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21.2 Studying populations page 711

21.2 Studying populations page 711. Key concepts: How do ecologists determine the size of a population? What causes populations to change in size? What factors limit population growth?

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21.2 Studying populations page 711

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  1. 21.2 Studying populations page 711 • Key concepts: How do ecologists determine the size of a population? What causes populations to change in size? What factors limit population growth? • Key terms: Estimate, birth rate, death rate, immigration, emigration, population density, limiting factor, carrying capacity

  2. Determining Population Size • Some methods of determining population size are direct and indirect observations, sampling, and mark-and-recapture studies. • Direct observation – count all of its members • Indirect observation – counting nests, observing what the organisms use or leave behind • Sampling – count the number of organisms in a small area and multiply to estimate (approximate) actual population size

  3. Mark-and-recapture • Scientists mark the organisms, release them, then capture a bunch and see how many have marks and how many don’t. You can use this to estimate the number of organisms in the population.

  4. Changes in population size • Populations change in size when organisms join the population or when they leave. • Births and deaths • Birth rate: number of births per population in a certain amount of time • Death rate: “” deaths “” • The MAIN way individuals leave is by dying

  5. Population statement • If the birth rate is > death rate, then more organisms are coming in than going out, and population increases. • If the death rate > than birth rate, then more organisms are going out than coming in, and population decreases.

  6. Immigration and emigration • Immigration: moving into a population • Emigration: moving out of a population

  7. Population Density • Population density – the number of individuals in an area of a specific size. It can be written as • Population density = (# of individuals/unit area)

  8. Limiting factors • A limiting factor is an environmental factor that causes a population to decrease. • For example: some limiting factors are food and water, space, and weather conditions.

  9. Food and water • Organisms need them ;) • The largest population that an area can support is called its carrying capacity.

  10. Space • Another limiting factor for both plants and animals

  11. Weather • Amount of rainfall, temperature

  12. Please complete • Section 2 assessment in your notes – I will check it tomorrow • 1ab, 2abc, 3abc, 4

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