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

Abstract

ABSTRACTPremiseRafflesiaare 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.MethodsWe used Maxent species distribution modeling to identify areas with suitable habitat forR. lagascae,R. lobata, andR. speciosaand theirTetrastigmahost species. These analyses were carried out for current climate conditions as well as two future climate change scenarios.Key resultsWhereas species distribution models indicated suitable environmental conditions for theTetrastigmahost species in many parts of the Philippines, considerably fewer areas have suitable conditions for the threeRafflesiaspecies. 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.ConclusionsOur 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 threeRafflesiaspecies, rather than the environmental requirements of theirTetrastigmahost species.