Chapter 20


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Chapter 20

  1. 1. Chapter 20 Populations
  2. 2. 3 Properties of Populations <ul><li>Population Size </li></ul><ul><li>Population Density </li></ul><ul><li>Population Dispersion </li></ul>
  3. 3. Population Size <ul><li>Population-groups of organisms that belong to the same species and live in a particular area at one time </li></ul><ul><li>Population size-number of individuals a population has </li></ul><ul><li>Sometimes there are too many to count so a sampling is used. </li></ul><ul><li>Scientists count a number of organisms in a certain area and multiply the area. </li></ul>
  4. 4. Population Density <ul><li>Population density-measures how crowded a population is </li></ul><ul><li>The number is always expressed as the number of individuals per unit of area or volume </li></ul><ul><li>Some areas are densely populated and others are sparsely populated </li></ul>
  5. 5. Population Dispersion <ul><li>Dispersion is the spatial distribution of individuals within a population. </li></ul><ul><li>There are three types of dispersion. </li></ul><ul><li>Clumped dispersion occurs because resources and living space is clumped or because of behavior, herding </li></ul><ul><li>Even dispersion is the result of social behavior and organisms stay as far away from each other as possible </li></ul><ul><li>Random dispersion results from wind distribution of seeds so plants usually have a random dispersal </li></ul>
  6. 6. Types of Dispersion
  7. 7. Population Dynamics <ul><li>All populations are dynamic, meaning they change in size and composition over time. </li></ul><ul><li>Birth rate-number of births over time </li></ul><ul><li>Death rate (mortality rate)-number of deaths over time </li></ul><ul><li>Life expectancy- how long on average an individual is expected to live </li></ul>
  8. 8. Stop assignments: Lesson of the Kaibab homework: Population Growth Graph
  9. 9. Age Structure <ul><li>Age structure-distribution of individuals among different ages in a population </li></ul><ul><li>Different countries have different age structures. </li></ul><ul><li>We can use graphs to compare age structure. </li></ul>
  10. 15. Survivorship Curves <ul><li>The mortality rate data of different species tend to conform to one of three curves on a graph. </li></ul><ul><li>Type I organisms are more likely to die later in life. (humans and elephants) k-selected </li></ul><ul><li>Type II organisms have a linear look because the probability of dying does not change. (birds) </li></ul><ul><li>Type III organisms are more likely to die earlier in life. (oysters, salmon, insects) r-selected </li></ul>
  11. 16. Survivorship Curves
  12. 17. More Curves
  13. 18. Population Growth Rate <ul><li>Growth rate- the amount by which a population’s size changes over time </li></ul><ul><li>Immigration-individuals moving into a population </li></ul><ul><li>Emigration-individuals moving out of a population </li></ul>
  14. 19. <ul><li>STOP </li></ul><ul><li>Assignments: Human Population Growth graph </li></ul><ul><li>Homework: w.s 20-1 </li></ul>
  15. 20. Exponential Growth Model <ul><li>Exponential Model- population increases rapidly after only a few generations; the larger the population gets, the faster it grows </li></ul><ul><li>Limiting factor-a factor that restrains or stops the growth of a population </li></ul><ul><li>Limiting factors are available resources, space, waste accumulation, population density </li></ul>
  16. 22. Logistic Growth Model <ul><li>Logistic model-builds on the exponential model but adds the limiting factors. </li></ul><ul><li>Carrying capacity (K)- the number of individuals the environment can support over a long period of time </li></ul><ul><li>Once carrying capacity is reached, the population remains constant </li></ul>
  17. 24. Population Regulation <ul><li>Density-independent factors-weather, flood, fires; these reduce the population regardless of size </li></ul><ul><li>Density-dependent factors- food, nesting sites, illness; these occur as a result of population size </li></ul>
  18. 25. Perils of small populations- Inbreeding <ul><li>The rapidly growing human population has caused extreme reductions in the populations of some other species and subspecies. </li></ul><ul><li>Fewer than 200 Siberian tigers remain in the wild due to over hunting and habitat destruction </li></ul><ul><li>The California condor is down to 9 individuals. </li></ul><ul><li>Fewer individuals means inbreeding or mating with relatives. </li></ul><ul><li>This mean the babies will be more likely to have defects or diseases. </li></ul>