Post on 09-Aug-2020
© 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