POPULATIONS & CARRYING CAPACITY 02 June 20101Populations.ppt

POPULATIONS & CARRYING CAPACITY

02 June 2010 1Populations.ppt

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,– Random, uniform,

clumped, • (appropriate scale)


Dynamic characteristics of populations

• Age distribution,– proportions of young, middle-aged, old– Differs in growing, stable, decreasing populations


Changes in populations

• Growth

• Decline

• May affect size, density, dispersion, age distribution.

• May be affected by size, density, dispersion, age distribution.



• 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



• 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.)


Population growth

– B > D

– Exponential growth, dN/dt = rN• N = number, pop.size

• r = biotic potential, intrinsic rate of increase.


Population growth

• Exponential growth unlimited– dN/dt = rN

• Unrealistic

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

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

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


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.



Pribloff reindeer


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.


Population growth, biotic potential, & life history strategy.


Various species have various strategies for coping with a

variable world.


Two general types ofLife History Strategies

Life History trait r-adapted, Opportunistic

K-adapted, 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 of Opportunistic and Equilibrium species– Opportunistic have Type III

– Equilibrium have Type I


Life History Strategies

• Fluctuating populations of two interacting populations– Based on pelts sold by Canadian trappers to the Hudson Bay

Company, ~1840-1940.


Documents

POPULATIONS & CARRYING CAPACITY 02 June 20101Populations.ppt