11 june 2015 pop-ecol2108.ppt1 populations & carrying capacity

11 June 2015 Pop-Ecol2108.ppt 1

POPULATIONS & CARRYING CAPACITY


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


Age Structure



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.



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

• Instantaneous growth rate dN/dt = rN

• Unrealistic


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


Population growth

• Do real populations grow according to the logistic model (equation)?• Bacteria

• Collared turtledove in Gr. Britain


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

Pribloff reindeer

• St. Paul Island



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.


“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)


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

• Examples:FlyRobinDandelionBisonOak

Life History Strategies

• Survivorship curves• “Late loss”

(type I curve)• K-strategists

• “Early loss” (type III curve)

• r-strategists

• Type II ?


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


Population Regulation


• Density-dependent controls i.e. “biotic components.”

• Competition

• Territoriality

• Stress responses to crowding

• Disease, parasitism

• Predation Wolf, moose

Isle Royale N. P.



Population Regulation

• Density-independent controls i.e. “abiotic components.”

• Drought,

• extreme temperatures,

• Light (or lack of),

• Oxygen (or shortage),

• etc.

11 june 2015 pop-ecol2108.ppt1 populations & carrying capacity

Documents

capacity slide

ppt12 slide

britain slide

ppt3 slide

ppt4 slide

ppt6 slide

ppt13 slide

populations n