Population Growth

1. Population Growth • Exponential growth • No population can continue to grow indefinitely. • At high densities, growth becomes density-dependent. (Fig. 48.3) • All populations eventually reach the carrying capacity of their habitat. (the max number that can be supported by available resources).

2. Figure 48.3 Carrying capacity Population size Time

3. Case Studies Explaining How Population Size Changes Over Time • Humans exhibiting density-dependent growth (Fig. 48.5a,b)

4. Figure 48.5a Historical growth 6 1999: 6 billion 1900: 1.5 billion 5 1700: 600 million 4 1500: 400 million Human population (billions) 3 1 A.D.: 150–200 million 2 4–5 million 1 0 10,000 B.C. 8000 6000 4000 2000 0 2000 A.D. Year

5. Figure 48.5b Recent growth 12 11 10 High 1998 Projections Medium 9 8 Low 7 Human population size (billions) 6 5 4 3 2 1950 1970 1990 2010 2030 2050 Year

6. Figure 48.5c 1992 Projections Projected population in 2050 Fertility rate 12.5 billion High 10.15 billion Medium Low 7.8 billion The 1992 projections for 2050 are higher than those from 1998 primarily because the earlier projections did not account for the impact of AIDS.

7. Population Structure • Age structure • Developed nations have an age distribution that tends to be even. (Fig. 48.9a) • Developing nations have an age distribution that is bottom-heavy (mostly young individuals). (Fig. 48.9b)

8. Figure 48.9a More-developed countries 100 1998 data 95 90 85 2050 projections 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 60 40 20 0 20 40 60 (In millions) Females Males

9. Figure 48.9b Less-developed countries 100 95 1998 data 90 85 2050 projections 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 300 200 100 100 200 300 (in millions) Females Males

10. Population Structure • Geographic structure • Many species exist as a metapopulation. • Small, isolated populations, even those on nature reserves, are unlikely to survive over the long term. (Fig. 48.10a-c)

11. Figure 48.10a A metapopulation is made up of small, isolated populations. Individuals Habitat patches

12. Figure 48.10b Although some subpopulations go extinct over time...

13. Figure 48.10c …migration can restore or establish subpopulations.

14. Figure 48.11

15. Demography and Conservation • Demography: the study of factors that determine the size and structure of populations through time.

16. Demography and Conservation • Life tables • Summarize the probability that an individual will survive and reproduce in any given year over the course of its lifetime. (Fig. 48.13a) • Survivorship - Ix = Nx / N0 • Fecundity: the number of female offspring produced by each female in a population.

17. Figure 48.13a Three general types of survivorship curves 1000 Type l High survivorship 100 Type ll Low survivorship Number of survivors (Nx) Low survivorship Steady survivorship 10 1 Type lll High survivorship 0.1 Age

18. Demography and Conservation • Life tables • Contain useful pieces of information, such as survivorship, fecundity, and net reproductive rate.

19. Figure 48.14a Life table Age (x) Survivorship (lx) Fecundity (mx) 0 (birth) 0.0 0.33 3.0 1 2 0.2 4.0 0.2 5.0 3

20. Demography and Conservation • Life tables • Can be used to make population projections and guide conservation programs.

21. Demography and Conservation • Population viability analysis (PVA) • A model that estimates the likelihood that a population will avoid extinction for a given time period. • Combine demographic models with geographic structure and rate and severity of habitat disturbance.

22. Demography and Conservation • Population viability analysis (PVA) • Populations are considered viable if they have a 95% probability of surviving for at least 100 years.

23. Demography and Conservation • Population viability analysis (PVA) • Currently being used by natural resource managers. (Fig. 48.15a,b)

24. Box 48.1, Figure 1