Behavioral Ecology and Sociobiology

, Volume 36, Issue 6, pp 421–429 | Cite as

Groups confuse predators by exploiting perceptual bottlenecks: a connectionist model of the confusion effect

  • David C. Krakauer


Aggregation is a well documented behaviour in a number of animal groups. The “confusion effect” is one mechanism thought to mitigate the success of predators feeding on gregarious prey and hence favour aggregation. An artificial neural network model of prey targeting is developed to explore the advantages prey species might derive through a tendency to group. The network illustrates how an abstract model of the computational mechanisms mediating the perception of prey position is able to show a degradation in performance as group size increases. The relationship between group size and predator confusion has a characteristic decreasing decelerating shape. Prey “oddity” is shown to reduce the impact of the confusion effect, thereby allowing predators to target prey more accurately. Hence shoaling behaviour is most profitable to the prey when prey phenotypes are visually indistinguishable to a predator. Futhermore it is shown that prey “oddity” is relatively more costly in large groups than in small groups and the implications for assortative schooling are discussed. Both the model and the results are intended to make the general point that cognitive constraints will limit the information that a nervous system can process at a number of different levels of neural organization.

Key words

Confusion effect Groups Oddity Perceptual Constraints Shoal 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Alport A (1989) Foundations of cognitive science. MIT Press, CambridgeGoogle Scholar
  2. Broadbent DE (1965) Information processing in the nervous system. Science 22:457–462Google Scholar
  3. Bullock TH, Horridge GA (1965) Structure and function in the nervous systems of invertebrates, vol 2. Freeman, San FranciscoGoogle Scholar
  4. Calvert WH, Hedrick LE, Brower LP (1979) Mortality of the monarch butterfly, Danaus plexippus: avian predation at five overwintering sites in Mexico. Science 204:847–851Google Scholar
  5. Churchland P, Sejnowski T (1994) The computational brain. MIT Press, CambridgeGoogle Scholar
  6. Dawkins R, Krebs JR (1979) Arms races between and within species. Proc R Soc Lond B 205:489–511Google Scholar
  7. Dowling JE (1987) The retina: an approachable part of the brain. Belknap Press, CambridgeGoogle Scholar
  8. Duncan P, Vigne N (1979) The effect of group size in horses on the rate of attacks by blood-sucking flies. Anim Behav 27:623–625Google Scholar
  9. Enquist M, Arak A (1993) Selection of exaggerated male traits by female aesthetic senses Nature 361:446–448Google Scholar
  10. Foster SA, Treherne JE (1981) Evidence for the dilution effect in the selfish herd from fish predation on a marine insect. Nature 295:466–467Google Scholar
  11. Grossberg S (1984) Some normal and abnormal behavioural syndromes due to transmitter gating of opponent processes. Biol Psychiatry 19:1075–1117Google Scholar
  12. Hamilton WD (1971) Geometry of the selfish herd. J Theor Biol 39:295–311Google Scholar
  13. Hinton GE, Shallice T (1991) Lesioning an attractor network: investigations of acquired dyslexia. Psychol Rev 98:74–95Google Scholar
  14. Kenward RE (1978) Hawks and doves: factors effecting success and selection in goshawk attacks on wood-pigeons. J Anim Ecol 47:60–449Google Scholar
  15. Krakauer DC (1995) Simple connectionist models of spatial memory in bees. J Theor Biol 172:149–160Google Scholar
  16. Landeau L, Terborgh J (1986) Oddity and the “confusion effect” in predation. Anim Behav 34:146–153Google Scholar
  17. Laughlin SB (1983) The roles of parallel channels in early visual processing by the arthropod compound eye. In: Ali MA (ed) Photoreception and vision in invertebrates Plenum, New York, pp 457–481Google Scholar
  18. Laughlin SB (1990) Coding effiiciency and visual processing. In: Blakemore C (ed) Vision, coding and efficiency. Cambridge University Press, CambridgeGoogle Scholar
  19. Magurran AE, Pitcher TJ (1987) Provenance, shoal size and the sociobiology of predator evasion behaviour in minnow shoals. Proc R Soc Lond B 229:439–465Google Scholar
  20. Major PF (1978) Predator-prey interactions in two schooling fishs, Caranx ignobilis and Stolephorus purpureus. Anim Behav 26:77–760Google Scholar
  21. Marr D (1982) Vision. Freeman, San FranciscoGoogle Scholar
  22. Milinski M (1977a) Do all members of a swarm suffer the same predation? Z Tierpsychol 45:373–388Google Scholar
  23. Milinski M (1977b) Experiments on the selection by predators against spatial oddity of their prey. Z Tierpsychol 43:311–325Google Scholar
  24. Milinski M (1990) Information overload and food selection. In: Hughes RN (ed) Behavioural mechanisms of food selection (NATO ASI Series G: Ecological Sciences, vol 20). Springer, Berlin Heidelberg New York, pp 721–736Google Scholar
  25. Myers JP, Conners PG, Pitelka FA (1981) Territory size in wintering sanderlings: the effects of prey abundance and intruder density. Auk 96:551–561Google Scholar
  26. Ohguchi O (1981) Prey density and selection against oddity by three spined sticklebacks. Adv Ethol 23:1–79Google Scholar
  27. Pitcher TJ, Parish JK (1993) Functions of shoaling behaviour in teleosts. In: Pitcher TJ (ed) Behaviour of teleost fishes. Chapman Hall, LondonGoogle Scholar
  28. Pulliam HT (1976) The principle of optimal behaviour and the theory of communities. In: Klopfer PH, Bateson PPG (eds) Perspectives in ethology. pp 311–332. Plenum Press, New YorkGoogle Scholar
  29. Pulliam HR, Caraco T (1984) Living in groups: is there an optimal group size? In: Krebs JR, Davis NB (eds) Behavioural ecology: an evolutionary approach, 2nd edn. Blackwell, Oxford, pp 122–147Google Scholar
  30. Ranta E, Lindström K, Peukhuri N (1992) Size matters when three spined sticklebacks go to school. Anim Behav 43:160–162Google Scholar
  31. Rumelhart DE, McClelland JL (1986) Parallel distributed processing: explorations in the microstructure of cognition, vol 1. Foundations. MIT Press, CambridgeGoogle Scholar
  32. Sarnat BH, Netsky MG (1981) Evolution of the nervous system, 2nd edn. Oxford University Press, OxfordGoogle Scholar
  33. Schaller GB (1972) The Serengeti lion. University of Chicago Press, ChicagoGoogle Scholar
  34. Seghers BH (1974). Schooling behaviour in the guppie (Poecilia reticulata): an evolutionary response to predation. Evolution 28:486–489Google Scholar
  35. Schmidt RJ, Strand SW (1982) Cooperative foraging by yellowtail, Seriola lalandei (Carangidae), on two species of fish prey. Copeia 714-717Google Scholar
  36. Smolensky P (1986) Harmony theory. In: Rumelhart DE, McClelland JL (eds) Parallel distributed processing, vol 1 MIT Press, Cambridge, pp 194–281Google Scholar

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • David C. Krakauer
    • 1
  1. 1.BBSRC NERC Behaviour and Ecology Group, Department of ZoologyUniversity of OxfordOxfordUK

Personalised recommendations