title: How to plot several regression lines in same scatter plot in R?
body: <p>I have a dataframe with data of <strong>body temperature (Tb), substrate temperature (Ts)</strong> for several individuals of <strong>both sexes</strong> and comming from <strong>three different populations</strong> like this:
  (I made up this table since I couldn't manage to share my full table, but I have around 30 individuals from each pop)</p>
  
  <pre><code>pop  sex  tb  ts
  bo    m     37   30
  bo    m     39   29
  bo    f     36   36
  pa    m     40   34
  pa    f     37   28
  pa    m     37   33
  pa    f     36   26
  re    f     35   24
  re    f     37   29
  re    m     38   30
  </code></pre>
  
  <p>I want to assess the relationship between Tb and Ts but not only for the species but for each population separately in order to identify possible differences in slopes among them. </p>
  
  <pre><code>my.regression &lt;- lm(tb ~ ts*pop*sex, data = mydata)
  </code></pre>
  
  <p>I managed to plot a scatter plot with different colors, one byeach of my populations. However, I couldn't plot my regressions lines. I searched for answers everywhere: about how to add the regression lines by group...(not in stackoverflow, not even with the help of almighty google, youtube tutorials, R book, R graphics books and so on)</p>
  
  <p>All I want is to plot one regression line by each population. Something similar to <img src="https://i.stack.imgur.com/SKRjX.gif" alt="this plot"> </p>