Differences in niche allow the coexistence of closely related species. If niche difference is essential for species coexistence, taxa that have many closely-related coexisting species may have high rates both in speciation and niche divergence during their evolution. Thus, we expect a positive correlation between speciation and niche diversification rates. We tested whether families having high speciation rates had high niche diversification rates for tropical trees of Lambir Hills National Park in Borneo.
Phylogeny of 699 coexisting species was estimated using three regions of chloroplast DNA. We quantified life-form, demographic, and habitat niches of each species using tree census data. Speciation and niche diversification rates were estimated with Bayesian Analysis of Macroevolutionary Mixtures (BAMM).
Speciation rates of families were correlated positively to diversification rates of life-form and habitat niches. However, phylogenetic generalized least squares (PGLS) selected a model including only habitat niche diversification to explain the difference of family speciation rate.
The results suggest that rapid speciation coincided with habitat diversification is an important factor for the coexistence of many closely related species in the study forest.