1. Copyright © 2009 Pearson Education, Inc.  Idealized models describe two kinds of population growth –Exponential growth –Logistic growth 36.4 Idealized models predict patterns of population growth

2. Time Number of individuals (N) 0 K G = rN (K – N) K

4. Copyright © 2009 Pearson Education, Inc. 36.5 Multiple factors may limit population growth  The logistic growth model –Population growth slows and ceases as population density increases –Increasing population density results in a decrease in birth rate, an increase in death rate, or both

5. Density of females Clutch size 0 10 20 30 40 50 60 7080 2.8 3.0 3.2 3.4 3.6 3.8 4.0

6. Copyright © 2009 Pearson Education, Inc.  Abiotic factors may reduce population size before other limiting factors become important 36.5 Multiple factors may limit population growth

7. Apr MayJun Jul AugSepOct Nov Dec Number of aphids Exponential growth Sudden decline

8. Copyright © 2009 Pearson Education, Inc.  Most populations fluctuate in numbers 36.5 Multiple factors may limit population growth

9. Time (years) Number of females 197519801985199019952000 0 20 40 60 80

10. Copyright © 2009 Pearson Education, Inc. 36.6 Some populations have “boom-and-bust” cycles  Some populations fluctuate in density with regularity  Boom-and-bust cycles –Food shortages –Predator-prey interactions

11. Lynx Snowshoe hare Lynx population size (thousands) Hare population size (thousands) Year 1850187519001925 0 40 80 120 160 0 3 6 9

12. Copyright © 2009 Pearson Education, Inc. 36.7 EVOLUTION CONNECTION: Evolution shapes life histories  Life history –Series of events from birth to death  r/K selection –r-selective traits –K-selective traits

13. MalesFemales Experimental transplant of guppies Predator: Killifish; preys mainly on small guppies Guppies: Larger at sexual maturity than those in pike-cichlid pools Pools with killifish, but no guppies prior to transplant Predator: Pike-cichlid preys mainly on large guppies Guppies: Smaller at sexual maturity than those in killifish pools 11 years later Mass of guppies at maturity (mg) 40 80 120 160 200 67.5 76.1 161.5 185.6 Age of guppies at maturity (days) MalesFemales 20 40 60 80 100 48.5 58.2 85.7 92.3 Control: Guppies from pools with pike-cichlids as predators Experimental: Guppies transplanted to pools with killifish as predators

14. Predator: Killifish; preys mainly on small guppies Experimental transplant of guppies Guppies: Larger at sexual maturity than those in pike-cichlid pools Pools with killifish, but no guppies prior to transplant Predator: Pike-cichlid preys mainly on large guppies Guppies: Smaller at sexual maturity than those in killifish pools

15. MalesFemales Mass of guppies at maturity (mg) MalesFemales 40 80 120 160 200 67.5 76.1 161.5 185.6 Age of guppies at maturity (days) 20 40 60 80 100 48.5 58.2 85.7 92.3 Control: Guppies from pools with pike-cichlids as predators Experimental: Guppies transplanted to pools with killifish as predators 11 years later

16. Copyright © 2009 Pearson Education, Inc. 36.8 CONNECTION: Principles of population ecology have practical applications  Sustainable resource management –Maximum sustained yield

17. 1960 Yield (thousands of metric tons) 1970198019902000 0 100 200 300 400 500 600 700 800 900

18. Copyright © 2009 Pearson Education, Inc. THE HUMAN POPULATION

19. Copyright © 2009 Pearson Education, Inc. 36.9 The human population continues to increase, but the growth rate is slowing  Human population is expected to continue increasing for several decades  95% of the increase is in developing nations

20. 1500 Year Population increase Total population size Total population (in billions) 15501600 1650 1700175018001850190019502000 2050 0 2 4 6 8 10 20 40 60 80 100 Annual increase (in millions)