Ecosystems and Communities (Chapter 4)
An organism’s tolerance range for temperature, precipitation, and other abiotic factors helps determine where it lives. Biotic factors, such as competition, predation, and herbivory also help to determine an organism’s potential habitat and niche.
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4.1 Climate
A region’s climate is defined by year-after-year patterns of temperature and precipitation. Global climate is shaped by many factors, including solar energy trapped in the biosphere, latitude, and the transport of heat by winds and ocean currents. |
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4.2 Niches and Community Interactions
A niche is the range of physical and biological conditions in which a species lives and the way the species obtains what it needs to survive and reproduce. By causing species to divide resources, competition helps determine the number and kinds of species in a community and the niche each species occupies. Predators can affect the size of prey populations in a community and determine the places prey can live and feed. Herbivores can affect both the size and distribution of plant populations in a community and can determine the places that certain plants can survive and grow. Biologists recognize three main classes of symbiotic relationships in nature: mutualism, parasitism, and commensalism. |
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4.3 Succession
Ecosystems change over time, especially after disturbances, as some species die out and new species move in. Secondary succession in healthy ecosystems following natural disturbances often reproduces the original climax community. Ecosystems may or may not recover from human-caused disturbances. |
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4.4 Biomes
Biomes are described in terms of abiotic factors like climate and soil type, and biotic factors like plant and animal life. Mountain ranges and polar ice caps are not usually classified into biomes because they are not easily defined in terms of a typical community of plants and animals. |
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4.5 Aquatic Ecosystems
Aquatic organisms are affected primarily by the water’s depth, temperature, flow, and amount of dissolved nutrients. Freshwater ecosystems can be divided into three main categories: rivers and streams, lakes and ponds, and freshwater wetlands. Estuaries serve as spawning and nursery grounds for many ecologically and commercially important fish and shellfish species. Ecologists typically divide the ocean into zones based on depth and distance from shore. |
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