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Population

Population. Chapter 8. Principles of Population Ecology. Population Ecology = deals with species populations in an area and how/why those numbers fluctuate over time. Study how a population responds to its environment. Populations cannot increase indefinitely

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Population

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  1. Population Chapter 8

  2. Principles of Population Ecology • Population Ecology = deals with species populations in an area and how/why those numbers fluctuate over time. • Study how a population responds to its environment. • Populations cannot increase indefinitely • environmental pressures called “limiting factors” • Population Density= # of individuals of a species /area or volume at a given time • Age Structure:# of males and females at each age from birth to death. Competition, predation, disease

  3. World Map

  4. … by Population

  5. … by Gross Domestic Product

  6. … by Child Mortality

  7. … by People living with HIV/AIDS

  8. Current World Population Global population was 6,904,947,450On March 10, 2011 • The global population grows by: • Nearly 2.3persons per seconds • Nearly 8,343 persons per hour • Over 200,234 persons per day • Over 73 million persons per year

  9. THE UNITED STATES POPULATION According to the U.S. Census Bureau, the resident population of the United States, projected to 03/14/12 at 14:57 UTC is: 313,181,425 COMPONENT SETTINGS FOR MARCH 2012 One birth every 8 seconds One death every12 seconds One international migrant (net) every 46 sec Net gain of one person every15 sec.

  10. Human Population Dynamics There are just three sources of change in population size: • Fertility • Mortality "natural decrease" refers to population decline resulting from more deaths than births • Migration Net migration is the number of immigrants minus emigrants

  11. How do Populations Change in Size? • Birth Rate (b) = # births per 1000 people / year • Death Rate (d) = # deaths per 1000 people / year • Growth Rate (r) = natural increase of a population, ( % / year ). Called “natural increase” in human pops. • Dispersal: • Immigration (i) = entering a pop. • Emigration (e) = exiting a pop. r = b – d r = ( b – d ) + ( i - e )

  12. Example 1: Total Population = 10,000 200 Births/year (20 births/1000 people) 100 Deaths/year (10 deaths/1000 people) r = b – d r = 20/1000 – 10/1000 r = 0.02 – 0.01 r = 1% per year Example 2: Total Population = 10,000 100 Births/year 50 Deaths/year 10 Immigrants 100 Emigrants r = ( b – d ) + ( i – e ) r = (10/1000 – 5/1000) + (1/1000 – 10/1000) r = (.01 – .005) + (.001 – .01) r = -0.004 …or -0.4% If r = 0, pop size does not change. If r is positive, pop size is growing. If r is negative, pop size is decreasing.

  13. Doubling Time • Time it takes for a population to double itself, assuming that the current growth rate does not change. DT=70/AGR% • You may be given the doubling time and asked to calculate the AGR% (EASY MATH!)

  14. WHY DO WE USE 70 FOR DOUBLING TIME??? It is all about math man… Thanks Mrs. Toth!

  15. World population is growing at a rate of about 1.7% • IF this rate continues, the population will double in ~ 42 years ( 70/1.7 = 42) • Unabated, such a rate would lead to a point about 2000 years when the mass of humanity would weigh more, and be larger, than the Earth. Luckily, the global population rate is decreasing... Dip in the growth rate from1959-1960, for instance, was due to the Great Leap Forward in China. During that time, both natural disasters and decreased agricultural output in the wake of massive social reorganization caused China's death rate to rise sharply and its fertility rate to fall by almost half.

  16. AGE STRUCTURE DIAGRAMS Which histogram you would consider to be: Declining, Expanding, or Stable WHY???

  17. Age Structure Diagrams Pre-reproductive & Reproductive age groups are nearly equal Fewer people will be parents of the next generation Largest population in pre-reproductive years Positive Population Growth Momentum!! Pre-reproductive group is smaller Pop will fall

  18. More Developed – 1999 & 2050 World - 1999 Less Developed – 1999 & 2050 Least Developed – 1999 & 2050 Source: http://www.un.org/esa/population/publications/aging99/a99cht3.htm

  19. DEVELOPING or DEVELOPED?

  20. DEVELOPING or DEVELOPED?

  21. DEVELOPING or DEVELOPED?

  22. DEVELOPING or DEVELOPED?

  23. Tracking the baby-boom generation in the United States

  24. The Power of the Pyramids! • Put your name on your paper. • Look at the back of your page… • Find 2 other students who have DIFFERENT countries as you. • You’re making Age-Sex Histograms today. • Make ‘em colorful and fun! Don’t spend too much time “prettying it up” – you have analysis questions to do! • Calculator time-saver: • If you’re using a TI-83, store the # you’re dividing by as a letter. It’ll save tons of time!

  25. Maximum Population Growth • Biotic Potential or Intrinsic Rate of Increase • Max. rate at which a pop could increase under ideal conditions. • Life History Characteristics affect biotic potential. • Age at which reproduction begins • Fraction of life when reproduction is possible • # reproductive periods per lifetime • # offspring produced during each reproductive period • Generally… • Smaller organisms have high biotic potential. • Larger organisms have low biotic potential.

  26. World Pop 1800-2100 Based on UN 2004 Projections (red, orange, green) & US Census Bureau historical estimates (black). 10.9 9.3 7.9

  27. EXPONENTIAL GROWTH ALL organisms show Exponential Growth… …IF they’re growing at their biotic potential (time may vary) J-shaped curve Increase or decrease competition? EXPONENTIAL MODEL Is crowding a problem? YES!

  28. CARRYING CAPACITY “K” Carrying Capacity (K)= # organisms that the environment can support over a given time. • Fluctuates due to environmental changes or limiting factors! ENVIRONMENTAL RESISTANCE • abiotic (light, temp, nutrients, weather, etc) • biotic (food, prey, disease, adaptable, etc) Forms an S- shape graph Limits population growth Feedback loop… + or – ? LOGISTIC MODEL

  29. LOGISTIC Curves: show fluctuations!

  30. LOGISTIC Curves: show fluctuations!

  31. S-shaped Curves:a CRASH could occur!! WHY would this happen? Resources are exhausted!

  32. Why is estimating carrying capacity for an individual country misleading, based on what you know about human civilization & resource use? IMPORTS ENVIRONMENT ALTERATION TRANSPORTATION IMMIGRATION EXCHANGING SERVICES EXPORTS MOTHER NATURE EMIGRATION TECHNOLOGY

  33. r strategists Recall: r = growth rate! r-selected species have a high growth rate Characteristics: Small body size Early maturity Short life span Large broods Little or no parental care Usually in unpredictable environments (long-term survival low) Low ability to compete Mosquitoes & Weeds K strategists Recall: K = carrying cap. Maximize survival when the pop. is near K. Characteristics: Few offspring Long life spans Slow reproduction Late reproduction Parental care Large body size Usually in stable environments Humans, Owls, Trees,Whales Reproductive Strategies

  34. Survivorship • Probability that a given individual in a population will survive to a particular age. • Type I = prob. of death greatest when old. • Type III = prob. of death greatest when young. • If early death is avoided, survival chance is high • Type II = prob. of death equal through life. • Death events have little age bias. THESE ARE GENERALIZATIONS!! (few species fit 1 curve)

  35. Survivorship curves changethroughout life for most species.

  36. Factors that Affect Population Size • Density-Dependent Factors • Effects of the factor are changed with a changing population size • Examples: • Disease • Competition for resources (food, space, etc) • Predator-prey relationships • Density-Independent Factors • Effects of the factor are unchanged with a changing population size • Examples: • Typically abiotic factors • Random weather events

  37. Predator-Prey Curve

  38. Case-in-Point: Predator-Prey Dynamics on Isle Royale • Moose wandered to this island by crossing the frozen Lake Superior – Population Boomed! • Wolves wandered there later – Population Boomed! Moose dec. due to being over K – Lack of Food! DD or DI? Moose over K Moose inc. due to few predators Canine Parvovirus Wolves inc. due to more food Wolf dec. due to less food

  39. Boom – Or – Bust Cycle Lemming Population • population is increasing, and density-dependent factors are increasingly severe. (2) Population is declining, and density-dependent factors are increasingly relaxed.

  40. Current Human Population • Between 2001 and 2002 – World Population increased by 78M. • Not due to increased birth rate – it declined! • It’s due to a decreased death rate! • Why? • Better medicine • Better technology • Lots of reasons! Human Population (1800 – present)

  41. Projecting Future Population • Population continues to increase • Growth rate continues to decrease • Prediction: • Growth rate will continue to decrease slowly until zero population growth is attained (b = d) b and r in Mexico (1900 – 2000) Mexican Revolution

  42. Types of Fertility Rates that Affect Human Population Growth • Total fertility rate (TFR) • The average number of children born to a woman • Average in developed countries = 1.5 • Average in developing countries = 3.8 • Worldwide 1990: 3.1 now: 2.8 • Replacement fertility rate (RFR) • The number of children a couple must have to replace themselves • A RFR of 2.1 for developed countries with low infant and child mortality rates • Africa RFR = 2.5

  43. This graph is based on different fertility rates. 2002:2.8 children/woman If it declines to 1.5, population will be 7.9 B If it declines to 2.5, population will be 10.9 B small changes make a BIG difference! ??? What is Earth’s K ??? 4 B – 16 B?? Based on standards of living, resource consumption, technology, and waste generation. Projecting Future Population 2000 UN Estimates World population will be between… 10.9 B 9.3 B = “most likely” 7.9 B Projections use estimates of future b, d, and migration.

  44. Highly Developed / Developed Low r, low b highly industrialized low infant mortality (# deaths age 0-1 per 1000 live births) Longer life expectancy High avg. per capita GNI PPP (amt. goods & services the average citizen could buy) Developing High b, high r Less industrialized overall Shorter life expectancy Lowest avg. GNI PPP Can be moderately developed or less developed. Moderately developed is just that… moderate! Demographics The applied branch of sociology that deals with population statistics

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