Phylogenetic diversity patterns in Himalayan forests reveal evidence for environmental filtering of distinct lineages

Abstract

Abstract. Large-scale environmental gradients have been invaluable for unraveling the processes shaping the evolution and maintenance of biodiversity. Environmental gradients provide a natural setting to test theories about species diversity and distributions within a landscape with changing biotic and abiotic interactions. Elevational gradients are particularly useful because they often encompass a large climatic range within a small geographical extent. Here, we analyzed tree communities in plots located throughout Arunachal Pradesh, a province in northeast India located on the southern face of the Eastern Himalayas, representing one of the largest elevational gradients in the world. Using indices of species and phylogenetic diversity, we described shifts in community structure across the landscape and explored the putative biotic and abiotic forces influencing species assembly. As expected, species richness and phylogenetic diversity decreased with increasing elevation; however, contrary to predictions of environmental filtering, species relatedness did not show any clear trend. Nonetheless, patterns of beta diversity (both taxonomic and phylogenetic) strongly suggest lineage filtering along the elevational gradient. Our results may be explained if filtering is driving the assembly of species from distinct evolutionary lineages. New metrics exploring community contributions to regional taxonomic and phylogenetic beta diversity provided additional evidence for the persistence of unique communities at high elevations. We suggest that these patterns may be consistent with filtering on glacial relicts, part of once more diverse clades with convergent traits suited to climates at the last glacial maximum, resulting in random or over-dispersed community assemblages at high elevations. We propose that these high-elevation sites with evolutionarily distinct species represent possible regions for conservation priority that may provide refugia for species threatened by current warming trends.

Plant species richness across the Himalaya driven by evolutionary history and current climate

“…5). By contrast, Shooner et al (2018) found a weak tendency for trees sampled on 500-to 5000-m 2 plots in Arunachal Pradesh to be more phylogenetically clustered at low elevations. Seemingly contradicting this finding, fieldwork in the eastern Himalaya has shown that in small plots, herbs peak at the point where shrubs decline (Bhatta et al 2018); we also found that the decline in herbs shallows at this point (Fig.…”

“…Yan et al (2013) presented an analysis of the adjacent Qinghai-Tibetan Plateau, most of which lies above 4000 m, but they included a section adjacent to northeast India that extends below 1000 m. They found a general increase in clustering with elevation, but at a slower rate at mid-elevations. By contrast, Shooner et al (2018) found a weak tendency for trees sampled on 500-to 5000-m 2 plots in Arunachal Pradesh to be more phylogenetically clustered at low elevations. Our findings may reconcile these observations because we show clustering does not monotonically increase from the lowest to highest elevations.…”

“…A possible issue is the impact of human disturbance, especially recent disturbance, on species distributions. This may be more of a problem when analyses are based on sampling of local sites (Carpenter 2005, Shooner et al 2018, Rana et al 2019. Here, we base our analysis on compilations of entire regions based on compiled records over more than 100 yr.…”

A multifaceted approach to analyzing taxonomic, functional, and phylogenetic β diversity

“…As far as we are aware, the extension proposed in this work is the most general in literature, because other similar propositions that seek to expand the Legendre and De Cáceres framework lack some important characteristics presented in the original proposition. Shooner et al (2018) proposed a phylogenetic informed LCBD (also called PLCBD) by using a phylogenetic distance matrix containing PhyloSor values (Bryant et al 2008) for calculating phylogenetic local contribution of sites. Because the use of a phylogenetic distance matrix among sites only allows BD to be decomposed into the local contribution component, it is not possible to obtain the portion of BD that accounts for species contribution to the total variation of the metacommunity (SCBD component).…”

Plant community responses to environmentally friendly piste management in northeast Iran

“…The zero order of phylogenetic Hill diversity of the two areas is similar (Figure ). This finding may be due to the intensive grazing history, or the unfavorable climate conditions of the areas—the presence of strong environmental filtering in two landscapes leads to similar phylogenetic community composition (Shooner et al, ). In short‐term, EFPM howsoever could not lead to the improvement of plant phylogenetic richness.…”