Biology 570

Discussion

Davidson and Andrewartha 1948

UPLOAD YOUR ANSWERS TO BLACKBOARD AND BRING A TYPED COPY TO CLASS

1. What historical pattern of population change in thrips did Andrewartha use to argue for the importance of weather (see introduction)?

2. What was actually measured and for how long? Was the sampling adequately replicated?

3. In Section 4 (Daily fluctuations) - look at Fig 3 for an example of the change in population with time.

   1. These measurements were taken for the 60 days preceding a population peak - why is this?

   2. What were the independent variables chosen for study? See section 4b.

   3. Why are all of these variables measured several days earlier than the population sizes?

   4. The authors claim that x1, x3 and x5 are all independent of one another, and that x2, x4 and x6 are independent of one another. Do you agree or disagree and why?

   5. Looking Tables 7 - 10, which variables showed the strongest correlations with thrips population size?

4. What factors had the strongest correlations with year-to-year changes in thrips density (Tables 13-20)?

5. What are the authors trying to say with Fig 5? The caption says that it relates to density independent factors, but the solid curve is a logistic (density dependent curve).

6. What are Andrewartha's opinions regarding the balance of populations (Discussion part d)? Does he believe that predation or competition have any influence on population dynamics?