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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

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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? - PowerPoint PPT Presentation

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Page 1: 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? • Key terms: Estimate, birth rate, death

rate, immigration, emigration, population density, limiting factor, carrying capacity

Page 2: 21.2 Studying populations page 711

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

Page 3: 21.2 Studying populations page 711

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.

Page 4: 21.2 Studying populations page 711

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

Page 5: 21.2 Studying populations page 711

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.

Page 6: 21.2 Studying populations page 711

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

Page 7: 21.2 Studying populations page 711

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)

Page 8: 21.2 Studying populations page 711

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.

Page 9: 21.2 Studying populations page 711

Food and water• Organisms need them ;)• The largest population

that an area can support is called its carrying capacity.

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Space• Another limiting factor for both

plants and animals

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Weather• Amount of rainfall, temperature

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