Q274 · Practice questionTechnology-activeComplex familiar7 marks
QUESTION 274 (7 marks)
A breeding program models females in three one-year age classes. The table gives births per female during a step, the proportion surviving into the next age class, and initial counts. Offspring enter the youngest class; no females survive beyond the oldest class. Fractional expected counts are permitted.
a)[2 marks]
Write the Leslie matrix and the initial population column vector in youngest-to-oldest order.
b)[3 marks]
Determine the earliest integer year step at which the total female count falls below 150. Show the neighbouring totals.
c)[2 marks]
Give one limitation of the prediction and explain its possible effect.
WORKED SOLUTION
7 marksPractice marking scheme
ANSWER
(a) , . (b) Year step 4; totals are 167.6 at step 3 and 139.04 at step 4. (c) Constant age-specific birth and survival rates may not remain valid.
Worked solution
(a) Birth rates form the top row; survival rates lie on the subdiagonal. The table is a set of rates, not the top-row population values.
(b) , total 218. Then , total 173.6. Next , total 167.6. Finally , total 139.04. The first step below 150 is 4; the preceding total is 167.6.
(c) The model holds rates fixed despite changing habitat, resources or management. If survival falls, the decline could be faster than predicted; if conditions improve, the threshold could be reached later. An explained alternative limitation is acceptable.
Equivalent justified methods accepted; respect any requested proof method.
Exact values unless specified. Sketches assessed by mathematical features, not artistic quality.
Part a: Place birth and survival rates correctly in L.
Part a: Write the correct initial column vector.
Part b: Iterate the model using the correct initial vector.
Part b: Identify step 4 with total 139.04.
Part b: Show earlier totals and the step-3 total to establish earliest crossing.
Part c: Identify a relevant assumption or limitation.
Part c: Connect it to the reliability or direction of the prediction.
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