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Measuring Populations

Measuring Populations. Introduction. If you had one male and one female elephant in the wild They would reproduce every so often and have a baby elephant That would increase the population Over a short time the elephants would have a much larger population. Introduction.

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Measuring Populations

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  1. Measuring Populations

  2. Introduction • If you had one male and one female elephant in the wild • They would reproduce every so often and have a baby elephant • That would increase the population • Over a short time the elephants would have a much larger population

  3. Introduction • The elephants could grow to 19 million elephants in just 750 years • So why isn’t the world overrun by elephants? • There are factors that keep populations around the same size

  4. Population Growth Rate • The growth rate is the amount that a population changes over a set time • The growth rate could be positive • This would mean more organisms • The growth rate could be negative • This would mean less organisms

  5. Population Growth Rate • To have a positive growth rate, there would have to be… • More individuals that are born than die • More individuals that immigrate than emigrate • To have a negative growth rate there would have to be… • More individuals that die than are born • More individuals that emigrate than immigrate

  6. Population Growth Rate • Many organisms cannot emigrate or immigrate • Plants, Fungi, animals that are separated by a boundary • If you are going to have to worry about organisms that emigrate or immigrate, you will be specifically told

  7. Population Size • We know that researchers often use samples when working with populations • These sample sizes are often 1000 • It allows us to compare one population to a different population

  8. Population Size • If talking about births in a year we would put it in terms of 1000 • A researcher could say there are 52 births of 1000 in a year • This would mean that for every 1000 organisms there are 52 born every year

  9. Population Size • The same could be said for death rate • Researchers could have a death rate of 43 of 1000 per year • This would mean for every 1000 organisms there would be 43 that die every year

  10. Population Size • To actually figure out how many organisms would be in the population during the next year we would follow a simple formula • (Birth Rate – Death rate) x Population = Estimated Population Change

  11. Example Workspace • Grab a partner and lets try an example • For the Amare Fish of Owdijtown there is a birth rate of 100 of 1000 • For the Amare Fish of Owdijtown there is a death rate of 50 of 1000 • The population of Amare Fish in Owdij Lake is currently 1000 • What is the estimated population change next year?

  12. The Exponential Model • As long as a birth rate is larger than the death rate, there should be an increase in growth • One type of increase in growth is exponential growth • This means that the population grows very rapidly

  13. The Exponential Model • In exponential growth the rapid growth has no restrictions from the environment • Bacteria often show this • Their need for resources is so small and their new environment is often so large that they have no limit to their resources http://www.youtube.com/watch?v=gEwzDydciWc

  14. The Exponential Model

  15. The Logistic Model • The logistic model shows a population that grows but then has a limiting factor • A limiting factor is something that halts a populations growth • Space, amount of food and amount of water are good examples of limiting factors

  16. The Logistic Model • In the logistic model there is rapid growth until the growth reaches a limiting factor • When the population hits the limiting factor, it stops growing • The population remains fairly consistent after reaching the limiting factor

  17. The Logistic Model

  18. Population Regulation • The factors that regulate population size can be affected by density • This breaks up the regulating factors for a population to… • Density dependent • Density independent

  19. Population Regulation • Density dependent factors depend upon how many organisms are packed into a local area • Factors such as resources, territory and availability of mates all depend on how many organisms are in an area

  20. Population Regulation • Density independent factors regulate the population without having to do with density • Things like weather, floods and fires • It does not matter how many organisms are in an area if there is a fire

  21. Population Fluctuations • Populations can depend upon the amount of food, water and habitat • What is another way that populations can be affected? • Predator and prey relationships are also very important

  22. Population Fluctuations • There is a very famous study of Snowshoe Hares and Lynx • These two have a very classic predator prey relationship • The Lynx hunts and kills the snowshoe hare

  23. Video • http://www.youtube.com/watch?v=xWm6037urxs

  24. Population Fluctuations • After seventy years of observations, a very interesting trend arouse • It was noticed that every year there was an increase in hares, there was an increase in Lynx shortly after • This is because there was more energy to have more babies

  25. Population Fluctuations • Every year there was a decrease in hares, there was a decrease in Lynx shortly after • This is because there was not enough energy to have a lot of babies

  26. Population Fluctuations • It also works in reverse, if the level of Lynx goes down, then the level of hare goes up shortly after • If the numbers of Lynx goes up, the level of hare goes down shortly after

  27. Predator Prey Dynamics • On an island off Lake Superior a study was done that illustrates predator and prey relationships • This island was relatively isolated and had no major land mammals • During a hard winter in the early part of the century a group of Moose crossed the ice and started a population

  28. Predator Prey Dynamics • Ecologists noted their arrival and started recording their populations • In 1949, a similar event happened with a small pack of wolves • Because of the isolation and the lack of other large mammals, this was an ideal system

  29. Predator Prey Dynamics • Ecologists noted that every year there was a rise in the moose population, there was a rise in the wolf population right after • Ecologists also noted that every year there was a dip in the moose population, there was a dip in the wolf population right after

  30. Predator Prey Dynamics • The moose population and the wolf population are regulated by environmental resistance • More wolves means it is harder for the moose to survive (Environmental Resistance) • Too many moose and there will not be enough food (Environmental Resistance) • Not enough moose and the wolves will die (Environmental Resistance)

  31. Predator Prey Dynamics • In the winter of 1996 there was a very severe snowfall and in the summer there was an infestation of ticks • This caused a sharp decrease in the moose population • It also caused kept the wolf population low for a long time

  32. Video http://www.techtube.mtu.edu/watch.php?v=254

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