Populations.ppt 1

POPULATIONS & CARRYING CAPACITY

Populations.ppt 2

Population

• Number of individuals of a species in a defined place and time.

Populations.ppt 3

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

Populations.ppt 4

Changes in populations

• growth

• decline

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

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

Populations.ppt 5

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)

Populations.ppt 6

Population growth

– B > D– Exponential growth, dN/dt = rN

• N = number, pop.size

• r = biotic potential, intrinsic rate of increase.

Populations.ppt 7

Population growth

• Exponential growth unlimited

• Unrealistic

Populations.ppt 8

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

Populations.ppt 9

Population growth

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

– Collared turtledove in Gr. Britain

Populations.ppt 10

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

Populations.ppt 11

Populations.ppt 12

Pribloff reindeer

Populations.ppt 13

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

Populations.ppt 14

Population growth, biotic potential, & life history strategy.

Populations.ppt 15

Various species have various strategies for coping with a variable

world.

Populations.ppt 16

“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)

Populations.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

Populations.ppt 18

Life History Strategies

• Examples:– Fly– Dandelion– Robin– Bison– Oak

Populations.ppt 19

Population regulation

• Density-dependent controls– Food shortage, predators, disease, etc.– i.e. “biotic components.”

• Density-independent controls– Drought, extreme temperatures, lack of light,

shortage of O2, etc.

– i.e. “abiotic components.”