Bioclimatic niches of selected endemic Ixora species on the Philippines: predicting habitat suitability due to climate change

The pantropical genus Ixora is highly diverse, with several species endemic to the Philippines. Owing to their endemic nature, many of these species are endangered and little is known about their basic biology. This study aimed to establish baseline information about the bioclimatic niches of Ixora species endemic to the Philippines, determine suitable areas and potential range shifts under future climate conditions, and identify priority areas for conservation and future research. Locality records of 12 endemic Ixora species from the Philippine archipelago were analyzed, with a particular focus on the five most abundant species I. auriculata, I. bartlingii, I. cumingiana, I. macrophylla, and one island endemic species, Ixora palawanensis. Bioclimatic variables from the WorldClim database at 2.5′ resolution were used, with a focus on annual means and seasonality of temperature and precipitation as well as precipitation of the warmest quarter. Analysis of the relationships of the species locations with the bioclimatic variables showed that the bioclimatic niches of the five focal Ixora species generally had narrow temperature and wider precipitation niches. Species distribution modeling with the model Maxent suggested that I. auriculata and I. bartlingii will likely shift their geographic distributions southwards under predicted levels of climate change, while I. cumingiana and I. macrophylla were found to likely expand their ranges. Ixora palawanensis, in contrast, was predicted to decrease its potential distribution with future climate change. Further, results of species distribution modeling for the rare endemic Ixora species I. bibracteata, I. chartacea, I. ebracteolata, I. inaequifolia, I. longistipula, I. luzoniensis, and I. macgregorii were presented, which, however, had much less observation points and therefore only provide a first estimate of potential species distributions. The generated potential habitat suitability maps can assist policy makers in designing conservation strategies for the species and in identifying areas with potential to withstand climate change until at least 2080.