Phylogenetic structure of moth communities (Geometridae, Lepidoptera) along a complete rainforest elevational gradient in Papua New Guinea

Abstract

We use community phylogenetics to elucidate the community assembly mechanisms for Geometridae moths (Lepidoptera) collected along a complete rainforest elevational gradient (200-3700 m a.s.l) on Mount Wilhelm in Papua New Guinea. A constrained phylogeny based on COI barcodes for 604 species was used to analyse 1390 species x elevation occurrences at eight elevational sites separated by 500 m elevation increments. We obtained Nearest Relatedness Index (NRI), Nearest Taxon Index (NTI) and Standardised Effect Size of Faith's Phylogenetic Diversity (SES.PD) and regressed these on temperature, plant species richness and predator abundance as key abiotic and biotic predictors. We also quantified beta diversity in the moth communities between elevations using the Phylogenetic Sorensen index. Overall, geometrid communities exhibited phylogenetic clustering, suggesting environmental filters, particularly at higher elevations at and above 2200 m a.s.l and no evidence of overdispersion. NRI, NTI and SES.PD showed no consistent trends with elevation or the studied biotic and abiotic variables. Change in community structure was driven by turnover of phylogenetic beta-diversity, except for the highest 2700-3200 m elevations, which were characterised by nested subsets of lower elevation communities. Overall, the elevational signal of geometrid phylogeny was weak-moderate. Additional insect community phylogeny studies are needed to understand this pattern.

Fig 1. Wilhelm elevational gradient with eight study sites at 500 m elevational increments from 200 to 3700 m a.s.l (blue to red).

The Mt. Insert: Map of Papua New Guinea with Mt. Wilhelm study area shown in red square. Reprinted from Moses et al. [36] under a CC BY licence, with permission from Jimmy Moses, original copyright 2021.

Fig 2

Species richness (A) and Faith’s phylogenetic diversity (B) of Geometridae moth communities along Mt. Wilhelm elevational gradient. Y-axis are observed species richness (A) and Faith’s PD (B) both fitted with second order linear model function with elevation as an explanatory variable.

Fig 3

Phylogenetic structure of geometrid moths on Mt. Wilhelm elevational gradient based on NRI (A), NTI (B) and SES.PD (C). In each plot, the horizontal dashed lines at 1.96 and -1.96 demarcated area of randomly distributed communities while the sites ≥1.96 show phylogenetic clustering (NRI, NTI) or low phylogenetic diversity (SES.PD) and the sites ≤-1.96-line indicated phylogenetic over-dispersion (NRI, NTI) or high phylogenetic diversity (SES.PD). NRI = Nearest relatedness index, NTI = Nearest taxon index, SES.PD = Standardised effect size of Faith’s PD.

Fig 4

Sorensen measure of community dissimilarity (A) and Phylogenetic Sorensen beta-diversity (B) among the eight geometrid communities on Mt. Wilhelm transect. The values range from 0 for highly similar (blue squares) to 1 for dissimilar (yellow squares) paired communities.