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    • #8170

      Hellow!I’m Willie.
      I have two GRE Biology questions, and I hope someone could explain why those answers are.
      Queation refers to the following data computed from a field study

      Year No. of Acres No. of Pheasants No. of Foxes
      1980 (12) (200) (6)
      1981 (18 ) (180) (14)
      1982 (10) (80) (18 )
      1983 (16) (100) (12)
      1984 (20) (140) (8 )
      The greatest change in population density from either species occurs by the year?
      (A) 1980
      (B) 1981
      (C) 1982
      (D) 1983
      (E) 1984

      The answer is B but I couldn’t understand how to calculate No. of Foxes.
      According to my results, the greatest change in Pheasants is in 1981, but in Foxes is in 1982. So, I am so confused why the answer is B.

      Which of the following has the greatest potential to produce a new species of plants?
      (A) Increased ploidy
      (B) Inbreeding
      (C) Increased fitness
      (D) Polymorphism
      (E) Mutations

      The answer is A and my choice is E. Why?
      I hope somebody could help me answer those questions, and I will thanks very much for that.

    • #75795

      1: Divide n by acres for each species per year. Write it out in a table: (year) (pheasant density n/acres) (fox density n/acres).

      The question is worded very oddly, "from either species" is a confusing choice of words. Does it mean that you are to look for the greatest density change, whether it be pheasant or fox? Or that you’re to try to find the year with the greatest combined density change of both fox and pheasant.
      I would assume it’s the first.
      Secondly, is it looking for total change? (ie change from 1980 to the given year?) or for annual change? (ie change from the previous year to the given year).
      Again I would go with the first.

      So, by year, your pheasant density would be (in units of n/acre):
      1980: 200/12 = 16.67
      1981: 180/18 = 10.0
      1982: 80/10 = 8
      1983: 100/16 = 6.25
      1984: 140/20 = 7

      Fox would be:
      1980: 6/12 = .5
      1981: 14/18 = .78
      1982: 18/10 = 1.8
      1983: 12/16 = .75
      1984: 8/20 = .4

      So take those density rates and determine how they compare to the original density. It might also be worthwhile to try to compare them to the previous year. Perhaps make a table in this format:
      (year) (pheasant density) (fox density) (pheasant density difference from 1980) (fox density difference from 1980) (pheasant density difference from [year – 1]) (fox density difference from [year – 1]).
      It might help to do this in excel.

      Honestly, I’m not sure how they came up with their answer, because the question is rather confusing…

      Question 2:
      changes in ploidy can occur in one generation, and prevent individuals from reproducing with their former species, thus creating a new reproductively isolated species. Search for examples on the internet, specifically Tragopogon.

      The other mechanisms take multiple generations or additional factors.

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