Distributions of Amazonian Melastomataceae Species Along a Soil Gradient

Abstract

We describe how abundance of a large number of Amazonian Melastomataceae species and morphospecies varies in relation to soil base cation concentration (Ca+Mg+K+Na), a variable that summarises the availability of three plant macronutrients. We used these results for testing several ecological hypotheses about species abundance, niche breadth, and niche optimum. We modelled the abundance of individuals of 205 species in 284 quantitative inventory transects with soil chemical data in Amazonian non-inundated rainforests. All Melastomataceae species except one were restricted to just a part of the observed soil gradient, with more species having their optima at low than at high base cation concentration. The most abundant species did not have wider niches than less abundant ones along the gradient, which challenges the idea that the most abundant rainforest plants are habitat generalists. For infrequent species, the optimum value estimates based on different transect subsets varied, but with a minimum of 20 sites the optima appeared reliable enough to allow inferring local soil base cation concentration. We provide information on niche characteristics of 81 such relatively frequent Melastomataceae species.