Document: DAV-3-51-10

Mouse population eruptions in New Zealand forests: The role of population density and seedfall.

CHOQUENOT, D.* and W.RUSCOE

Landcare Research New Zealand, Lincoln, New Zealand ¹

Abstract:
Eruptive mouse populations provide an opportunity to test ideas about how intrinsic and extrinsic factors interact to limit small mammal populations. We analysed 25 years of mouse density and autumn beech seedfall data from a mosaic forest in New Zealand consisting of beech and podocarp/broadleaf stands, to test the effect mouse density and seedfall had on rates of increase (r) for an eruptive mouse population. For transitions from autumn to winter and winter to spring, r was related to the magnitude of seedfall and mouse density. For transitions from spring to summer and summer to autumn, r was related to mouse density alone. The strong density-dependence we observed in r for this population was confirmed using PBLR analysis. Density-dependence could reflect the influence of intrinsic social factors, intraspecific competition for food, or the effects of parasites, diseases or predators. While there are currently insufficient data to differentiate between these factors, limited data on mouse offtake by stoats is consistent with a role of predation. Mouse density was more volatile in beech forest than in podocarp/broadleaf forest, maximum rates of increase and decrease both being greater in the former. This volatility led to densities being higher in podocarp/broadleaf stands when overall density was low, and higher in beech stands when overall density was high. Collectively, these results suggest that between eruptions, mice persist in podocarp/broadleaf stands, erupting in adjacent beech stands when autumn seedfall is sufficient to prolong winter reproduction and elevate survival.

Keywords: density-dependence, mice, population eruption, rate of increase

This abstract is being presented at: 10:30 AM in session:
Oral Session #21: Small Mammal Population Ecology.