# Differential Equations : Predator / Prey Models

Part a)

Given the following predator prey model where x(t) is the predator population and y(t) is the prey population:

dx/dt = - ax + bxy + (z1)*x

dy/dt = cy - gxy +(z2)*y

Here both z1 and z2 can be positive or negative; parameters a, b, c, g are all defined to be positive.

Parameters z1 and z2 can represent an external introduction of species at a constant rate (positive values) or an external harvesting of the species at a constant rate (a negative values).

Under what conditions of z1 and z2 can the trivial fixed point (both species evolve to extinction) become stable (in both directions not a saddle node)

Interpret these results.

Part b)

Given the following predator prey model where x(t) is the predator population and y(t) is the prey population:

dx/dt = - a*x + b*xy -----Q

dy/dt = c*y - g*xy ------P

Solve the second equation, equation P, for the predator population (x) and simplify. Then show that the average predator population over one cycle or period T is equal to c/g.

Note that the populations are periodic so y(T) = y(0) and x(T) = x(0)

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#### Solution Summary

Differential equations and parameters are used to analyze a predator / prey model. The solution is detailed and well presented. The response was given a rating of "5/5" by the student who originally posted the question.