Chapter 53 Population Ecology

Population Dynamics…  Changes that occur in: Population size Density Dispersion Age distribution  …due to environmental change or stress.

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)

Types of Growth  Exponential growth (J-shaped curve)  Logistic growth (S- shaped curve) – pop levels off around carrying capacity.

Types of Growth (cont)  “Boom and Bust”  Population overshoots carrying capacity, then has dieback (death/emigration).

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).

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)

Human Population History

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.

Factors affecting death rates  1. Increased food supply.  2. Better nutrition.  3. Improved health care/technology.  4. Improved sanitation/hygiene.  5. Safer water supplies.

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.

Predicting Populations  Rapid growth (Kenya) – large numbers of younger people.  Slow growth (US)  Zero or negative growth (Sweden) – small numbers of young people.