FIG. 1. Model of a direct interception feeder. (A) Prey particles of radius rp (red) initially arrive
(in the co-moving frame) with velocity −U. They follow the flow (blue) and additionally move
randomly with Brownian diffusion. The prey are captured by the predator of radius a (black filled
circle), when coming within a close distance . The encounter surface is shown as dashed circle.
(B) In the advective-diffusive case, at large P´eclet number, we consider a concentration field (red)
that is only depleted in a thin boundary layer around the absorber, the thickness d of which can
be estimated. Sketch in (B) adapted from Friedlander 23.
the prey, that can be analytically treated and that account for the modified trajectories of
small spherical particles in an external flow that here is provided by the moving predator
In this study we simulate the advective-diffusive capture of finite-sized prey on an interception
feeder that we approximate as a towed sphere in Stokes flow. The clearance rate
is numerically calculated as function of prey size, which determines the physical prey size
selection of the organism. We compare the results to analytical formulas and for sloppy
feeders we extract characteristic contact times that we compare to analytical formulas for
entrainment times. With a typical marine particle size spectrum we calculate total capture
rates and compare to the feeding rates of filter feeding microbes. We further discuss
trade-offs and optimum foraging strategies of sloppy feeders.
MODEL OF DIRECT INTERCEPTION FEEDERS
Our model of a direct interception feeder consists of a spherical body of radius a, that
moves with constant velocity U. The swimming speed is assumed to scale linearly with the