Ecological niche differentiation in Chiroxiphia and Antilophia manakins (Aves: Pipridae)

Species distribution models are useful for identifying the ecological characteristics that may limit a species' geographic range and for inferring patterns of speciation. Here, we test a hypothesis of niche conservatism across evolutionary time in a group of manakins (Aves: Pipridae), with a focus on Chiroxiphia boliviana, and examine the degree of ecological differentiation with other Chiroxiphia and Antilophia manakins. We tested whether allopatric sister species were more or less similar in environmental space than expected given their phylogenetic distances, which would suggest, respectively, ecological niche conservatism over time or ecologically mediated selection (i.e. niche divergence). We modeled the distribution of nine manakin taxa (C. boliviana, C. caudata, C. lanceolata, C. linearis, C. p. pareola, C. p. regina, C. p. napensis, Antilophia galeata and A. bokermanni) using Maxent. We first performed models for each taxon and compared them. To test our hypothesis we followed three approaches: (1) we tested whether C. boliviana could predict the distribution of the other manakin taxa and vice versa; (2) we compared the ecological niches by using metrics of niche overlap, niche equivalency and niche similarity; and (3) lastly, we tested whether niche differentiation corresponded to phylogenetic distances calculated from two recent phylogenies. All models had high training and test AUC values. Mean AUC ratios were high (>0.8) for most taxa, indicating performance better than random. Results suggested niche conservatism, and high niche overlap and equivalency between C. boliviana and C. caudata, but we found very low values between C. boliviana and the rest of the taxa. We found a negative, but not significant, relationship between niche overlap and phylogenetic distance, suggesting an increase in ecological differentiation and niche divergence over evolutionary time. Overall, we give some insights into the evolution of C. boliviana, proposing that ecological selection may have influenced its speciation.