Chapter 37 - Chapter 37 Lecture Outline Introduction...

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Chapter 37 Lecture Outline Introduction Dining In A. A special food chain. 1. Some insects go to extremes of interdependence. For example, chalcid wasps parasitize the eggs of ichneumon wasps, which have been laid in Apanteles wasp eggs, which have been laid in Pieris (cabbage butterfly) caterpillars (which eat cabbages) (chapter-opening photos). 2. One would be tempted to think such food chains could go on forever, as suggested by Jonathan Swift’s poem about fleas on fleas. However, there are good reasons this cannot be so. B. This chapter focuses on two interrelated levels of ecology: 1. Community structure and function depend on the interactions among organisms. 2. Ecosystem structure and function depend on the interactions of the community with its abiotic environment. I. Structural Features of Communities Module 37.1 A community includes all the organisms inhabiting a particular area. A. A community is an assemblage of all populations of organisms living close enough together for population interaction (Figure 37.1). The four main properties of a community are presented below. Review: The hierarchical organization of life (Module 1.1). 1. Species diversity refers to the variety of species present and has two components: richness (the number of different species) and relative abundance (the number of individuals of each species). A community with individuals divided equally among four species is very different from a community with the same species unequally represented. 2. The nature of the dominant organisms is an important property. This can involve either vegetation or animals. The dominant species in Figure 37.1 are the grasses. NOTE: Another example is the dominance of mosses, shrubs, grasses, and lichens in alpine tundras and the clumps of different vegetation groups (Module 34.17). 3. The response to a disturbance by a community illustrates the stability of the community, the ability to resist change, and the return of the original species’ composition and structure. 4. The fourth property of communities is their trophic structure, the nutritional relationships among all the components (Modules 37.9–37.11). B. There are four interspecific interactions that tie populations together in communities: competition, predation, herbivory, and symbiosis. These interactions are all influenced by evolution through natural selection. Module 37.2 Competition may occur when a shared resource is limited.   A. Interspecific competition occurs when two species are competing for the same resources. Competition between two species can inhibit the growth of both populations, sometimes to the point where one is eliminated. B. In the 1930s, Gause studied interspecific competition between two species of paramecium. When grown in separate cultures with the same amount of food being added each day, each species’ population followed a logistic growth curve (Module 36.4). When grown together, one species of paramecium eliminated its competitor. C.
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Chapter 37 - Chapter 37 Lecture Outline Introduction...

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