Wood mouse population dynamics: Interplay among seed abundance seasonality, shrub cover and wild boar interference

Small rodents play a key role in forest ecosystems as common prey, but also as prevalent seed consumers and dispersers. Hence, there is a great interest in disentangling the factors involved in their population dynamics. We conducted an intensive 2-year field study to test the relative role of seasonality in seed abundance, shrub cover and wild boar interference on the population dynamics of wood mice, Apodemus sylvaticus, in a Mediterranean oak forest. Wood mice demographic parameters varied strongly with the seasonal variations in acorn availability on the ground. Mice survival and abundance dropped drastically during summer, the period of acorn scarcity, but rose again in autumn when acorn-fall began. Specifically, female abundance was associated with the temporal changes in acorn availability on the ground, but were randomly distributed in space whereas males showed a spatially aggregated pattern during the acorn-abundant seasons (autumn-winter). In contrast to studies conducted in sparse oak forests in drier environments, spatial variability in shrub cover and wild boar foraging activity did not affect directly the population dynamics of wood mice. This could be due to the presence of an abundant shrub layer and a closed canopy in our forest that enhance environmental conditions and provides shelter against predators and ungulates. Our study highlights that the relative importance of environmental factors and intraguild competition on rodent dynamics may be highly context-dependent, varying greatly among different sites. We suggest that the relationships between acorn dispersers and oaks are more reciprocal than previously considered.