12; populations


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12; populations

  1. 1. Lecture 12: Populations Populations
  2. 2. Human Population <ul><li>Humans live on every continent, but are not evenly spread </li></ul><ul><ul><li>Concentrated on coasts </li></ul></ul><ul><ul><li>Asia, esp. China and India, has 56% of world’s population </li></ul></ul>
  3. 3. Human Populations <ul><li>Growth rate is the difference between the number of individuals born and the number of individuals who die each year </li></ul><ul><li>Human growth rate is approximately 1.3% annually </li></ul><ul><li>At this rate, the doubling time of the human population is 35 years </li></ul>
  4. 4. Human Population <ul><li>A doubling of the population means a doubling of the resources needed to sustain those individuals </li></ul><ul><li>However, people in different parts of the world do not use resources in the same way </li></ul>
  5. 5. Carrying capacity <ul><li>Population growth becomes zero when there are not enough resources for the population to continue to grow </li></ul><ul><li>Carrying capacity is the number of individuals an environment can sustain </li></ul><ul><li>What is Earth’s carrying capacity for humans? We don’t really know. </li></ul>
  6. 6. Different Regions <ul><li>More developed countries have a high standard of living, and a lower growth rate in general </li></ul><ul><ul><li>US has one of the highest growth rates for a more developed country: 0.6% vs. 0.2% for much of Europe </li></ul></ul>
  7. 7. Different Regions <ul><li>Less developed countries have a lower standard of living and a higher growth rate </li></ul><ul><ul><li>Asia has the highest growth rate, due to high childbirth and relatively low adult mortality </li></ul></ul><ul><ul><li>Africa has a lower growth rate, even though birth rates are very high, adult mortality is also high due to HIV/AIDS </li></ul></ul>
  8. 8. Replacement Reproduction <ul><li>This is each couple having two children- replaces themselves </li></ul><ul><ul><li>Will eventually result in zero growth rate, but perhaps not initially if many children are entering the population </li></ul></ul>
  9. 9. Environmental Impact <ul><li>Impact of a population measured by </li></ul><ul><ul><li>1. per capita resource consumption </li></ul></ul><ul><ul><li>2. pollution per unit of resource used </li></ul></ul><ul><li>Overpopulation can be seen in less developed countries, but more developed countries use many many more resources </li></ul><ul><ul><li>Ex. more developed countries use 60% of fossil fuels, 80% of metals </li></ul></ul>
  10. 10. Populations <ul><li>When the environment is stable, populations become adapted to it and tend to increase to carrying capacity </li></ul><ul><li>When the environmental conditions change, the population must adapt again- the populations tends to decrease in size until adapted again </li></ul>
  11. 11. Resources <ul><li>Resources - components of the environment needed to support organisms </li></ul><ul><ul><li>light, space, water, food, mates, shelter </li></ul></ul><ul><ul><li>Availability of resources influences distribution of organisms </li></ul></ul>
  12. 12. Distribution <ul><li>Can be clumped, random, or uniform </li></ul><ul><li>A species occurs in a range - an area that has appropriate resources for it </li></ul><ul><li>Population density - how many individuals occur per unit area </li></ul><ul><ul><li>In general, declines with increasing body size </li></ul></ul>
  13. 13. Demographics <ul><li>Availability of resources + population characteristics = demographics </li></ul><ul><ul><li>Age structure- how many of each age class </li></ul></ul><ul><ul><ul><li>Ex. box turtle populations </li></ul></ul></ul><ul><ul><li>Survivorship- how the age of death influences population size </li></ul></ul><ul><ul><ul><li>Type I- death likely at old age </li></ul></ul></ul><ul><ul><ul><li>Type II- death risk same for all ages </li></ul></ul></ul><ul><ul><ul><li>Type III- death risk high when young </li></ul></ul></ul>
  14. 14. Demographics <ul><li>Biotic Potential - highest possible rate of population growth given unlimited resources </li></ul><ul><ul><li>Number of offspring, survival until reproductive age, etc. </li></ul></ul>
  15. 15. Patterns of Population Growth <ul><li>Exponential growth- can typically last only as long as resources are unlimited </li></ul>
  16. 16. Patterns of Population Growth <ul><li>Logistic Growth - Population growth levels off when resources are limited </li></ul>
  17. 17. Patterns of Population Growth <ul><li>Logistic growth has 4 phases: </li></ul><ul><ul><li>Lag phase- growth is slow b/c number of individuals is small </li></ul></ul><ul><ul><li>Exponential phase- growth is accelerating due to biotic potential </li></ul></ul><ul><ul><li>Deceleration phase- rate slows due to increased competition among individuals </li></ul></ul><ul><ul><li>Stable equilibrium phase- births and deaths are about equal </li></ul></ul>
  18. 18. Patterns of Population Growth <ul><li>Stable eq. phase occurs at the carrying capacity for that system </li></ul><ul><li>Uses- for resources used by humans, we want to keep things either stable or in exponential phase, because if get too few, will be in lag phase </li></ul><ul><ul><li>Ex. fisheries </li></ul></ul><ul><li>For pests, best to reduce carrying capacity, not individuals </li></ul>
  19. 19. Human Growth Curve
  20. 20. Factors that Regulate Growth <ul><li>Density- Independent Factors - many abiotic factors </li></ul><ul><ul><li>Weather, natural disasters </li></ul></ul><ul><ul><li>Intensity of effect not dependent on population size </li></ul></ul>
  21. 21. Factors that Regulate Growth <ul><li>Density-Dependent Factors - Usually biotic </li></ul><ul><ul><li>Percentage of population affected depends on population size </li></ul></ul><ul><ul><li>Typically interactions between individuals </li></ul></ul>
  22. 22. Density-Dependent <ul><li>Competition - individuals try to use a resource that is in limited supply </li></ul><ul><ul><li>Not all individuals will get enough of that resource to survive </li></ul></ul><ul><ul><li>If more or less of the resource becomes available, the population size may shift </li></ul></ul><ul><ul><li>Resource partitioning can occur among different age classes </li></ul></ul>
  23. 23. Density- Dependent <ul><li>Predation - One organism eats another </li></ul><ul><ul><li>Effect increases as prey increase in density, because they become easier to find (competition for hiding spots) </li></ul></ul><ul><ul><li>Cycles often exist between predator and prey densities </li></ul></ul>
  24. 24. Snowshoe Hares & Canada Lynx
  25. 25. Life History <ul><li>Life history - the mix of characteristics and traits that one species exhibits </li></ul><ul><li>Two general patterns: </li></ul><ul><ul><li>Opportunistic species </li></ul></ul><ul><ul><li>Equilibrium species </li></ul></ul>
  26. 26. Life History <ul><li>Opportunistic species: </li></ul><ul><ul><li>exponential growth </li></ul></ul><ul><ul><li>small </li></ul></ul><ul><ul><li>mature early </li></ul></ul><ul><ul><li>short life </li></ul></ul><ul><ul><li>many offspring </li></ul></ul><ul><ul><li>ex. insects, weeds </li></ul></ul>
  27. 27. Life History <ul><li>Equilibrium species: </li></ul><ul><ul><li>logistic growth </li></ul></ul><ul><ul><li>best adapted individuals leave most offspring </li></ul></ul><ul><ul><li>large </li></ul></ul><ul><ul><li>long life </li></ul></ul><ul><ul><li>few offspring </li></ul></ul><ul><ul><li>slow to mature </li></ul></ul><ul><ul><li>Ex. birds, large mammals </li></ul></ul>
  28. 28. Extinction <ul><li>When every individual of a species disappears </li></ul><ul><li>Opportunistic species at less risk for extinction </li></ul><ul><li>Three factors influence risk for equilibrium species </li></ul><ul><ul><li>Size of geographic range </li></ul></ul><ul><ul><li>Habitat tolerance </li></ul></ul><ul><ul><li>Size of local populations </li></ul></ul>
  29. 29. Extinction <ul><li>Most resistant to extinction will have wide range, large population size, and wide habitat tolerance, least resistant will be the opposite </li></ul><ul><li>What would the most vulnerable population look like? </li></ul>
  30. 30. Ecology <ul><li>The study of the interactions between all the living and non-living parts of an environment </li></ul>