“The tanagers are a group of 370 species of songbird found throughout Central and South America that occur in a great diversity of habitats,” according to an abstract by EEB graduate student Pascal Title. “Thanks to recent genetic analyses, the group has received a taxonomic overhaul, such that North American species like the Western, Hepatic, Summer, and Scarlet Tanager are no longer truly tanagers (they’re cardinals now), and the famous Darwin’s Finches are now true tanagers. Given the large number of species, and the diversity of environments that they occupy, we set out to test whether high rates of tanager niche evolution have played a role in generating this diversity.”
Title and his coauthor, Kevin Burns, Department of Biology, San Diego State University, published Rates of climatic niche evolution are correlated with species richness in a large and ecologically diverse radiation of songbirds in Ecology Letters. Title’s advisor is Professor Dan Rabosky.
“To capture the environments that these species occupy, we harnessed the wealth of information found in natural history collections by compiling location information associated with over 340,000 museum records. By examining geographic and environmental data in association with a phylogeny of the tanagers, we found a strong association between the number of species in different tanager groups, and their ability to diversify into new environments. For example, the tanager group that includes the brightly colored core tanagers has both the highest number of species and occupies the broadest set of environments. This indicates that tanager groups with less ability to adapt to new environments might end up with fewer species than those groups where species are able to adapt quickly and ecologically diverge. This research points to ecological characteristics as potentially important in the generation of high tanager diversity in the Neotropics and contributes to such patterns as the latitudinal biodiversity gradient.”
Tanagers are one of the most prominent groups in the Neotropics, representing 12 percent of all regional bird species. The tanager family, Thraupidae, is the largest songbird family, representing nearly 10 percent of all songbird species.
“Tanagers are an ideal system for studying the evolution of ecological niches,” the paper states. “This clade of Neotropical birds consists of 371 species that have radiated across most of Central and South America. They are found in 27 of the 29 terrestrial habitats identified in the Neotropics and are distributed at elevations ranging from coastlines to Andean highlands.”
Most surprising and one of the most interesting results of the study for Title was the finding that species that belong to larger tanager clades occupy a climatic niche that is proportionally narrower. “This suggests that if species are able to specialize and become adapted to narrower ranges of climatic conditions, then this allows for more species to accumulate. As this is investigated in other groups, we will see if this is a common pattern, or if it is restricted to organisms with particular life history traits, geographic distributions or other ecological characteristics.”
Next, Title is interested in taking a closer look at sister species across different tanager groups, and examining how they differ in terms of geographic distribution and climatic space occupancy, specifically. “This would allow me to gain a better understanding of how the broader patterns discussed so far play out for closely related species.”