What explains the high island endemicity of PhilippineRafflesia? A species distribution modeling analysis of three threatened parasitic plant species and their hosts

Abstract

Premise: Rafflesia are rare holoparasitic plants. In the Philippines, all but one species are found only on single islands. This study aimed to better understand the factors contributing to this distribution pattern. Specifically, we sought to determine whether narrow environmental tolerances of host and/or parasite species might explain their island endemicity, or, instead or in addition, the limited distribution of Rafflesia species is the result of a narrow overlap between the environmental requirements of host and parasite. Methods: We used Maxent species distribution modeling to identify areas with suitable habitat for R. lagascae, R. lobata, and R. speciosa and their Tetrastigma host species. These analyses were carried out for current climate conditions as well as two future climate change scenarios. Key results: Whereas species distribution models indicated suitable environmental conditions for the Tetrastigma host species in many parts of the Philippines, considerably fewer areas have suitable conditions for the three Rafflesia species. Some of these areas are found on islands from which they have not been reported. All three species will face significant threats as a result of climate change. For R. lagascae and R. lobata, these may include a loss of suitable area as a result of changes to the distribution of their host species. Conclusions: Our results suggest that limited inter-island dispersal abilities and/or specific environmental requirements are likely responsible for the current pattern of island endemicity of the three Rafflesia species, rather than the environmental requirements of their Tetrastigma host species.