POPULATIONSPOPULATIONS

Ch 5.1Ch 5.1

EcologyEcology

Population ReviewPopulation Review

• What is a population?What is a population?

• Groups of individuals that belong to the Groups of individuals that belong to the same species and live in the same areasame species and live in the same area

• Give an example from a biome.Give an example from a biome.

Population CharacteristicsPopulation Characteristics

1)1) Geographic DistributionGeographic Distribution

2)2) Population DensityPopulation Density

3)3) Growth RateGrowth Rate

4)4) Age Structure*Age Structure*

Each factor listed above is equally important in Each factor listed above is equally important in determining the future of a population.determining the future of a population.

(ex: endangered vs. overpopulated)(ex: endangered vs. overpopulated)

Geographic DistributionGeographic Distribution

• Also called “range”Also called “range”

• Area (size) inhabited by a populationArea (size) inhabited by a population

• Ex: Northern Cardinals and Cedar Ex: Northern Cardinals and Cedar WaxwingsWaxwings

Northern CardinalNorthern Cardinal

Cedar WaxwingsCedar Waxwings

Population DensityPopulation Density

• Number of individuals per unit areaNumber of individuals per unit area• Main characteristicMain characteristic to describe a population to describe a population• Varies greatly depending on species and Varies greatly depending on species and

quality of ecosystemquality of ecosystem• Ex 1Ex 1: : CactiCacti vs. vs. Rainforest Fig TreesRainforest Fig Trees….Which is more ….Which is more

dense?dense?• Ex 2Ex 2: Science Daily (Dec. 7, 2000) — Nov. 22, 2000 -- : Science Daily (Dec. 7, 2000) — Nov. 22, 2000 --

Zoologists from the University of Toronto have cracked Zoologists from the University of Toronto have cracked the ecological puzzle of how animals - in this case the the ecological puzzle of how animals - in this case the arctic ground squirrelarctic ground squirrel - manage to control their own - manage to control their own population in the northern boreal forest of Canada. population in the northern boreal forest of Canada.

Growth RatesGrowth Rates

• Natural populations can grow, decline, Natural populations can grow, decline, or stay the sameor stay the same

• Depends on 3 factors:Depends on 3 factors:• Birth RateBirth Rate• Death RateDeath Rate• Individuals entering or leaving populationIndividuals entering or leaving population

• Immigration (in) and Emigration (out)Immigration (in) and Emigration (out)• Give an example for the terms above!Give an example for the terms above!

ExamplesExamples

• What will happen to the following What will happen to the following population (grow, decline, stay the population (grow, decline, stay the same) immediately and later.same) immediately and later.

1.1. The EPA protects sea otters from The EPA protects sea otters from hunting. hunting.

2.2. Killer whales prey on sea otters.Killer whales prey on sea otters.

Exponential GrowthExponential Growth

• With abundant space and food, With abundant space and food, protection from disease and predators, protection from disease and predators, a population will increase in size a population will increase in size exponentiallyexponentially

1.1. Reproduce at constant rateReproduce at constant rate2.2. Unlimited ResourcesUnlimited Resources3.3. Begins slowly, then takes off!Begins slowly, then takes off!Ex: Doubling effect of bacteriaEx: Doubling effect of bacteria

Consider this…Consider this…

• Bacteria have the fastest rates of reproduction Bacteria have the fastest rates of reproduction among living thingsamong living things

• Assume “binary fission” (doubling) occurs every 20 Assume “binary fission” (doubling) occurs every 20 minutesminutes

• 20 min= 2 bacteria20 min= 2 bacteria• 40 min= 4 bacteria40 min= 4 bacteria• 60 min=8 bacteria60 min=8 bacteria• 120 min = 64 bacteria120 min = 64 bacteria• 3 hrs = 512 bacteria3 hrs = 512 bacteria• 24 hrs = 4,720,000,000,000,000,000,000 bacteria24 hrs = 4,720,000,000,000,000,000,000 bacteria

Charting Exponential GrowthCharting Exponential Growth• J-shaped curve = unlimited resources J-shaped curve = unlimited resources

and growthand growth

Logistic GrowthLogistic Growth

• As shown prior, exponential growth only lasts As shown prior, exponential growth only lasts for a short whilefor a short while

• Logistic growth occurs when growth slows or Logistic growth occurs when growth slows or stops after exponential growth occursstops after exponential growth occurs

• Results from:Results from:• Birthrate drops/Death rate increasesBirthrate drops/Death rate increases• Immigration slows/Emigration increasesImmigration slows/Emigration increases• Both can result from lack of space and resourcesBoth can result from lack of space and resources

Charting Logistic GrowthCharting Logistic Growth

• ““S” shaped curveS” shaped curve• Shows “Shows “carrying carrying

capacitycapacity” of an ” of an ecosystem ecosystem (maximum # of (maximum # of organisms based on organisms based on available resources)available resources)

• Why does the Why does the population remain population remain constant towards constant towards the end of the the end of the curve?curve?

Bringing it all Together!Bringing it all Together!

Why is the carrying capacity Why is the carrying capacity not a flat line?not a flat line?