d) Based on your S317 studies, name and explain the type of natural selection operating in this song sparrow analysis of bird beak length change.

6.4 P0.05 6.2 6.0 5.8 mean beak depth of fosterlings/mm 5.6 5.4 5.2 5.6 6.0 6.4 (b) foster parent mean beak depth/mm Figure 1 (a) Biological parent mean beak depth is plotted against mean beak depth of offspring. (b) Foster parent mean beak depth is plotted against mean beak depth of fosterlings