Water column processes differentially influence richness and diversity of neutral, lumpy and intransitive phytoplankton assemblages

Neutrality, lumpy coexistence and intransitive population dynamics are mechanisms that, in theory, influence biodiversity. In this research, we focus on simulated phytoplankton assemblages that are species-supersaturated because of these mechanisms. We investigate how various water column processes alter mechanism functioning and consequently biodiversity. The water column processes on which we focus are extinguishing light availability with depth, vertical diffusivity, upward diffusive flux of nutrients from lower layers and/or the benthos, particle sinking, and a rescue effect. We explore the influence of these water column processes on phytoplankton biodiversity by characterizing assemblages' α- and β-level richness and diversity. Previous work found that intransitive systems' richness and biodiversity were more sensitive to hydraulic mixing and immigration than those of neutrality and lumpy coexistence. With our expanded modeling framework, our findings are similar in regards to α richness and diversity, but have a more complicated story from the perspective of β richness and diversity where the influence of spatial heterogeneity arising from various water-column processes is dependent upon the phytoplankton assemblage type.