The Nature of Ecology
Ecology is a study of the connections among organisms and their living and nonliving environment. The cell is the basic unit of life in organisms. An organism is either prokaryotic or eukaryotic.
Organisms may reproduce by asexual reproduction or sexual reproduction. Organisms that reproduce sexually are classified as members of the same species if they can interbreed.Members of a species that reside in the same area at the same time constitute a population. A population normally lives in a particular habitat and shows genetic diversity. Populations of many species make up a community. An ecosystem is a community and its nonliving environment.
4-2 The Earth's Life-Support Systems
The lower portion of the earth's atmosphere is the troposphere. The next layer is thestratosphere. The portions of the earth's atmosphere, hydrosphere, and lithosphere in which living organisms exist constitute the biosphere.
Life on the earth is sustained by three interconnected factors: the one-way flow of energy from the sun through the biosphere and back into space, the cycling of matter that living organisms need as nutrients for their survival, and gravity.
4-3 EcosystemConcepts and Components
Biologists have classified the terrestrial portion of the biosphere into biomes. Each has a distinct climate and specific life forms. Marine and freshwater portions of the biosphere are divided into aquatic life zones.
Abiotic components of an ecosystem are physical and chemical factors that influence living organisms. Each population has a range of tolerance to variousabiotic factors and its tolerance limits determine its abundance and distribution. The number of organisms in a population can be affected by a single limiting factor.
Most producers capture sunlight energy and make carbohydrates by way of photosynthesis. Some producers carry out chemosynthesis. All other organisms in an ecosystem are consumers or heterotrophs.
Most organisms release energy by aerobicrespiration, which requires oxygen. Some get energy by anaerobic respiration.
Biological diversity is an important renewable resource.
4-4 Connections: Food Webs and Energy Flow in Ecosystems
Organisms get the food and nutrients they need by participating in a food chain. Various food chains can link together to form a food web. Each organism in an ecosystem can be assigned to a trophic level inits food chain or food web. Each trophic level contains a certain amount of biomass. The transfer of energy between these levels has a certain ecological efficiency.
Food chains can be represented as a pyramid of energy flow. Biomass storage in various trophic levels of a food chain or webs can be represented by a pyramid of biomass. The number of organisms at each trophic level in a food chain orweb can be represented by a pyramid of numbers.
4-5 Primary Productivity of Ecosystems
Gross primary productivity is the rate at which producers use photosynthesis to make more biomass. It varies across the earth. Net primary productivity affects the number of consumers in an ecosystem.
The planet's net primary productivity (NPP) ultimately limits the number of consumer organisms (including humans)that can survive on the earth. Humans now use, waste, or destroy about 27 percent of the earth's total NPP and 40 percent of the NPP of the planet's terrestrial ecosystems. This share is expected to increase and thus threaten the habitats and food supplies of other species.
4-6 Connections: Matter Cycling in Ecosystems
Nutrients, atoms, ions, and molecules are continuously cycled in nutrientcycles or biogeochemical cycles. The hydrologic cycle collects, purifies, and distributes the earth's water. Other examples are the carbon cycle, the nitrogen cycle, the phosphorus cycle, and the sulfur cycle. Human activities are altering these cycles.
4-7 How Do Ecologists Learn about Ecosystems?
Ecologists use field research and laboratory research to gather data. They use systems analysis to...
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