Drift Drives Foraminiferal Community Assembly on a Carbonate Platform

Community composition is determined by four processes: drift, selection, dispersal, and speciation. The crucial issue in understanding community assembly is disentangling the relative importance of those processes. However, this issue has not been adequately addressed in benthic foraminiferal communities. A comprehensive study of benthic foraminiferal community composition, co-occurrence network, and community assembly was conducted on the Xisha carbonate platform. The community composition was determined via the environmental DNA (eDNA) technique. Heavy metals (Co, Cr, Cu, Ni, Pb, V, and Zn), grain size, loss on ignition (LOI), organic carbon, and pH were chosen for environmental measurement. We evaluated the effects of environmental variables on the community composition and the co-occurrence network, revealing that the former was affected only by organic carbon, whereas the latter was affected by both organic carbon and pH. Null and neutral models demonstrated that foraminiferal community assembly was driven by ecological drift instead of selection. The β-NTI (a measure of the relative importance of deterministic and stochastic processes) had strong and positive correlations with community β-diversity (compositional differences between pairs of communities) and network β-diversity (structural differences between pairs of subnetworks). A conceptual model was offered to explain how heterogeneous selection and stochastic processes interact to affect the two β-diversities. This study is the first to quantitatively assess the effects of variation in the relative importance of deterministic and stochastic processes on community β-diversity and network β-diversity in foraminifera; it provides new insight into the mechanisms underlying β diversity.