Primary and secondary resource pulses in an alpine ecosystem: snow tussock grass (Chionochloa spp.) flowering and house mouse (Mus musculus) populations in New Zealand

Abstract

Context. Rodent populations in many parts of the world fluctuate in response to resource pulses generated by periodic high seed production (masting) by forest trees, with cascading effects on predation risk to other forest species. In New Zealand forests, populations of exotic house mice (Mus musculus) irrupt after periodic heavy beech (Nothofagus spp.) seedfall. However, in alpine grasslands, where snow tussock grasses (Chionochloa spp.) also flower and set seeds periodically, little is known about house mouse population dynamics. Aims. Our primary objective was to test for an increase in alpine mouse density following a summer when snow tussocks flowered profusely. We also estimated mouse density in adjacent montane forest over 2 years, and assessed mouse diet, to predict their potential impacts on native species. Methods. Flowering intensity of Chionochloa was assessed by counting flowering tillers on permanent transects (2003–06). Mouse density was estimated with capture–mark–recapture trapping in alpine (2003–07) and forest (2003–04) habitats. Mice were also collected and their stomach contents analysed. Flowering or fruiting of alpine shrubs and herbs, and beech seedfall at forest sites, were also measured. Key results. Chionochloa flowered profusely in austral summer 2005/06. Between autumn (May) and spring (November) 2006, mean alpine mouse density increased from 4 ha–1 to 39 ha–1, then declined to 8 ha–1 by autumn (May 2007). No mice were captured in 768 trap-nights during the following spring (November 2007). Prior to the mouse irruption, mouse density was consistently higher at alpine (0.4–4.0 mice ha–1) than at montane forest (0.02–1.8 mice ha–1) sites (in 2003–04). Alpine mouse diet was dominated by arthropods before mast flowering, and by seeds during it. Conclusions. The density and dynamics of alpine mice in relation to intensive snow-tussock flowering were similar to those in New Zealand beech forest in relation to beech masts. Implications. We predict the timing and duration of periods of heightened predation risk to native alpine fauna, as the result of pulses in mouse density and likely associated pulses in the density of stoats (Mustela erminea), a key exotic predator.

Soil nutrient supply modulates temperature‐induction cues in mast‐seeding grasses

“…Changes in masting patterns can also affect community and trophic cascades . For Chionochloa, these changes will directly affect the population dynamics of non-native mammals, i.e., mice and their stoat predators, and may have large cascading impacts for the conservation of endangered bird species, e.g., takahe (Porphyrio hochstetteri; Wilson and Lee 2010).…”

Population dynamics of house mice without mammalian predators and competitors

“…Population densities of house mice after larger mammals were removed from the Maungatautari forest were similar to those observed after masting events in New Zealand beech forest and alpine grassland (Ruscoe et al 2001(Ruscoe et al , 2004Wilson & Lee 2010). If this mainland forest sanctuary is typical of non-masting forest locations in New Zealand, then eradication of larger mammals from these reserves may not generate the very high mouse population densities estimated on some offshore islands without other mammals (e.g.…”

“…In forests with other invasive mammals present on the New Zealand mainland, house mouse population density is usually < 6 mice ha -1 (Murphy 1989;Ruscoe et al 2001Ruscoe et al , 2004Wilson & Lee 2010), but can reach 50 ha -1 after periodic high seedfall (masting) in forests dominated by masting tree species (Ruscoe et al 2001(Ruscoe et al , 2004. The highest mouse population density estimate from the New Zealand mainland is 160 ha -1 in small forest patches surrounded by pasture and rank grass in the partially fenced biodiversity sanctuary on Tawharanui Peninsula, Auckland Region (Goldwater 2007;Goldwater et al 2012).…”

“…In turn, predation by abundant mice on oceanic islands lacking other terrestrial mammals can significantly affect indigenous biota (Angel et al 2009;Simberloff 2009). Mice also become numerous when food is plentiful (King 1983;Wilson & Lee 2010). Extensive mouse plagues in the wheat-growing areas of south-eastern Australia follow rainfall and other possible prerequisites, such as reduced rates of predation and disease (Pech et al 1999;Krebs et al 2004;Singleton et al 2007).…”

Impacts of introduced mammalian predators on New Zealand’s alpine fauna

“…They generally reach higher population densities in areas with dense ground cover, and habitat choice is a trade-off between access to food and safety from predation (Ylönen et al 2002;Ruscoe & Murphy 2005). We are aware of only one published assessment of mouse diet in the alpine zone (alpine grasslands, Borland Valley, Fiordland) (Wilson et al 2006;Wilson & Lee 2010). In this habitat, mouse diet appeared to be dominated by invertebrates during non-tussock-mast years and by Chionochloa tussock seed during a mast seedfall year, when mouse density increased from 4 ha -1 to 39 ha -1 (Wilson & Lee 2010).…”