Inter-specific competition can have evolutionary effects that may result in character displacement. Darwin’s Finches present a unique opportunity to study the evolutionary consequences of such interactions. It has been widely recognized that their beaks shape and sizes have been key in the process of diversification and speciation, resulting in a variety of beaks each adapted to a specific food source. Some observations have hinted that character displacement as a product of inter-specific competition occurs in these organisms, but so far this has not been tested. In this study we aim at testing the role of competition and specialization in structuring beak morphological diversity across several species and islands of the Galapagos archipelago. We hypothesize that if competition is an important driver of diversity, then competing species in sympatry will show highest morphological diversification (i.e. character displacement). Conversely, if species don’t compete for specific food resources, their beak morphology will be independent of the presence of competitors in their community. We tested these hypotheses in two groups of Darwin’s Finches: Ground Finches and Tree Finches. Using geometric morphometrics to measure and compare beak shapes, we placed 15 landmarks on the upper beak of museums specimen pictures. This allowed us to partition the variation of beak morphology in shape and size independently. We generated beak geometries of 303 specimens belonging to two species of Ground Finches (Large Ground Finch and Medium Ground Finch), and 184 specimens belonging to four species of Tree Finches (Small, Medium and Large Tree Finches, and Woodpecker Finch).
Results/Conclusions
The Medium and Large Ground Finches showed no signs of character displacement, both the size and shape of their beaks were not significantly different in sympatric or allopatric conditions. On the other hand, the beaks of both the Small and Large Tree Finches become smaller in communities with high competition. In terms of beak shape, species in communities with high competition showed larger inter-specific differences than when in communities with low competition, indicating a morphological response to competitors. We conclude that competition can elicit an evolutionary response in these animals, although this response is not pervasive. Our results support the role of competition in community assembly and evolution in adaptive radiations