© Cengage Learning 2015 p711

Chapter 26 – Population Ecology

© Cengage Learning 2015

• How populations

interact with one

another and with

their environment

• Demographics

– Size

– Density

– Distribution

Population Ecology

© Cengage Learning 2015

• Size: Total number of individuals

• Density: Number of individuals per unit area

or volume

• Distribution: Location of individuals relative

to each other

Population Demographics

© Cengage Learning 2015

Estimating Population Size/Density

• Impractical to count all members of a

population

• Plot sampling

– Used to estimate population size of not very

mobile animals and plants

• Mark-recapture sampling

– Used to estimate population size of mobile or

hidden animals

© Cengage Learning 2015

Population Dynamics

© Cengage Learning 2015

Exponential Growth

• Number of new

individuals increases

each generation,

although growth rate

stays the same

• J-shaped curve

• Only occurs with

unlimited resources

© Cengage Learning 2015

Exponential Growth

© Cengage Learning 2015

What Constrains Population Growth?

• Two categories of limiting factors

– Density-dependent factor

• Factor that limits population growth and has a

greater effect in dense populations than less dense

ones

• Examples: pathogens and parasites

– Density-independent factor

• Factor that limits population growth and arises

regardless of population density

• Examples: fires and earthquakes

© Cengage Learning 2015

Logistic Growth

• Growth rate slows as the population approaches

the habitat’s carrying capacity (K)

• S-shaped curve

• Limiting factors cause growth rate to slow and

level off

© Cengage Learning 2015

Life History Patterns

• Life history pattern

– A set of traits related to growth, survival, and

reproduction such as life span, age-specific

mortality, age at first reproduction, and

number of breeding events

• Cohort

– Group of individuals born during the same

interval

© Cengage Learning 2015 Figure 40-7 p718

Survivorship Curves

Graphs showing how many members of a

cohort remain alive over time

© Cengage Learning 2015 Figure 40-8 p719

r-selected K-selected

• Short-lived

• Fast maturing

• Large # offspring

• Low parental care

• Long-lived

• Late maturing

• Small # offspring

• High parental care