Population Ecology

1
Chapter 53

• Population Ecology

2
Population Dynamics

• Changes that occur in
• Population size
• Density
• Dispersion
• Age distribution
• due to environmental change or stress.

3
Population Size

• Limits to population growth
• (births immigration) (deaths emigration)
• Carrying capacity (k)-- of individuals that an
  environment can sustain indefinitely determined
  by
• Biotic potential (maximum capacity for pop.
  growth)
• Environmental resistance (all factors that limit
  growth)
• G r x
  N
• (growth over time) (rate of increase) (pop
  size)

4
Types of Growth

• Exponential growth (J-shaped curve)
• Logistic growth (S-shaped curve) pop levels off
  around carrying capacity.

5
Types of Growth (cont)

• Boom and Bust
• Population overshoots carrying capacity, then has
  dieback (death/emigration).

6
Reproductive Strategies

• r-selected species
• Opportunist insects and rodents.
• Many, small young.
• Reproduce early and often.
• Little parental care most young die.
• High pop growth rate (r).

• K-selected species
• Competitor large mammals and birds.
• Few, larger young.
• Reproduce later and not as often.
• Care of young most survive.
• Stable pop size near carrying capacity (k).

7
Survivorship Curves

• Different reproductive patterns lead to different
  age structures in the population.
• Late loss (green) K-selected species.
• Early loss (red) r-selected species.
• Constant loss (black)

8
Human Population History
9
Factors affecting birth rates

• 1. Children needed to work.
• 2. Living in urban areas.
• 3. Cost of raising kids.
• 4. Opportunities for women.
• 5. Infant mortality.

• 6. Ave age of marriage.
• 7. Pensions.
• 8. Legal abortions.
• 9. Birth control.
• 10. Religious beliefs.

10
Factors affecting death rates

• 1. Increased food supply.
• 2. Better nutrition.
• 3. Improved health care/technology.
• 4. Improved sanitation/hygiene.
• 5. Safer water supplies.

11
Age Structure Diagrams

• shows the proportion of the population of each
  sex at each age level.
• Looks at 3 age categories
• 0 to 14 yrs (pre-reproductive)
• 15 to 44 yrs (reproductive)
• 45 (post-reproductive)
• (number of women impacts fertility rates)
• Can be used predict population growth and study
  economic impact.

12
Predicting Populations

• Rapid growth (Kenya) large numbers of younger
  people.
• Slow growth (US)
• Zero or negative growth (Sweden) small numbers
  of young people.