The Influence of Microtopography and Soil Properties on the Distribution of the Speciose Genus of Trees,Inga (Fabaceae:Mimosoidea), in Ecuadorian Amazonia

In tropical forests, much of the plant diversity is due to a large number of congeneric taxa. It is unclear what ecological processes are responsible for the number and composition of co‐occurring species in these forests. Here, we present strong evidence that microhabitat heterogeneity may contribute to the coexistence of many different Inga species in just 100 ha. We examined their patterns of abundance and diversity in 75 transects related to the edaphic variables: soil water content, pH and soil texture at three different microtopographical units (ridges, slopes and valleys). We used two different approaches: Inga community level analyses and individual‐species analyses. Multivariate analyses, controlled for spatial autocorrelation, demonstrated that species show a distributional gradient mainly related to soil water content and to a lesser degree pH. Individual‐species analyses determined that obligate microhabitat restriction is uncommon: only 2 of 37 species analyzed were restricted to a single microhabitat. Habitat association analyses, however, identified a number of species characteristic of the ridge, slope and valley microhabitats. We conclude that the environmental setting plays an important role in the Inga community assembly but is not sufficient to explain the coexistence of 37 sympatric species at a single site.