Population Growth and Reproductive Patterns

Factor Affecting Population Size

Population Size (N) – = Population Change Births + Immigration Deaths + Emigration – = birth rate and death rate reported as the number per thousand people; zero population growth (ZPG) occurs when births balance deaths

Population Change If the birth/immigration rate are less than the death/emigration rate than the population decreases If the birth/immigration rate are greater than the death/emigration rate than the population increases

Density Factors and Population Growth Dynamic characteristics of populations Size, number of individuals (N) Density (N/ area) Dispersion, uniform, clumped, random appropriate scale Age distribution, proportions of young, middle-aged, old

Density Factors and Population Growth 2 Categories: Density-Dependent Factors Density-Independent Factors

Density Dependent Density-dependent controls More of an effect as population increases Biotic components. Competition Territoriality Disease, parasitism Predation Stress responses to crowding

Lynx and Hare

Density-Independent Density-independent controls Population size has no effect Abiotic components Drought, extreme temperatures, Light (or lack of), Oxygen (or shortage), etc.

2 Types of Population Growth 1. Exponential Growth 2. Logistic Growth

Exponential Growth As the population gets larger, it also grows faster - Unchecked growth - J shaped curve

Logistic Growth Growth is determined by limiting factors S shaped curve - food availability - disease - predators - lack of space - due to these factors populations may stabilize keeping the population at or below the carrying capacity

What is Carrying Capacity? Is the maximum population a habitat can support indefinitely Population exceeds it, for long periods, degrades its environment and reduces future carrying capacity

Carrying Capacity The number of organisms of one species that an environment can support indefinitely

Population Growth US has over 300 million people Growth is determined by biotic potential and carrying capacity

Reproductive Strategies R Strategists Short life span Small body size Reproduce quickly Have many young Little parental care Ex: cockroaches, weeds, bacteria

Reproductive Strategies K Strategists Long life span Large body size Reproduce slowly Have few young Provides parental care Ex: humans, elephants

Survivorship Curves Type I individuals survive well early in life and generally live many years.  At an advanced age, the death rate increases dramatically.  Examples include large mammals.   Type II individuals have a death rate that is relatively constant at any age. Examples include lizards, hydra, and some small mammals. Type III individuals initially have a rather low chance of survival.  Those that do survive may live to an advanced age.  Examples include many fish and other marine organisms.

Age Structure Curves A population pyramid, or age pyramid or age picture diagram or age structure diagram, is a graphical illustration that shows the distribution of various age groups in a population (typically that of a country or region of the world), which forms the shape of a pyramid when the population is growing. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species.

Activity: Where Do You Stand? Rank the following statements from 1-10; 1 (Strongly Disagree) to 10 (Strongly Agree) Be ready to take your stand and discuss your opinions with your classmates.

1. Because our population will soon be at seven billion people and continues to grow, we need to expand land area available for living and growing food by cutting down the rain forest.

2. Without reducing rapid population growth, it will be impossible to solve the world’s global challenges.

3. With seven billion people commuting from one place to another, drilling for more oil is necessary to fuel more cars.

4. In order to feed our population, we must use pesticides, chemical fertilizers, and genetically modified crops to increase farm yields.

5. With new technologies used to gather fish, we must have international laws to ensure seafood is harvested sustainably.

6. The Earth can support seven billion people now and will be able to support any number of human in the future.

7. In an effort to feed a population of seven billion, people in developed countries should reduce the amount of meat they consume.

8. Science and technology will ensure that food production and energy supplies keep up with the demands of a growing population.

9. With human population at seven billion, we must protect endangered species habitats by not developing on them for any reason.

10. There is nothing I can do to help alleviate population pressures.

11. Governments in countries with fast-growing populations should make laws to limit the number of children that couples can have.

12. In a real crunch, jobs are more important than environmental quality.

13. With seven billion people on the planet, water pollution is inevitable and we should not waste money trying to prevent it.

14. Even though I am only one person in seven billion, I still have a responsibility to keep the Earth healthy; what I do makes a difference.

15. Automobile makers in this country should be required by law to make all their vehicles fuel efficient, even though the vehicles may become more expensive.

16. If China and India can each take care of over a billion people on relatively the same size land as the U.S., then the U.S. should accept immigrants until it reaches a billion people as well.

18. Arable land should never be used for housing, businesses, or other non-agricultural uses because we need all available farmable land to produce food.

What is Urbanization? The movement of people from rural areas to cities Depend on resources outside the city

Why are big cities growing? Increase in birth rates Immigration Poor are moving to larger cities and away from rural areas

How are cities growing Cities have grown from 2% to 45% since 1950 By 2050, 66% of all people in the world will live in urban areas 75% of the U.S. population lives in urban areas occupying 3% of the country’s land area

Effect of Cities Heat Island The enormous amount of heat is in the center of the city 3º to 5º C (5º--9ºF) higher than the surrounding countrysides

Benefits of Urban Development Better education system Medical services Social Service programs

Problems of Urban Development Infectious diseases Inadequate water system Poor sewer systems Exposure to pollution