buffer = 10;
N1 = linspace(-buffer,k+buffer);

% Nullcline for N1
plot(zeros(1,length(N1)),N1,'r');
hold on;
N2 = k - N1;
plot(N1,N2,'r');

% Nullcline for N2
plot(N1, zeros(1,length(N1)));
N2 = k - a*N1;
plot(N1,N2);

xlabel('N_1');
ylabel('N_2');
axis([-buffer k+buffer -buffer k+buffer]);

plot(0,0,'ko');
plot(k,0,'ko');
plot(0,k,'ko');

disp = 2;

str1 = ['(N_1,N_2)* = (0,0)'];
t1 = text( 0+disp, 0+disp, str1 );
set( t1, 'FontWeight', 'Bold' );

str2 = ['(N_1,N_2)* = (k,0)'];
t2 = text( k+disp-25, 0+disp, str2 );
set( t2, 'FontWeight', 'Bold' );

str3 = ['(N_1,N_2)* = (0,k)'];
t3 = text( 0+disp, k+disp, str3 );
set( t3, 'FontWeight', 'Bold' );

title('Nullclines in the absence of predators');