Chapter 5Populations

5-1 How Populations Grow• I. Characteristics of Populations

– A. geographic distribution- or range describes the area inhabited by a population (ex. Few cubic centimeters of apple (bacteria) to millions of square kilometers of Pacific Ocean (whales)

– B. population density- number of individuals per unit area (ex. Tall saguaro cactuses and smaller desert plants)

– C. population growth- affected by number of births, deaths, and individuals entering and leaving population • immigration and emigration (ex. Otters/sea urchins/kelp/killer

whales)

– D. age structure- youth in a population is going to predict a more rapid growth (ex. US population vs. Rwanda population)

• II. Exponential growthA. If a pop. has abundant space and food and

is protected from predators and disease- the pop. size will increase indefinitely

B. Occurs when a population grows at a constant rate- starts slow then grows quickly

C. Called a J-shaped curve

• III. Logistic Growth• A. When resources become less available the

growth slows or stops• B. The population reaches the carrying

capacity which is the number of organisms that the particular environment can support

• C. Called a S-shaped curve

5-2 Limits to Growth• Limiting factor- something that causes the population

to decrease• I. Density-dependent limiting factors

– A. Competition- when populations get crowded organisms compete for:• 1. food• 2. water• 3. space• 4. sunlight• 5. other essentials

Density Dependent Limiting Factors– B. predation- ex. Chart of wolf and moose (p. 126)– C. parasitism and disease- like predators,

parasites take nourishment often weakening and cause death (ex. Cordyceps fungus that infects insects)

II. Density-independent limiting factors– A. Unusual weather- tornados, hurricanes– B. Natural disasters- fire, rain– C. Seasonal cycles- frost, drought– D. Human activities- damming rivers, clearing forest

5-3 Human Population Growth• Human Population- Dot Video

• A. The human population cannot keep growing forever because the earth and its resources are limited

• B. Demography- study of human populations– 1. With advances in nutrition, sanitation and

medicine more children survive and adults live longer

– 2. As societies modernize, increase level of education, and raise their standard of living, families have fewer children

– 3. Demographic transition has occurred in the U.S., Europe, and Japan

– 4. Much of today’s population occurs in 10 countries with India and China in the lead

Chapter 6 (pg 152) Pollution• Biological magnification- concentrations of a

harmful substance that increase in organisms at a higher trophic levels

• DDT pesticide problem– Cheap, long activity, kills many types of insects,

controls pests and mosquitoes– Hazardous: nonbiodegradable and organisms don’t

eliminate it from their bodies– The pesticide remains in tissues of plants and

passed to the herbivores and omnivores– Top predator fish-eating birds were affected the

most, causing thin eggs shells and death of offspring and the threatening of their populations