21.2 Studying populations page 711
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Transcript of 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
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
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.
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
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.
Immigration and emigration• Immigration: moving into a population• Emigration: moving out of a population
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)
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.
Food and water• Organisms need them ;)• The largest population
that an area can support is called its carrying capacity.
Space• Another limiting factor for both
plants and animals
Weather• Amount of rainfall, temperature
Please complete• Section 2 assessment in your notes – I will check it tomorrow• 1ab, 2abc, 3abc, 4