Paper 1, Section I, B

Mathematical Biology
Part II, 2014

A population model for two species is given by

dNdt=aNbNPkN2dPdt=dP+cNP\begin{aligned} &\frac{d N}{d t}=a N-b N P-k N^{2} \\ &\frac{d P}{d t}=-d P+c N P \end{aligned}

where a,b,c,da, b, c, d and kk are positive parameters. Show that this may be rescaled to

dudτ=u(1vβu)dvdτ=αv(1u)\begin{aligned} &\frac{d u}{d \tau}=u(1-v-\beta u) \\ &\frac{d v}{d \tau}=-\alpha v(1-u) \end{aligned}

and give α\alpha and β\beta in terms of the original parameters.

For β<1\beta<1 find all fixed points in u0,v0u \geqslant 0, v \geqslant 0, and analyse their stability. Assuming that both populations are present initially, what does this suggest will be the long-term outcome?