Natural enemies shape changes in plant diversity across a humidity gradient in central Panama

Tropical forests are extremely divers. Over 300 tree species can coexist in a single hectare and as many as 16,000 tree species may exist in the Amazon basin alone. Why are tropical forests so remarkably diverse? This is a key, unresolved question facing Ecology. One persistent explanation for plant species coexistence in tropical forests, the Janzen-Connell mechanism, postulates that density-dependent mortality mediated by fungal pathogens and insect herbivores, puts locally rare species at an advantage, preventing any one species from dominating. Evidence from vegetation plots suggests that this form of density-dependence plays a key role in the maintenance of plant diversity in the tropics.
Still, most theories explaining species coexistence emphasize on local processes, while one of the clearest and best-documented patterns in global plant diversity is the strong correlation between diversity and humidity at regional to global scales. While differential drought sensitivity is an important determinant of changes in plant species composition along humidity gradients, alternative mechanisms are needed to explain positive diversity-humidity correlations.
Here, we will show novel findings from a large field-based study in Central Panama where we tested whether humidity drives variations in tropical plant diversity through its influence on interactions between plants and their natural enemies.