Predation of beech seed by mice: effects of numerical and functional responses

Summary

• 1
  The functional response of post-dispersal seed predators (house mouse, Mus musculus) to absolute densities of southern beech seed (Nothofagus solandri var. cliffortioides) was studied in laboratory and field trials. House mice showed a Type II (hyperbolic) functional response to seed availability and this was not modified by the presence of an alternative food source.
• 2
  Maximum daily intake rate of beech seeds during field trials averaged 1042 seeds mouse⁻¹. This is sufficient to provide house mice with both the energy and protein required for growth and reproduction.
• 3
  We explicitly incorporated the functional response into the numerical response of house mice to beech seed, measured for field populations monitored in a New Zealand beech forest. House mice showed a strong numerical response to beech seed intake rate that was modified by some density-dependent mechanism(s).
• 4
  We developed a model that simulated seedfall, house mouse population growth and seed reserve depletion over one year. We found that the previously reported decline in house-mouse populations in beech forests during spring and summer is likely to be related to spring beech seed germination that renders seed no longer available as a food source for house mice.
• 5
  From our simulation model it does not appear that house-mouse populations can completely eat-out beech seed reserves prior to germination in a year of large seedfall. ‘Masting’ behaviour in New Zealand native beech trees is therefore sufficient to satiate an eruptive population of an exotic mammalian omnivore, despite the lack of a long co-evolutionary interaction.