Population Growth Population Growth

Sharks

Fish

Clarifying Objective 2.1.4 Explain how ecosystems can be relatively stable over hundreds or thousands of years, even though

populations may fluctuate due to availability of food and shelter, as well as the number of predators, or disease.

A A populationpopulation includes any species living in a particular includes any species living in a particular area. Most organisms live in area. Most organisms live in socialsocial groupsgroups because because

doing so provides several advantages: increased doing so provides several advantages: increased protectionprotection from predators, increased chances for from predators, increased chances for

matingmating, and effective , and effective huntinghunting techniquestechniques..

PopulationsPopulations

PopulationPopulation growthgrowth refers to an refers to an increaseincrease in in the the sizesize of a population over time of a population over time

Population Growth = Population Growth = Birth RateBirth Rate - - Mortality RateMortality Rate

An increase in birth rate or a decrease in mortality An increase in birth rate or a decrease in mortality rate will cause an increase in population growthrate will cause an increase in population growth

Population growth can also be affected by immigration, individuals moving in, or

emigration, individuals moving out.

GraphsGraphs are used to are used to analyzeanalyze population population growthgrowth

X axis - Years

Y axisNumber

of Grocery Stores

Number of grocery stores in Randolph CountyNumber of grocery stores in Randolph County

LinearLinear Growth is when the numbers Growth is when the numbers increaseincrease steadily by the steadily by the samesame amount (2, 4, 6…) amount (2, 4, 6…)

X axis - Years

Y axisNumber

of Grocery Stores

Number of grocery stores in Randolph CountyNumber of grocery stores in Randolph County

ExponentialExponential Growth is when the numbers Growth is when the numbers increaseincrease by a by a largerlarger amount each time amount each time

(2, 4, 16, 256…)(2, 4, 16, 256…)

X axis - Years

Y axisNumber

of Grocery Stores

Number of Grocery Stores in Wake CountyNumber of Grocery Stores in Wake County

PopulationsPopulations tend to tend to increaseincrease exponentiallyexponentially in that as they grow in that as they grow larger they begin increasing faster larger they begin increasing faster

Slow IncreaseSlow Increase Rapid IncreaseRapid Increase

The The J – Curve J – Curve Shows Exponential Shows Exponential Population GrowthPopulation Growth

All ecosystems have a All ecosystems have a limitedlimited amount of amount of resourcesresources or or factorsfactors to to

support populationssupport populations

All organisms All organisms need need waterwater, ,

foodfood, space for , space for habitatshabitats, and , and

sanitary sanitary conditions.conditions.

As populations increase, there is As populations increase, there is moremore competitioncompetition for the same for the same

resourcesresources

Populations begin to die out due to Populations begin to die out due to diseasedisease, , starvationstarvation, or , or thirstthirst

Therefore, any ecosystem can only Therefore, any ecosystem can only support a certain amount of support a certain amount of

individuals individuals

CarryingCarrying CapacityCapacity refers to the refers to the

maximummaximum numbernumber of of individuals an individuals an ecosystem can ecosystem can

supportsupport

If a population goes If a population goes aboveabove the the carryingcarrying capacitycapacity, it cannot be sustained and , it cannot be sustained and eventually the population will eventually the population will crashcrash..

If the population size, after a population crash, If the population size, after a population crash, goes goes belowbelow a a criticalcritical numbernumber, it will not be able , it will not be able

to revive its population and is classified as to revive its population and is classified as endangeredendangered..

Most natural populations Most natural populations fluctuatefluctuate aroundaround the the carryingcarrying capacitycapacity

The The S – CurveS – Curve shows logistic growth shows logistic growth where a population begins to where a population begins to stabilizestabilize

as it reaches its carrying capacityas it reaches its carrying capacity

The The carryingcarrying capacitycapacity is is determineddetermined byby

limitinglimiting factorsfactors such such as amount of as amount of

available resources or available resources or ability to fight off ability to fight off

diseasesdiseases

Limiting factors that restrain population Limiting factors that restrain population growth and do not depend upon the initial growth and do not depend upon the initial

size of the population are called size of the population are called DensityDensity--IndependentIndependent FactorsFactors

FloodsFloodsFiresFires

EarthquakesEarthquakesCold SpellsCold SpellsHot SpellsHot SpellsDroughtDrought

Limiting factors that restrain population Limiting factors that restrain population growth and do depend upon the initial size growth and do depend upon the initial size

of a population are called of a population are called Density-DependentDensity-Dependent FactorsFactors

Food ShortagesFood ShortagesWater ShortagesWater Shortages

DiseasesDiseasesHabitat SpaceHabitat Space

CompetitionCompetition between species that between species that compete for the compete for the samesame resourcesresources can also affect population growthcan also affect population growth

Gray Seal Gray Seal

Sabel Island Sabel Island

Lance Fish Lance Fish Harbor Seal Harbor Seal

OneOne population will usually population will usually outout competecompete the the otherother causing a decline in causing a decline in

the other populationthe other population

Harbor Seal in

Grey Seal in mixed

MonthsMonths

PredatorPredator – – PreyPrey Relationships also affect Relationships also affect Population Growth Population Growth

Increase in predators Increase in predators cause a decrease in preycause a decrease in prey

As prey decreases, the As prey decreases, the predator decreasespredator decreases

As predators decrease, As predators decrease, prey increasesprey increases

As prey increases, As prey increases, predator increasespredator increases

There is always a There is always a delayeddelayed relationshiprelationship in in growth and decline between the two growth and decline between the two

populations populations

Predation not only removes the very old, the very Predation not only removes the very old, the very young, and the weaker members from a population, it young, and the weaker members from a population, it

also helps also helps regulateregulate the the preyprey populationpopulation..

If the predators do not keep the prey population in If the predators do not keep the prey population in balance, the carrying capacity is exceeded and the balance, the carrying capacity is exceeded and the

prey may starve due to prey may starve due to overgrazingovergrazing..