Spatial segregation of subordinate species is not controlled by the dominant species in a tropical coastal plant community

Abstract

Subordinate species composition and distribution are regarded as a result of the dominant species structure. However, the spatial organization of subordinate species can also be related to dispersal abilities and interactions (competition and facilitation) within subordinate species. Here, we tested the influence of dominant species on subordinate species and examined traits of subordinate species together with their spatial patterns within a tropical coastal plant community. We hypothesized that the identity of dominant species determines subordinate abundance, and dispersal and persistence trait values variation, within coexisting subordinate species. Moreover, we expected that functionally similar subordinate species aggregate in space, regarding these values. We used the relative abundance of shrubs and trees from 83 vegetation patches in 2ha of Restinga vegetation in southeastern Brazil. We determined trait value dissimilarities between dominant and subordinate species and within subordinates, and tested for the effect of the dominant species on subordinate abundance and trait values variation. Spatial cross-correlation functions were estimated for the four most abundant subordinate species with spline and Moran's I cross-correlograms. Our results showed that dominant and subordinate species exhibit contrasted trait values for dispersal and persistence. However, the composition of subordinate species in patches and the variation in their functional traits were not controlled by the identity of dominant species. Surprisingly, subordinate species segregated in space. Spatial segregation was related to dissimilar trait values within subordinates. However, the identity of dominants and patch size had no control over subordinates’ abundance. We suggest that such spatial segregation can result from competitive interactions. Dissimilar functional trait values within subordinate species seem to explain the spatial segregation of these species, principally led by differences in seed production and potential allelopathic interactions (e.g. Myrtaceae species). Therefore, independently of the identity of dominant species, subordinate species have a direct effect on the community composition of the Restinga vegetation. Together, our findings considerably increase knowledge on subordinate species in tropical plant communities and provide new insight into the potential role of subordinate species in community assembly.