[BIO 1306] Ch55_Lecture

[BIO 1306] Ch55_Lecture - 55 Community Ecology 55 Community...

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55 Community Ecology
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55 Community Ecology 55.1 What Are Ecological Communities? 55.2 What Processes Influence Community Structure? 55.3 How Do Species Interactions Cause Trophic Cascades? 55.4 How Do Disturbances Affect Ecological Communities? 55.5 What Determines Species Richness in Ecological Communities?
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55.1 What Are Ecological Communities? An ecological community consists of all the species that live and interact in a given area. In the early twentieth century, two plant ecologists debated the nature of communities. Henry Gleason argued that plant communities were loose associations of species; each species was distributed based on its environmental requirements.
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55.1 What Are Ecological Communities? Frederick Clements argued that plant communities were tightly integrated “superorganisms.” Communities in similar areas would have the same species. Studies of plant species distributions showed that different combinations of plants occurred in different locations, supporting Gleason’s view.
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Figure 55.1 Plant Distributions along an Environmental Gradient
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55.1 What Are Ecological Communities? Thus, ecological communities are not assemblages that move together as a unit. Each species has unique interactions with its environment. Nevertheless, ecologists still wish to understand how these loose assemblages of species function.
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55.1 What Are Ecological Communities? Organisms in a community can be divided into trophic levels based on their source of energy. Photosynthesizers or primary producers are autotrophs that get their energy directly from sunlight. All heterotrophs consume, directly or indirectly, the energy-rich molecules made by the primary producers.
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55.1 What Are Ecological Communities? Herbivores eat plants, and constitute the primary consumer level. Organisms that eat herbivores are secondary consumers . Organisms that eat secondary consumers are tertiary consumers . Detritivores or decomposers eat dead bodies and waste products.
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Table 55.1 The Major Trophic Levels
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55.1 What Are Ecological Communities? Organisms that get their food from more than one trophic level are omnivores . Many species are omnivores, and trophic levels are not clearly distinct, but the concept is a useful way of thinking about energy flow in a community.
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55.1 What Are Ecological Communities? A sequence in which a plant is eaten by an herbivore, which is eaten by a secondary consumer, etc. can be diagrammed as a food chain . Food chains are interconnected to make food webs .
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Figure 55.2 Food Webs Show Trophic Interactions in a Community
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What Are Ecological Communities? Most communities have only four to five trophic levels. Energy is lost between trophic levels. Diagrams showing energy or
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[BIO 1306] Ch55_Lecture - 55 Community Ecology 55 Community...

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