Modeling the range expansion of butterflies into the southern US

Recent records indicate that several butterfly species are shifting their native ranges due to global warming. Examples of this phenomenon have been documented for many European butterflies, where range pattern shifts have been relatively well-monitored. The range-limiting factors for American butterflies, however, are still largely unknown. We studied 16 species of butterflies that have been recently reported in the Lower Rio Grande Valley of Texas, an area several hundred kilometers north of their respective, native historical ranges. We correlate 19 climatic variables with historical distributional data to characterize the ecological requirements of these target species using two different species distribution models (GARP and MaxEnt). Contrary to our expectations, our findings show that for some species climatic variables by themselves cannot explain why these species are shifting their ranges. We suggest developing further studies (e.g., demographic) for these species including modeling the distribution of larval host plants.