The role of climate change and niche shifts in divergent range dynamics of a sister-species pair

The datasets collected here were used to generate species distribution models for the great-tailed grackle (Quiscalus mexicanus) and boat-tailed grackle (Quiscalus major) as part of publication by Summers et al. 2022. The publication abstract is included below.Species ranges are set by limitations in climate tolerances, habitat use, and dispersal abilities. Understanding the factors governing species range dynamics remains a challenge that is ever more important in our rapidly changing world. Species ranges can shift if environmental changes affect available habitat, or if the habitat breadth or connectivity of a species changes. The ability of a species to rapidly expand their geographic range through changes in their habitat breadth, also known as niche shifts, has been linked to behavioral flexibility, the ability to change behavior when circumstances change. We tested how changes in habitat availability, habitat breadth, or habitat connectivity contributed to divergent range dynamics in a sister-species pair. The highly behaviorally flexible great-tailed grackle (Quiscalus mexicanus) has expanded its range northward from Texas to South Dakota in the past 40 years, while its closest relative, the boat-tailed grackle (Quiscalus major), has remained tied to the coasts of the Atlantic Ocean and the Gulf of Mexico. We created species distribution and connectivity models trained on citizen science data from 1970-1979 and 2010-2019 to determine how suitable habitat ranges,habitat breadth, and range-wide connectivity have changed for both species. We found that the two species occupy distinct habitats and that the habitat of the great-tailed grackle has shifted to include a larger breadth of urban, arid environments farther from natural water sources. Meanwhile, the boat-tailed grackle has remained limited to warm, wet, coastal environments. We found no evidence that changes in habitat connectivity affected the ranges of either species. Overall, our results suggest that a change in habitat breadth drove the rapid range expansion of the great-tailed grackle, while climate change shaped minor shifts in the available range of the boat-tailed grackle. The expansion in habitat breadth of the great-tailed grackle is consistent with observations that species with high behavioral flexibility can rapidly expand their geographic range by using human-altered habitat. This investigation identifies how opposite responses to anthropogenic change drive divergent range dynamics, elucidating the factors that have and will continue to shape species ranges.