Set ratio on subplot after resizing window

Hi all,

Since I don't know how to do a few things (like putting lines on the title of subplots), I'm using some annotation stuff, getting the generated code and pasting it on my regular plots. The catch is: the annotations only get to the right places when I maximize the window, but that makes a previously almost square subplot become a rectangle. I need it to be a square (same dimensions on X and Y) on the final figure. How can I arrange that?

For instance, my code is something like this:

titulo{1} = 'I';
titulo{2} = 'II';
titulo{3} = 'III';
titulo{4} = 'IV';

figure

cmapInt = [1, 0, 0; 1, 1, 1; 0, 0, 1];

cmapPlot = [
    1  0   0
    0   0.7   0
    0   0   0.9
    0.5   0.5   0.5];

aMax = 4;

%%matrizes de interação
position = [1 5 9 13];

for a = 1:aMax
    subplot(4,4,position(a)),...
        imagesc(rand(50).*(ceil(rand(50)*3)-2)
        colormap(cmapInt)
        caxis([-1 1])
        xlim([1 50])
        ylim([1 50])
        title(titulo{a})
        set(get(gca, 'Title'), 'Color', cmapPlot(a,:), 'FontWeight','bold');
        h = get(gca, 'Title');
        set(h, 'Units', 'normalized');
        set(h, 'Position', [0,1,0]);
        set(h, 'HorizontalAlignment', 'left');
        set(h, 'VerticalAlignment', 'bottom');

          if a == 4
              xlabel('Espécie')
          end
  end

% Red line
annotation('rectangle',...
    [0.14771875 0.935672514619882 0.12665625 0.00584795321637261],...
    'FaceColor',[1 0 0],...
    'Color',[1 0 0]);

% Green line
annotation('rectangle',...
    [0.14771875 0.49508771929824 0.12665625 0.00584795321637261],...
    'FaceColor',[0 0 1],...
    'Color',[0 0 1]);

% Blue line
annotation('rectangle',...
    [0.14771875 0.716842105263155 0.12665625 0.00584795321637261],...
    'FaceColor',[0 0.498039215686275 0],...
    'Color',[0 0.498039215686275 0]);

% Gray line
annotation('rectangle',...
    [0.14771875 0.276315789473684 0.12665625 0.00584795321637261],...
    'FaceColor',[0.501960784313725 0.501960784313725 0.501960784313725],...
    'Color',[0.501960784313725 0.501960784313725 0.501960784313725]);

%%curvas de perda de diversidade funcional
for a = 1:4
    hold on
        subplot(4,4,[2 16]), ...
            plot(rand(1,50),...
            'Color', cmapPlot(a,:))
        box off
end

      hold on
          subplot(4,4,[2 16]), ...
              plot(rand(1,50)*2, '--black')
         box off

         xlabel('Extinções')
         ylabel('Grupos Remanescentes')

Thanks!