Instead of
for i=1:length(R)
% this is the survival equation considering resources and predators
survival(X,Y)=(X.*R(i))+((1-X).*(R(i).*(0.5)/1+0.5))-(Y.*0.5);
end;
Just have this:
% this is the survival equation considering resources and predators
survival = (X.*R)+((1-X).*(R.*(0.5)/1+0.5))-(Y.*0.5);
You don't use (x,y) after survival because it's an array. And you don't use (i) after R because you can just use R and do the whole array in one shot (no for loop needed).