Interspecific occupancy-abundance relationship of benthic diatoms changes seasonally with attachment mode in a tropical river.

The positive occupancy-abundance relationship (OAR) is considered a ubiquitous pattern and well explained by species niches. However, OAR can change largely with functional groups. Benthic diatoms in tropical rivers are subject to seasonal hydrological disturbance. Their OAR can be affected by their attachment mode and shows a strong seasonality with precipitation. We investigated benthic diatoms in a river basin in South China during wet and dry seasons. Using hierarchical models, we detected the seasonal effects of niche position and breadth on diatom occupancy, abundance, and OAR for the three attachment groups. Multilevel modeling demonstrated that niche position was the main predictor that substantially explained the variations in diatom occupancy. Compared with niche breadth, niche position had a larger effect on the abundances of strongly and moderately attached diatoms; but it had a smaller effect on that of weakly attached diatoms. Weakly attached diatoms had the lowest OAR slope, and moderately attached diatoms had the highest slope. The OAR slope exhibited marked seasonality and positively correlated with precipitation. Attachment mode is a key functional trait that largely determines the distribution and abundance of diatoms and mediates their OAR. Our study provides insight into diatom-based biological monitoring of tropical streams and rivers. [ABSTRACT FROM AUTHOR]