. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LIFE IN TRANSITION 219 inertial realm. The necessity for an effective escape from predators has driven the evolution of the streamlined form of copepods. When a large copepod escapes, toroidal vortices are found in its wake as larger appendages translate larger parcels of water (Fig. 2). A toroidal shape can be viewed as a vortex ring due to the vorticity produced by viscosity between the jet and the ambient fluid (Weihs, 1977). A toroidal vortex gets larger by entrainment of surrounding fluid and slower by loss of its origi
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. LIFE IN TRANSITION 219 inertial realm. The necessity for an effective escape from predators has driven the evolution of the streamlined form of copepods. When a large copepod escapes, toroidal vortices are found in its wake as larger appendages translate larger parcels of water (Fig. 2). A toroidal shape can be viewed as a vortex ring due to the vorticity produced by viscosity between the jet and the ambient fluid (Weihs, 1977). A toroidal vortex gets larger by entrainment of surrounding fluid and slower by loss of its original impulse (Shariff and Leonard, 1992; as cited by Vogel. 1994). Analyses of the change in volume and distance traveled by the toroidal vortex allow an estimate of the relative importance of dif- fusive to advective forces within this copepod wake. Here, 250 ms after the copepod has released the torus, the torus continued to grow by 20% over the past 50 (see Fig. 3; Table 3). The water continues to coast s after the source has left the scene, further evidence of entrance into an inertial realm. In fact, it takes another 2 s before the Peclet number approaches 1 and advection is balanced by diffusion (from Table 1. Eq. 2. Pe = 1 when U = 1 ju,m s~'; from Table 3, Eq. 3, t = s for U = 1 /urn s '). Since these wakes were visualized within a strong density gradient, they may be smaller and slower than natural wakes formed in an ambient density gradient (see Gries et al., 1999) and may inaccurately estimate the time needed to reach a balance between advection and diffusion. During this time, odor placed within the torus is dispersed by advection. A signal of mixed modality is created when the concentrated odor of excreted metabolites is encased in the jet-like wake shed by an escaping copepod. The concentration of odorant in the wake will be more dilute than that in the laminar trail because viscous forces do not restrict the advective disrup- tion of odors within the
Size: 1030px × 2426px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
