Ficus is rich in number of genera and underlies a large portion of tropical plant diversity. Recent studies of woody species in three diverse neotropical genera have found evidence for niche partitioning along spatial environmental gradients and within local sites, suggesting that partitioning is prevalent even among closely related species. Hypotheses for the diversity of Ficus have focused on reproductive isolation and rapid speciation while few studies have investigated niche partitioning.
In cooperation with researchers from the University of Columbia, Prof. CAO Min and his team of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study in the 20-ha tropical seasonal rainforest dynamics plot in Xishuangbanna (21°36'50'' N, 101°34'36'' E). They studied the functional and phylogenetic diversity of co-occurring Ficus species and individuals in the 20-ha plot in order to characterize mechanisms maintaining diversity across the plot. They studied six traits (leaf area, succulence, specific leaf area, maximum diameter at breast height (DBH), fruit size, and latex exudation) for 22 Ficus species and 335 individuals greater than or equal to10 cm DBH on the 20-ha forest plot.
They addressed the following questions: 1) Does filtering associated with topography drive spatial variation in Ficus assemblages, promoting diversity across topographic gradients? 2) Are traits associated with resource use and biotic interactions associated with niche partitioning, promoting species and functional diversity among neighboring trees? 3) Is evolutionary relatedness associated with trait similarity and whether co-occurring species are more or less related than expected? 4) Do individual-level trait patterns change the interpretation of the mechanisms that promote Ficus species and functional diversity?
Their analysis revealed three key properties of mechanisms that likely maintain diversity among closely related Ficus species in Xishuangbanna. First, filters associated with elevation appeared to promote Ficus functional diversity. Second, within-site niche variation associated with leaf traits may promote diversity of co-occurring Ficus and neighboring species. Third, evidence for trait-based topographic filtering and within-site niche variation was strongest when considering individual level variation, suggesting intraspecific variation in responses to environment that may weaken the role of species-level niche partitioning in promoting species diversity.
Their findings suggested that niche partitioning along abiotic gradients and within sites promotes functional diversity of Ficus species, although high intraspecific variation may reduce the role of niche partitioning in species coexistence. As efforts expand to sample intraspecific trait variation, we expect researchers to further illuminate mechanisms that maintain diversity that may be obscured by species-mean approaches.
The study entitled “The role of functional traits and individual variation in the co-occurrence of Ficus species” has been published online in Ecology.
20-ha plot of Xishuangbanna