1Lecture 2Lecture 2Population EcologyPopulation Growth, Competition and PredationPopulation EcologyPopulation Growth, Competition and PredationBFLF Biology ConceptsBFLF Biology Concepts•Population growth• Intraspecfic Competition (Interspecfic)• Predation (Parasitism/Virulence)•Behavior•Evolution?•Population growth• Intraspecfic Competition (Interspecfic)• Predation (Parasitism/Virulence)•Behavior•Evolution?2The Tragedy of the CommonsThe Tragedy of the Commons• Open pasture can support 10 cattle• Currently grazed by 10 herdsmen each with one• Open pasture can support 10 cattle• Currently grazed by 10 herdsmen each with one• One of the herdsmen adds one more if he can make a profit. • Adding one more animal = less food for each animal, but since he only has only 1/10 of the herd, he has to pay only 1/10 of the cost. • One of the herdsmen adds one more if he can make a profit. • Adding one more animal = less food for each animal, but since he only has only 1/10 of the herd, he has to pay only 1/10 of the cost. The Tragedy of the CommonsThe Tragedy of the Commons• Shrinking profit margins ⇒either go out of business or also add more animals. • Mutual exploitation continues until overgrazing and erosion destroy the pasture system, and all the herdsmen are driven out of business…• Hardin 1968• Shrinking profit margins ⇒either go out of business or also add more animals. • Mutual exploitation continues until overgrazing and erosion destroy the pasture system, and all the herdsmen are driven out of business…• Hardin 19683St. Matthew Island CollapseSt. Matthew Island Collapse• Small number of reindeer colonized the island•Increase rapidly• Use up all of the resources•Population collapses• Small number of reindeer colonized the island•Increase rapidly• Use up all of the resources•Population collapsesPopulation GrowthPopulation Growth• Exponential Growth• Exponential GrowthPopulation SizePopulation SizeTimeTimeNt= N0ertNNtt= N= N00eertrtdN/dt = rNdN/dt = rNdN/dt = rNNt= popln @ time tr = growth rateNNtt= = poplnpopln@ time t@ time tr = growth rater = growth rate4Population GrowthPopulation Growth• Exponential Growth• Exponential GrowthPopulation SizePopulation SizeTimeTimedN/dt = rNdN/dt = rNdN/dt = rNhigh rhigh rmoderate rmoderate rlow rlow rPopulation GrowthPopulation Growth• Exponential Growth– Discrete Time Nt+1= Nt* R•R = average reproduction• Exponential Growth– Discrete Time Nt+1= Nt* R•R = average reproduction5Population GrowthPopulation Growth• Logistic Growth (Malthus)• Intraspecific competition• Logistic Growth (Malthus)• Intraspecific competitionPopulation SizePopulation SizeTimeTimedN/dt = rN(1- N/K)dN/dt = rN(1- N/K)Carrying Capacity of Environment (K)Carrying Capacity of Environment (K)Period of Exponential GrowthPeriod of Exponential Growth Nt=N0KN0+ (K− N0)e−r0tPopulation Density (N)Population Density (N)Density-dependent death rate - dDensity-dependent death rate -dDensity-independent birth rate - bDensity-independent birth rate -bEquilibrium DensityEquilibrium Density1 dNN dt1dNN dtPopulation Density (N)Population Density (N)Density-independent death rateDensity-independent death rateDensity-dependent birth rateDensity-dependent birth rate1 dNN dt1 dNN dtPopulation Density (N)Population Density (N)Density-dependent death rateDensity-dependent death rateDensity-dependent birth rateDensity-dependent birth rateDensity-Dependant Factors Regulate Population SizeDensity-Dependant Factors Regulate Population Size1 dNN dt1 dNN dtr = b-das N r stabilizingr = b-das N r stabilizing6Population GrowthPopulation Growth• Logistic Growth– Discrete Time Nt+1= Nt(1+r(1-Nt/K))•R = average reproduction•K = carrying capacity• Logistic Growth– Discrete Time Nt+1= Nt(1+r(1-Nt/K))•R = average reproduction•K = carrying capacityWhich graph of population growth could not be generated by this equation? Nt+1= Nt(1+r(1-Nt/K))Which graph of population growth could not be generated by this equation? Nt+1= Nt(1+r(1-Nt/K))•A•B•A•B•C•D•C•D•E -They could all be generated•F -None could be generated•E -They could all be generated•F -None could be generated7Population GrowthPopulation Growth• Logistic Growth– Discrete Time Nt+1= Nt(1+r(1-Nt/K))•Limit Cycles•Chaos• Logistic Growth– Discrete Time Nt+1= Nt(1+r(1-Nt/K))•Limit Cycles•ChaosReal Population GrowthReal Population Growth8• Human population growth• Human population growth9Human Population Age DistributionMore Developed CountriesHuman Population Age DistributionMore Developed CountriesAge IntervalAge IntervalNumber of people (Millions)Number of people (Millions)FemalesFemalesMalesMales80 - 9070 - 8060 - 7050 - 6040 - 5030 - 4020 - 3010 - 200 -1080 - 9070 - 8060 - 7050 - 6040 - 5030 - 4020 - 3010 - 200 -10Long periods of no net growth lead to even distributionLong periods of no net growth lead to even distributionPopulation Summary for the USPopulation Summary for the US200020252050http://blue.census.gov/10Population Age DistributionLess Developed CountriesPopulation Age DistributionLess Developed CountriesAgeAge300300300300Number of people (Millions)Number of people (Millions)FemalesFemalesMalesMalesPopulation Summary for UgandaPopulation Summary for Uganda200020252050http://blue.census.gov/Very high reproductive rate11Human Population GrowthHuman Population GrowthYearYearPopulation (Billions)Population (Billions)112233445566Agriculture & domestification of animalsAgriculture & domestification of animals4 million4 million7 million7 millionHunter GatherersHunter GatherersAdapted from: Cohen, “How Many People Can the Earth Support”Adapted from: Cohen, “How Many People Can the Earth Support”10,000 BC10,000 BC8,000 BC8,000 BC2,000 AD2,000 AD004,000 BC4,000 BCBubonic PlagueBubonic PlagueIndustrial RevolutionIndustrial Revolution(1400)(1400)(1800)(1800)Modern Medicine (reduced mortality)Modern Medicine (reduced mortality)(1900)(1900)Fossil FuelFossil Fuel6,289,870,258*(4/30/2003)http://www.census.gov/main/www/popclock.htmlhttp://www.census.gov/main/www/popclock.html6,363,174,549(4/28/2004)6,432,150,287(4/22/05)Now projected to reach 9 Billionand level off6 Billion (1999)6 Billion (1999)http://www.census.gov/ipc/prod/wp02/wp02-1.pdf12Demographic TransitionDemographic TransitionStage 1High birth rateHigh, but fluctuatingdeath rateStage 1High birth rateHigh, but
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