Let the joint production function be

Where a is the instantaneous rate of growth of the monkey population, g is the instantaneous rate of growth of the ground animal population, a is the rate at which monkeys are being harvested, and g is the rate at which ground animals are being harvested.  L=1 is the total amount of labor input, and s is the proportion spent in gun hunting.  An increase in s can be interpreted as meaning either that hunters are better at the shooting, or they have found where the monkeys live.  The function is strictly quasi-convex in the harvest rates.  We can also use this function to describe the two populations over time using some parametric assumptions.

By increasing the harvest rates we can slow population growth and even cause it to decline.
Using the implicit function theorem we can find the rate of transformation between ground and arboreal animals; the slope of the production possibilities frontier.

This result is negative as guaranteed by the assumption of quasiconvexity of the joint production function.  As more time is needed to hunt monkeys relative to other animals the PPF becomes steeper.  This is illustrated in the following graph.

With some more parametric assumptions we can show the same thing by plotting two PPF's

Blue PPF is when hunters become  less effective, rpresented by an increase in s.