function metapop_lines(imi,ext,alfa)
% plots a state space rendering of the Levins'equation
%imi - global immigration rate
%alfa - shape constant for the rescue effect (if == 0 -> standard Levins's equation)

x=0:1/100:1;
plot(x,imi.*x.*(1-x));
hold on;
plot(x,(ext.*x)./(1+alfa.*ext.*x),'r');