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Commonness patterns and the size of the species pool along a tropical elevational gradient: insights using a new quantitative tool


G. Arellano, Depto de Biodiversidad y Conservación, Real Jardín Botánico, CSIC, Plaza de Murillo 2, ES-28014 Madrid, Spain, and Depto de Biología, Área de Botánica, Univ. Autónoma de Madrid, Calle Darwin 2, ES-28049 Madrid, Spain. E-mail:


The goal of this study was a quantitative assessment of two-dimensional commonness in the lowland, dry, and montane tropical forests of the Madidi region (Bolivia). This region spans a large elevational and environmental gradient, with great diversity differences among sites. We aimed to correlate commonness patterns at different scales with elevation and with the size of the species pool. We also developed 1) a measure of ecological commonness and 2) a criterion to separate common from uncommon species; both based on the h index of academic productivity. With this approach, we calculated the 1) mean commonness of all species of the community; 2) proportion of common species of the community; and 3) mean commonness of the common species. The results showed that the commonness patterns in the Madidi region are strongly linked to the size of the species pool, independently of the environmental heterogeneity involved and the type of forest and spatial scale considered. Although these factors do not affect the general quality of the community, they do influence differences in commonness among species. Overall, we identified strong support for the oligarchy hypothesis, regardless of the strength of the pattern, and conclude that a quantitative approach to commonness could lead to great insights into community structure.