Meeting Abstract
Bladderworts, a genus of carnivorous plants, are among the smallest and fastest suction feeders. Their traps, typically 1 to 5 mm in diameter, catch zooplankton that ranges in size up to the diameter of the trap opening (100 to 300 microns). At such a small gape, bladderworts could be expected to feed in the viscous flow regime. However, experiments have shown that the traps generate extremely fast-onset, strong suction pressures, which in turn generate fast enough flows to allow bladderworts to escape the viscous flow regime. We used mathematical models (computational fluid dynamics and analytical models) to explore the effects of gape diameter, pressure, and time to peak pressure on the flow generated by bladderwort traps. We found that the flow generated by bladderwort suction events is inertia-dominated. In contrast to first-feeding larval fish, which have a similar gape diameter to bladderwort traps, we found that bladderworts are not near the lower size limit. Previous theoretical and experimental studies on larval fish found that larval fish suction-feed near the lower size limit, where small changes in size have a large effect on flow and capture success. In bladderworts, similar changes in gape size do not significantly affect flow, and the traps continue to feed in the inertia-dominated flow regime. Our computational models further predict that time to peak pressure (instantaneous onset versus gradual onset) has no strong effect on suction flow characteristics that correlate with prey capture success, such as peak flow speed and peak spatial pressure gradient; we found no evidence of unsteady effects enhancing flow speed or spatial pressure gradient. We conclude that bladderworts feed in the inertial flow regime mainly due to the high pressures that they generate rather than due to the fast onset of pressure.
