11 June 2015 Pop-Ecol2108.ppt1 POPULATIONS & CARRYING CAPACITY.
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Transcript of 11 June 2015 Pop-Ecol2108.ppt1 POPULATIONS & CARRYING CAPACITY.
11 June 2015 Pop-Ecol2108.ppt 2
Population
• Number of individuals of a species in a defined place and time.
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.ppt 3
11 June 2015 Pop-Ecol2108.ppt 5
Changes in populations
• growth
• decline
• May affect size, density, dispersion, age distribution.
• May be affected by size, density, dispersion, age distribution.
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.ppt 6
11 June 2015 Pop-Ecol2108.ppt 7
Population growth
B > D
Exponential growth, dN/dt = rN• N = number, pop.size
• r = biotic potential, intrinsic rate of increase.
11 June 2015 Pop-Ecol2108.ppt 8
Population growth
• Exponential growth unlimited
• Instantaneous growth rate dN/dt = rN
• Unrealistic
11 June 2015 Pop-Ecol2108.ppt 9
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
11 June 2015 Pop-Ecol2108.ppt 10
Population growth
• Do real populations grow according to the logistic model (equation)?• Bacteria
• Collared turtledove in Gr. Britain
11 June 2015 Pop-Ecol2108.ppt 11
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
11 June 2015 Pop-Ecol2108.ppt 14
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
11 June 2015 Pop-Ecol2108.ppt 15
Population growth, biotic potential, & life history strategy.
Various species have various strategies for coping with a variable world.
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“Natural selection”
• Phenotypes preserved that maximize fitnessFitness = 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 offspringMust increase S for each (or lower fitness)
11 June 2015 Pop-Ecol2108.ppt 17
Life History Strategies: Two general types
Life History trait r-strategists, Opportunistic
K-strategists, Equilibrium
Offspring Many, small (high r) Fewer, large (low r)
Offspring survival Low High
Parental care Rare Common
Reproductive age Early Later
Reprod. “seasons” 1-few Many
Habitat Unstable, temporary Stable, permanent
Competitiveness Low High
Population regulation Density independent Density dependent
Population fluctuation Irruptive Stable near K
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.ppt 19
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
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Population Regulation
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• Density-dependent controls i.e. “biotic components.”
• Competition
• Territoriality
• Stress responses to crowding
• Disease, parasitism
• Predation Wolf, moose