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Populations

Populations. How populations are described and how they grow. . Mr. Roes Living Environment. How do we define a population?. A population has four important characteristics: it’s geographic distribution , population density , growth rate , and age structure. .

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Populations

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  1. Populations How populations are described and how they grow. Mr. Roes Living Environment

  2. How do we define a population? • A population has four important characteristics: it’s geographic distribution, population density, growth rate, and age structure.

  3. 1. Geographic Distribution: • The distribution of a population is often also referred to as the range of that population. Giraffe African Elephant

  4. 1. Geographic Distribution: • The range of an organism is variable. • It could be as small as a few centimeters, or as big as millions of square miles. How might the range of a population affect it?

  5. 2. Population density: The number of individuals per unit area. • The population density of a species will vary greatly depending on the biotic and abiotic factors of that specific ecosystem.

  6. 3. Growth Rate: • The growth rate of a population will be affected by many different factors.

  7. 3. Growth Rate: • The growth rate of a population is determined by three different factors; the number of births, the number of deaths, and the number of individuals that enter or leave the population. • In essence, a population will change in size depending on how many individuals are added to it or removed from it.

  8. 3. Growth Rate: • Add this in your notes: • Immigration—Individuals moving into a population. • Emigration—Individuals moving outof a population.

  9. Exponential growth: • Under ‘perfect conditions’ and with unlimited resource, a population will grow exponentially.

  10. Exponential growth: • The length of time required for an organism to grow and mature before reproducing impacts the rate of population growth. • One day of E Coli reproduction could lead to 4,720,000,000,000,000,000,000 bacteria. • 750 years of Elephant reproduction could lead to 20 million elephants.

  11. Logistic Growth: • In nature, populations cannot simply grow to unlimited numbers. • Eventually, a population’s growth rate begins to decrease and will eventually reach zero due to various factors.

  12. Logistic Growth: • Logistic growth rate occurs when an organism goes through a period of exponential growth, and then enters a period of little or no growth. • The point at which a population’s growth rate levels out is called the carrying capacity of the ecosystem for that population. • Mnemonic device for logistic growth; The population growth rate graph for a population undergoing logistic growth is “S ” shaped because the population shows a slowing or stopping of growth.

  13. Carrying Capacity: • During periods of logistic growth, the population’s rate of growth slows down because of the competition for resources. • The carrying capacity is the number of organisms of one population that an environment can support.

  14. Limiting factors: • An ecosystem has many different factors. Some factors will encourage a population to grow and flourish. Other factors will cause a population to shrink. • Liming factors are any of those factors that cause the rate of a population’s growth to decrease. • Limiting factors can be divided into two groups; Density-Dependent Factors, and Density-Independent Factors.

  15. Limiting factors: • Density-Dependent Factors—any limiting factor that depends on the density of a population. These are factors only when the population is of a certain density. • Competition • Predation • Parasitism • Disease

  16. Limiting factors: • Density-Independent Factors—any limiting factor that doesn’t depend on the density of a population. These are factors regardless of whether or not the population density is large. • Unusual weather • Natural disasters • Seasonal cycles

  17. Limiting factors: • Predator-Prey Relationships—Populations in nature are often controlled through levels of predation. • Think about your food chains! • In predator-Prey relationships, a population of prey species will temporarily increase. • In time, the increase in the population of prey is followed by the increase in population of the predators. • The increased amount of predators eventually leads the prey population to decrease. • After a period of time, the predator population will then decrease. This opens the door for the prey species to increase in population once again.

  18. Limiting factors: A Predator-Prey Relationship.

  19. Limiting factors: A Predator-Prey Relationship.

  20. Limiting factors: A Predator-Prey Relationship.

  21. Age Structures: • The age structure of a population will affect its growth rate and its ability to withstand limiting factors. • Age structure diagrams visualize the age structures of a certain population.

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