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POPULATIONS & CARRYING CAPACITY 02 June 20101Populations.ppt

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Population number of individuals of a species in a defined place and time. 02 June 2010 2Populations.ppt

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Dynamic characteristics of populations Size, number of individuals (N) Density (N/ area) Dispersion, – Random, uniform, clumped, (appropriate scale) 02 June 2010 3Populations.ppt

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Dynamic characteristics of populations Age distribution, – proportions of young, middle-aged, old – Differs in growing, stable, decreasing populations 02 June 2010 4Populations.ppt

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Changes in populations Growth Decline May affect size, density, dispersion, age distribution. May be affected by size, density, dispersion, age distribution. 02 June 2010 5Populations.ppt

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Changes in populations Growth – Expansion of species populations may lead to evolution of new species Decline – Shrinking species populations may lead to extinction Small populations Narrowly specialized species 02 June 2010 6Populations.ppt

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Changes in populations ΔN = +B +I –D –E – +B = births (birth rate) – +I = immigrants (immigration rate) – – D = deaths (death rate) – – E = emigrants (emigration rate) – (For many [most] natural populations I and E are minimal.) 02 June 2010 7Populations.ppt

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Population growth – B > D – Exponential growth, dN/dt = rN N = number, pop.size r = biotic potential, intrinsic rate of increase. 02 June 2010 8Populations.ppt

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Population growth Exponential growth unlimited – dN/dt = rN Unrealistic

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Population growth Logistic growth, – dN/dt = rN (1 - N/K) N = number, population size r = biotic potential, intrinsic rate of increase. K = carrying capacity – Better represents real populations

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Population growth Logistic growth, – dN/dt = rN (1 - N/K) N = number, population size r = biotic potential, intrinsic rate of increase. K = carrying capacity – Better represents real populations

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Logistic model Logistic model works, to a point. – Real organisms have time lags for growth, time to develop eggs, flowers, etc. seasonality, longevity – Real populations may exceed carrying capacity. Easter Island Pribloff Reindeer Kaibab Deer 02 June 2010 12Populations.ppt

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Easter Island Discovered by Polynesians ~ A.D. 1000 Population grew to several thousand – Used trees for canoes to hunt dolphins – Used wood for cooking – Also ate birds, eggs, vegetables Resources (trees) depleted – No canoes, no dolphins – Warfare over land, food resources Population fell to ~ 100 when discovered by Dutch, Easter Sunday 1722. 02 June 2010 13Populations.ppt

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02 June 2010 14Populations.ppt

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Pribloff reindeer 02 June 2010 15Populations.ppt

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Logistic model Carrying capacity modeled as a constant. May be variable – Interspecific competition, – Seasonal change, resources abundant in summer, rainy season; resources scarce in winter, dry season – Events may alter resource availability, storms, mild years, human intervention. 02 June 2010 16Populations.ppt

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Population growth, biotic potential, & life history strategy. 02 June 2010 17Populations.ppt

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Various species have various strategies for coping with a variable world. 02 June 2010 18Populations.ppt

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Two general types of Life History Strategies Life History traitr-adapted, Opportunistic K-adapted, Equilibrium OffspringMany, small (high r)Fewer, large (low r) Offspring survivalLowHigh Parental careRareCommon Reproductive ageEarlyLater Reprod. seasons1-fewMany HabitatUnstable, temporaryStable, permanent CompetitivenessLowHigh Population regulationDensity independentDensity dependent Population fluctuationIrruptiveStable near K

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Life History Strategies Survivorship curves of Opportunistic and Equilibrium species – Opportunistic have Type III – Equilibrium have Type I 02 June 201020Populations.ppt

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Life History Strategies Fluctuating populations of two interacting populations – Based on pelts sold by Canadian trappers to the Hudson Bay Company, ~1840-1940. 02 June 201021Populations.ppt

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