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Understanding Populations

Understanding Populations. How Populations Change in Size. Charles Darwin once calculated that a single pair of elephants could theoretically produce 19 million descendants within 750 years. Darwin made the point that the actual number of elephants is limited by their environment.

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Understanding Populations

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  1. Understanding Populations How Populations Change in Size

  2. Charles Darwin once calculated that a single pair of elephants could theoretically produce 19 million descendants within 750 years. Darwin made the point that the actual number of elephants is limited by their environment.

  3. What is a Population? • Is all the members of a species living in the same place at the same time. • The word population refers to the group in general and also to the size of the population – the number of individuals it contains.

  4. Properties of Populations • Described in terms of size, density or dispersion. • Density = number of individuals per unit area • Dispersion = distribution or arrangement of its individuals • Can be even, clumped, or random

  5. Clumped Uniform Random

  6. How Does a Population Grow? • A change in the size of a population over a given period of time is the growth rate. • The growth rate is: birth rate – death rate * Growth rates can be positive, negative or zero.

  7. How Fast Can a Population Grow? • A species’ biotic potential is the fastest rate at which its population can grow. • The biotic potential is limited by the reproductive potential- the maximum number of offspring each member can produce.

  8. Population Growth cont. • Reproductive potential increases when individuals produce more offspring at a time, reproduce more often, and reproduce earlier in life. • Reproducing early shortens the generation time (average time it takes to reach a reproductive age)

  9. Exponential Growth • Exponential growth means that populations grow faster and faster (example: dogs) • Exponential growth occurs in nature only when populations have plenty of food and space, and have little or no competition or predators.

  10. What Limits Population Growth? • Carrying capacity • Resources • Competition within a population

  11. Types of Population Regulation • Cause of death in a population may be density dependent or density independent. • Density dependent – deaths occur because of crowding in a population. • Density independent – a certain proportion of a population dies regardless of the population’s density.

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