Wild boar population fluctuations in a subtropical forest: the crucial role of mast seeding in Ryukyu Islands, Japan

Mast seeding drives large-scale population fluctuations in forest-dwelling animals, including the wild boar Sus scrofa. Many studies of the masting effects on population dynamics of wild boars have been conducted in cool- and warm-temperate forests; however, studies on wild boar populations inhabiting subtropical forests, which have more diverse plant resources than temperate forests, are limited. The mast seeding effects of Castanopsis sieboldii on the reproductive schedule and population fluctuations of wild boars inhabiting the subtropical climate zone of the Ryukyu Islands (Japan) were investigated using 14 years of camera trap data. The reproductive schedule, estimated based on the emergence of piglets, varied in response to masting. The piglet emergence during the January–February period was higher in the years after masting than in the years that followed non-masting events, evidencing that the reproductive season started earlier and lasted longer in the years after masting. The Bayesian state-space model incorporating direct density-dependence and masting effects revealed that the relative population size was negatively affected by the population size of the previous year and positively affected by the previous year’s occurrence of masting. These observations indicate that masting is a critical factor driving population dynamics of wild boars living in subtropical forests and also highlight the importance of mast seeding effects on population fluctuations of wild boars when developing management plans for these animals.