Abstract
Niche-based and neutrality-based theories are two major classes of theories explaining the assembly mechanisms of local communities. Both theories have been frequently used to explain species diversity and composition in local communities but their relative importance remains unclear. Here, we analyzed 57 assemblages of angiosperm trees in 0.1-ha forest plots across China to examine the effects of environmental heterogeneity (relevant to niche-based processes) and spatial contingency (relevant to neutrality-based processes) on phylogenetic structure of angiosperm tree assemblages distributed across a wide range of environment and space. Phylogenetic structure was quantified with six phylogenetic metrics (i.e., phylogenetic diversity, mean pairwise distance, mean nearest taxon distance, and the standardized effect sizes of these three metrics), which emphasize on different depths of evolutionary histories and account for different degrees of species richness effects. Our results showed that the variation in phylogenetic metrics explained independently by environmental variables was on average much greater than that explained independently by spatial structure, and the vast majority of the variation in phylogenetic metrics was explained by spatially structured environmental variables. We conclude that niche-based processes have played a more important role than neutrality-based processes in driving phylogenetic structure of angiosperm tree species in forest communities in China.
Highlights
Species in a local community are a subset of those in the species pool of the region where the local community is located
If environmental filtering processes play a dominant role in structuring species assemblages, one would expect that the proportion of variation in community structure explained by environmental variables
If spatial contingency is a more important determinant of phylogenetic structure of the species assemblages, one would expect that the proportion of variation explained by spatial variables to be greater than that explained by environmental variables
Summary
Species in a local community are a subset of those in the species pool of the region where the local community is located. Niche-based theories suggest that deterministic processes (such as environmental filtering and species interactions) determine species composition of local communities[2, 3], whereas neutrality-based theories suggest that stochastic processes (such as historical processes that influence the species pool and dispersal limitations) determine the assembly of local communities[4]. Deterministic processes are expected to be strong drivers of community structure in harsh environments whereas stochastic processes may dominate in local communities with benign environmental conditions[8]. Empirical studies have found that spatial effects are important in regulating phylogenetic structure[21] because dispersal limitations alone can cause closely related species to occupy nearby sites, and environmental variables tend to have a strong spatial structure[22]. If spatial contingency is a more important determinant of phylogenetic structure of the species assemblages, one would expect that the proportion of variation explained by spatial variables to be greater than that explained by environmental variables
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