Chapter 53 Population Ecology

Population Dynamics… Population: same species, same area, interbreeding Changes that occur in: Population size Density Dispersion Age distribution …due to environmental change or stress.

Population Size (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)

Limits to population growth (a form feedback control) Density-independent factors: birth/death rates don’t change with population density (extreme weather, natural disasters, certain human activities) Density-dependent factors: As population density increases, birth rate falls and/or death rate increases (competition for resources such as food, water, light, space; disease; predation; wastes)

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 (it’s about energy) 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 human 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 human 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 – large numbers of younger people. Slow growth (US) Zero or negative growth – small numbers of young people.