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Understanding the causes underlying population dynamics of animals has challenged ecologists for decades.Both endogenous(e.g.,competition,predation)and exogenous(e.g.,climate,disturbance)factors influence population dynamics.Among exogenous factors,much attention has been paid to understanding the role of food availability in the last decade.Stored seeds in caches or hoards play an important role in overwinter survival and following reproduction of food hoarding animals.Previous studies have suggested that annual fluctuations in forest small mammals are influenced by seed crops.However,seeds of local tree species differ significantly in various seed traits.Tannins,secondary chemical compounds found in many plants seeds,exert harmful impacts on seed eating animals.Therefore,plants bearing seeds with different levels of tannins are expected to regulate population dynamics of food hoarding animals in contrasting ways.In this study,we surveyed population dynamics of two food hoarding animals,Korean field mice Apodemus peninsulae and Siberian chipmunks Tamias sibiricus,and seed availabilities of two dominant tree species with contrasting tannin concentrations,Mongolian oak Quercus mongolica(high tannin)and filbert hazelnut Corylus mandshurica(low tannin)for nine years.Our results showed that both A.peninsulae and T.sibiricus actively stored seeds of the two tree species either by using scatter-or larder-hoarding,although seed masting of the two species was highly asynchronized.Seed masting of Q.mongolica in previous year caused significant decrease in population size of T.sibiricus but increase in that of A.peninsulae in the next year.However,seed masting of C.mandshurica in previous year increased the population sizes of both A.peninsulae and T.sibiricus in the next year.Indoor experiments further showed that feeding only Q.mongolica acorns caused death of all tested individuals of T.sibiricus within 15 days; while all A.peninsulae survived successfully the same food supply.In contrast,both T.sibiricus and A.peninsulae survived when feeding seeds of C.mandshurica.Our results show that the influences of seed availability of the two local trees on survival and population dynamics of A.peninsulae and T.sibiricus differ interspecifically,indicating that the effect of food availability on population dynamics is much more complicated than ever thought.Different responses of hoarding animals to tannins indicate that different levels of chemical defense compounds in seeds may act as a biological filter in altering the population dynamics of food hoarding animals.Future work should be directed at separation,identification and analysis of tannin-degrading bacteria in intestines in animals.