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Safety in numbers: shoal size choice by minnows under predatory threat

Summary

Larger animal groups often provide greater protection from predators. An individual might therefore be expected to join the larger of two groups. To test this, we hypothesized that fathead minnows would choose to associate with the larger of two shoals and that the presence of a predatory largemouth bass would influence their shoal size choice. Individual minnows were presented with a series of choices between two shoal sizes, ranging from 1 to 28 fish, both with and without a predator present. Although responses were highly variable, minnows displayed an ability to choose between shoal sizes even when size differences were small, preferring the larger shoal whenever a size preference was shown. In the presence of a predator, minnows made quicker shoaling decisions and showed a strong tendency to avoid very small shoals.

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Hager, M.C., Helfman, G.S. Safety in numbers: shoal size choice by minnows under predatory threat. Behav Ecol Sociobiol 29, 271–276 (1991). https://doi.org/10.1007/BF00163984

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  • DOI: https://doi.org/10.1007/BF00163984

Keywords

  • Size Difference
  • Strong Tendency
  • Large Animal
  • Animal Group
  • Largemouth Bass