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

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.