Comparison of a common and rare species of Mimosa (Mimosaceae) in Central Brazil

The aim of this study was to verify differences in the biology of a common widespread species (Mimosa claussenii Benth.) and three rare endemics (Mimosa decorticans Barneby, M. heringeri Barneby, and M. setosissima Taub.). We studied three populations of M. claussenii and one population of each rare species at four localities in central Brazil. We compared the population structure, phenology, fruit set, seed predation, germination, establishment and root/shoot ratio in these six populations. The endemic species occurred in higher densities and smaller individuals were more abundant. When in sympatry, the rare and common species showed a significant negative correlation of density. Mimosa claussenii occurred in drier and rocky environments, whereas M. decorticans and M. setosissima occurred in moister habitats. Rare species had higher levels of fruit set, more viable seeds per individual, and heavier seeds. Mimosa setosissima had the highest level of germination and establishment rate, but did not survive away from its endemism centre. The common species had a higher root/shoot ratio. Overall, the biological aspects studied indicated an advantage in reproductive biology for the rare in relation to the common species. The small geographical range of the rare species may be related to edaphic isolation and climatic changes in the Quaternary.