Phylogenetic turnover patterns consistent with niche conservatism in montane plant species

Abstract

Summary A fundamental aim in community ecology is to elucidate the processes structuring communities. The key to understanding community patterns is to account for species differences and similarities in how they respond to large‐scale environmental gradients and partition local resources. Using phylogenetic relationships as a representation of species’ ecological differences, we use phylogenetic beta‐diversity (PBD) to examine how patterns of community relatedness change across space. Specifically, we examine how PBD informs our understanding of the processes (spatial or environmental) directing species assembly along montane environmental gradients – in particular, whether patterns are consistent with niche conservatism. Also, we examine the depth of phylogenetic turnover to see where in evolutionary history shared environmental tolerances appear conserved. For angiosperm communities situated to the east and west of the Continental Divide (CD) in the Rocky Mountain National Park in CO, USA, we compare nine beta‐diversity indices (taxonomic, TBD: Jaccard, Bray–Curtis and Gower; PBD: PhyloSor, UniFrac, Dnn, Dpw, Rao's D and Rao's H) to changes in space, environment and environment controlling for space with the partial PROTEST method. We find that PBD differs from taxonomic beta‐diversity and some PBD metrics were redundant with one another (i.e. Rao's D & Dpw and UniFrac & PhyloSor). The indices’ different sensitivities to evolutionary depth affected their responses to environmental and spatial gradients: TBD consistently associated greater with all factors (space, environment and environment controlled for space) than PBD metrics; PBD metrics more sensitive to recent changes were more highly correlated with all factors than those metrics sensitive to turnover deeper in the phylogeny. Generally, beta‐diversity associated strongest with environment and least with space. Synthesis. Taxonomic and phylogenetic beta‐diversity complements each other to provide an enhanced perspective of the process governing community structure. Together, they depict patterns expected under niche conservatism for the Rocky Mountain angiosperm communities, that is, species’ names change faster than their evolutionary relationships across space.