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Chapter 36

Chapter 36. Population Dynamics. The Spread of Shakespeare's Starlings The European Starling has become an abundant and destructive pest in North America Introduced in 1890 because of mention in Shakespeare Like the human population, is expanding and uncontrolled

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Chapter 36

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  1. Chapter 36 Population Dynamics

  2. The Spread of Shakespeare's Starlings • The European Starling has become an abundant and destructive pest in North America • Introduced in 1890 because of mention in Shakespeare • Like the human population, is expanding and uncontrolled • Population ecology is concerned with changes in population size and the factors that regulate populations over time

  3. 36.1 Population ecology is the study of how and why populations change • A population is a group of individuals of a single species that occupy the same general area • Boundaries defined in relation to question being studied

  4. POPULATION STRUCTURE AND DYNAMICS • 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 • Environmental and social factors influence the spacing of individuals in various dispersion patterns • Clumped • Uniform • Random

  5. Video: Flapping Geese (clumped) Video: Albatross Courtship (uniform) Video: Prokaryotic Flagella (Salmonella typhimurium) (random)

  6. 36.3 Life tables track mortality and survivorship in populations • Life tables show how long an individual of a given age is expected to live • Survivorship curves plot the proportion of individuals alive at each age • Type I: Many individuals survive to maturity • Type II: Mortality constant over life span • Type III: High death rates for the very young, lower for those that survive longer

  7. LE 36-03 100 I 10 Percentage of survivors (log scale) II 1 III 0.1 0 50 100 Percentage of maximum life span

  8. 36.4 Idealized models help us understand population growth • Exponential growth model gives an idealized picture of unregulated population growth • Under ideal conditions, whole population multiplies by a constant factor

  9. G = rN describes the J-shaped curve of exponential growth • G = population growth rate • r = intrinsic rate of increase • Population members' maximum capacity to reproduce • N = population size

  10. LE 36-04a Time Number of Cells 70 0 minutes 1 = 20 60 20 2 = 21 50 4 40 = 22 Number of bacterial cells (N) 60 8 = 23 40 16 80 = 24 30 100 32 = 25 20 120 (= 2 hours) 64 = 26 G =rN 512 3 hours = 29 10 4,096 4 hours = 212 0 8 hours 16,777,216 = 224 140 20 40 100 120 0 60 80 12 hours 68,719,476,736 = 236 Time (min)

  11. Logistic growth model represents the slowing of population growth as a result of limiting factors • Limiting factors: environmental factors that restrict population growth • G = rN(K - N)/K describes the S-shaped curve of logistic growth • K = carrying capacity • (K - N)/K accounts for the leveling off of the curve

  12. LE 36-04b 10 8 Breeding male fur seals (thousands) 6 4 2 0 1945 1915 1925 1935 Year

  13. LE 36-04c G =rN (K - N) K G =rN K Number of individuals (N) 0 Time

  14. Predictions of logistic growth model for natural populations • Growth rate low when population is either small or large • Growth rate highest when population is at intermediate level • Does not fit any natural population perfectly • Useful starting point for studying population growth

  15. 36.5 Multiple factors may limit population growth • Population growth is density dependent • Birth rates decline and death rates rise in response to increasing population density • Organisms compete for limited resources • Density affects health of organisms • Abiotic factors may limit population growth before limiting factors become important

  16. LE 36-05a 4.0 3.8 3.6 Clutch size 3.4 3.2 3.0 2.8 10 20 30 40 50 60 70 80 0 Density of females

  17. LE 36-05b Exponential growth Sudden decline Number of aphids May Aug Oct Nov Dec Apr Jul Sep Jun

  18. Most populations are regulated by a mixture of factors and show fluctuation over time

  19. LE 36-05c 80 60 Number of females 40 20 0 1980 1985 1990 2000 1975 1995 Time (years)

  20. 36.6 Some populations have "boom-and-bust" cycles • Some populations fluctuate in density with regularity • May have complex causes • Example: snowshoe hare and lynx cycles

  21. LE 36-06 Snowshoe hare 160 120 9 Lynx population size (thousands) Lynx Hare population size (thousands) 80 6 40 3 0 0 1900 1925 1850 1875 Year

  22. LIFE HISTORIES AND THEIR EVOLUTION • 36.7 Evolution shapes life histories • An organism's life history is the series of events from birth through reproduction to death • Key life history traits • Age of first reproduction • Frequency of reproduction • Number of offspring • Amount of parental care

  23. Natural selection will favor the combination of life history traits that maximizes an individual's output of viable, fertile offspring • "Big-bang" vs. reproduction throughout life span • r-selection • Maximizes reproductive success in uncrowded, unpredictable environments • Individuals mature early, produce many offspring

  24. K-selection • Common when population density is close to carrying capacity • Later maturity and reproduction • Few, well-cared-for offspring • Concept of r- and K-selection has been criticized as oversimplified • Has stimulated research on factors influencing evolution of life histories (example: guppies)

  25. LE 36-07b Experimental transplant of guppies Predator: Killifish; preys mainly on small, immature guppies Guppies: Larger at sexual maturity than those in pike-cichlid pools Predator: Pike-cichlid; preys mainly on large, mature guppies Guppies: Smaller at sexual maturity than those in killifish pools

  26. CONNECTION • 36.8 Principles of population ecology have practical applications • Principles of population ecology are useful in sustainable resource management • Maximum sustained yield • Improvement of habitat or provision of additional habitat to increase K • Reduction of population size • Challenged by economic and political pressures

  27. THE HUMAN POPULATION CONNECTION • 36.9 Human population growth has started to slow after centuries of exponential increase • The human population now stands at over 6.4 billion • Even with slowing growth, predicted to reach 7.3 to 8 billion by 2025

  28. LE 36-09a 6 5 4 Human population size (billions) 3 2 The Plague 1 0 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. 2000 A.D. 0

  29. What is Earth's human carrying capacity? • Ecological footprint • Amount of land needed to support human demands on Earth's resources • Exceeds ecological capacity in many countries • World is already in ecological deficit • Problem is not just overpopulation, but overconsumption • Possible limiting factors: food, space

  30. LE 36-09b 16 14 12 New Zealand 10 USA Germany Ecological footprint (ha per person) Australia 8 Netherlands Japan Canada Norway 6 Sweden UK 4 Spain World 2 China India 0 14 16 0 2 4 6 10 12 8 Available ecological capacity (ha per person)

  31. LE 36-09c Traffic in downtown Cairo, Egypt Manhattan, New York City Refugee camp in Zaire

  32. 36.10 Birth and death rates and age structure affect population growth • Demographic transition • Shift from high birth rates and death rates to low birth rates and death rates • Has occurred in most developed countries • Population size continues to grow until birth rate equals death rate • Reduced family size key • Related to status of women

  33. LE 36-10a 50 40 30 Birth or death rate per 1,00 0 population 20 Birth rate Death rate 10 0 1900 1975 2000 2050 1950 2025 1925 Year

  34. Age structure of a population • Proportion of individuals in different age groups • Affects population's future growth • Indicates social conditions • Varies in developing and developed countries • Demographic differences • Infant mortality • Life expectancy at birth

  35. LE 36-10b Slow growth Rapid growth Decrease Afghanistan United States Italy Male Male Male Female Female Female Age 85+ 80 7579 707 6569 606 5559 505 4549 404 3539 Primary reproductive ages 303 2529 202 1519 101 59 0 4 4 4 4 4 8 6 2 0 2 4 6 8 6 2 0 2 6 6 2 0 2 6 Percent of population Percent of population Percent of population

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