Abstract
Traditionally, ecologists use lattice (regional summary) count data to simulate tree species distributions to explore species coexistence. However, no previous study has explicitly compared the difference between using lattice count and basal area data and analyzed species distributions at both individual species and community levels while simultaneously considering the combined scenarios of life stage and scale. In this study, we hypothesized that basal area data are more closely related to environmental variables than are count data because of strong environmental filtering effects. We also address the contribution of niche and the neutral (i.e., solely dependent on distance) factors to species distributions. Specifically, we separately modeled count data and basal area data while considering life stage and scale effects at the two levels with simultaneous autoregressive models and variation partitioning. A principal coordinates of neighbor matrix (PCNM) was used to model neutral spatial effects at the community level. The explained variations of species distribution data did not differ significantly between the two types of data at either the individual species level or the community level, indicating that the two types of data can be used nearly identically to model species distributions. Neutral spatial effects represented by spatial autoregressive parameters and the PCNM eigenfunctions drove species distributions on multiple scales, different life stages and individual species and community levels in this plot. We concluded that strong neutral spatial effects are the principal mechanisms underlying the species distributions and thus shape biodiversity spatial patterns.
Highlights
How large numbers of species coexist at a local scale (,1 km2) is a challenging question for ecologists
Without categorizing trees into different DBH classes, many studies have verified that neutral spatial effects are the principal determinants of species distribution patterns [18,36,37]. He et al [21] demonstrate that tree species distributions maintain aggregated patterns at all life stages, and we demonstrate here that neutral spatial effects are the dominant driver of tree species distributions throughout life stages
Our results show that environmental variables do contribute to the tree species distributions to some extent, but both simultaneous autoregressive (SAR) and variation partitioning analyses demonstrate that neutral spatial effects are dominant in this plot
Summary
How large numbers of species coexist at a local scale (,1 km2) is a challenging question for ecologists. With the rapid improvement of computer technology and statistical tools, itis feasible to integrate both niche and neutral processes into models to analyze species distribution data. Analytical methods, such as regression [1], ordination and machine learning, can be used to investigate the mechanisms underlying species coexistence [2,3]. Ecologists have used individual lattice count data to simulate species distributions at the individual species or community levels [4,5] In this method, trees are always counted as individuals regardless of factors such as age, size, branching and whether re-sprouting has occurred. The habitat associations of tree species may vary across life stages [6,7], and tree intensity variation across lattices may be insufficient to reflect species distribution patterns
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