Climatic amplitude is a predictor of geographic range size in Mexican morning glories (Ipomoea L., Convolvulaceae)

Abstract

Background: Elucidating the determinants of species’ geographic distributions is a fundamental goal of ecology and biogeography, as they can inform about key biological processes, with implications for conservation. Goal: Evaluate whether realized climatic amplitude (a proxy for niche breadth) is an ecological correlate of geographic range size in morning glories in Mexico, a highly diverse group of plants of worldwide socio-economic relevance, but still poorly studied. Methods: Based on a dataset of > 30,000 records of which > 7,000 were manually georeferenced, we calculated geographic range size (using convex hull polygons and buffered occurrence points), and climatic amplitude (using three first axes of Principal Components based on 19 Worldclim variables, and focusing on temperature, precipitation, and seasonality), and explored their relationship using general linear models and phylogenetic generalized least squares. Results: All models show that climatic amplitude explains a high proportion of variation in geographic range size for our dataset (up to > 69 %). We find no evidence of tradeoffs related to temperature and precipitation niche breadths. Through review of reported records, we update the number of species of Ipomoea reported for Mexico to 178. Conclusions: Much of the variation in geographic range size in Mexican Ipomoea can be explained by realized climatic amplitude, and this result is not driven by phylogenetic history. We discuss cases where despite large geographic range sizes, narrow climatic amplitudes can signify higher risks for species in the face of changing environments.