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Understanding Population Counts in Ecosystems: Methods and Approaches

This resource explores the methods of counting populations within ecosystems, focusing on organisms and their environments. It defines key concepts such as organisms, ecosystems, populations, and communities, illustrating how to identify the three biggest populations in a specific area, such as a pond. The document covers census techniques, including actual and sample censuses, and their accuracy. Methods like random sampling and mark-and-recapture are discussed, alongside the importance of understanding population density. Engage with thought-provoking questions to deepen comprehension.

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Understanding Population Counts in Ecosystems: Methods and Approaches

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Presentation Transcript

  1. 0 COUNTING POPULATIONS How many are there?

  2. Organism-Any living thing

  3. Ecosystem • Collection of all the organisms in an area AND the non-living parts of the environment

  4. 0 Population • The total number of one species living in a defined region

  5. 0 Community • Several populations in the same area that interact with each other

  6. 0 What are the 3 biggest populations in this pond community?

  7. 0

  8. How big is each population? • How can we figure out how many individuals are in each population? • A census is a count of a population

  9. Census • True census – actual count • Sample census – estimate of population • A sample census is made by marking off small areas or plots and counting in the areas

  10. 0 What are the 3 biggest populations in this pond community?

  11. 0 ACTUAL COUNT • Each member of a population is counted one by one

  12. 0 Which population was easiest to count?Which was most difficult? Why?

  13. 0 SAMPLE CENSUS • Mark off a small area or plot. • Count the population in one plot. • Multiply by the total number of plots to get an estimate for the whole area.

  14. 0 RANDOM SAMPLES

  15. 0 ACCURACY??? • Why was the last census not very accurate? • What could we do to make it more accurate? • Where have you already done a sample census?

  16. Transect-Draw a line through an ecosystem and count along it.

  17. Transect

  18. Population densityNumber of individuals that live in a unit area

  19. Population density Examples: • There are 270 people per square mile in Pennsylvania • There are 25 deer per square mile in PA

  20. 0 DISCUSSION QUESTIONS • Why is a sample a good way to count a population? • What are some disadvantages to using a sample? • What could you do to sample a population of animals that do not stay in one place?

  21. 0 MARK AND RECAPTURE • A way to count organisms that move or are hard to see. • Catch, mark, let go, catch again. • Use a formula to estimate the number.

  22. Review question • Is Mark and Recapture a true census or a sample census? • For the following animals, what method would be most appropriate for getting a census?

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