Will They Still Be Together? Distribution Modeling of Six Co-Occurring Species of Swertia (Gentianaceae) in Asia

Investigating the factors determining the co-existence of closely related species is key to understanding how biodiversity is structured and maintained. To this end, we seek to comprehend the geographical distribution of species, their range overlap, and the evolutionary and ecological mechanisms that promote co-existence in ecological communities. In the Anthropocene, climate change dramatically shapes ecosystems along with species distributions. Here, we focus on six co-occurring species of Swertia (Gentianaceae). For instance, all of them grow within an area of 2 km2 in the north of Kunming city, occupying different microhabitats. We employed the maximum entropy model (MaxEnt) and a geographic information system (ArcGIS) to predict how future climate change will impact their distribution. We also tested the relationship between ecological niche overlap and phylogenetic distance among these species. We found that these six species co-occur in the mountains of Yunnan, Sichuan, and Guizhou provinces. Precipitation in the warmest quarter, mean temperature of driest quarter, solar radiation, annual temperature range, and elevation influence their distribution. In the predicted future climate, four outcrossing species, S. bimaculata, S. kouitchensis, S. punicea, and S. cincta, will expand their distribution range. The other two self-pollinating species, S. macrosperma and S. nervosa, will experience range contractions. We found no significant correlation between ecological niches and the phylogenetic distances of these species. Under the future climate scenarios, the six species of Swertia plants will tend to grow in clusters, suggesting a higher likelihood of co-occurrence in the future, and creating a potentially high level of habitat and resource competition among them. These findings hold significant implications for the conservation of Swertia.