Résumé
Convergence occurs in both species traits and community structure, but how
convergence at the two scales influences each other remains unclear. To
address this question, we focus on tropical forest monodominance, in which
a single, often ectomycorrhizal (EM) tree species occasionally dominates
forest stands within a landscape otherwise characterized by diverse
communities of arbuscular mycorrhizal (AM) trees. Such monodominance is a
striking potential example of community divergence resulting in
alternative stable states. However, it is observed only in some tropical
regions. A diverse suite of AM and EM trees locally codominate forest
stands elsewhere. We develop a hypothesis to explain this geographical
difference using a simulation model of plant community assembly.
Simulation results suggest that in a region with a few EM species (e.g.,
South America), EM trees experience strong selection for convergent traits
that match the abiotic conditions of the environment. Consequently, EM
species successfully compete against other species to form monodominant
stands via positive plant-soil feedbacks. By contrast, in a region with
many EM species (e.g., Southeast Asia), species maintain divergent traits
because of complex plant-soil feedbacks, with no species having traits
that enable monodominance. An analysis of plant trait data from Borneo and
Peruvian Amazon was inconclusive. Overall, this work highlights the
utility of geographical comparison in understanding the relationship
between trait convergence and community convergence.