BI 105A Environmental Biology Professor Jill Nissen Montgomery College Fall 2006

1. BI 105AEnvironmental Biology Professor Jill Nissen Montgomery College Fall 2006

2. A Crowded World Chapter 8 Population Change

3. How do populations change in size? • The growth rate (r) of a population is the birth rate (b) minus the death rate (d): r = b – d • In addition to birth and death rates, migration must be considered when examining local populations:

5. Biotic Potential The maximum rate at which a population could grow (r) under ideal conditions

6. Carrying Capacity (K) The largest population size that can be sustained indefinitely by a particular environment

7. Factors Affecting Birth Rate and Death Rate

8. Population Growth Curves • Exponential population curve Maximum population growth (biotic potential) is realized • Logistic growth curve Environmental resistance & carrying capacity set limits

9. Exponential Population Growth • the graph has a J-shape • the larger the population gets, the faster it grows • occurs when organisms reproduce at their biotic potential • can not continue forever, eventually some factor limiting

10. Logistic Population Growth • the graph has an S-shape • the larger the population gets, the slower it grows • occurs when resources are limiting • With time the population size will approach and level off at the carrying capacity

11. A Population Crash • Overshooting the carrying capacity can lead to a population crash • An abrupt decline from high to low population density

12. Reproductive Strategies Each species has its own life history strategy

13. r-Selected Species • Short development time • Small body size • Short lifespan • Many small offspring • Early reproductive age • Usually one reproductive event per lifetime • Little or no parental care Dandelions Cockroaches

14. K-Selected Species • Long development time • Large body size • Long lifespan • Fewer, larger offspring • Late reproductive age • Usually more than one reproductive event per lifetime • High parental care Tawny Owls Elephants

15. Survivorship Curves Type I = Late loss (K) Type III = Early loss (r) Type II = Constant loss

16. The survivorship of most species can be compared to these curves – What type of curve does the human species have?

17. Factors Affecting Population Size Density – Dependent Factors • Effect increases as population increases • Biotic factors such as disease or competition Density – Independent Factors • Effect not influenced by population size • Abiotic factors such as weather conditions or fire

18. Human population size Exponential growth • 1800 - It took thousands of years for the human population to reach 1 billion • 1930 – 130 years later, 2 billion • 1960 – 30 years later, 3 billion • 1975 – 15 years later, 4 billion • 1987 – 12 years later, 5 billion • 1999 – 12 years later, 6 billion • http://www.census.gov/main/www/popclock.html NOT due to increase in birth rate • In the past 200 years, while the population has grown from 1 billion to 6 billion, the birth rate (b) has actually decreased • The increase in population is due to a decrease in the death rate (d) due to better food production, health care, and sanitation

19. Logistic growth • Scientists predict the growth rate will decrease until zero population growth is obtained, by about the end of this century • The J-shaped curve will be replaced by an S-shaped curve • We can control human population growth with family planning Source: Untied Nations, World Population Prospects, The 1998 Revision

20. Demographics of Countries Highly Developed Countries • Have low rates of population growth and low infant mortality rates • USA, Canada, France, Germany, Sweden, Australia, Japan Moderately Developed Countries • Have higher rates of population growth and higher infant mortality rates • Mexico, Turkey, Thailand, South America Less Developed Countries • Have the highest birth rates, the highest infant mortality rates, and the shortest life expectancies • Bangladesh, Ethiopia, Laos, Cambodia

21. Population Age Structure Can be used to predict population changes Less Developed

22. Fertility in the U.S. Replacement Level (2.0)

23. The United States has one of the highest rates of population increase of all the highly developed countries (0.6%) and this figure only includes birth and death, not immigration • Immigration has a greater effect on population size in the US than in many other countries • Since 1992 the US has accepted about 1 million legal immigrants annually • Add to that an estimated 300,000± unauthorized immigrants per year

24. The Immigration Reform and Control Act (IRCA) is the basic immigration law in effect in the U.S. IRCA gives priority to all of the following immigrating peoples: • those with family members already living in the U.S. • those who can fill vacant jobs • those who are refugees seeking asylum

25. Review Objectives Principles of Population Ecology• Define population ecology.• Define growth rate (r) and explain the four factors that produce changes in population size.• Use intrinsic rate of increase, exponential population growth, and carrying capacity to explain the differences between J-shaped and S-shaped growth curves.Reproductive Strategies• Define survivorship and describe type I, type II, and type III survivorship curves.Factors that Affect Population Size• Distinguish between density-dependent and density-independent factors that affect population size and give examples of each.The Human Population• Define demography and summarize the history of human population growth.Demographics of Countries• Explain how highly developed and developing countries differ in population characteristics such as infant mortality rate, total fertility rate, and age structure.• Explain how population growth momentum works. Demographics of the United States• Briefly describe the Immigration Reform and Control Act (IRCA).