黄河三角洲植物生态位和生态幅对物种分布-多度关系的解释

物种分布与多度间的正相关格局非常普遍，但该格局的生态机制却一直不太明确。研究者提出了很多假说来解释这种分布-多度关系，其中物种的生态幅和生态位（资源可利用性）机制的研究较多。为了验证物种的生态幅和生态位是否能解释物种的多度-分布格局，本文研究了黄河三角洲地区湿地植物分布、多度、生态位和生态幅间的关系，结果表明：该区物种分布与多度呈显著正相关，且均与生态幅显著正相关，物种分布与生态位显著负相关，但物种多度与生态位相关性不显著。这说明物种的分布越广，其多度越高，环境容忍度越大；而可利用资源更多的物种分布更广，环境容忍度越大的物种多度越多，资源可利用性对该区物种多度影响不大。本研究说明物种生态幅能解释物种分布-多度正相关格局，而生态位假说不能很好的解释这一格局；应该还有其他因素一起解释这一物种分布-多度正相关格局。

Explaining the abundance-distribution relationship of plant species with niche breadth and position in the Yellow River Delta

Species abundance and distribution are often correlated, such that the positive abundance-distribution pattern means the widespread species tend to be abundant, and narrowly distributed species rare. Several hypotheses have been proposed to explain the positive relationship between abundance and distribution, but the mechanisms behind this pattern still remain poorly understood. Among these hypotheses, the niche breadth and the niche position (or habitat availability) hypothesis are the most investigated, since the niche-based model predicts that both distribution and abundance mirror the degree to which local environmental conditions meet the requirements of species. We used outlying mean index to measure the niche position and the niche breadth of each species in the 436 quadrats collected in the three estuaries of the Yellow River Delta. The distribution of each species was represented as the number of sites occupied. We tested the relationship between the distribution and abundance of plant species with a specific aim to examine if this relationship follows the mechanistic basis of the niche-based (niche breadth and niche position) hypothesis. We estimated the relationship using ordinary least-squares regressions. There was a significant positive relationship (R2a=0.75) between the distribution and abundance of the plant species. We found a significant positive relationship between the niche breadth and abundance, and the regional distribution. The niche breadth explained 19% of the variation in abundance but 42% of the variation in distribution. There was a significant negative relationship between the distribution and the niche position, but the relationship between the abundance and the niche position was not significant. The niche position explained 46% of the variation in distribution. These results suggest that some widely distributed species tend to be, on average, locally abundant, and have wider niche breadth and lower marginality of niche position with regard to the environmental factors than the species that have more restricted distributions. When the relationship was significant, both the niche position and the niche breadth explained less than half of the variation in abundance and distribution, this suggests that not only niche-based processes, but also other mechanisms are likely to act in concert in determining the relationship between distribution and abundance of the plant species. Although there was some unexplained variability around the relationship, the niche breadth was more consistently related to the positive abundance-distribution relationship than the niche position. The positive pattern generally exhibited by the abundance-distribution relationships, has consequences for several areas of applied ecology, including conservation, harvesting, biological invasions and biodiversity inventory.