How do we model population dynamics as growth slows?

1. How do we model population dynamics as growth slows?

2. Logistic Growth (Transitional Phase) • Logistic growth (transition phase) occurs when population growth slows or stops following a period ofexponential growth • Creates an “S” shaped curve • Population growth may slow or stopfor a number of reasons: • Birthrate ↓ death rate ↑immigration ↓ emigration ↑ • At some point, the growth of a population willlevel off

3. Comparing Exponential and Logistic Growth

4. Carrying Capacity

5. Carrying Capacity (K) • The maximum number of individuals that a particular habitat can support (i.e. sustain, without depleting or degrading the resources) • For most species, carrying capacity is fairly easy to calculate • It is complicated for humans

6. The classical ‘Sigmoid’ Population growth curve Most plant and animal populations follow this type of growth

7. Classic Lodkik-Volterra predator-prey modelling

8. Population fluctuations

9. Population fluctuations Birds in decline: How do they work that out?....

10. What is happening in this population graph?

11. Some formulae (you don’t need to know these!) (Reference: http://www.nature.com/scitable/knowledge/library/how-populations-grow-the-exponential-and-logistic-13240157 • Exponential growth: • Logistic Growth (Transitional phase):

12. Homework : Zebra Mussel Webquest (Population Study) Zebra mussel population Dynamics Webquest

13. A B A

14. 5.3.2, 5.3.3 K = carrying capacity r = rate of reproduction N0 = starting population A B A

15. Let’s Review: What are the four factors that affect populations?

16. The study of human population dynamics: Demography • How has the human population changed over time? • Why do population growth rates vary in countries throughout the world? • What is the ‘demographic transition’ and why should I care? • What is the ‘carrying capacity’ of the biosphere for humans?

17. Historical Overview • Welcome to the Anthropocene!....

18. World population, 500 BC – 2010 AD • Until the 1800s the world's population grew slowly for thousands of years. • In 1820 the world's population reached one billion. • In the early 1970s, the world's population reached three billion. • In 1999, less than 30 years later, the population doubled to six billion. • The global rate of population growth is now one billionevery 13 years.

19. Historical Overview • Human Population growth

20. Why was the ‘Lag Phase’ of the human population so prolonged?

21. The present…and the future? http://www.bbc.co.uk/news/magazine-15449959 7.12.12

22. Human Population Dynamic predictions Here are the United Nations Predictions for population change over the next 100 yearsUN World population prospects (Image: http://esa.un.org/unpd/wpp/P-WPP/htm/PWPP_Total-Population.htm) 7.12.12

23. Watch this video and write down the reasons for the growth in the world’s population • BBC report on the 7th Billion...

24. Why did the human population begin to rise... Increased survival rate (i.e. decreased death rate) • Improved agricultural technology and techniques • Industrial Revolution • Stability of food supplies • Improved sanitation • Improved medical knowledge • Improved healthcare • High birth rate

26. Birth/Death Rates

27. Some say NO: People can find or manufacture additional resources to keep pace with population growth. Nations become stronger as their populations grow. Some say YES: Not all resources can be replaced. Even if they could, quality of life suffers. Nations do not become stronger as their populations grow. Is population growth really a problem?

28. Modelling population and its consequences Some models show population growth leading to resource depletion, which can result in declining food production, industrial output, and population

29. The Demographic Transition model

31. Explaining the demographic transition model • Over the past 100 years, population growth in ‘economically developed countires’ has slowed dramatically • The model to explain this change is called the Demographic Transition Model • It has 5 key stages

32. Stage 1 • Total population is low but balanced – high birth and high death rates • ‘Pre-industrial’

33. Stage 2 • Death rates fall as sanitation and health care improve • Birth rates remain high • Population increases

34. Stage 3 • Total population rises rapidly • Birth rates slow as contraception is made available and fewer children needed to work • Death rates still falling

35. Stage 4 • Total population high but balanced by low birth rate and low mortality • Desire for smaller families

36. Stage 5 • Total population decreasing • Desire for smaller families • People have children later in life

37. Where is your country? • Learning about the 'New Demography'

38. Where is your country? • Most wealthy countries are in Stage 4 • Several European countries are in stage 5: • Russia has lost 5.7 M since the breakup of the Soviet Union • Germany, Italy: population is decreasing • Most developing countries are in Stage 2 • Most population growth in the world is contributed by only 10 countries, with China and India leading

39. Population profiles and age-structure diagrams

40. Demographers predict future growth using models called ‘pyramids’/age-structure diagrams • let's look at population pyramids!

41. Mozambique, 2000: Stage 1 of the demographic transition model

42. Mozambique, 2025: Stage 2 of the demographic transition model

43. UK, 2000: Stage 4 of demographic transition

44. UK, 2025: Stage 5 of demographic transition

45. What does human demography mean for the future of our planet? • Will today’s emerging nations pass through the demographic transition? • Do you believe that national governments should implement policies, subsidies, or other programs to reduce birth rates? • UN data...