Community Phylogenetics in Tropical Rainforests

Abstract

Community phylogenetics examines the evolutionary relationships among species co-occurring within ecological assemblages, revealing how historical diversification and present-day environmental filtering jointly structure biodiversity. Tropical rainforests, which harbour more than 50% of terrestrial species despite covering less than 7% of Earth's land surface, represent ideal systems for community phylogenetic analysis because of their exceptional species richness, complex vertical stratification, and long evolutionary histories. This study quantified community phylogenetic structure across 48 one-hectare plots distributed along elevational gradients (200-2,800 m a.s.l.) in three Neotropical rainforest regions: the Colombian Choco, the Peruvian Amazon, and the Atlantic Forest of Brazil. Using a time-calibrated molecular phylogeny encompassing 1,847 vertebrate and arthropod species, we computed net relatedness index (NRI), nearest taxon index (NTI), and phylogenetic diversity (PD) metrics for each plot. Lowland communities exhibited significant phylogenetic overdispersion (mean NRI = -2.14 +- 0.87), consistent with competitive exclusion as the primary assembly process. Montane communities above 1,800 m showed phylogenetic clustering (mean NRI = +1.98 +- 0.74), indicative of strong environmental filtering. Phylogenetic diversity peaked at mid-elevations (1,000-1,400 m) and correlated positively with rainfall seasonality (r = 0.73, p < 0.001) and negatively with temperature variability (r = -0.61, p < 0.001). Land-use intensity significantly eroded phylogenetic diversity across all elevations, with logged forests retaining only 68.4% of old-growth PD values. These findings provide empirical support for dual-filter assembly theory and identify mid-elevation zones as phylogenetic diversity hotspots warranting priority conservation attention.