Exercise 10

Consider a small rodent that lives for three years. Once again, we can separate a population of females into juveniles, yearlings, and adults. Suppose that, each year,

• Half of the juveniles live to be yearlings.

• One quarter of the yearlings live to be adults.

• Adult females produce eight female offspring.

• None of the adults survive to the next year.

1. Writing the populations of juveniles, yearlings, and adults in year $k$ using the vector $\xvec_k=\threevec{J_k}{Y_k}{A_k}$, find the matrix $A$ such that $\xvec_{k+1} = A\xvec_k$.

2. Show that $A^3=I$.

3. What are the eigenvalues of $A^3$? What does this say about the eigenvalues of $A$?

4. Verify your observation by finding the eigenvalues of $A$.

5. What can you say about the trajectories of this dynamical system?

6. What does this mean about the population of rodents?

7. Find a population vector $\xvec_0$ that is unchanged from year to year.