title: plotting the means with confidence intervals with ggplot
body: <p>I have some data that I have gathered from a model. I want to plot the size of a population over time. I have the population size at each time step, and 100 replicates. I would like to plot the mean population size for each time step, and also the 95% confidence intervals (as a shading if possible).</p>
  
  <p>I haven't used <code>ggplot</code> before. I have just been using the ordinary (base) plots in R so far. But I want to see what the <code>ggplot</code> would look like.</p>
  
  <p>Here's what I have so far:</p>
  
  <pre><code>ggplot(data=model1, aes(x=steps., y= pop-size, col='blue')) + 
     geom_line()
  </code></pre>
  
  <p>This plots all the points, and it looks good, but I don't know how to just plot the means and add the confidence intervals.</p>