M R S . P I TTA LU G A – 8 T H G RA D E S C I E N C E

POPULATION ECOLOGY

NC ESSENTIAL STANDARD

• 8.L.3 – Understand how organisms interact with and respond to the biotic and abiotic components of their environment• 8.L.3.1 – Explain how factors such as food, water, shelter,

and space affect populations in an ecosystem

• I can classify examples of factors that limit a population’s growth as either density-independent or density-dependent.

WHAT IS A POPULATION?

• A group of organisms belonging to the same species that live in a particular area.• Described based on size, density, or distribution.

POPULATION DISTRIBUTION

• Dispersion is the pattern of spacing among individuals within the boundaries of the population• Clumped – individuals

are grouped in clusters• Uniform – individuals are

evenly distributed• Random – each

individual is positioned independent of the others

POPULATION DENSITY

• Result of the processes that add individuals to a population and those that remove individuals.• Immigration – individuals moving into an area• Emigration – individuals moving away from an area• Birth rate – number of births in a population• Death rate – number of deaths in a population

• Determined by finding the number of individuals in a given area• Pop. Density = # of individuals ÷ unit of area

• Affected by limiting factors

Births

Births and immigrationadd individuals toa population.

Immigration

Deaths and emigrationremove individualsfrom a population.

Deaths

Emigration

LIMITING FACTORS

• Factors that can cause a population size to decrease.• Density-dependent factors – only affect a population

when the density reaches a certain level• Competition• Predation• Disease

• Density-independent factors – affect a population regardless of the density• Natural disasters• Temperature• Human activities

SOMETHING TO THINK ABOUT

• Suppose your parents offer you a choice for allowance this month: You may have $5 a week OR you will get a penny on the 1st and each day afterward, they will double the amount from the day before. Which do you choose, and why?

POPULATION GROWTH

• Exponential Growth (J-curve)• Shows populations growing unrestricted and very rapidly• Resources are plentiful, birth rate and immigration are

high• Unrealistic and unstainable• Human population is currently growing at an exponential

rate

• Logistic Growth (S-curve)• Shows populations growing rapidly but then leveling off• Resources are limited• Carrying capacity – the maximum number of organisms

that the environment can support based on available resources

• More realistic growth model

POPULATION GROWTH