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What are populations and communities?. A population is a group of individuals that belong to the same species and live in the same area. A community is an assemblage of different populations that live together in a defined area.
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What are populations and communities? • A population is a group of individuals that belong to the same species and live in the same area. • A community is an assemblage of different populations that live together in a defined area. 1. Compare and ContrastHow is a population different from a community?
What are external factors? • • Organisms, populations, and communities respond to events and environmental conditions. • • A stimulus is information that causes a response in an organism, population, or community. • External factors, or external stimuli, come from the environment. 2. DefineWhat is a stimulus?
What are biotic and abiotic factors? • Abiotic factors include any physical, or nonliving, part of the environment. • Biotic factors include any living part of the environment. 3. Apply ConceptsIdentify one biotic factor and one abiotic factor in your classroom environment.
Why do organisms respond to external factors? • Organisms respond to external environmental factors because they must maintain homeostasis. • Homeostasis is a condition of relatively constant internal physical and chemical conditions. • For an organism to maintain homeostasis, conditions such as temperature must be within a range of tolerance. 4. DefineWhat is homeostasis?
How do organisms respond to external factors? • Organisms respond to external factors in ways that maintain homeostasis. • For example, when the temperature around you becomes very warm, you sweat. • As sweat evaporates, it carries heat away from the surface of your skin. This is a response to the external factor of heat, and it helps your body maintain a stable internal temperature. 5. Apply ConceptsWhen you respond to thirst by drinking water, how are you maintaining homeostasis?
How do populations respond to external factors? • Populations respond in ways that reflect the efforts of individual members to maintain homeostasis. • All of the important characteristics of populations—growth rate, age structure, geographic range, density, and distribution—respond to external factors. 6. IdentifyIdentify five characteristics of populations that can respond to external environmental factors.
How do growth rates respond to external factors? • If individuals are under stress because of factors like insufficient food or temperature beyond their normal range, they will probably have few offspring. • The population will then grow more slowly than normal. • In contrast, if external conditions change in ways that are favorable for individual organisms, a population’s growth rate can increase. • Carrying capacity is the maximum number of individuals of a particular species that a given environment can support. 7. Relate Cause and EffectWhat may happen to population growth if external conditions change favorably?
How does age structure respond to external factors? • If many individuals are stressed, they may reproduce less frequently or not at all. • Then, the age structure of their population will shift. It will consist of relatively more older individuals. • In contrast, if environmental factors become favorable, more offspring may be produced. The age structure will shift toward greater numbers of younger organisms. 8. SequenceWhen external factors become favorable, what may happen to a population’s age structure?
What are population density and population distribution? • Population density describes how closely together individuals within a population are within an area. • Population distribution describes how individuals within an area are arranged. Typical distribution patterns are random, uniform, and clumped. 9. Define What is population distribution?
What controls the range of a population? • Plants and animals typically live in a certain geographic area known as a range. The range also typically has an upper and lower elevation limit. • Ranges are populations’ responses to external factors. • Some animals, such as the Golden Plover, migrate in response to shifts in temperature and rainfall. They have a summer range and a winter range. 10. DefineWhat is a range?
What can make a range change? • When external factors change, a population’s range can shift. • The range of the Edith’s Checkerspot butterfly stretches along the west coast of North America. • In the southernmost part of the butterfly’s former range, many populations have become extinct. In the northern part of the range, new populations have started. • Researchers have concluded that this range shift is a response to rising atmospheric temperatures. 11. Relate Cause and EffectWhat accounts for the northward shift of the Edith’s Checkerspot butterfly’s range?
How do communities respond to external factors? • A community responds to environmental factors in ways that reflect responses of its individual organisms and populations. • Changing external factors may alter community structure, species composition, and biodiversity. • Changes in biotic and abiotic factors may benefit some species but increase stress on others. • For example, a storm may knock down tall trees, allowing sunlight to reach the forest floor. Then, sun-loving plants may thrive, while shade plants may decline. 12. InferHow can changing external factors affect biodiversity?
