Collector Motion Affects Particle Capture in Physical Models and in Wind Pollination.

Particle capture is important for ecological processes in aquatic and terrestrial ecosystems. The current model is based on a stationary collector for which predictions about capture efficiency (η; flux of captured particles ∶ flux of particles) are based on the collector flow environment (i.e., collector Reynolds number, Rec; inertial force ∶ viscous force). This model does not account for the movement of collectors in nature. We examined the effect of collector motion (transverse and longitudinal to the flow) on η using a cylindrical model in the lab and the grass species Phleum pratense in the field. Collector motion increased η (up to 400% and 20% in the lab and field, respectively) and also affected the spatial distribution of particles on collectors, especially at low Rec. The effect was greatest for collectors moving transversely at large magnitude, which encountered more particles with higher relative momentum. These results, which differ from the stationary model, can be predicted by considering both Rec and the particle dynamics given by the Stokes number (Stk; particle stopping distance ∶ collector radius) and helped to resolve an existing controversy about pollination mechanisms. Collector motion should be considered in wind pollination and other ecological processes involving particle capture.