Critical-sinking-velocity conjecture for phytoplankton diffusion competition

Consider the two-species phytoplankton competition model with equal advection rates $\alpha_1=\alpha_2=\alpha$, equal growth functions $g_1=g_2$, equal additional diffusion parameters $d_1=d_2$, and distinct horizontal diffusion rates. Critical-sinking-velocity conjecture. There exist critical sinking velocities $\alpha_{\min}$ and $\alpha_{\max}$ such that the slower diffuser wins if $\alpha<\alpha_{\min}$, the faster diffuser wins if $\alpha>\alpha_{\max}$, and the two species coexist if $\alpha\in(\alpha_{\min},\alpha_{\max})$. This predicts a transition from slow-diffusion selection to fast-diffusion selection, with coexistence at intermediate sinking velocities.