Another theme is the emergence of large gelatinous body plans among planktonic
lter feeders. Gelatinous organisms are characterised by a much more watery body
composition than the typical cell. In order to understand and quantify the general
trade-os for lter feeders with dierent body plans we developed an energy budget
model. The model accounts for energy intake from prey collection and energy expenditure
from active ow creation as well as basal respiration. The prey clearance rates of
lter feeders are found to be limited by the maximum force that their biological motor
can create. The lter area per body biomass needs to be large to prevent starvation.
Thus a simple, but wide-ranging result of the model is that larger organisms (with a
large biomass) have a stronger need than microbes to increase their area and they do
this by becoming gelatinous.
As a last study of this project we explore the eect of prey size on prey capture
rates by organisms, which encounter their prey directly on the cell surface. We numerically
calculate the advective-diusive capture of nite-sized prey on a spherical
cell in a simple Stokes ow. We nd high capture rates both for the smallest and the
largest prey, and we identify a minimum of the capture rate for intermediate prey. We
rationalise and explain the observed trends in an analytical model for the capture of
nite-sized prey. We additionally investigate \sloppy" feeders, which exhibit severe
prey losses when the predator-prey contact time is short. Sloppy feeders mainly lose
small diusive particles, such that they predominantly capture the largest prey.