Abstract
In marine ecosystems, acquired phototrophs – organisms that obtain their photosynthetic ability by hosting endosymbionts or stealing plastids from their prey – are omnipresent. Such taxa function as intraguild predators yet depend on their prey to periodically obtain chloroplasts. We present a new theory for the effects of acquired phototrophy on community dynamics by analysing a mathematical model of this predator–prey interaction and experimentally verifying its predictions with a laboratory model system. We show that acquired phototrophy stabilises 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 95% of carbon from photosynthesis) acquired phototrophs form blooms.