Biotic interactions and limitations to explain their effects on a neotropical savanna plant community

Abstract

Ecological communities result from the interaction of different sorts of biotic and abiotic processes. Here, we assess the effects of two target plants that show different interactions with their surrounding (neighborhood) vegetation, on species richness, abundance, and diversity of communities, to address the influence of different biological processes in the formation of a plant community. We compared communities of savannas in Central Brazil, South America, in plots with Hancornia speciosa or with Himatanthus obovatus (Apocynaceae), or none of them (Control plots). We analyzed the communities from different stratum (herb and woody) and with different species abundance (rare, common, and abundant). We used two cut-off methods to define classes of species abundance, one based on the number of individuals and other on the percentage of species sampled (quartile of abundances). We collected 16,979 individuals, representing 161 species and 48 families. Regardless of the cut-off method, communities with H. speciosa or H. obovatus showed more rare species than communities without them (Control plots). Our findings confirm the ecological effects of Hancornia speciosa and Himatanthus obovatus shaping the structure of surrounding vegetation. We also found that the cut-off methods for abundance classes directly influence our perception of the rare species composition in a community and, consequently, affects our interpretations about the dynamics that produce rarity. Thus, it is important that community studies justify the application of the cut-off method in the definition of rare species, according to their aims and the spatial scale in question.