Competitive interactions between tropical trees

Background/Question/Methods

Species coexistence in the highly diverse tropical forests poses a considerable challenge to ecologists. Functional traits and phylogenetic relationships of co-occurring species provide the opportunity to distinguish the signatures of stochastic and deterministic assembly processes in communities. However, as multiple processes can produce similar patterns of community composition, it remains difficult to implicate one particular mechanism. A promising way towards a more mechanistic understanding of the processes shaping communities is to quantify the linkage between individual performance and its local neighborhood.

Combining demographic data from a lowland rainforest 50 ha plot in Ecuador with six functional traits and phylogeny for ca. 1100 tropical tree species, we use spatially-explicit neighborhood models to quantify the relative importance of functional similarity and phylogenetic relatedness in predicting the effects of competitive interactions between tropical tree species on growth rate. For each species, we estimate model parameters using maximum likelihood and compare alternate models using the Aikake Information Criterion corrected for small sample size.

Results/Conclusions

The importance of competitive interactions on growth rate varies across tropical tree species. Among the most abundant species in the plot, we find that some species are insensitive to neighborhood effects, while other species are strongly affected by the functional similarity of neighbors. Exploring the relationship between maximum growth rate and functional traits across tropical tree species, we show that maximum growth rate strongly correlates with several traits including leaf size. These results suggest that the relative influence of competitive interactions on growth vary with species temperament. Combining demographic processes and functional traits, our study provides a better understanding of the ecological mechanisms underlying species coexistence in the hyper diverse tropical forests.