Contents lists available at ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon Multiple facets of rarity among rain forest trees in the Western Ghats of India Priya Davidar a,d, ⁎ , François Munoz b,c , Jean-Philippe Puyravaud d , D. Mohandass a , V.S. Ramachandran e a Department of Ecology & Environmental Sciences, Pondicherry University, Kalapet, Pondicherry 605014, India b Université Grenoble Alpes, Laboratoire d'Écologie Alpine, 38000 Grenoble, France c French Institute of Pondicherry, 11 St Louis Street, Pondicherry 605001, India d Sigur Nature Trust, Mavinhalla PO, Nilgiris 643223, Tamil Nadu, India e Centre for Environmental Studies, Amrita Vishwa Vidyapeetham, Ettimadai, Coimbatore 641112, India ARTICLE INFO Keywords: Endemism India IUCN Rain forest Rarity Trees Western Ghats ABSTRACT We collated data on the latitudinal, elevation and seasonality ranges, local densities, stature and dispersal mode of 514 evergreen tree species (≥10 cm girth at breast height), including 317 endemics, from the rain forests of the Western Ghats (WG) of India using two complementary databases, (i) 68 tree inventory plots, and (ii) the Atlas of Endemics. We tested the hypotheses that (i) regional rarity would be associated with local rarity and narrower ecological amplitudes, (ii) shorter and mechanically dispersed trees would be rarer, (iii) higher pro- portion of endemic species would be rare (iv) regionally wide ranging species would be locally rare, and lo- calised species would be denser, (v) families with single species would be relicts in this biome, (vi) larger families would have a higher proportion of rare and endemic species. We used Atlas records in a generalised least square model acknowledging phylogenetic relationships, to test hypotheses (i) to (ii), and non parametric tests for (iii) to (vi). We identifed rare species using binary cut-ofs and compared these with IUCN threat status. Rarity was associated with (i) narrower ecological amplitudes and shorter stature, independent of phylogeny, (ii) 18 wide ranging and locally sparse, 41 narrow ranging and locally dense species, (iii) relict species and families, (iv) larger families. Rare species were more likely to be threatened, but 39% were not evaluated. We identifed zones of rare endemics to help with conservation planning. The WG rain forests have a unique evolutionary history and potential that require increased conservation measures. 1. Introduction Rarity is a multifaceted, scale-dependent concept involving local abundance, regional distribution and niche breadth (Rabinowitz, 1981; Hartley and Kunin, 2003; Boulangeat et al., 2012; Slatyer et al., 2013), and lies at the cross-roads of community assembly, biogeography and evolution (Chesson and Warner, 1981; Hubbell and Foster, 1986a; Vermeij and Grosberg, 2018). Species rarity is of major interest for biological conservation (Gaston, 1994), as in general, species with low abundances (local rarity) and restricted distribution (regional rarity) tend to be more vulnerable to extinction than those that are numerous and widespread (Terborgh and Winter, 1980). The issue is especially crucial in tropical rainforests where most tree species are rare, both locally and regionally (Hubbell and Foster, 1986b; Gentry, 1988; Slik et al., 2015). However, the causes and consequences of pervasive rarity among tropical trees are still unknown (Leigh Jr et al., 2004), and the relative impact of diferent mechanisms is still unclear (May et al., 2016). Understanding the processes underlying commonness and rarity is needed to design efcient conservation and management strategies. Two basic kinds of ecological processes can explain rarity de- pending on local adaptation and spatial dynamics: frstly, locally rare species can be regionally rare due to environmental limitation and niche specialization (Brown, 1984; Gaston, 1994; Boulangeat et al., 2012; Slatyer et al., 2013), secondly rarity can result from a balance between local survival and colonization dynamics, irrespective of a variation in ecological specialization across species (Hubbell et al., 1999; Hubbell, 2001). Species could also be sparse at the margins of their geographical distribution, being sink populations for which mor- tality is higher than natality but immigration maintains occurrence (Hanski, 1982; Brown, 1984). The evolution of biological properties could have allowed adapta- tion to diferent niches and entailed a variation of local and regional rarity across lineages (Ricklefs and Renner, 2012). Recent empirical evidence also suggests that locally rare tree species are functionally https://doi.org/10.1016/j.biocon.2018.10.014 Received 19 August 2017; Received in revised form 7 August 2018; Accepted 8 October 2018 ⁎ Corresponding author at: Department of Ecology & Environmental Sciences, Pondicherry University, Kalapet, Pondicherry 605014, India. E-mail addresses: pdavidar.ees@pondiuni.edu.in (P. Davidar), fmunoz@univ-grenoble-alpes.fr (F. Munoz). Biological Conservation 228 (2018) 110–119 0006-3207/ © 2018 Elsevier Ltd. All rights reserved. T