Phytogeography of New Guinean orchids: patterns of species richness and turnover

Aim The aims of this study were (1) to assess the spatial distribution of orchid species richness in New Guinea, and (2) to examine patterns of species turnover in the orchid community through phytogeographical regionalization. We aimed to achieve these goals using botanical collection records, species distribution models (SDMs) and partitioning around medoids (PAM) clustering. Location New Guinea, the Bismarck Archipelago and surrounding islands. Methods We combined 6760 collection records of 532 orchid species with 16 uncorrelated environmental predictor variables, to model species distributions at 5 arc-min resolution, using the presence-only modelling algorithm, Maxent. All SDMs were tested for significant deviation from random expectation using bias-corrected null models. The results from significant SDMs were stacked to create a map of orchid species richness. The same significant SDMs were used to derive phytogeographical regions through a PAM cluster analysis. Results Of the 532 modelled species distributions, 283 showed significantly stronger correlation with environmental conditions than expected by chance alone. It is inferred that the central mountain ranges of eastern New Guinea, including part of the Papuan Peninsula, harbour the highest levels of orchid species richness. The study area was divided into eight phytogeographical regions that maximized internal community similarity among orchids. Two of these regions are found almost exclusively in western New Guinea, while the remainder are more evenly distributed. Main conclusions Our study provides an objective assessment of the distribution of relative orchid species richness in New Guinea. The eight derived phytogeographical regions are largely consistent with existing knowledge of the island's internal biogeography. These findings give insight into one of the global hotspots of orchid diversity, and improve our understanding of the phytogeography of New Guinea.