Observing character displacement from process to pattern in a novel vertebrate community

Ecological character displacement, whereby shifts in resource use in the presence of competingspecies leads to adaptive evolutionary divergence, is widely considered an important process incommunity assembly and adaptive radiation. However, most evidence for character displacementhas been inferred from macro-scale geographic or phylogenetic patterns; direct tests of theunderlying hypothesis of divergent natural selection driving character displacement in the wildare rare. Here, we document character displacement between two ecologically similar lizards(Anolis sagrei and A. cristatellus) experiencing novel contact. We identify directional selectionduring the incipient stages of sympatry in a new community that corresponds to repeated traitdivergence across multiple established sympatric communities. By identifying the role of naturalselection as character displacement unfolds, we connect how natural selection operating at shorttimescales may drive broader patterns of trait distributions at larger spatial and temporal scales.