Local spatial variation in the population dynamics of two tree species in a region of Atlantic Rainforest, SE Brazil

Abstract

The population dynamics of species with distinct geographic distribution ranges and local abundances can be differently influenced by environmental differences at both the regional and local scales. Here, we test for local spatial variation in the dynamics of different populations of two tree species with these distinct characteristics. We took advantage of one population census and carried out a new census of two populations of Faramea picinguabae M.Gomes (Rubiaceae) and Mollinedia schottiana (Spreng.) Perkins (Monimiaceae) at two non-contiguous, permanent 1-ha plots (B and E) located at a region of Atlantic Rainforest, SE Brazil. The plots differed in declivity and soil coverage by rocky boulders. The annual population growth rate (λ) differed only for F. picinguabae (λB = 1.009, λE = 0.959), which presents restricted geographic distribution range and low local abundance in relation to M. schottiana (λB = 0.982, λE = 0.987). The decline in three out of four populations may result from a severe drought in SE Brazil in the last decade. The increase in F. picinguabae at plot B is likely a response to the lower soil coverage by rocky boulders at this plot. Even though we evaluated only two populations of two species, our conclusions open a new venue for the investigation of population dynamics. Within the same forest, some species might show spatial variation in population dynamics mediated by environmental differences at the local scale, while others might not. In the long term, differences among species are likely to result in important changes in community structure and dynamics, as well as in ecosystem functions.