Exploitative competition of invaders differentially influences the diversity of neutral, lumpy and intransitive phytoplankton assemblages in spatially heterogeneous environments

Recent theoretical research suggested that species-supersaturated phytoplankton assemblages sustained through neutrality, lumpy coexistence or intransitivity were sensitive to immigration, quickly losing diversity following invasions. The presence of source patches, however, may facilitate persistence of species-supersaturation in the face of invaders. We explore that notion here through simulation analyses of more detailed spatially explicit models depicting one- and two-dimensional systems (“pipe” and “two-eddy” models, respectively) where water circulation is governed over a range of advection and turbulent diffusion. For the pipe model, when advection and turbulent diffusion are low, and when advection is high and turbulent diffusion is low, resident assemblages are more resistant to invaders. But at intermediate rates of advection and with increases to turbulent diffusion, assemblages are more quickly impacted by invaders. For the two-eddy model, when advection and turbulent diffusion are low, resident assemblages are again resistant to invaders, but only for lumpy assemblages. In contrast to the “pipe” model, resistance to invaders of neutral and lumpy assemblages is high when advection and turbulent diffusion are high. For both model configurations, intransitive assemblages were much more sensitive to invaders, suggesting that intransitivity might not be as prevalent a biodiversity-sustaining mechanism in spatially heterogeneous plankton systems.