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

Abstract

<h3>Premise</h3><p><em>Rafflesia</em> 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.</p><h3>Methods</h3><p>We used Maxent species distribution modeling to identify areas with suitable habitat for <em>R. lagascae</em>, <em>R. lobata</em>, and <em>R. speciosa</em> and their <em>Tetrastigma</em> host species. These analyses were carried out for current climate conditions and two future climate change scenarios.</p><h3>Key results</h3><p>Although species distribution models indicated suitable environmental conditions for the <em>Tetrastigma</em> host species in many parts of the Philippines, considerably fewer areas are inferred to have suitable conditions for the three <em>Rafflesia</em> 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.</p><h3>Conclusions</h3><p>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 <em>Rafflesia</em> species, rather than environmental requirements of their <em>Tetrastigma</em> host species.</p>