Predator–prey encounter and capture rates in turbulent environments

Abstract

Lay AbstractIn this article, we review the ways in which turbulent water flow affects predator–prey encounter and capture rates. In quiet environments, zooplankton rely on self‐induced motions to encounter their prey. However, flows in nature, the oceans in particular, are usually turbulent. Fluid turbulence is very effective at mixing the water and can also greatly enhance the encounter rate between predators and prey—especially when both are carried passively by the flow. In this sense, there is an advantage for planktonic predators to be in a turbulent environment, but turbulence can also reduce the probability of prey capture. Our estimates suggest that there is an optimum turbulence level where the gain by enhanced encounter rates is balanced by reduced capture rates. These optimum conditions can be expressed mathematically in terms of the basic variables describing the problem, where the water flow is characterized by its kinematic viscosity, the turbulence by the specific energy dissipation rate, and plankton by their capture range and opening angle of its field of reception and a minimum time needed for capturing prey. The velocities of the self‐induced motions with respect to the local flow are also important. Turbulence not only affects the relative motion between predator and prey but also disturbs signals from the sensory organs on their antennae. Enhanced turbulence levels can be interpreted as noise by plankton by giving rise to random velocity variations along their antennae. This noise can be misinterpreted as a signal of the presence of prey. Similarly, prey can interpret such disturbances as false evidence of a predator. In the first case, a predator can attack even in absence of prey, while in the latter case prey can be seen to perform escape responses in the absence of a predator. Simple mathematical models can explain the basic features of this problem and help to increase our understanding of plankton ecology.