Oecologia

, Volume 80, Issue 1, pp 100–110

Flexible search tactics and efficient foraging in saltatory searching animals

  • W. John O'Brien
  • Barbara I. Evans
  • Howard I. Browman
Original Papers

DOI: 10.1007/BF00789938

Cite this article as:
John O'Brien, W., Evans, B.I. & Browman, H.I. Oecologia (1989) 80: 100. doi:10.1007/BF00789938

Summary

Foraging is one of the most important endeavors undertaken by animals, and it has been studied intensively from both mechanistic-empirical and optimal foraging perspectives. Planktivorous fish make excellent study organisms for foraging studies because they feed frequently and in a relatively simple environment. Most optimal foraging studies of planktivorous fish have focused, either on diet choice or habitat selection and have assumed that these animals used a cruise search foraging strategy. We have recently recognized that white crappie do not use a cruise search strategy (swimming continuously and searching constantly) while foraging on zooplankton but move in a stop and go pattern, searching only while paused. We have termed thissaltatory search. Many other animals move in a stop and go pattern while foraging, but none have been shown to search only while paused. Not only do white crappie search in a saltatory manner but the components of the search cycle change when feeding on prey of different size. When feeding on large prey these fish move further and faster after an unsuccessful search than when feeding on small prey. The fish also pause for a shorter period to search when feeding on large prey. To evaluate the efficiency of these alterations in the search cycle, a net energy gain simulation model was developed. The model computes the likelihood of locating 1 or 2 different size classes of zooplankton prey as a function of the volume of water scanned. The volume of new water searched is dependent upon the dimensions of the search volume and the length of the run. Energy costs for each component of the search cycle, and energy gained from the different sized prey, were assessed. The model predicts that short runs produce maximum net energy gains when crappie feed on small prey but predicts net energy gains will be maximized with longer runs when crappie feed on large prey or a mixed assemblage of large and small prey. There is an optimal run length due to high energy costs of unsuccessful search when runs are short and reveal little new water, and high energy costs of long runs when runs are lengthy. The model predicts that if the greater search times observed when crappie feed on small prey are assessed when they feed on a mixed diet of small and large prey, net energy gained is less than if small prey are deleted from the diet. We believe the model has considerable generality. Many animals are observed to move in a saltatory manner while foraging and some are thought to search only while stationary. Some birds and lizards are, known to modify the search cycle in a manner similar to white crappie.

Key words

Optimal foraging behavior Predation cycle Behavioral ecology Saltatory search 

List of Abbreviations

Components of the search cycle and dimensions of the location space

SST (sec)

Successful search time — the average time stationary prior to a pursuit

USST (sec)

Unsuccessful search time — the average time stationary prior to a run

PT (sec)

Pursuit time-PL/SS — the time to pursue prey at a given distance away. It is calculated by dividing the pursuit distance by swim speed

RT (sec)

Run time-RL/SS — the time to complete a run of a given length. It is calculated by dividing the run length, by swim speed

PL (cm)

Pursuit length-distance moved to attack prey

RL (cm)

Run length-distance moved between consecutive searches

SS (cm/sec)

Swim speed — the speed of movement during a pursuit or run

LS (l)

Location space — the area or volume within which prey are located. In the case of white crappie the search space is shaped like a pie wedge with the fish positioned at the apex of the wedge

LA (o)

Location angle—the angle of the wedge-shaped search space

LH (cm)

Location height—the height of the wedge-shaped search space

LD (cm)

Location distance—the length of long axis of the wedge-shaped search space.

Components of the location probability model

RND

Random number-random number generated through BASICA

SV (l)

Search volume—the volume of water actually searched after one run of given length

SVMAX (l)

Maximum search volume—the greatest search volume that can be based upon LA, LH, LD and unaffected by the previous search

SVR (l)

Search volume researched—that volume of SVMAX that is researched where RL<LD (see Appendix A)

SVo

Search volume unsearched—that volume of SVMAX not previously searched

AD (#/1)

Absolute density—the density of zooplankton prey in numbers per liter

VD (#)

Visual density—the number of zooplankton prey in the search volume

LP (%)

Location probability—the probability that one or more prey are in the search volume

Components of the net energy gain model

NEG (cal/sec)

Net energy gain-total calories ingested, less total calories used, divided by total time.

Ee (cal)

Energy expended on the search cycle

Ei (cal)

Energy intake

ep (cal)

Energy content of a given individual prey

Pi

Total number of prey ingested

er (cal)

Energy expended while searching

es (cal)

Energy expended while swimming

Tt (sec)

Total time-time expended to eat a given number of prey

Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • W. John O'Brien
    • 1
  • Barbara I. Evans
    • 1
  • Howard I. Browman
    • 1
  1. 1.Department of Systematics and EcologyUniversity of KansasLawrenceUSA
  2. 2.Institute of NeuroscienceUniversity of OregonEugeneUSA

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