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Chapter 5

Chapter 5. Population Ecology. Counting individuals. What constitutes an individual organism?. Variations on the individual. Unitary organisms - one zygote per embryo produces one organism. Variations on the individual.

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Chapter 5

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  1. Chapter 5 Population Ecology

  2. Counting individuals • What constitutes an individual organism?

  3. Variations on the individual • Unitary organisms - one zygote per embryo produces one organism

  4. Variations on the individual • Modular organisms - one zygote per embryo produces one module, which eventually produces more modules like itself • Branching or shoot development in plants, budding in Hydra, sponges, fungi

  5. How to count individuals in a population • Some organisms - possible to easily count all individuals • Others must be subsampled and estimated • Plants and some animals - quadrat • Soil, water dwellers - volume • Animals - mark and recapture

  6. Mark and recapture • Random sample • Release • Try to recapture • Theory - marked individuals will remix within population; proportion marked in next sample represents proportion in entire population

  7. Mark and recapture example Population size (N) #marked on Day 1 Total catch on Day 2 # of recaptures = (# marked on Day 1) x (Total catch on Day 2) # of recaptures N =

  8. Gilmore Creek Brown Trout 200 m stream reach = 840 m2 area 4.2 m average stream width Day 1: 169 trout captured, marked, released Day 2: 178 trout captured 80 marked (recaptures), 98 unmarked N = (# marked ) x (total catch Day 2) # of recaptures N = 169 x 178 = 377 trout 377 trout/840 m2 = 80 0.45 trout m2

  9. Life cycles • Patterns of birth, death, growth are dictated by an organism’s life cycle • 5 main types of life cycles

  10. Life cycle types • Annual • Overlapping iteroparity • Overlapping semelparity • Continuous semelparity • Continuous iteroparity

  11. Semelparous • Individual organism has single reproductive event during its life, then dies • Invests large amount of energy in reproduction

  12. Iteroparous • Individual may have many reproductive events during season or life • Invests lesser proportion of resources in reproduction

  13. Annuals • 12 months or less to complete life cycle • Discreet, non-overlapping generations • May or may not overwinter as non-seed/egg • May be either semelparous or iteroparous • Annual may be a misnomer for some plants with seeds that do not always germinate the year after being produced • Seeds may lie dormant in seed bank for several years before germinating

  14. Overlapping iteroparity • Overlapping generations (yearlings, 2-year-olds, etc.), iteroparous • Distinct breeding season • Examples: temperate-zone trees, long-lived, seasonally breeding vertebrates (deer, most fish, snakes, birds)

  15. Overlapping semelparity • Overlapping generations (several age classes present [at least biennial]), semelparous • New offspring in population every year (distinct breeding season) • Require 2 or more years to mature and reproduce, then die • Most common in plants, also in some species of octopus, salmon

  16. Continuous semelparity • No distinct breeding season because of favorable environmental conditions • Many overlapping ages continually growing, reproducing, dying • Example: some animals in tropical oceans

  17. Continuous iteroparity • No distinct breeding season • Many overlapping ages • Example: humans

  18. Life tables • Used to follow changes in births, deaths, growth of population through time • Of differing complexity and usefulness depending on life cycle of organism being examined • Easiest for annuals, more difficult for other types

  19. Life table variables x life stage or age class ax total number of individuals observed at each stage or class lx proportion of original number of individuals surviving to the next stage or class; survivorship dx proportion of original number of individuals dying during each stage or class; mortality qx mortality rate for each stage or class kx "killing power;"  Fx total fecundity, or reproductive output of entire population, for each stage or class mx individual fecundity, or mean reproductive output, for each stage or class lxmx number of offspring produced per original individual during each stage or class; product of survival and reproduction R0 basic reproductive rate

  20. Cohort life table Group of individuals “born” within same short time interval is followed from birth through death of last survivor

  21. Grasshoppers - a cohort life table

  22. Phlox - a cohort life table

  23. Static life tables • Life tables more difficult to construct for longer-lived organisms, and those with many overlapping generations • Difficult to follow single cohort throughout entire life (many years) • Static life table is produced - snapshot in time

  24. Static life tables • Need information on total population size and its age structure at some point in time • Can get messy if older age classes have more individuals than younger age classes • Different mortality, recruitment • May need to smooth data to get things to work

  25. Red deer - a static life table

  26. Survivorship Curves • Depict what proportion of population remains alive at various points in life • 3 basic patterns displayed by living things

  27. Survivorship Curves • Type I - little mortality throughout early life • Mortality concentrated in older age groups • Example: humans

  28. Survivorship Curves • Type II - constant rate of mortality throughout life • Constant proportion die age time/age interval • Example: corals, squirrels

  29. Survivorship Curves • Type III - high early mortality • Survivors have little mortality until old age • Example: plants, fishes

  30. Population Dynamics and Growth

  31. Exponential Growth • ideal habitat • -maximum reproduction • -unlimited resources Population size (N) Increase often followed by crash Time (t)

  32. Reindeer on an Alaskan island 2,000 1,500 Number of reindeer 1,000 500 1910 1920 1930 1940 1950 Year

  33. Moose and wolves on Isle Royale 5,000 Moose population Wolf population 4,000 3,000 Number of moose 100 90 80 2,000 70 60 Number of wolves 50 40 1,000 30 20 500 10 0 1900 1910 1930 1950 1970 1990 2000 Year 1999

  34. Logistic Growth Carrying capacity -accelerating, decelerating K -growth slows as population size approaches carrying capacity Population size (N) -number that environment can support indefinitely Time (t) Carrying capacity set by limiting factor

  35. Sheep in Tasmania 2.0 1.5 Number of sheep (millions) 1.0 .5 1800 1825 1850 1875 1900 1925 Year

  36. Human population growth-exponential or logistic?

  37. Human population growth-exponential or logistic? -appears exponential -history may suggest logistic -periods of rapid growth followed by stability

  38. Human population growth-exponential or logistic? Cultural evolution -tool-making revolution -agricultural revolution -industrial (technological) revolution

  39. Carrying capacity for humans Set by: -famine -disease -warfare Will these become more common as population approaches carrying capacity?

  40. Population Demographics • What affects human population size and growth rate? Birth rate and death rate Migration rate Fertility rate Age structure Average marriage age

  41. Population Change = (Births + Immigration) – (Deaths + Emigration) Factors Affecting Human Population Size • Population change equation • Zero population growth (ZPG) • Birth rate (number/1000 people/year) • Death rate (number/1000 people/year)

  42. Birth and death rates • U.S. - 16 and 9 (7 or 0.7%) • Rwanda - 52 and 18 (34 or 3.4%) • World - 26 and 9 (17 or 1.7%) 32 30 28 26 Births per thousand population 24 22 20 18 End of World War II 16 Demographic transition Depression Baby boom Baby bust Echo baby boom 14 0 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Year

  43. Infant deaths per 1,000 live births <10 <10-35 <36-70 <71-100 <100+ Data not available Factors Affecting Death Rate • Life expectancy • Infant mortality rate (IMR)

  44. Rate of Natural Increase Rate of natural increase = crude birth rate–crude death rate Developing Countries Developed Countries 50 50 Crude birth rate 40 40 Rate of natural increase Rate of natural increase Rate per 1,000 people © 2004 Brooks/Cole – Thomson Learning 30 30 Crude birth rate Crude death rate 20 20 Crude death rate 10 10 0 0 1800 2000 1775 1850 1900 1950 2050 1800 2000 1775 1850 1900 1950 2050 Year

  45. Annual world population growth <1% 1-1.9% 2-2.9% 3+% Data not available Natural Rate of Increase 1% - triple in 100 years 2% - 7X in 100 years

  46. Migration Rates • Affect regional populations • e.g., United States • Net gain of 4/1000 people/year • Add to 7 from BR - DR = 11 (1.1%)

  47. Fertility Rates • Average number of children born to a woman during her childbearing years (ages 15-44) • Replacement level fertility rates for ZPG • Total fertility rates

  48. Fertility Rates • Replacement level fertility rates for ZPG - developed countries - 2.1/woman - developing countries - 2.5 - total world - 2.3-2.4

  49. Fertility Rates • Total fertility rates - developed countries - 1.9 (U.S. 1.8) - developing countries - 3.8 (Rwanda-8.5, Kenya-8.0) - total world - 3.4

  50. Births per woman < 2 4-4.9 2-2.9 5+ No Data 3-3.9 Fertility Rates

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