title: Adding significance levels in faceted plots with two results in the same x axis
body: <p>I know that there are many questions already open to add significance level in ggplot2 in faceted plots. However, as a R beginner, I did not found a solution for my plot. 
  My data (.txt file) is available in this link:</p>
  
  <p>1drv.ms/t/s!AsLAxDXdkA9Mg8oXdJ-qxD5AeB4KAw </p>
  
  <p>There are four columns: three factor levels (temperature, parasitoid species and behavior) and a numeric level (number of parasitism and host-killing).</p>
  
  <p>I run the plot with the code:</p>
  
  <pre><code>    ggplot(mydata, aes(x = temperature, y = value, fill = species)) +  
  facet_grid(. ~ behavior) +
  stat_summary(fun.y = mean, geom = "bar", position = "dodge", stat="identity") +
  stat_summary(fun.data = mean_sdl, fun.args = list(mult = 1) +
  labs(x = "Temperature", y = "Nº of parasitized or host-killed larvae") +
  theme(legend.position = "bottom", legend.title = element_blank(),  legend.text = element_text(size = 11, face = "italic"))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/0iJis.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0iJis.png" alt="enter image description here"></a></p>
  
  <p>Now I want to add the significance level in each plot, comparing separately the results in Parasitism and Host-Killing in both temperatures. So I have 6 contrasts in each plot. I tested the option using the function stat_compare_means. However, as advised in this Rblogger tutorial (<a href="https://www.r-bloggers.com/add-p-values-and-significance-levels-to-ggplots/" rel="nofollow noreferrer">https://www.r-bloggers.com/add-p-values-and-significance-levels-to-ggplots/</a>) I should make a list telling what I want to compare. But, in this case, I have two results  for 25°C and two for 30°C. How I could create this list mentioning all the contrasts? 
  If anybody could clarify for me how I can solve this, it would help me a lot. Thanks. </p>