Paper 4, Section I, C

Mathematical Biology
Part II, 2019

(a) A variant of the classic logistic population model is given by:

dx(t)dt=α[x(t)x(tT)2]\frac{d x(t)}{d t}=\alpha\left[x(t)-x(t-T)^{2}\right]

where α,T>0\alpha, T>0.

Show that for small TT, the constant solution x(t)=1x(t)=1 is stable.

Allow TT to increase. Express in terms of α\alpha the value of TT at which the constant solution x(t)=1x(t)=1 loses stability.

(b) Another variant of the logistic model is given by this equation:

dx(t)dt=αx(tT)[1x(t)]\frac{d x(t)}{d t}=\alpha x(t-T)[1-x(t)]

where α,T>0\alpha, T>0. When is the constant solution x(t)=1x(t)=1 stable for this model?