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11 June 2015 Pop-Ecol2108.ppt1 POPULATIONS & CARRYING CAPACITY
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11 June 2015 Pop-Ecol2108.ppt2 Population Number of individuals of a species in a defined place and time.
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Dynamic characteristics of populations Size, number of individuals (N) Density (N/ area) Dispersion, uniform, clumped, random appropriate scale Age distribution, proportions of young, middle-aged, old 11 June 2015 Pop-Ecol2108.ppt3
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Age Structure 11 June 2015 Pop-Ecol2108.ppt4
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11 June 2015 Pop-Ecol2108.ppt5 Changes in populations growth decline May affect size, density, dispersion, age distribution. May be affected by size, density, dispersion, age distribution.
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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. 11 June 2015 Pop-Ecol2108.ppt6
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11 June 2015 Pop-Ecol2108.ppt7 Population growth B > D Exponential growth, dN/dt = rN N = number, pop.size r = biotic potential, intrinsic rate of increase.
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11 June 2015 Pop-Ecol2108.ppt8 Population growth Exponential growth unlimited Instantaneous growth rate dN/dt = rN Unrealistic
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11 June 2015 Pop-Ecol2108.ppt9 Population growth Logistic growth, dN/dt = rN (K - N)/ K N = number, pop.size r = biotic potential, intrinsic rate of increase. K = carrying capacity Better represents real populations
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11 June 2015 Pop-Ecol2108.ppt10 Population growth Do real populations grow according to the logistic model (equation)? Bacteria Collared turtledove in Gr. Britain
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11 June 2015 Pop-Ecol2108.ppt11 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 Kaibab Deer Pribloff Reindeer
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Pribloff reindeer St. Paul Island 11 June 2015 Pop-Ecol2108.ppt13
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11 June 2015 Pop-Ecol2108.ppt14 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
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11 June 2015 Pop-Ecol2108.ppt15 Population growth, biotic potential, & life history strategy. Various species have various strategies for coping with a variable world.
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11 June 2015 Pop-Ecol2108.ppt16 “Natural selection” Phenotypes preserved that maximize fitness Fitness = Reproductive rate X Survivorship to increase R may decrease S to increase S may decrease R Given certain quantity of energy = food More smaller eggs more smaller offspring Low S for each Fewer larger eggs few larger offspring Must increase S for each (or lower fitness)
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11 June 2015 Pop-Ecol2108.ppt17 Life History Strategies: Two general types Life History traitr-strategists, Opportunistic K-strategists, Equilibrium OffspringMany, small (high r)Fewer, large (low r) Offspring survivalLowHigh Parental careRareCommon Reproductive ageEarlyLater Reprod. “seasons”1-fewMany HabitatUnstable, temporaryStable, permanent CompetitivenessLowHigh Population regulationDensity independentDensity dependent Population fluctuationIrruptiveStable near K
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11 June 2015 Pop-Ecol2108.ppt18 Life History Strategies Examples: Fly Robin Dandelion Bison Oak
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Life History Strategies Survivorship curves “Late loss” (type I curve) K-strategists “Early loss” (type III curve) r-strategists Type II ? 11 June 2015 Pop-Ecol2108.ppt19
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Cost of parental care Parental care affects survival of parents Normal brood = 5-6 nestlings Enlarged broods = 7-8 nestlings Reduced broods = 3-4 nestlings 11 June 2015 Pop-Ecol2108.ppt20
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Population Regulation 11 June 2015 Pop-Ecol2108.ppt21 Density-dependent controls i.e. “biotic components.” Competition Territoriality Stress responses to crowding Disease, parasitism Predation Wolf, moose
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Isle Royale N. P. 11 June 2015 Pop-Ecol2108.ppt22
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11 June 2015 Pop-Ecol2108.ppt23 Population Regulation Density-independent controls i.e. “abiotic components.” Drought, extreme temperatures, Light (or lack of), Oxygen (or shortage), etc.
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