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Abstract
The mechanisms driving the spatial patterns of species richness and composition are essential to the understanding of biodiversity. Numerous studies separately identify the contributions of the environment (niche process) and space (neutral process) to the species richness or composition at different scales, but few studies have investigated the contributions of both types of processes in the two types of data at the landscape scale. In this study, we partitioned the spatial variations in all, exotic and native understory plant species richness and composition constrained by environmental variables and space in 134 plots that were spread across 10 counties in Hainan Island in southern China. The 134 plots included 70 rubber (Hevea brasiliensis) plantation plots, 50 eucalyptus (Eucalyptus urophylla) plantation plots, and 14 secondary forest plots. RDA based variation partitioning was run to assess the contribution of environment and space to species richness and composition. The results showed that the environmental variables alone explained a large proportion of the variations in both the species richness and composition of all, native, and exotic species. The RDA results indicated that overstory composition (forest type here) plays a leading role in determining species richness and composition patterns. The alpha and beta diversities of the secondary forest plots were markedly higher than that of the two plantations. In conclusion, niche differentiation processes are the principal mechanisms that shape the alpha and beta diversities of understory plant species in Hainan Island.
Highlights
Understanding how the number of species and species composition vary from place to place is pivotal to explaining the maintenance of biodiversity [1,2]
The most abundant species in the rubber plantation was Acroceras munroanum, which is a native species of Hainan Island
Through separate variation partitioning with redundancy analysis (RDA) on the composition data of exotic and native species between the environmental variables and the principal coordinates of neighbor matrices eigenfunctions (PCNMs), we found that the environmental variables always outperform the PCNMs (Figure S6)
Summary
Understanding how the number of species (richness) and species composition vary from place to place is pivotal to explaining the maintenance of biodiversity [1,2]. Many studies have investigated the mechanisms underlying the patterns of species richness [3], but the forces that determine the patterns of species composition, key to understanding ecosystem function, conservation, and management [4], have not been systematically explored [1]. This scenario did not change until recently in response to the neutral theory raised by Hubbell [5]. Legendre et al [7] analyzed the contributions of topography and space to the spatial patterns in the richness and composition of tree species in a 24-ha subtropical forest plot at the local scale (
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