Size traits determine the abundance distribution of tropical eutrophic phytoplankton over time

Abstract Environmental filtering and limiting similarity are two important ecological processes that drive species abundance distribution. However, little is known about the influence of these processes on the assembly of phytoplankton communities in eutrophic ecosystems over the time. Here, we evaluated the relationships between species relative abundances and ecological dissimilarity, surface-to-volume ratio, and volume differences for phytoplankton communities over 21 years, in a shallow tropical eutrophic reservoir. Further, we tested the influence of environmental variability over time on the strength of these relationships. We found a negative relationship between relative abundance and surface-to-volume ratio and volume differences between species, that is, the most abundant species in phytoplankton communities tended to be similar in these body size traits. Our findings evidenced that species abundance distribution was more consistent with the environmental filtering processes than with limiting similarity. Furthermore, we discovered that these relationships are weakened with the increase in water transparency and strengthened with the increase of soluble reactive phosphorus concentration. These results are probably related to the fact that the reservoir has a highly specialized pool of species. Our outcomes emphasize that in a nutrient-rich environment and during cyanobacterial blooms, species coexistence over time relies significantly on niche similarity and surface:volume ratio and volume.