The role of learned song in the evolution and speciation of Eastern and Spotted towhees
Fig 6
Geographic distribution of random forest model predictions of Spotted and Eastern towhee species identity.
Predictions were based on a model trained on 16 song features from samples of Spotted towhees and Eastern towhees. (A) We trained a model on song data from the entire geographic range of both species (NSpotted_towhee = 796; NEastern_towhee = 796) and tested how well it predicted the species identification of a subset of all song samples (Ntest = 697; accuracy = 89.5%). (B) The same results from (A) are plotted based on the percent of trees in the random forest classifier that supported the correct species identification; when less than 50% of trees supported the correct identification, the classifier made an incorrect species prediction. The average confidence in species classifications tended to decrease toward the zone of overlap for both species. (C) We then trained a second model on a subset of samples obtained only from the non-overlap zone (NSpotted_towhee = 796; NEastern_towhee = 796) and tested it on a random subsample of song bouts from both the zone of non-overlap (Ntest_nonoverlap = 216; accuracy = 93.5%) and the zone of overlap (i.e., 102°W - 91°W; Ntest_overlap = 216; accuracy = 84.3%). (D) The same results from (C) are plotted based on the percent of trees in the random forest classifier that supported the correct species identification; again, the average confidence of species identifications tended to decrease toward the zone of overlap for both species. (E) We used the same model from panels C and D to predict species identity of song bouts from recordings of “hybrid/unsure” towhees (Npredict = 27). The model predicted that 16 of these “hybrid/unsure” recordings were Spotted towhees and 11 were Eastern towhees, with no discernable longitudinal gradient in the predictions. The dotted line represents the zone of overlap determined by the co-occurence of Eastern towhee and Spotted towhee song recordings (102°W - 91°W). Base maps (panels A, C, and E) were made with Natural Earth (http://www.naturalearthdata.com/).