Unit2 Ecology Ib Populations Ppt2003


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Unit2 Ecology Ib Populations Ppt2003

  1. 1. Ecology I Population Ecology
  2. 2. <ul><li>Why is it important? </li></ul><ul><ul><ul><ul><ul><li>assessing health of population </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>determining endangered or threatened status </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>predicting population dynamics </li></ul></ul></ul></ul></ul>
  3. 3. Population size <ul><li>… is the number of individuals present at a given time. </li></ul>The passenger pigeon was once North America’s most numerous bird, but it is now extinct.
  4. 4. Population density <ul><li>… is the number of individuals per unit area. </li></ul>In the 19th century, the flocks of passenger pigeons showed high population density.
  5. 5. Population distribution <ul><li>… is the spatial arrangement of individuals. </li></ul><ul><li>Random </li></ul><ul><li>Uniform </li></ul><ul><li>Clumped </li></ul>
  6. 6. Population growth <ul><li>Populations grow, shrink, or remain stable, depending on rates of birth, death, immigration, and emigration. </li></ul><ul><li>(crude birth rate + immigration rate) – </li></ul><ul><li>(crude death rate + emigration rate) </li></ul><ul><li> = growth rate </li></ul>
  7. 7. Two Modes of Population Growth <ul><li>Exponential growth </li></ul><ul><li>Logistic growth </li></ul><ul><li>Represent two different growth patterns or Strategies of populations </li></ul>
  8. 8. Exponential Growth <ul><ul><li>Also known as a J-curve </li></ul></ul><ul><ul><li>Growth is a fixed percentage of the whole (e.g., 10% per day or year) </li></ul></ul><ul><ul><li>Population is growing at its full biotic potential </li></ul></ul>
  9. 9. Exponential growth in a growth curve <ul><li>Population growth curves show change in population size over time. </li></ul><ul><li>Scots pine shows exponential growth </li></ul>
  10. 10. Biotic Potential <ul><li>Maximum possible growth rate of a population. </li></ul><ul><ul><li>Absence of limitations to growth </li></ul></ul><ul><li>Example : </li></ul><ul><ul><li>2 cats plus all their kittens make how many cats in 10 years? </li></ul></ul><ul><ul><ul><li>2 litters/year </li></ul></ul></ul><ul><ul><ul><li>2.8 surviving kittens per litter </li></ul></ul></ul><ul><ul><ul><li>Breeds for 10 years (“breeding life”) </li></ul></ul></ul>(Drum roll…)
  11. 11. ANSWER: <ul><li>80,399,780 cats!!! </li></ul>Do you need a cat?
  12. 12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Biotic Potential J curve Time Population Carrying Capacity <ul><li>Carrying Capacity: </li></ul><ul><li>MAXIMUM number of individuals that can be supported </li></ul><ul><ul><li>in a given AREA. </li></ul></ul><ul><ul><li>FOREVER. </li></ul></ul>Can Populations Grow Forever?
  13. 13. <ul><li>Oscillations : </li></ul><ul><ul><li>Populations overshoot the carrying capacity and experience a dieback </li></ul></ul><ul><ul><li>Can be regular or irregular </li></ul></ul><ul><ul><li>Overshoot When a population surpasses the carrying capacity of its environment or population explosion </li></ul></ul><ul><ul><li>Dieback Population crash </li></ul></ul>
  14. 14. Malthusian Growth <ul><ul><li>Thomas Malthus: </li></ul></ul><ul><ul><li>18 th century economist </li></ul></ul><ul><ul><li>Believed human populations tend to grow until they exhaust their resources and become subject to famine, disease or war </li></ul></ul>
  15. 15. Population growth: Oscillations <ul><li>Some populations fluctuate continually above and below carrying capacity, as with this mite. </li></ul>
  16. 16. Population growth: Dampening oscillations <ul><li>In some populations, oscillations dampen, as population size settles toward carrying capacity, as with this beetle. </li></ul>
  17. 17. r-Selected Species <ul><li>r = Growth rate </li></ul><ul><ul><li>Reproduce young </li></ul></ul><ul><ul><li>High reproductive rates </li></ul></ul><ul><ul><li>Many small offspring </li></ul></ul><ul><ul><li>Short-lived </li></ul></ul><ul><ul><li>Found in unstable or unpredictable environments </li></ul></ul>
  18. 18. Examples of r-Selected Species <ul><li>Weeds, bacteria, insects, algae, small mammals </li></ul>
  19. 19. Logistic Growth <ul><ul><li>Also known as S-curve </li></ul></ul><ul><ul><li>Growth slows as the population approaches Carrying Capacity </li></ul></ul><ul><ul><li>Populations stabilize at carrying capacity </li></ul></ul>
  20. 20. K-Selected Species <ul><li>K = Carrying Capacity </li></ul><ul><ul><li>Reproduce later in life </li></ul></ul><ul><ul><li>Low reproductive rates </li></ul></ul><ul><ul><li>Fewer large offspring </li></ul></ul><ul><ul><li>Long-lived </li></ul></ul><ul><ul><li>Stable or predictable environments </li></ul></ul>
  21. 21. Examples of K-Selected Species <ul><li>Elephants, great apes, hippopotamus, whales, humans (?) </li></ul>
  22. 22. What Determines Population Size or Carrying Capacity? <ul><li>Environmental Resistance </li></ul><ul><ul><li>All the limiting factors that tend to reduce population growth rates </li></ul></ul><ul><li>Balance between biotic potential & environmental resistance determines growth rate </li></ul>
  23. 23. Environmental resistance Carrying capacity Stabilized population size Exponential growth Limiting factors: Water Space Food Predators Disease LE 4-11
  24. 24. Predator – prey cycles <ul><li>Population dynamics of predator – prey systems sometimes show paired cycles: ups and downs in one drive ups and downs in the other. </li></ul>
  25. 25. Density dependence <ul><li>Often, survival or reproduction lessens as populations become more dense. </li></ul><ul><li>Density-dependent factors that account for the logistic growth curve </li></ul><ul><ul><ul><ul><li>Intraspecific competition </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Interspecific competition </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Predation </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Disease </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Fire (for a population of fire prone plant) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Parasitism </li></ul></ul></ul></ul><ul><li>Other factors occur regardless of density and are density-independent factors. </li></ul><ul><ul><ul><ul><li>Floods </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Drought </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Extreme temperatures </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Pollution </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Fire </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Salinity </li></ul></ul></ul></ul>
  26. 26. Exponential Growth Example Caribou Population <ul><ul><ul><ul><ul><li>What does this show? </li></ul></ul></ul></ul></ul><ul><li>Population overshot the carrying capacity, causing a “die-off”, or sudden reduction in population. </li></ul>What we observed (actual data):
  27. 27. Exponential Growth Example <ul><li>Let’s turn back the clock to the 1930’s… </li></ul><ul><ul><li>How might wildlife managers make the curve level-off to a stable population? </li></ul></ul><ul><li>Hunt them? </li></ul><ul><li>Add predators? </li></ul><ul><li>Sterilize them? </li></ul><ul><li>Move them? </li></ul><ul><li>Let them starve? </li></ul><ul><li>Import food? </li></ul>
  28. 28. QUESTION: Review <ul><li>Which is a K-selected species? </li></ul><ul><ul><li>a. A dragonfly that lays 300 eggs and flies away </li></ul></ul><ul><ul><li>b. An oak tree that drops its acorns each year </li></ul></ul><ul><ul><li>c. A bamboo plant that flowers only once every 20 years </li></ul></ul><ul><ul><li>d. A human who raises three children </li></ul></ul><ul><ul><li>e. A fish on the second trophic level </li></ul></ul>
  29. 29. QUESTION: Review <ul><li>How can you tell that this population growth curve shows exponential growth? </li></ul><ul><ul><li>a. Population is increasing. </li></ul></ul><ul><ul><li>b. Data points match curve closely. </li></ul></ul><ul><ul><li>c. Population is rising by the same number during each interval. </li></ul></ul><ul><ul><li>d. Population is rising by the same percentage during each interval. </li></ul></ul>
  30. 30. QUESTION: Review <ul><li>This shows growth ending at a(n) . </li></ul><ul><ul><li>a. exponential… carrying capacity </li></ul></ul><ul><ul><li>b. intrinsic… equilibrium </li></ul></ul><ul><ul><li>c. logistic… carrying capacity </li></ul></ul><ul><ul><li>d. runaway… equilibrium </li></ul></ul><ul><ul><li>e. logistic… extinction </li></ul></ul>