K and r strategistsK and r strategists

Understanding Population GrowthUnderstanding Population Growth

1.1. Exponential Growth ModelExponential Growth Model

Exponential growth:Exponential growth: The rate of expansion (growth) of a population under ideal conditions.

Exponential Growth (J curve)Exponential Growth (J curve)

• Example:Example: bacteriabacteria

Number ofindividuals (N)

Time

produces a J-shapedJ-shaped curve

Understanding Population GrowthUnderstanding Population Growth

2. Logistic Growth Model2. Logistic Growth Model

logistic growth:logistic growth: Environmental factors restrict the growth of a population

(The factors are called: limiting factors.limiting factors.)

K: Carrying CapacityK: Carrying Capacity

• The maximummaximum population size that a particular environmentenvironment can sustainably supportsupport over a relatively long period of time time (K)(K).

Logistic Growth (S curve)Logistic Growth (S curve)

• Example: turtles in a pondExample: turtles in a pond

Number ofindividuals (N)

Time

produces a S-shapedS-shaped curve

K

Draw an s-curve and draw a j-curve

• Label each with the lag phase the growth phase, the stationary phase

Factors That Limit Factors That Limit Population GrowthPopulation Growth

1. Density-Dependent Factors:1. Density-Dependent Factors:

a. Population-limiting factorsPopulation-limiting factors whose effects depend on population densitypopulation density.

b. The greater the pop, the greater the effects.

Examples: Examples: 1. Limited food supply

2. Disease

3. Predation

4. Nesting sites

Factors That Limit Factors That Limit Population GrowthPopulation Growth

2. Density-Independent Factors:2. Density-Independent Factors:

a. Population-limiting factorsPopulation-limiting factors (abiotic) whose occurrence is notnot affected by pop densitypop density.

b. the greater the population, the greater the effects

Examples: Examples: 1. Earthquakes

2. Fires

3. Hurricanes

4. Freeze in the fall

Boom and Bust SpeciesBoom and Bust Species

• A rapid increase (boom)(boom) in a population followed by a sharp decline (bust)(bust).

• Examples:Examples:

a. DaphniaDaphnia in a pond

number of individuals

in pop.

Time

boomboom bust

Boom and Bust SpeciesBoom and Bust Species

• Sometimes speciesspecies (carnivore)(carnivore) depend on other species (prey)species (prey) for food.

• Example: Example: SnowshoeSnowshoe harehare and lynxlynx

number of individuals in pop.

Years

Evolution Shapes Life HistoriesEvolution Shapes Life Histories

• Life History:Life History:

Series of events from birthbirth through reproductionreproduction to deathdeath.

• Two basic types of life history strategies:Two basic types of life history strategies:

1. Opportunistic life history1. Opportunistic life history

(r-selected species)(r-selected species)

2. Equilibrial life history2. Equilibrial life history

(K-selected species)(K-selected species)

1. Opportunistic life history1. Opportunistic life history(r-selected species)(r-selected species)

Characteristics:Characteristics:1. maturing time: short

2. life span: short

3. mortality rate: often high

4. times female is reproductive: usually once

5. age at first reproduction: early

6. size of offspring: small

7. parental care: none

8. Size of organism: small

2. Equilibrial life history2. Equilibrial life history(K-selected species)(K-selected species)

Characteristics:Characteristics:1. maturing time: long

2. life span: long

3. mortality rate: often low

4. times female is reproductive: often many

5. age at first reproduction: late

6. size of offspring: large

7. parental care: often extensive

8. Size of organism: tend to be large

Life History ExamplesLife History Examples

r-selected species:r-selected species:

1. Garden weeds

2. Insects

3. Desert flowers

K-selected species:K-selected species:

1. Humans

2. Apes

3. Elephants

Survivorship CurvesSurvivorship Curves

• Late LossLate Loss

High survival ratesHigh survival rates until old age.

Example:Example:

% of survivors

% of maximum life span

humanshumans

Survivorship CurvesSurvivorship Curves

• Constant LossConstant Loss

IntermediateIntermediate between the extremesextremes.

Example:Example:

% of survivors

% of maximum life span

squirrelsquirrel

Survivorship CurvesSurvivorship Curves• Early LossEarly Loss

High mortalityHigh mortality rates as larvaelarvae but decreased mortalitydecreased mortality at later ages.

Example:Example:

% of survivors

% of maximum life span

oystersfrogsinsects