The biogeography of a mimicry complex is revealed by a citizen-science butterfly monitoring program

Many ecological and evolutionary questions require data gathered over large geographic scales that are rarely obtainable from single-focus, traditional scientific studies.   Large-scale, volunteer-driven monitoring efforts offer unique opportunities to address questions at scales out of reach of individual researchers; however, the value of publicly collected scientific data has been hotly debated.  Here we illustrate the value of citizen science data from the long-running North American Fourth of July Butterfly Count Programs by showing how the knowledge of relative abundance is critical for understanding the biogeography of a mimicry system.   In this case, the pipevine swallowtail (Battus philenor) is an unpalatable putative model for the red-spotted purple (Limenitis arthemis astyanax).   However, there is also a non-mimetic subspecies, the white admiral (Limenitis arthemis arthemis), whose range extends much farther north of the mimetic morph.  The ranges of the two sub-species overlap extensively (approximately 6 degrees of latitude) where they form a hybrid zone.  The maintenance and position of the southern border of this hybrid zone cannot be explained by the range of the model.  However, our analysis shows that the hybrid zone begins where the proportion of the model (B. philenor) to the mimic (L. a. astyanax) drops off to near zero.  At the exact same latitude, the proportion of the mimetic to non-mimetic sub-species begins to fall.   The relative proportion of each species over a large geographic area shows the profound geographic influence of this unpalatable model, supporting a batesian mimicry complex.