Let $w$ be the number of worms (in millions) and $r$ the number of robins (in thousands) living on an island. Suppose $w$ and $r$ satisfy the following differential equations, which correspond to the slope field in Figure 11.76 $$frac{d w}{d t}=w-w r, quad frac{d r}{d t}=-r+w r$$
For the case discussed in Problem 9, estimate the maximum and minimum values of the robin population. Estimate the number of worms when the robin population reaches its minimum.