Explaining species diversity remains an essential pursuit for ecologists, yet the mechanisms allowing competing species to coexist are challenging to identify and investigate. Fluctuations in reproductive output can facilitate coexistence between competing species of long-lived organisms. The theoretical literature suggests that this mechanism, termed the “storage effect,” is likely to be important in numerous systems. Despite this potential, its role in promoting diversity has rarely been assessed in any specific systems. Here we propose to determine if the storage effect can explain the coexistence of tree species in the diverse tropical forest on Barro Colorado Island, Panama. This tropical forest has been monitored for more than thirty years and analysis of the data have already indicated that seed production between species is highly asynchronous, a primary requirement for the storage effect to facilitate coexistence among long-lived species. To determine if coexistence in this community could be maintained by recruitment fluctuations, we construct a model of tree dynamics that include species-specific recruitment through seed, seedling, and adult stages. We look for evidence of the storage effect in the BCI tree community using seedling production data in the model. We use a simulation to identify those species that potentially depend on the storage effect. We also develop a metric based on stochastic approximations of the model to quantify the relative strength of the storage effect and provide a community- wide summary.
Results/Conclusions
Simulations reveal that asynchronous recruitment can facilitate coexistence for large groups of species. The distribution of a community-wide competition metric indicates that inter-annual recruitment events are timed such that recruitment competition is low between the majority of tropical tree species. This research provides a general framework that can be used to look for evidence of the storage effect in other forest communities, a crucial step for understanding how important the storage effect is for maintaining coexistence among species.
