Virtual reality of planktivores:a fish's perspective of prey size selection

Abstract

Tradit~onally, field studies of size selective predation by visual-feeding planktivorous fish compare the size distribution of prey in stomachs to that of zooplankton measured in the field However, the size frequency of prey perceived by a fish may differ from that measured by researchers using integrative plankton nets. In this study, a mechanistic spatial foraging model was developed to test the hypothesis that size-selective predation by visual-feeding planktivorous fish can arise simply by random encounters with prey. Our model was based on movement of a single predator and a size structured prey population distributed in 3-dimensional space. The model assumed that a predator's encounters with prey was a function of prey size and predatol-swimming speed. Upon encounter, the predator either selected prey by random choice or the largest apparent size. The size frequency and distance distribution of prey encountered, selected, and captured were estimated using Monte Carlo techniques. The model performance was initially evaluated wlth hypothetical prey slze frequencies, and different light attenuation coefficients, capture efflciencies, visual distances and predator swimming speeds. Simulation results showed that the size frequency of prey encountered randomly by a predator is very different from the size frequency of the a i n b~e n t prey In the environment The s l r c frequency of prey selected by random c h o~c c only differed from that selected by appal-ent size choice when visual distance was greater than reactive distance. Prey distance distribution, which was defined as frequency of prey encountered a t different distances, showed that as prey density increased predators sclected prey at closer distances by the largest apparent size choice than by random choice. We also tested the model specifically for the bay anchovy Anchoa mitchilli. Ambient zooplankton size frequencies found in m~d-Chesapeake Bay were used to predict the size frequencies of zooplankton consumed by fish. Predicted prey size frequency in the diet matched the size frequency of zooplankton found in bay anchovy stomachs. We conclude that prey slze selection by fish can be described mechanistically by differentlal random encounter from a flsh's perspective, and that behavioral choice plays a minor role In prey size selection.

Prey availability and selective foraging in shorebirds

“…This is largely due to the recognition, by a number of authors, that prey availability is a dynamic, changing property of the predator's environment (e.g. Charnov et al 1976;Zwarts 1990;Ens et al 1993;Kalejta 1993;Anholt & Werner 1995;Skutelsky 1995;Luo et al 1996). The importance of viewing prey availability from the perspective of the prey has also improved our understanding of selective foraging (Zwarts & Wannink 1989;Wolda 1990;Kersten et al 1991;Ens et al 1993;Thetmeyer & Kils 1995).…”

“…Our understanding of these biological patterns depends fundamentally on accurate measurements of food availability, a notoriously difficult task (Hutton 1990;Wolda 1990;Luo et al 1996). Our sensory limitations and strengths can prevent us from perceiving the environment in the way our study animals do (Blake et al 1990;Dodge et al 1990;Hutton 1990;Dusenbury 1992;Lovette & Holmes 1995).…”

On the advantages and disadvantages of larval stages in benthic marine invertebrate life cycles

“…Bailey & Houde 1989, Fuiman 1989, Cowan & Houde 1992, Heath 1992, Litvak & Leggett 1992, Pepin & Shears 1995, Cowan et al 1996, Elliott & Leggett 1996, Gleason & Bengston 1996, Letcher et al 1996, Luo et al 1996, Olson 1996. In some of these studies greater-sized larvae escaped (e.g.…”

Overlap in distribution and diets of Atlantic mackerel (Scomber scombrus), Norwegian spring-spawning herring (Clupea harengus) and blue whiting (Micromesistius poutassou) in the Norwegian Sea during late summer

“…Many marine fishes are opportunistic feeders and readily switch feeding preferences in space and time (Greenstreet et al 1998;Jennings & Kaiser 1998;Reynolds 2008). Selectivity for particular sizes or species of prey may reflect the ease and energetic costs of capture (Werner & Hall 1974;Luo et al 1996;Moteki et al 2001) and should change with the concentration, distribution and abundance of the prey (Mayer & Wahl 1997;Munk 1997).…”