Species diversity may be causally influenced by the genetic diversity of a dominant species. As tropical forests have very high species diversity, it is not clear whether the pattern of species-genetic diversity correlation (SGDCs) depends on the ecological role of focal species. 

In a study published in Plant Diversity, researchers from the Xishuangbanna Tropical botanical Garden (XTBG) of the Chinese Academy of Sciences tried to reveal the underlying mechanisms of species co-existence in species-rich communities. They found that the adaptive genetic diversity of dominant species contributed to species co-existence and community assembly. 

The researchers used high-throughput DNA sequencing to derive the adaptive, neutral and total genetic diversity of two co-occurring tree species, a canopy dominant tree species, Parashorea chinensis, and an understory-abundant tree species, Pittosporopsis kerrii, that may shape community characteristics in the Xishuangbanna tropical seasonal rainforest.

They also quantified patterns of species-genetic diversity correlation of the two species and the species of the communities. 

By employing structural equation modelling (SEM), the researchers further deciphered the hierarchical relationships among the genetic diversity and species diversity of the two species and environmental variables. 

The study showed that the adaptive genetic diversity of the understory-dominant species, Pi. kerrii, and rarefied tree species richness were negatively correlated, but that there was no significant correlation between the adaptive genetic diversity of the canopy-dominant species Pa. chinensis, the largest biomass in the community. 

The SEM analysis revealed that the two levels of biodiversity were causally connected, as increased adaptive genetic diversity led to increased species diversity by promoting co-existence.

Soil nitrogen availability was the key driver of the observed species-genetic diversity correlations. The availability of soil nitrogen had a significant role in structuring species diversity and the adaptive genetic diversity of the canopy dominant species. 

"Our results reveal the significant ecological role of dominant species in competitive interactions and the regulation of community structure, and they highlight the important ecological connection between genetic diversity and species diversity," said Dr. LI Qiaoming, first author of the study.