1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Ecology Definitions Population growth Population regulation Environmental factors that regulate growth Human population growth and regulation

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population ecology is the study of populations in relation to environment – Including environmental influences on population density and distribution, age structure, and variations in population size

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dynamic biological processes influence population density, dispersion, and demography A population – Is a group of individuals of a single species living in the same general area

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density is the result of a dynamic interplay – Between processes that add individuals to a population and those that remove individuals from it Figure 52.2 Births and immigration add individuals to a population. BirthsImmigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population.

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Potential for population increase It is quite high A single bacterium can reproduce by fission every 20 min, in 36 hours there will be enough bacteria to form a layer foot deep over the entire world A pair of elephants could produce a population of 19 million in 750 years

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Geometric/Exponential Models Populations in which reproduction is restricted to a particular season of the year have non-overlapping generations. Their growth is modeled using geometric equations (time interval is discrete) In populations in which reproduction happens continuously, their growth can be modeled using exponential equations (time interval is continuous)

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How do populations grow? We can envision a population consisting of few individuals living in an ideal, unlimited environment; the only restrictions: inherent physiological limitations due to life history – The population will increase in size with: Change in population size during time interval =Births+Immigration−Deaths−Emigration during time interval

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Verbal equation of population growth For simplicity: Change in population size during time interval = Births during time interval − Deaths during time interval

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential model Change in population size during time interval = Births during time interval − Deaths during time interval Let N = population size; t = time, ΔN = change in population size; Δt = change in time

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Then now we have: ΔN/Δt= B−D Where: B= No. of births in the population during the time interval D= No. of deaths in the population during the time interval

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings We can now express births and deaths as the average number of births and deaths per individual during a specified time interval: b = per capita birth rate d = per capita death rate We can obtain the numbers of births and deaths in a population by multiplying the per capita birth rate times the population size and the per capita death rate times the population size. Hence, we can revise the population growth equation using the per capita rates: ΔN/Δt = bN − dN

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings We combine the per capita birth and death rates into the per capita growth rate: r = b − d A population grows when r is positive, declines when r is negative, or stays the same when r = 0

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings We can now rewrite the equation using the per capita growth rate: ΔN/Δt = rN Assuming reproduction happens continuously, we can use differential calculus notation to express the equation as follows: dN/dt = rN

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a population increasing under ideal environmental conditions, the per capita growth rate may assume the maximum growth rate for the species called intrinsic rate of increase, r max. The equation for exponential population growth is then: dN/dt = r max N

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential population growth – Results in a J-shaped curve Figure 52.9 0 5 1015 0 500 1,000 1,500 2,000 Number of generations Population size (N) dN dt  1.0N dN dt  0.5N

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The J-shaped curve of exponential growth – Is characteristic of some populations that are rebounding Figure 52.10 1900 1920194019601980 Year 0 2,000 4,000 6,000 8,000 Elephant population

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic growth model includes the concept of carrying capacity Exponential growth – Cannot be sustained for long in any population A more realistic population model – Limits growth by incorporating carrying capacity

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Carrying capacity (K) – Is the maximum population size the environment can support

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Growth Model In the logistic population growth model – The per capita rate of increase declines as carrying capacity is reached

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings We construct the logistic model by starting with the exponential model – And adding an expression that reduces the per capita rate of increase as N increases Figure 52.11 Maximum Positive Negative 0 N  KN  K Population size (N) Per capita rate of increase (r)

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Logistic equation Maximum sustainable population size is K K − N tells us how many additional individuals can the environment sustain (K − N)/K tells us what fraction of K is still available for population growth Hence: dN/dt = rmaxN (K−N) K

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A hypothetical example of logistic growth Table 52.3

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic model of population growth – Produces a sigmoid (S-shaped) curve Figure 52.12 dN dt  1.0N Exponential growth Logistic growth dN dt  1.0N 1,500  N 1,500 K  1,500 0 51015 0 500 1,000 1,500 2,000 Number of generations Population size (N)

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How well do these populations fit the logistic population growth model?

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Populations are regulated by a complex interaction of biotic and abiotic influences There are two general questions we can ask – About regulation of population growth

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What environmental factors stop a population from growing? Why do some populations show radical fluctuations in size over time, while others remain stable?

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Change and Population Density In density-independent populations – Birth rate and death rate do not change with population density In density-dependent populations – Birth rates fall and death rates rise with population density

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density-Dependent Population Regulation Density-dependent birth and death rates – Are an example of negative feedback that regulates population growth – Are affected by many different mechanisms

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Competition for Resources In crowded populations, increasing population density – Intensifies intraspecific competition for resources Figure 52.15a,b 100100 0 1,000 10,000 Average number of seeds per reproducing individual (log scale) Average clutch size Seeds planted per m 2 Density of females 0 7010 2030 40506080 2.8 3.0 3.2 3.4 3.6 3.8 4.0 (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Territoriality In many vertebrates and some invertebrates – Territoriality may limit density

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cheetahs are highly territorial – Using chemical communication to warn other cheetahs of their boundaries Figure 52.16

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oceanic birds – Exhibit territoriality in nesting behavior Figure 52.17

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Health Population density – Can influence the health and survival of organisms In dense populations – Pathogens can spread more rapidly

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Predation As a prey population builds up – Predators may feed preferentially on that species

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Toxic Wastes The accumulation of toxic wastes – Can contribute to density-dependent regulation of population size

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Human population growth has slowed after centuries of exponential increase No population can grow indefinitely – And humans are no exception

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Global Human Population The human population – Increased relatively slowly until about 1650 and then began to grow exponentially Figure 52.22 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. 0 The Plague Human population (billions) 2000 A.D. 0 1 2 3 4 5 6

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Though the global population is still growing – The rate of growth began to slow approximately 40 years ago Figure 52.23 1950 19752000 2025 2050 Year 2003 Percent increase 2.2 2 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1.8

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regional Patterns of Population Change To maintain population stability – A regional human population can exist in one of two configurations

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Zero population growth = High birth rates – High death rates Zero population growth = Low birth rates – Low death rates

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The demographic transition – Is the move from the first toward the second state Figure 52.24 50 40 20 0 30 10 1750 1800 1850 1900 1950 2000 2050 Birth rate Death rate Birth rate Death rate Year SwedenMexico Birth or death rate per 1,000 people

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age Structure One important demographic factor in present and future growth trends – Is a country’s age structure, the relative number of individuals at each age

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age structure – Is commonly represented in pyramids Figure 52.25 Rapid growth Afghanistan Slow growth United States Decrease Italy Male Female Male FemaleMale Female Age 864202468864202468864202468 Percent of population 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age structure diagrams – Can predict a population’s growth trends – Can illuminate social conditions and help us plan for the future

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Global Carrying Capacity Just how many humans can the biosphere support?

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Estimates of Carrying Capacity The carrying capacity of Earth for humans is uncertain

47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Footprint The ecological footprint concept – Summarizes the aggregate land and water area appropriated by each nation to produce all resources it consumes and to absorb all wastes it generates – Is one measure of how close we are to the carrying capacity of Earth

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological footprints for 13 countries – Show that the countries vary greatly in their footprint size and their available ecological capacity Figure 52.27 16 14 12 10 8 6 4 2 0 0 2 4 68 1214 16 New Zealand Australia Canada Sweden World China India Available ecological capacity (ha per person) Spain UK Japan Germany Netherlands Norway USA Ecological footprint (ha per person)