Trait Dissimilarity and Hierarchy Predict Spatial Co-occurrence Patterns
of Tree Species in a Subtropical Forest
Abstract
1. The dissimilarity and hierarchy of trait values that characterize
niche and fitness differences, respectively, have been increasingly
applied to infer mechanisms driving community assembly and to explain
species co-occurrence patterns. Here, we predict that limiting
similarity should result in the spatial segregation of functionally
similar species, while functionally similar species will be more likely
to co-occur together either due to environmental filtering or
competitive exclusion of inferior competitors (hereafter hierarchical
competition). 2. We used a fully mapped 50-ha subtropical forest plot in
southern China to explore how pairwise spatial associations were
influenced by trait dissimilarity and hierarchy between species in order
to gain insight into assembly mechanisms. We assessed pairwise spatial
associations using two summary statistics of spatial point patterns at
different spatial scales and compared the effects of trait dissimilarity
and trait hierarchy of different functional traits on the interspecific
spatial associations. These comparisons allow us to disentangle the
effects of limiting similarity, environmental filtering and hierarchical
competition on species co-occurrence. 3. We found that trait
dissimilarity was generally negatively correlated with interspecific
spatial associations, meaning that species with similar trait values
were more likely to co-occur together and thus supporting environmental
filtering or hierarchical competition. We further found that leaf area,
wood density and maximum height had stronger trait hierarchy effects on
the pairwise spatial associations relative to their corresponding trait
dissimilarity effects, which suggests that hierarchical competition
played a more (or at least equally) important role in structuring our
forest community compared to environmental filtering. 4. This study
employed a novel method to disentangle the relative importance of
multiple assembly mechanisms in structuring co-occurrence patterns,
especially the mechanisms of environmental filtering and hierarchical
competition, which lead to indistinguishable co-occurrence patterns.
This study also reinforced the importance of trait hierarchy rather than
trait dissimilarity in driving neighborhood competition.