Conclusion
By comparing distribution patterns for plants families of Malesia, this study offers valuable insights on the mechanisms underlying elevational range-sizes of flora on tropical mountains and their potential response to changing environments. The synthesis of our findings is that long-term climate stability, in the sense of both centers of richness within lowland tropical forests as well as the consistently equatorial position of landmasses over millions of years, is linked to how much average range-sizes increase with elevation (ERR slope). Positive ERR slopes may indicate changes in ecological strategies, such as a shift from communities driven by biotic competition at lower elevations to ones that are more tolerant of abiotic stressors with increasing elevation. In contrast neutral, or even negative, ERR slopes may indicate directional expansion out of habitats with high abiotic variation, such as transitioning downward from montane habitats into lowland forests, or tectonic movement of landmasses towards the equator. Our findings indicate that lowland endemics of landmasses with consistent positioning near the equator (e.g. Sundaland) may be disproportionately at a higher risk of extinction as environmental conditions change and become more variable.