尺度与密度:测定不同尺度下的种群密度

Scale and density: measuring local neighborhood density at different spatial scales

群落中的种群密度由于空间尺度的变化而存在着一定差异,那么,某一种群的密度随着空间尺度的变化会发生怎样的变化?抑或某一物种相对于另一物种而言,随着空间尺度的变化其密度会怎样变化?这是与尺度有关的种群密度问题,当属生态学的基本问题。该文提出这样的问题,并把不同尺度下的种群密度称之为尺度密度(scale density)。O-Ring函数的实质是计算不同尺度下的种群密度。因此,在研究实例中,应用O-Ring函数计算了典型草原处于不同恢复阶段的羊草(Leymus chinensis)种群、米氏冰草(Agropyron michnoi)种群,以及米氏冰草种群相对于羊草种群在不同尺度下的种群密度,结果发现:羊草和米氏冰草2个种群的尺度密度,在小尺度范围内严重退化群落均高于恢复演替群落,这一结果验证了"胁迫梯度假说",同时表明该结果是放牧胁迫下正相互作用所致;通过比较羊草种群与米氏冰草相对于羊草的尺度密度发现,在严重退化的群落中,羊草与米氏冰草的种间关联为负联结,这种负联结是由正相互作用引起的,而在恢复8年和恢复21年群落中,二者之间是正联结,当为竞争所致。该实例说明分析种群密度随尺度变化的规律对于深入认识生态学问题可能会有很大帮助。

Aims Population density changes with spatial scales in plant communities. Surprisingly, few previous studies explored this theme, despite the possibility that variation in density with spatial scales should be significant for detecting ecological phenomena and answering ecological problems. In this study, we call variation in density with spatial scales （the local neighborhood density at different spatial scales） as scale density. Methods O-Ring function can measure the local neighborhood density at different spatial scales. We used it to measure scale densities of Leymus chinensis, Agropyron michnoi and A. michnoi relative to L. chinensis in differ-ent restorative successional stages in steppe community in Inner Mongolia. Important findings Local densities of two populations （L. chinensis and A. michnoi） were both higher in a de-graded community than the other two restoration communities, which demonstrated the ＂stress gradient hypothe-sis＂ and further illustrated that the ecological phenomena were induced by facilitation. By comparing the scale densities of L. chinensis and A. michnoi relative to L. chinensis, we found that L. chinensis and A. michnoi were negatively associated as induced by facilitation in a degraded community, and positively associated as induced by competition in the other two restoration communities. Findings illustrate that analyzing the variation in the popu-lation density with spatial scales in plant communities is valuable in ecology.