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Oceanic islands are cradles for diversity. Differences in predation pressures and lack of competition on islands are thought to drive both phenotypic and species diversification. While most work exploring these patterns has focused on life history, behavioral and morphological traits, many island species are uniquely colorful. Yet, a recent study of island bird coloration found that insular species are duller than continental species. Whether such shifts in color are associated with increased rates of color evolution on islands remains unknown. Here, we incorporate geometric morphometric techniques to study plumage color diversity in a speciose clade of colorful birds that inhabit nearly all areas of the globe—kingfishers (Aves: Alcedinidae). In particular, we test two hypotheses: (i) that plumage complexity enhances interspecific rates of color evolution and (ii) that plumage color diversity is elevated on islands. Our results show that more complex plumages result in more diverse colors among species and plumage color evolves faster on islands. Importantly, we found that insular species did not have more complex plumages than their continental relatives. Thus, complexity may be a key innovation that facilitates response to divergent (or relaxed) selection pressures on islands. Lack of support for competition driving rates of evolution along different color axes hints at an allopatric model of color evolution in which species adapt to local conditions on different islands. This work demonstrates how a truly multivariate treatment of color data can reveal evolutionary patterns that might otherwise go unnoticed.

Turnover in species composition between sites, or beta diversity, is a critical component of species diversity that is typically influenced by geography, environment, and biotic interactions. Quantifying turnover is particularly challenging, however, in multi-host, multi-parasite assemblages where undersampling is unavoidable, resulting in inflated estimates of turnover and uncertainty about its spatial scale. We developed and implemented a framework using null models to test for community turnover in avian haemosporidian communities of three sky islands in the southwestern United States. We screened 776 birds for haemosporidian parasites from three genera (Parahaemoproteus, Plasmodium, and Leucocytozoon) by amplifying and sequencing a mitochondrial DNA barcode. We detected infections in 280 birds (36.1%), sequenced 357 infections, and found a total of 99 parasite haplotypes. When compared to communities simulated from a regional pool, we observed more unique, single-mountain haplotypes and fewer haplotypes shared among three mountain ranges than expected, indicating that haemosporidian communities differ to some degree among adjacent mountain ranges. These results were robust even after pruning datasets to include only identical sets of host species, and they were consistent for two of the three haemosporidian genera. The two more distant mountain ranges were more similar to each other than the one located centrally, suggesting that the differences we detected were due to stochastic colonization-extirpation dynamics. These results demonstrate that avian haemosporidian communities of temperate-zone forests differ on relatively fine spatial scales associated with adjacent sky-islands. Null models are essential tools for detecting turnover in complex, undersampled, and poorly known systems.