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.