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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
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