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Keywords:

  • Allee effect;
  • critical density;
  • extinction;
  • functional response;
  • predator satiation

Summary

1. Allee effects may result in negative growth rates at low population density, with important implications for conservation and management of exploited populations. Theory predicts prey populations will exhibit Allee effects when their predator exhibits a Type II functional response, but empirical evidence linking this positively density-dependent variation in predator-induced individual mortality to population growth rate and probability of extinction is lacking.

2. Here, we report a demonstration of extinction due to predator-driven Allee effects in an experimental Daphnia-Chaoborus system. A component Allee effect caused by higher predation rates at low Daphnia density led to positive density dependence in per capita growth rate and accelerated extinction rate at low density.

3. A stochastic model of the process revealed how the critical density below which population growth is negative depends on the mechanistic details of the predator–prey interaction.

4. The ubiquity of predator–prey interactions and saturating functional responses suggests predator-driven Allee effects are potentially important in determining extinction risk of a large number of species.