1. Copyright © 2009 Pearson Education, Inc. POPULATION STRUCTURE AND DYNAMICS

2. Copyright © 2009 Pearson Education, Inc. 36.1 Population ecology is the study of how and why populations change  Population –A group of individuals of a single species that occupy the same general area  Individuals in a population –Rely on the same resources –Are influenced by the same environmental factors –Are likely to interact and breed with one another

3. Copyright © 2009 Pearson Education, Inc.  A population can be described by the number and distribution of individuals  Population dynamics is the interactions between –Biotic and abiotic factors  It is the cause of variation in population sizes –A population increases through birth and immigration –Death and emigration out of an area decrease the population 36.1 Population ecology is the study of how and why populations change

4. Copyright © 2009 Pearson Education, Inc. 36.2 Density and dispersion patterns are important population variables  Population density is the number of individuals of a species per unit area or volume  Examples of population density –The number of oak trees per square kilometer in a forest –The number of earthworms per cubic meter in forest soil

5. Copyright © 2009 Pearson Education, Inc.  Within a population’s geographic range, local densities may vary greatly  The dispersion pattern of a population refers to the way individuals are spaced within their area  Dispersion patterns can be –Clumped –Uniform –Random 36.2 Density and dispersion patterns are important population variables

7. Copyright © 2009 Pearson Education, Inc.  In a clumped pattern individuals are grouped in patches 36.2 Density and dispersion patterns are important population variables

8. Copyright © 2009 Pearson Education, Inc.  In a uniform pattern individuals are equally spaced in the environment 36.2 Density and dispersion patterns are important population variables

9. Copyright © 2009 Pearson Education, Inc.  In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way 36.2 Density and dispersion patterns are important population variables

10. Copyright © 2009 Pearson Education, Inc. 36. 3 Life tables track survivorship in populations  Life tables track survivorship over the life span of individuals in a population  Survivorship curves plot the proportion of individuals alive at each age –Type I –Type II –Type III

11. Percentage of maximum life span Percentage of survivors (log scale) 0 50100 0.1 1 10 100 III II I

12. Copyright © 2009 Pearson Education, Inc. 36.4 Idealized models predict patterns of population growth  Exponential growth model –The rate of population increases under ideal conditions –Calculated using the equation G = rN –G is the growth rate of the population –N is the population size –r is the per capita rate of increase

13. Time (months) Population size (N) 0 1 23 4 567 89 10 1112 0 50 100 150 200 250 300 350 400 450 500

15. Copyright © 2009 Pearson Education, Inc.  Logistic growth model –This growth model takes into account limiting factors –Limiting factors are environmental factors that restrict population growth –Formula 36.4 Idealized models predict patterns of population growth

16. Year Breeding male fur seals (thousands) 1915 1925 19351945 0 2 4 6 8 10

17. 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

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

19. 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

20. 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

21. 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

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

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

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

25. 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

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

27. 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: populations with rapid growth and maturation; little postnatal care; also known as “opportunistic populations” –K-selective traits: populations with a roughly constant size whose members have low reproductive rates. Lots of postnatal care required. “K” = Kids!

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

29. Copyright © 2009 Pearson Education, Inc. 36.10 CONNECTION: Age structures reveal social and economic trends  Age structure diagram –Reveals a population’s growth trends

30. Age 1980 Birth years Male Female 2005 2030 Birth years Male Female Birth years Male Female 80+ before 1900 before 1926 before 1951 1951-551926-301901-1905 75-79 70-74 1906-10 1931-35 1956-60 1961-651936-40 1911-15 65-69 60-64 55-59 1916-201941-451966-70 1971-751946-50 1921-25 50-541926-301951-55 1976-80 1981-851956-60 1931-35 45-49 40-44 1936-40 1961-651986-90 1991-95 1966-70 1941-45 35-39 30-34 1946-501971-75 1996-2000 2001-05 1976-801951-55 25-29 20-24 1956-60 1981-852006-10 2011-15 1986-901961-65 15-19 10-14 1966-701991-952016-20 2021-25 1996-2000 1971-75 5-9 0-4 1976-80 2001-2005 2026-30 1210864202 4 6 8 12 Population in millions Total population size = 363,811,435 Population in millions Total population size = 295,734,134 12 10 86 4 2 0 24 6 8 12 10864202 4 6 8 12 Population in millions Total population size = 227,726,463

33. Copyright © 2009 Pearson Education, Inc. You should now be able to 1.Explain the factors that determine the characteristics of a population 2.Describe exponential growth and the factors that produce logistic growth of a population 3.Explain the limiting factors that influence population growth 4.Distinguish between r- and K-strategies 5.Describe and give examples of the different types of life histories