Vandermeer, J.H., & Perfecto, I. 2006 A keystone mutualism drives pattern in a power function.. Science 311(5763): 1000-1002.

Notes: A study was conducted in southern Mexico to investigate the distribution of a scale insect (Coccus viridis) in an organic coffee farm. The data on the frequency distribution of insect number per tree suggested a power function, as shown by the approximately linear nature of the points. Underlying biological processes may account for both the power function and its deviation. High cluster deviation was a consequence of the key mutualism operative in the system (between C. viridis and Azteca instabilis).