Species abundance-Cdistribution relationship and its interpretation in plant communities on the Songnen grasslands, China

Abstract

* Key Laboratory of Vegetation Ecology, Ministry of Education, Institute of Grassland Science, Northeast Normal Univer- sity, Changchun 130024 Abstract: The species abundance-distribution relationship (SAD) is a key issue in biodiversity science, yet there is no consensus about the mechanism that shape the SAD. The two most widely-recognized explana- tions are Brown's niche breadth hypothesis and metapopulation dynamics theory. To test these two hypothe- ses on the Songnen grasslands, we investigated plant species growth-form composition and interpatch dis- tance in Leymus chinensis-forb community patches in 2007 and 2008. We employed a growth-form adaption index (GAI), a measure of species adaptation, as a surrogate for species niche breadth and employed shortest distance to nearest patch to indicate the dispersal and colonization process of plant species. Two-year data showed that a species' local abundance was positively correlated with this species' regional distribution. Fur- thermore, the SAD showed no obvious variation among years. Both abundance and distribution of a species were closely correlated with plant growth-form; species with higher abundance and wider distributions were mainly comprised of rhizomatous root, erect grass-like stem, or erect dicot stem growth forms. By contrast, species with lower abundance and narrow distributions were mainly comprised of basal rosette stem or bushy root growth forms. GAI was both positively and linearly correlated with abundance and distribution of a spe- cies. A few species were distributed widely, whereas most species were distributed more narrowly. This result directly supports the niche breadth hypothesis. Shortest distance to nearest patch exhibited a negative pow- er-law correlation with both abundance and distribution of a species, whereas no correlation was detected between species composition similarity index and distance of patch pairs, results which failed to support the metapopulation dynamic theory. We argue that dispersal processes may be an important potential mechanism