Minimum prey size, however, will be limited by hydrodynamic considerations
(encounter rate has a minimum against particle size as diffusion falls off before
other mechanisms increase rates; Rubenstein & Koehl,1977; Shimeta & Jumars,
1991 ) and the problems of dealing with extremely small particles.
It is reasonable to expect tuning of the size of filtering structures and collect-
ing elements to profitable prey size (determined by energy content and distri-
bution in the environment). Mean prey size (or other measure or central
tendency) may not scale isometrically as expected for maximum prey size.
Unfortunately, information on predator–prey size relationships for suspension
feeders is scarce and a general analysis has not yet been attempted.Body size and food availability (body size and solid–fluid interfaces)
Although large size may directly increase the size range of particles available to
an animal, body size can also influence the availability of particles through its
effects on flow regime. Physical interactions involving availability and the
deposition of particles depend on body size because of the link between body
size and flow regime. When considering benthic suspension feeders, body size
in conjunction with spatial positioning can determine the availability of sus-
pended particles. Hydrodynamic studies have highlighted the influence of
surface roughness on flow (Nowell & Church,1979; Nowell & Jumars,1984;
Eckman, 1990 ; Abelson & Denny, 1997 ), and this has been observed to relate
directly to animal size and positioning (Pawlik, Butman & Starczak,1991;
Friedrichs, Graf & Springer, 2000 ; Cardinale, Palmer & Collins,2002).
Any structure extending into the flow from the substratum will perturb the
local flow pattern, and the formation and shedding of vortices from benthic
suspension feeders can lead to differential deposition of particles downstream
(Vogel,1994 ; Abelson & Denny,1997 ; Turner,2000 ). In this case, the size of the
structure or animal determinesReand thus a characteristic wavelength for vortex
shedding. Vortices are shed at a rate determined by the Strouhal number (St), a
dimensionless frequency, dependent on the shape andReof the object (Vogel,
1994 ), and interact most strongly with the substratum downstream at a character-
istic distance related to shedding rate (Fig.2.4 ). Positive feedback may then occur
as increased deposition leads to increased feeding rates and hence growth of
downstream animals (Turner,2000 ). A further consequence is that growth itself
will alter the vortex shedding rate. An additional study (Abelson, Miloh & Loya,
1993 ) suggests that body morphology can determine the availability of food
particles. As morphology in this instance is characterized by a slenderness ratio
(height/diameter) body sizeper semay also play an important part, particularly if
an animal’s slenderness ratio changes through ontogeny because of the change in
Reassociated with its linear dimension parallel to the flow.
Since body size can influence sediment deposition in the local area, it will also
have strong effects on the importance of benthic suspension feeders as ecosystem26 S. HUMPHRIES