DOI: 10.5061/dryad.n02v6wwvx
title: Rare tree species have narrow environmental but not functional niches

description: 1. The majority of species in many communities are rare, and it is an
 enduring challenge to understand the mechanism of species rarity and
 commonness in local communities. The niche partitioning hypotheses posit
 that common species occupy wide and core positions, while rare species
 occupy narrow and outlying niche positions. We test these hypotheses here,
 simultaneously considering both an environmental and a functional
 perspective on niches. 2. We examined how niches correlate with species
 abundance in environmental and functional space by quantifying
 relationships between species abundance and niche width and niche
 position. Environmental niches were defined as the section of an
 environmental gradient where each species occurred, and functional niches
 using species traits thought to be related to resource acquisition.
 Hypotheses were tested using a dataset including functional traits
 collected from 4302 individual trees of 423 species and environmental data
 in one subtropical and one tropical forest in China. 3. Consistent with
 the niche partitioning hypotheses, rare species in our two study systems
 tended to occupy the edges of the functional and environmental niche
 space. This likely allows rare species to avoid competition from dominant
 species. On the other hand, rare species tended to have a similar or
 larger niche width than common species in functional space, which
 contrasts with their narrower niche width in environmental space. 4.
 Synthesis. Our results support the prediction that rare species occupy
 outlying niches to avoid competition with common species. We found
 inconsistent evidence, though, about the niche width of rare species. Rare
 species may be less constrained in functional space, and persist by dint
 of their functional lability and ability to use a variety of resources.
 Our work supports previously hypothesized mechanisms underlying local
 species abundance patterns, but highlights new idiosyncrasies when
 considering environmental niche or functional space alone.
description: This dataset was collected within two forest dynamic plots (FDP)
 in Zhejiang Province, southeastern China, and Yunnan Province,
 southwestern China. One plot, Gutianshan forest dynamics plot, was
 composed of subtropical broadleaved evergreen forest and the other
 (Xishuangbanna forest dynamics plot) was a tropical seasonal
 rainforest. In the Gutianshan plot, we measured four traits, specific leaf
 area, leaf area, leaf nitrogen content and leaf phosphorous content
 of 2,127 individuals belonging to 110 species. In Xishuanbanna plot, we
 sampled four leaf traits, which included specific leaf area, leaf area,
 leaf dry matter content and leaf thickness of 2175 individual trees
 belonging to 313 species.  We quantified niche width and position in the
 environmental hyperspace using ecological niche factor analysis
 (Hirzel<i> et al.</i> 2002), while we
 quantified niche width and position for individual traits, as well as for
 all traits combined in fucntional space using methods
 from Umaña<i> et
 al.</i> (2015). 
description: This dataset could be available after the paper is
 published.