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

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

Copyright © 2009 Pearson Education, Inc 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

Density of females Clutch size

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

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

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

Time (years) Number of females

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

Lynx Snowshoe hare Lynx population size (thousands) Hare population size (thousands) Year

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

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) Age of guppies at maturity (days) MalesFemales Control: Guppies from pools with pike-cichlids as predators Experimental: Guppies transplanted to pools with killifish as predators

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

MalesFemales Mass of guppies at maturity (mg) MalesFemales Age of guppies at maturity (days) Control: Guppies from pools with pike-cichlids as predators Experimental: Guppies transplanted to pools with killifish as predators 11 years later

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

1960 Yield (thousands of metric tons)

Copyright © 2009 Pearson Education, Inc. THE HUMAN POPULATION

Copyright © 2009 Pearson Education, Inc 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

1500 Year Population increase Total population size Total population (in billions) Annual increase (in millions)