In most organisms foraging implies elevated exposure to predators. Such foraging trade-offs are universal and are main determinants of the structure and function of ecosystems. Yet, in few organisms have such trade-offs been quantified. In a new paper published this week in PNAS we demonstrate for the smallest predators in the ocean - unicellular flagellates - that those species that most efficiently clear the ambient water for prey also run the highest predation risk, and we quantify this foraging trade-off.
Unicellular heterotrophic flagellates generate a feeding current by the beating of one or several flagella and collect bacterial prey arriving in the feeding current. However, the feeding current also attracts flow-sensing predators, hence the trade-off. We used a particular technique, micro- Particle Image Velocimetry, to quantify the feeding flows generated by 15 species of flagellates. Depending on the number, position, and kinematics of the beating flagella, the flagellates produce characteristic and very different flow architectures that are well described by simple fluid dynamic models. The observed flow fields allow us to estimate the clearance rates of the flagellates as well as the extension of the flow field that they produce. The latter is a measure of predation risk and is correlated with clearance rate, thus describing the trade-off. Furthermore, the risk-to-gain ratio varies consistently between flagellate types and flow architectures. The dinoflagellates, for example, with a very special flagella arrangement have a low risk to gain ratio compared to other flagellates with multiple flagella, consistent with their evolutionary success.
Read the paper here: https://doi.org/10.1073/pnas.2009930118
Nielsen LT, Kiørboe T (2021) Foraging trade-offs, flagellar arrangements, and flow architecture of planktonic protists. PNAS. https://doi.org/10.1073/pnas.2009930118