and water II. VOCABULARY
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