Acquired phototrophy stabilizes coexistence and shapes intrinsic dynamics in planktonic communities

In planktonic ecosystems, acquired phototrophs—organisms that obtain their photosynthetic ability by hosting endosymbionts or stealing plastids from their prey—are omnipresent. We present new theory for the effects of acquired phototrophy on community dynamics by analyzing a mathematical model of this predator-prey interaction and experimentally verifying its predictions with a laboratory model system. We show that strict acquired phototrophy stabilizes coexistence, but that the nature of this coexistence exhibits a ‘paradox of enrichment:’ as light increases, the coexistence between the acquired phototroph and its prey transitions from a stable equilibrium to boom-bust cycles whose amplitude increases with light availability. In contrast, heterotrophs and mixotrophic acquired phototrophs (that obtain <50% of their carbon from photosynthesis) do not exhibit such cycles. This prediction matches field observations, in which only strict (>90% of carbon from photosynthesis) acquired phototrophs (e.g. Mesodinium rubrum) form blooms.