It has long been recognized that rare species have increased risk of extinction, and it is an enduring challenge to understand how rare species simultaneously prevent competition exclusion and maintain their long-term population stability. Rare species might avoid competition from common species by using outlying niche position or narrow niche width. However, these competition avoidance strategies will lead to exceptional extinction risk that outlying niche positions could support only low populations and narrow niche width means that all or most individuals will suffer adverse conditions simultaneously. To maintain their population and coexist with common species, do rare species have predictably different niche from those envisaged by position hypothesis or niche width hypothesis? So far, we we found no studies explored mechanisms of rare species persistence from both perspectives of environmental and functional niche. To test these predictions of niche position hypothesis and niche width hypothesis, we compiled a dataset including functional traits collected from 5920 individual trees of 563 species and environmental data in four forests from temperate, subtropical and tropical forests in China.
Results/Conclusions
In four forests, species abundance was found to be negatively correlated with niche marginality (the deviation of niche position of a focus species from average niche position of all species in a community) in environmental and functional niche space. This suggested that rare species tend to occupy marginal position in both environmental and niche space. Species abundance was positively correlated with environmental niche width, but negatively correlated or was different from chance with functional niche width. This result suggested that rare species utilize a limited range of habitats, but exploit similar or larger functional space compared with common species. Our results demonstrate that rare species could avoid competition in environmental niche space, while they exploit larger or similar functional space unconstrained by those limiting environmental variables. We propose that the persistence of rare species could not be fully explained by environmental or functional niche alone.