The stochastic dilution hypothesis has been proposed to explain species coexistence in species-rich communities. The relative importance of the stochastic dilution effects with respect to other ...effects such as competition and habitat filtering required to be tested. In this study, using data from a 25-ha species-rich subtropical forest plot with a strong topographic structure at Badagongshan in central China, we analyzed overall species associations and fine-scale species interactions between 2,550 species pairs. The result showed that: (1) the proportion of segregation in overall species association analysis at 2 m neighborhood in this plot followed the prediction of the stochastic dilution hypothesis that segregations should decrease with species richness but that at 10 m neighborhood was higher than the prediction. (2) The proportion of no association type was lower than the expectation of stochastic dilution hypothesis. (3) Fine-scale species interaction analyses using Heterogeneous Poisson processes as null models revealed a high proportion (47%) of significant species effects. However, the assumption of separation of scale of this method was not fully met in this plot with a strong fine-scale topographic structure. We also found that for species within the same families, fine-scale positive species interactions occurred more frequently and negative ones occurred less frequently than expected by chance. These results suggested effects of environmental filtering other than species interaction in this forest. (4) We also found that arbor species showed a much higher proportion of significant fine-scale species interactions (66%) than shrub species (18%). We concluded that the stochastic dilution hypothesis only be partly supported and environmental filtering left discernible spatial signals in the spatial associations between species in this species-rich subtropical forest with a strong topographic structure.
Topography and space are two important factors determining plant species assemblages in forest communities. Quantification of the contribution of these two factors in determining species distribution ...helps us to evaluate their relative importance in determining species assemblages. This study aims to disentangle the effect of topography and space on the distributions of 14 dominant species in a subtropical mixed forest. Spearman correlation analysis and the torus-translation test were used to test the species–habitat associations. Variation partitioning was used to quantify the relative contributions of topography and space at three sampling scales and three life stages. Correlation analyses and torus-translation tests showed species abundance was mostly correlated with topographic wetness index, vertical distance from the channel network and convexity. Variation partitioning showed that pure topography, pure space and spatially structured topography explained about 2.1 %, 41.2 % and 13.8 % of the variation in species distributions, respectively. For nine species, total topography fractions peaked in 20 m quadrats. For ten species, the pure space fractions peaked in 50 m quadrats. For many species, the total topography fraction and the pure space fraction were larger for the most abundant life stages, which reflected the importance of sampling effect. However, some cases did not follow this trend suggesting that the effects of ecological processes such as habitat filtering, density dependence or dispersal limitation may exceed the sampling effects. In conclusion, we found that spatially structured topography and pure space primarily shaped the distribution of dominant tree species. Furthermore, their effects were both scale- and life stage-dependent.
Topographic and biotic factors determine forest biomass spatial distribution in a subtropical mountain moist forest Xu, Yaozhan; Scott B. FranklinauthorDepartment of Biological Sciences, University of Northern Colorado, Greeley, CO 80639, USA; Qinggang WangauthorKey Laboratory of Aquatic Botany and Watershed Ecology, Chinese Academy of Sciences, Wuhan 430074, ChinaDepartment of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China ...
2015
Journal Article
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