Ensemble forecast of climate suitability for the Trans-Himalayan Nyctaginaceae species

Oxybaphus himalaicus Edgew. (Nyctaginaceae) is the only native species of Oxybaphus occurring outside of the Western Hemisphere. Unfortunately, very little is known about the distribution of this species in Nepal, despite it being endemic to the Trans-Himalayas. In the earlier collections it was mis-identified as another very common Nyctaginaceae species Boerhavia diffusa L. We used species distribution modelling technique to determine the climate space of these two species. We used an SDM ensemble method in the BiodiversityR R-package to identified the bioclimatic variable that defines the climate space for B. diffusa and O. himalaicus. Species distributions were modelled using a subset of least correlated variables from bioclimatic data and elevation dataset. The most favourable conditions for B. diffusa were centrally located at well-drained and hot lowlands of Nepal whereas that of O. himalaicus was located in highlands valleys. Discontinuities in suitable climatic conditions coincided with biogeographical barriers associated with topographic transitions. The rising slope of mountains limit the climatic suitability of B. diffusa particularly due to low temperature and high aridity, whereas this condition was suitable for O. himalaicus. But presence of high Himalayas fragmented the suitable climatic condition for this species. We speculate that historic climatic changes associated with changes in the geology of the Himalayas, formed by tectonic forces and sculpted by weathering and erosion, are responsible for the fragmentation of habitat of this species. The extensive study of such a species could provide insight into the history of species colonization in the Himalayas, as well as the potential distribution of Himalayan species.