Distribution Estimate of the Invasive Alien Species Coreopsis lanceolata in Toyama Prefecture, Japan

Coreopsis lanceolata is an invasive alien species with a high dispersal capacity and the potential to outcompete native species. Although removal activities are underway in Toyama Prefecture, limited understanding of its distribution status and invasion patterns continues to make effective management challenging. In this study, I estimated the potential distribution of C. lanceolata in Toyama Prefecture using ecological niche modeling with MaxEnt. A visual field survey conducted from late May to early July 2024 confirmed the presence of this species at 166 points. Spatial thinning was applied to the occurrence data prior to model construction. The environmental variables included climatic, topographic, and land use factors. The resulting model showed high predictive performance, with an estimated distribution covering 34.9% of the grid cells in Toyama Prefecture. Specifically, 91.6% were located below 200 m elevation. The variables that contributed the most to the model were built-up area, forest area, and temperature. The response curve for the built-up area exhibited a unimodal pattern, whereas that for the forest area exhibited a monotonically decreasing trend, and the temperature response curve showed a sharp peak within a narrow temperature range. These results indicate that C. lanceolata predominantly occurs in lowland plains with moderate building development, and is unlikely to occur in forested mountainous areas. Additionally, I evaluated the potential occurrence of the species in cold environments using mean annual temperature data from municipalities in Hokkaido, where the species has been recorded. Based on the temperature response curve, 95.2% of municipalities were classified as unsuitable. This indicates that the temperature range of the occurrence data from the Toyama Prefecture was relatively narrow, which may have led to an underestimation of the potential for the species to occur in colder environments. Thus, C. lanceolata may spread beyond its current range in the Toyama Prefecture into colder habitats. The current distribution of C. lanceolata in Toyama Prefecture may remain in the expansion phase, increasing concerns regarding potential future invasions into mountainous regions.