Altitude as environmental filtering influencing phylogenetic diversity and species richness of plants in tropical mountains

Elucidating how multiple factors affect biodiversity and plant community assembly is a central issue in ecology, especially in vulnerable ecosystems such as tropical mountains. These studies are more relevant in global warming scenarios that induce the upward displacement of plant species towards reduced habitats and hostile environments in tropical mountains. This study aimed to analyze how altitude affects taxonomic and phylogenetic diversity in plant communities of tropical mountains. Thus, we tested if (i) increased altitude works as an environmental filtering promoting decreased species richness, decreased phylogenetic diversity, and increased phylogenetic clustering in these tropical mountains; and if (ii) plant communities of high altitude in tropical mountains are also result of recent diversification with plant species recently split shortening phylogenetic distances between closest related species. We tested effects of altitude on species richness and phylogenetic metrics using linear mixed-effects models. Mount Haleakala presented 114 species, Mount Kilimanjaro presented 231 species and Mount Purace presented 280 species. We found an environmental filtering effect with increasing altitude causing phylogenetic clustering, decreased phylogenetic diversity and decreased species richness. The decreasing phylogenetic distances between closest relatives are congruent with neo-endemics, suggesting recent plant diversification in high altitudes of tropical mountains, possibly driven by geographic isolation and environmental heterogeneity. Consequences of global warming should be monitored in tropical mountains focusing on distribution shifts.