Incorporating Cache Management Behavior into Seed Dispersal: The Effect of Pericarp Removal on Acorn Germination
Selecting seeds for long-term storage is a key factor for food hoarding animals. Siberian chipmunks (Tamias sibiricus) remove the pericarp and scatter hoard sound acorns of Quercus mongolica over those that are insect-infested to maximize returns from caches. We have no knowledge of whether these chipmunks remove the pericarp from acorns of other species of oaks and if this behavior benefits seedling establishment. In this study, we tested whether Siberian chipmunks engage in this behavior with acorns of three other Chinese oak species, Q. variabilis, Q. aliena and Q. serrata var. brevipetiolata, and how the dispersal and germination of these acorns are affected. Our results show that when chipmunks were provided with sound and infested acorns of Quercus variabilis, Q. aliena and Q. serrata var. brevipetiolata, the two types were equally harvested and dispersed. This preference suggests that Siberian chipmunks are incapable of distinguishing between sound and insect-infested acorns. However, Siberian chipmunks removed the pericarp from acorns of these three oak species prior to dispersing and caching them. Consequently, significantly more sound acorns were scatter hoarded and more infested acorns were immediately consumed. Additionally, indoor germination experiments showed that pericarp removal by chipmunks promoted acorn germination while artificial removal showed no significant effect. Our results show that pericarp removal allows Siberian chipmunks to effectively discriminate against insect-infested acorns and may represent an adaptive behavior for cache management. Because of the germination patterns of pericarp-removed acorns, we argue that the foraging behavior of Siberian chipmunks could have potential impacts on the dispersal and germination of acorns from various oak species.
Discriminatory pre-hoarding handling and hoarding behaviour towards germinated acorns by Niviventer confucianus
Germination is an important stage in the seed life cycle, but it decreases seed nutrients and increases secondary compounds, which is disadvantageous to seed hoarders or consumers. Therefore, seed hoarders often use pre-hoarding handling behaviour (PHB) to prevent the further deterioration of germinated seeds. Although PHB is an important component of seed dispersal ecology, few studies have described or estimated the effectiveness of PHB. In this study, we investigated the PHB and hoarding strategies of Niviventer confucianus Milne-Edwards towards germinated and ungerminated acorns (Quercus variabilis Bl.). We observed that N. confucianus (1) displayed radicle-excision behaviour towards germinated acorns; (2) often removed the pericarps of the germinated acorns more than those of ungerminated acorns before hoarding; and (3) tended to larder-hoard ungerminated acorns but scatter-hoard germinated acorns. Our results indicate that (1) PHB towards germinated seeds exists in this species as well as in members of the family Sciuridae; (2) N. confucianus consumed and hoarded acorns in different condition discriminately, and adopted a flexible strategy when hoarding perishable seeds. These pre-hoarding handling and hoarding behaviours are possibly evolutionary adaptations in rodents to manage and hoard easily germinated acorns and inevitably impacts on seed dispersal, seed fate, seed germination, and sapling recruitment.
Fruiting Phenology and Pre-dispersal Seed Predation in a Rainforest in Southern Western Ghats, India
The mid-elevation non-dipterocarp wet forests in southern Western Ghats, India are some of the largest stretches of undisturbed forest remaining in this biodiversity hotspot. We established a long-term study of tree phenology in this forest to study the effects of biotic and abiotic factors on phenological patterns. We measured seed predation of selected canopy trees across three years. Seed predation intensity was measured through seed fall, phenology by fruit fall, and animal abundance through transect sampling. A total of 42 tree species was sampled for phenology and 35 species for seed predation intensity. Nine of these species fruited annually, seven fruited once in two years and the remaining species fruited once in several years. Two primates and two arboreal squirrels were the major seed predators in the forest. Primates were responsible for some intact seed dispersal, while squirrels were obligate seed predators. For numerous tree species seed predators were the only seed dispersers. Seed predator abundance showed no significant changes across years except for the case of the lion tailed macaque, which appeared to show seasonal population movement. No community-wide mass fruiting phenomena were noticeable in the forest but there was significant variation in fruit availability between years. A few tree species appeared to show mast fruiting in certain years. A majority of the species suffered high levels of seed predation. Seed predation intensity decreased during mast fruiting events for certain species while for others it had no effect. There was no difference in predation intensity between annually and supra-annually fruiting species. Masting as a means of overcoming high seed predation at the population level in the Western Ghats was limited to only a few tree species.