环境科学概论教学课件(第二讲)

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Composition of an ecosystem
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Biotic environment
Abiotic environment
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Limiting factor: A shortage or absence of a
key factor restricts the success of the species; thus the factor is known as a limiting factor.
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Niche -- Role
Niche: is the functional role it has in its surroundings (its profession).
A beaver’s ecological niche includes building dams and flooding forested areas, killing trees, providing 14 habitat for waterbirds and other animals.
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Monarch butterflies lay their eggs on various kinds of milkweed plants. The larvae eat the leaves of the milkweed plant. Thus, monarchs are limited by the number of milkweeds in the area.
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The Mechanism of Natural Selection
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1. Individuals within a species showed variation; some of the variations were very useful and others were not. For example, individual animals that are part of the same species show color variations. Some colors make the animal more conspicuous while others make it less conspicuous. 2. Organisms within a species typically produce many more offspring than can survive. This means that there is not enough suitable habitat for all of the offspring to grow to maturity. One apple tree may produce hundreds of apples with several seeds in each apple, or a pair of rabbits may have three to four litters of offspring each summer, with several young in each litter. 3. The excess number of individuals results in a struggle for survival. Individuals within the population must compete with each other for food, space, mates, or other requirements that are in limited supply. If you plant 100 bean seeds in a pot, many of them will begin to grow, but eventually some will become taller and shade the remaining plants. Great homed owls typically produce two young at a time, but if food is in short supply, the larger of the two young will get the majority of the food. 4. Because of variation among individuals, some have a greater chance of surviving and reproducing than others. The competition for resources often results in the less fit individuals dying; therefore, they do not get a chance to reproduce themselves. Even if they do not die, they may mature more slowly and not be able to reproduce as many times as the more fit members of the species. 5. As time passes and each generation is subjected to the same process, the percentage of individuals showing favorable variations will increase and those having unfavorable variations will decrease. 16 Thus, the species will become better and better adapted to its environment.
CHAPTER TWO
Interactions: Environment and Organisms
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Bee and sunflower
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Soybean and rhizobium
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Fish and coral
Fish and shrimp
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eagle frog
paddy
grasshopper snake
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OBJECTIVES After reading this chapter, you should be able to: Identify and list abiotic and biotic factors in an ecosystem. . Explain the significance of limiting factor Distinguish between habitat and niche. Distinguish between a population and a species. Describe how the process of natural selection operates to shape the ecological nich of an organism. Describe the process that lead to speciation, extinction, and coevolution. Describe predator-prey, parasite-host, competitive, mutualistic, and commensalistic relationships. Differentiate between a community and an ecosystem. List some of the components of an ecosystem. Define the roles of producer, herbivore, carnivore, omnivore, and decomposer. . Describe energy flow in an ecosystem. Relate the concepts of food webs and food chains to trophic levels. Explain the cycling of nutrients such as nitrogen, carbon, and phosphorus through an ecosystem.
2 The Role of Natural Selection and Evolution
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Population: a group of individuals of the same species inhabiting a particular area at a specific time. Species : is a population of organisms in which the individuals are potentially able to interbreed and produce fertile offspring. Natural selection: is the process that determines which individuals within a species will reproduce and pass their genes to the next generation. Gene: is distinct pieces of DNA that determine the characteristics an individual displays. Evolution: the changes that can be seen in the genes and the characteristic displayed by successive generations of population of organisms over time.
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1 Ecological Concepts
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Ecology: is the study of the ways organisms interact with each other and with their nonliving surroundings. Environment: Everything that affects an organism during its lifetime is collectively known as its environment. it is useful to subdivide the concept of environment into abiotic (nonliving) and biotic (living) factors. Abiotic factors can be organized into several broad categories: energy, nonliving matter, and processes that involve the interaction of nonliving matter and energy. Biotic factors include all forms of life with which it interacts. Limiting Factors: A shortage or absence of a key factor restricts the success of the species; thus the factor is known as a limiting factor. Habitat: The habitat of an organism is the space that the organism inhabits, the place where it lives (its address) Niche: is the functional role it has in its surroundings (its profession).
Milkweed
Monarch Butterfly Caterpillar
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Environment is the home.
Habitat(生境）:The habitat of an organism is the space that the
organism inhabits, the place where it lives (its address) .
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Habitat -- Place The habitat of mosses is typically cool, moist, and shady, since many mosses die if they are subjected to drying. In addition, mosses must have a thin layer water present in order to reproduce sexually.