Lianas as a Keystone Guild in Tropical Forests: An Experimental Test

Marquette University, Milwaukee WI

Investigators

Abstract

Why is species diversity so remarkably high in tropical forests? Why don’t dominant competitors displace subordinate competitors, and thus, lower species diversity? These seemingly simple questions are critical for understanding how ecosystems function. Despite being core questions in the field of ecology, they remain unresolved. One promising explanation for the maintenance of tropical forest diversity is that there are guilds of important “keystone” species that maintain diversity by preventing the best competitor species from displacing subordinate competitor species. However, the keystone guild hypothesis has never been tested in tropical forests. In this study, the PI and collaborators will evaluate the keystone guild hypothesis as an explanation for the maintenance of the extraordinary tree species diversity in tropical forests. They will test the prediction that lianas (woody vines), which have a particularly strong negative effect on dominant tree species, prevent those dominant trees from displacing subordinate ones. They will utilize an ongoing, large-scale, long-term liana-exclusion experiment that the PI began in 2008. Species diversity affects ecosystem function, and therefore human and global health. Thus, this research will inform management decisions and ecosystem function in a highly diverse tropical forest. This study will also allow the PI to actively mentor promising students from groups that are underrepresented in science. The Keystone Species Concept (KSC) is a foundational theory to explain the maintenance of species diversity. The KSC has been tested primarily for predators in simplified marine communities; few studies have extended this concept beyond a single keystone species and beyond relatively simple communities. By expanding the KSC to include guilds, or groups of organisms with convergent life-history strategies, the KSC may be a powerful explanation for the maintenance of species diversity in many ecosystems. The PI will test the hypothesis that lianas are a keystone guild for the tropical tree community. Lianas compete intensely with trees, and recent evidence suggests that they suppress shade-tolerant tree populations more than shade-intolerant tree populations. By removing lianas, the established competitive balance among tree species (when lianas are present) may be altered, allowing the competitive dominant species to displace subordinate species and ultimately reducing tree community diversity. By comparing the change in tree species richness, diversity, and composition in the liana-removal and control plots (where lianas are present), the PI can, for the first time, determine whether lianas are a keystone guild that maintains tree species diversity in tropical forests. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.