Acorns containing deeper plumule survive better: how white oaks counter embryo excision by rodents

Several squirrel species excise the embryo of acorns of most white oak species to arrest germination for long‐term storage. However, it is not clear how these acorns counter embryo excision and survive in the arms race of coevolution. In this study, we simulated the embryo excision behavior of squirrels by removing 4 mm of cotyledon from the apical end of white oak acorns differing in embryo depths to investigate the effects of embryo excision on acorn germination and seedling performance of white oak species. The embryo depth in the cotyledons was significantly different among white oak acorns, with Quercus mongolica containing the embryo most deeply in the acorns. We found that artificial embryo excision significantly decreased acorn germination rates of Quercus variabilis, Quercus acutissima, Quercus aliena, Quercus aliena var. acutiserrata, Quercus serrata. var. brevipetiolata but not Q. mongolica. Artificial embryo excision exerted significant negative impacts on seedling performance of all oak species except Quercus aliena. Our study demonstrates the role of embryo depth of acorns in countering embryo excision by squirrels and may explain the fact that squirrels do not perform embryo excision in acorns of Q. mongolica with deeper embryos. This apparent adaptation of acorns sheds light on the coevolutionary dynamics between oaks and their seed predators.     

Bioclimatic perspectives in the distribution of Quercus ithaburensis Decne. subspecies in Turkey and in the Levant

Aim To define the bioclimatic tolerance ranges of the two Tabor oak subspecies. Prior to this definition, and considering the confusion in the literature regarding the Tabor oak subspecies geography, a reassessment of their present distribution is proposed. Location Turkey and the Levant. Methods The bioclimatic tolerance range of each subspecies was characterized by four parameters: (1) the humidity category (Q₂), (2) the winter variant (m) – the two basic variables used in Emberger's method for the definition of Mediterranean bioclimates, (3) the length of the dry season (LDS) and (4) its severity, expressed by the dry season water deficit (DSWD). The reference to the last two variables in the definition of bioclimatic tolerance ranges of Mediterranean species has so far never been considered. The concept of bioclimatic niche, based on the reference to these four parameters, is proposed and discussed. Results The reassessment of the Tabor oak subspecies distribution shows that their extents of occurrence do not overlap and are significantly distant. The comparison between the characteristics of each subspecies bioclimatic niche has highlighted three major differences: (1) The bioclimatic niche of the subspecies macrolepis is characterized by a great heterogeneity as it includes up to 10 distinct bioclimate types, whereas only four types have been found in the bioclimatic niche of the subspecies ithaburensis. (2) A 10 °C gap has been found between the winter variants of both bioclimatic niches. (3) The third major difference relates to the dry season characteristics: the bioclimatic niche of the subspecies ithaburensis is characterized by an LDS 40–75% longer than it is in the bioclimatic niche of the subspecies macrolepis. Moreover, and surprisingly, although the most arid humidity categories are found in the bioclimatic niche of the subspecies macrolepis, the bioclimatic niche of the subspecies ithaburensis is characterized by a significantly more severe dry season as the DSWD is 36–180% greater than in the bioclimatic niche of the subspecies macrolepis. It is suggested that the duration and the severity of the dry season is a major limiting factor in the spatial distribution of the subspecies macrolepis. Main conclusions The reference to the duration (LDS) and severity (DSWS) of the dry season is essential when defining the bioclimatic niche of Mediterranean species.     

Not only size matters: Acorn selection by the European jay (Garrulus glandarius)

A strong selection for acorn characteristics is expected to have evolved in the mutualistic relationship between the European jay (Garrulus glandarius) and the oak (Quercus spp.). Bossema's pioneer work suggested that jays do not select acorns randomly, but rather they preferentially select some size and species. Preference for some seeds over others may have implications on plant community dynamics by conferring advantages (or disadvantages) on the selected (avoided) seed characteristics. In this paper we test to what extent jays select acorns by species and/or by size and the relation between these two traits in Mediterranean oak species. The experiments consist of a set of field tests in which acorns from four different coexisting Mediterranean oak species (Quercus ilex, Quercus faginea, Quercus suber, and Quercus coccifera) were placed in artificial feeders accessible to wild jays. The acorns were previously measured to control individual acorn characteristics. Using video-recording techniques, we followed jay activity and the fate of each acorn (sequence of acorn selection and method of transport). Q. ilex acorns were preferred over other acorns, and Q. coccifera acorns were avoided when other acorns were available. Preference for Q. faginea and Q. suber acorns was intermediate, that is, they were preferred over Q. coccifera acorns but not over Q. ilex acorns. Large acorns were also preferred although acorn species selection was stronger than size selection. Jays selected species and size both by visual means and by using acorn area as an indicator of size. Acorns wider than 17–19 mm were carried in the bill because of throat limitation. Our results confirm Bossema's study on temperate oaks and extend it to Mediterranean oak species, revealing implications on mixed oak forest dynamics.     

Prolonged diapause and seed predation by the acorn weevil,Curculio robustus,in relation to masting of the deciduous oak Quercus acutissima

Many researchers have studied the relationship between masting by trees and seed predation by insects. Most of these studies have been plant centered, with little focus on the insect perspective. To estimate the effect of mast seeding on insect seed predators, the life‐history traits of these insects must also be considered because some seed insects can survive lean years by prolonged diapause. In this study, I examined larval infestation of acorns and life‐history traits of the acorn weevil, Curculio robustus (Roelofs) (Coleoptera: Curculionidae), in relation to acorn production of the deciduous oak Quercus acutissima Carruthers (Fagaceae) in a coppice stand in central Japan in 2004–2009. Curculio robustus females oviposit into Q. acutissima acorns, inside which the larvae develop. Mature larvae leave acorns and burrow into the soil, where they overwinter. Although germination did occur in acorns infested by weevil larvae, the percentage of germination was lower in acorns damaged by many larvae. Acorn production in Q. acutissima varied considerably among years. Both the number of C. robustus larvae infesting acorns and the percentage of acorns infested were affected by the amount of acorns produced by Q. acutissima, and two successive lean years appeared to have a considerable impact on C. robustus population size. Consequently, only a small fraction of the acorns produced were lost to predation in a mast year after two successive lean years. However, C. robustus could survive the two successive lean years because of prolonged larval diapause, probably leading to a marked decrease in population size. These findings suggest that masting in Q. acutissima succeeds as a predator satiation strategy in response to acorn damage by C. robustus, and that C. robustus has developed prolonged diapause as a counter‐adaptation.     

Acorn preference under field and laboratory conditions by two flightless Iberian dung beetle species (Thorectes baraudi and Jekelius nitidus): implications for recruitment and management of oak forests in central Spain

1. Recently, a mutualistic relationship has been described between some dung beetles (Thorectes lusitanicus and Mycotrupes lethroides) and oak species (Quercus suber, Q. canariensis, and Q. rubra), which could be crucial for ensuring seedling recruitment and sustaining the equilibrium of oak populations. For T. lusitanicus, a diet based on acorns during the reproductive period improved resistance to low‐temperature conditions and improved ovarian development. 2. In this paper, we conducted field and laboratory experiments to investigate the interaction between two potential acorn‐eating beetles, Thorectes baraudi and Jekelius nitidus, with Quercus suber. We determined the feeding preferences of both beetle species and estimated the rates of acorn manipulation by beetles according to habitat structure and several characteristics of the acorn, such as seed size and acorn infestation by weevils. 3. Results demonstrated the positive interaction between the dung beetle Thorectes baraudi and Quercus trees. Thorectes baraudi was clearly more attracted to volatiles of acorns than to dung. Jekelius nitidus, on the contrary, was either not or anecdotally attracted to acorns. On the contrary, in the case of Jekelius nitidus, the acorn attraction could be considered anecdotal or even accidental. Our field results demonstrated the acorn burying behaviour of T. baraudi in the oak forests of the Cabañeros National Park (Spain), suggesting a potential role of this beetle species as an active secondary acorn disperser. 4. This unexpected behaviour could be particularly important in Mediterranean oak forests and savannahs, where most Quercus species are strongly recruitment limited because of serious overgrazing problems.     

Responses to Drying of Recalcitrant Seeds of Quercus nigra L.

It has been suggested that rate of desiccation can influencethe expression of recalcitrant behaviour in seeds, thus complicatingthe task of determining which seeds are truly recalcitrant.The objective of this study was to see if variable rates ofdesiccation influenced such behaviour inQuercus nigra L., atree seed known to be recalcitrant. Acorn moisture content, leachate conductivity, and germinationwere determined at various times during desiccation at threerates at 27 and 40°C. Moisture contents and germinationdecreased as the severity of desiccation increased. Leachateconductivity increased slightly but was not a sensitive indicatorof loss of viability. The critical (lethal) moisture contentfor these acorns was 10–15%, although rehydration within48 h of reaching this level prevented death in about 25% ofthe acorns. At 27°C any desiccation treatment that producedlosses of 30–50mg of moisture per g of acorn dry weightper day should be suitable as a test for recalcitrance in thegenus. Apparent physiological or fungal damage at 40°C rulesout the higher temperature for such a test. Quercus nigra L.; desiccation rate; temperature; recalcitrant; leachate conductivity; germination; viability     

Partial acorn consumption by small rodents: implication for regeneration of white oak, <Emphasis Type="Italic">Quercus mongolica</Emphasis>

Partial consumption of acorns by rodents, birds, and insects has been widely reported in various oak species. However, to what extent these partially eaten acorns contribute to the regeneration of oak trees is poorly understood. To date, there is limited knowledge of the effects of seed availability on partial consumption of acorns. Herein, we released tagged Quercus mongolica acorns in two consecutive years with different seed crops, to explore the probability of partial acorn consumption. We also placed simulated partially consumed acorns in the field to investigate their contribution to regeneration of white oak. Our results showed that more acorns were partially eaten in a good crop year than in poor crop year, reflecting an effect of predator satiation on acorn partial consumption by rodents at the population level. Partially eaten acorns were more likely to be damaged at the basal end, suggesting consistent consumption preferences of small rodents. Although, partially consumed acorns were less likely to be scatter-hoarded by small rodents, they germinated more rapidly than the intact acorns in the field, offsetting the negative effects of the non-buried deposition. Despite lower germination rates, lightly damaged acorns exhibited greater growth of roots and shoots, suggesting a compensatory response to partial acorn consumption. Partial consumption may spread predation pressure on acorns and thus appears to be much better for the plant than total consumption by seed-eating animals. Therefore, partially consumed acorns as dispersal leftovers may play a potential role in natural regeneration of Quercus mongolica, especially in mast years. However, this role and the underlying mechanisms of partial acorn consumption by rodents, birds, and herbivore insects need further investigation.     

Acorn dispersal estimated by radio-tracking

Bird-dispersed seeds are difficult to track, especially in the case of long-distance dispersal events. To estimate the oak dispersal distance and the seed shadow generated by the European jay (Garrulus glandarius), we inserted radio-transmitters in 239 acorns, placed them in bird-feeders and then located them by radio-tracking. Using this methodology we located the exact caching site of 94 Quercus ilex and 54 Q. suber acorns and determined the caching habitat characteristics (vegetation type, distance, spatial distribution). The results show that: (1) there is no differences in the dispersal distance distribution between the different acorn species or sizes, (2) dispersal distances range from approximately 3 m up to approximately 550 m (mean = 68.6 m; median = 49.2 m), (3) recently abandoned fields and forest tracks were the sites preferred by jays to cache acorns, whereas fields and shrublands were avoided and (4) seed shadows showed acorn aggregation zones (i.e. clusters of caches) close to the feeder as well as isolated caches at longer distances. The results also suggest that radio-transmitters are a cheap and reliable way to determine seed shadows and quantify both seed dispersal and post-dispersal seed predation for medium to large seeds.     

The impact of the common rabbit on cork oak regeneration in SW Spain

Seed predation has traditionally been considered as simply a progressive loss of seeds. However, partial consumption of tree seeds may actually assist regeneration. We quantified partial consumption of acorns by the common rabbit (Oryctolagus cuniculus) in a cork oak forest in southwest Spain (Do?ana Natural Park). To examine the effects of partial consumption on germination and seedling emergence, we simulated two different levels of acorn predation (30 and 50?% cotyledon loss, representing light and heavy partial consumption, respectively). One-third of the sampled acorns presented evidence of consumption but most of the damage caused by partial consumption did not affect the acorn embryo (damage was mainly to non-vital parts of the propagule). Partial consumption caused more rapid germination and emergence than that was observed in intact acorns, but germination and emergence rate was unaffected. Heavy consumption of the acorn caused differences in root and shoot biomass as a consequence of cotyledon loss. In this greenhouse study, partial consumption was non-lethal to the acorns, and cotyledon biomass loss did not decrease the probability of successful establishment. Partially consumed seeds can therefore contribute significantly to the natural regeneration of Quercus coccifera, although it would be beneficial to conduct long-term studies focusing on seed traits and animal behaviour under field conditions.     

Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks

The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0%) as in Q. ilex (20.0%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60%) than in Q. ilex (21%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Acorn Pericarp Removal as a Cache Management Strategy of the Siberian Chipmunk,Tamias sibiricus

Numerous recent studies have revealed a variety of behavioral adaptations of rodents for maximizing returns from cached seeds. Herein we report on a novel behavior by the Siberian chipmunk (Tamias sibiricus) in northeastern China, by which they consistently remove the pericarp (shell) of Quercus mongolica acorns before dispersing and caching these nuts. We investigated the effects of pericarp removal on acorn germination, tannin concentrations, cache pilferage, and insect damage, to determine if and how pericarp removal facilitates cache management by Siberian chipmunks and whether or not such behavior influences seed fates. Chipmunks cached acorns only after the pericarps were removed. Chipmunks preferred pericarp‐removed acorns over intact acorns when removing them from seed stations for both consumption and caching. Pericarp removal did not affect germination or tannin concentration of cached Q. mongolica acorns, suggesting that the behavior is not an adaptation for long‐term storage and tannin decomposition. Acetone treatments of the pericarp and artificial pericarp removal failed to alter pilferage rates by Siberian chipmunks and wood mice (Apodemus peninsulae). Since damage of acorns by weevils often leads to cache losses, we also tested the effects of weevil infestation on cache decision following pericarp removal. Siberian chipmunks removed pericarps and then scatter hoarded significantly more sound than weevil‐infested acorns, strongly suggesting that pericarp removal is used to discriminate between the infested and non‐infested acorns. Thus, we argue that the primary function of this behavior is to ensure successful storage of sound acorns, at least for short‐term storage. Future studies should consider the potential impact of pericarp removal on weevil populations and long‐term patterns of seed survival and establishment from the Siberian chipmunk’s caches.     

昆虫寄生对辽东栎种子命运的影响

报道了昆虫寄生对辽东栎 Quercus liaotungensis 种子命运的影响。结果表明：（1）被昆虫寄生的种子发芽率明显低于正常成熟的种子,被昆虫寄生的种子或者不能发芽,或者能发芽但随后死亡;（2）从虫卵到老龄幼虫的发育在橡实内完成,当橡实落地后幼虫破壳而出,整个种子库的幼虫破壳时间延续2～50天,并非高度同步化;种子库的虫寄生率高达45.4%,以柞栎象Curculio dentipes为主,还有少量其它种类,如另一种象虫Curculio sp.、栗白小卷蛾 Cydia kurokoi 和螟蛾科（Pyralidae）的一未定名种;（3）昆虫寄生影响橡实成熟,测量种子大小分布表明,被昆虫寄生的种子的大小分布介于未成熟和成熟种子之间;（4）象虫寄生取食引起16.05% 的种子能量损失,显著低于对照组。结果证明昆虫寄生对辽东栎种子的命运有重要影响,是影响辽东栎种群更新的关键因素之一。     

Seed predation by mammals and forest dominance by Quercus oleoides,a tropical lowland oak

Summary Quercus oleoides Cham. and Schlecht is an unusual tree in several respects: it is an oak found in neotropical lowland forests, its distribution is not continuous but ratherdivided into many patches of various sizes, and it is a dominant in all the forests in which it occurs, attaining densities far higher than most species of tropical trees. This density pattern is related to the vulnerability of Q. oleoides acorns to predation by mammals. Observations of agoutis, deer, peccaries, squirrels, pocket mice and other seed consumers in Santa Rosa National Park, Costa Rica, showed that these mammals act only as predators, not dispersers, of Q. oleoides acorns. Experiments which involved placing acorns in deciduous forest where Q. oleoides does not occur, demonstrated that, due to high predation rates, the number of acorns produced by an isolated tree is far too low for adults to replace themselves.In oak forest, on the other hand, where the combined acorn crops of many oaks satiate the seed predators, acorn survivorship until germination is high enough to maintain the population. Furthermore, acorn survivorship in oak forest areas is inversely proportional to the apparent mammal density in those areas. Thus the pattern of forest dominance and patchy distribution is related to positively density-dependent acorn survivorship: where Q. oleoides is the forest dominant, it will survive, but if its density falls to the level typical of tropical trees, it will go locally extinct.     

Ecological significance of seed desiccation sensitivity in Quercus ilex

Background and Aims

Several widespread tree species of temperate forests, such as species of the genus Quercus, produce recalcitrant (desiccation-sensitive) seeds. However, the ecological significance of seed desiccation sensitivity in temperate regions is largely unknown. Do seeds of such species suffer from drying during the period when they remain on the soil, between shedding in autumn and the return of conditions required for germination in spring?

Methods

To test this hypothesis, the Mediterranean holm oak (Quercus ilex) forest was used as a model system. The relationships between the climate in winter, the characteristics of microhabitats, acorn morphological traits, and the water status and viability of seeds after winter were then investigated in 42 woodlands sampled over the entire French distribution of the species.

Key Results

The percentages of germination and normal seedling development were tightly linked to the water content of seeds after the winter period, revealing that in situ desiccation is a major cause of mortality. The homogeneity of seed response to drying suggests that neither intraspecific genetic variation nor environmental conditions had a significant impact on the level of desiccation sensitivity of seeds. In contrast, the water and viability status of seeds at the time of collection were dramatically influenced by cumulative rainfall and maximum temperatures during winter. A significant effect of shade and of the type of soil cover was also evidenced.

Conclusions

The findings establish that seed desiccation sensitivity is a key functional trait which may influence the success of recruitment in temperate recalcitrant seed species. Considering that most models of climate change predict changes in rainfall and temperature in the Mediterranean basin, the present work could help foresee changes in the distribution of Q. ilex and other oak species, and hence plant community alterations.     

The yeast <Emphasis Type="Italic">Candida railenensis</Emphasis> in the fruits of English oak (<Emphasis Type="Italic">Quercus robur</Emphasis> L.)

The cotyledons of whole intact acorns were shown to contain yeasts; their number increased sharply before acorn germination. The yeasts in the cotyledons are mainly represented by one species, Candida railenensis, with the number in the germinating cotyledons reaching 10⁷ CFU/g. After germination or exocarp destruction, the cotyledons were colonized by the usual epiphytic and litter yeasts Cryptococcus albidus, Rhodotorula glutinis, and Cystofilobasidium capitatum.     

Large acorns benefit seedling recruitment by satiating weevil larvae in <Emphasis Type="Italic">Quercus aliena</Emphasis>

Plants can enhance their seed viability and survival through reducing the fitness costs of herbivory by satiating seed predators at either plant or seed level, or both. The former satiates with production of large crops while the latter with large-sized seeds, enhancing the probability of seed survival. We analyzed both types of satiation in the interaction between the Quercus aliena and the weevil Curculio spp in 2 years with different crop size and acorn size. Larger crop size seemed to satiate less effectively weevils due to higher proportions of the seeds were attacked in oaks producing more crops of smaller acorns. However, prematurely abscission of infested acorns in large crop year might compensate this ineffectiveness. Larger acorns in lean year well satiated weevil larvae, as a larger acorn size increased the likelihood of embryo survival and seedling establishment. Although effective satiation by larger acorns would be negated by smaller seed crops, the proportion of attacked acorns that survived increased with large acorn size in lean year. These results highlighted the importance of annual variation in acorn size of Quercus aliena in satiating and defending weevil larval predations, consequently in successful seedling recruitment and establishment.     

Guild structures of seed insects in relation to acorn development in two oak species

We investigated patterns of acorn growth in Quercus variabilis Blume and Quercus serrata Thunb., seasonal trends in emergence of seed insects found in the acorns, oviposition periods of the insects and falling periods of insect-infested acorns. In Q. variabilis, two insect guilds were associated with acorn development: (i) the immature acorn feeding (IAF) guild [Curculionidae sp., Poecilips cardamomi (Schaufuss), and Characoma ruficirra (Hampson)]; and (ii) the mature acorn feeding (MAF) guild [Curculio robustus (Roelofs), Curculio sikkimensis (Heller), and Cydia glandicolana (Danilevsky)]. In Q. serrata, there were three guilds: (i) the pistillate flower feeding (PFF) guild (cynipid wasp); (ii) the IAF guild [sap absorption by Mechoris ursulus (Roelofs)]; and (iii) the MAF guild (M. ursulus, C. sikkimensis, Cydia danilevskyi (Kuznetzov), C. glandicolana and Autostichidae sp.). The succession of guilds during acorn development may be a consequence of the use by different species of the limited food resource. The lack of a PFF guild in Q. variabilis that was found in our field site would have a positive effect on IAF guilds in utilizing the acorns.     

Biennial acorn maturation and its relationship with flowering phenology in Iberian populations of <Emphasis Type="Italic">Quercus suber</Emphasis>

Since the XIX century, there is a controversy about the existence of biennial maturation of the acorns in Quercus suber L. While some authors recognised biennial cycles as an adaptation to habitats with short vegetative periods, other authors discarded the biennial pattern. Successive flowering events from spring to autumn and annual acorn ripening are proposed as an explanation of the multiple acorn crops typical of Iberian forests. To clarify this discussion, the presence of annual and biennial acorns was assessed in seven cork oak stands, covering a wide range of environmental conditions. In each stand, 100 individuals were sampled once in spring and once in autumn. Biennial acorns were observed with variable frequencies in all populations. There was a significant and positive relationship between latitude and the percentage of trees with biennial acorns within northern and central populations. On the contrary, this trend was not significant among southern populations. The hypothesis that the presence of biennial acorns in Quercus suber is related to individual female flowering phenology was confirmed in four populations located in the southwestern Iberian Peninsula. Unregarding local differences in the distribution of phenological stages anticipated trees bore significantly less biennial acorns than delayed individuals of the same stand. This result is coherent with the idea that the length of the vegetative period plays a crucial role in the frequency of annual and biennial acorn ripening patterns. The relationship between annual and biennial ripening cycles and the multiple acorn crops is discussed.     

Sweep-Net Sampling Acorns in Forested Wetlands

ABSTRACT We are unaware of any previous studies to evaluate using a sweep net to estimate abundance of red oak acorns (Quercus spp.) after they fall from tree crowns, sink to the ground in flooded bottomlands (i.e., sound acorns), and become potential food for animals or propagules for seedlings. We placed known numbers of white-painted red oak acorns of 3 size classes and used a sweep net to recover them in a flooded hardwood bottomland in Noxubee National Wildlife Refuge, Mississippi, USA. We recovered large acorns 1.96 and 1.32 times more often than small and medium acorns, respectively. Mean recovery rate of all marked acorns across size and density classes was 34.0 ± 7.0% (SE, n = 9). Thus, sweep-net sampling for sound acorns in flooded oak bottomlands may yield negatively biased estimates of acorn abundance, and investigators should consider using correction factors.     

Repeated radicle pruning of Quercus mongolica acorns as a cache management tactic of Siberian chipmunks

Many rodents hoard seeds as a means of ensuring food availability during scarcity. Siberian chipmunks (Tamias sibiricus) feed on acorns of white oak Quercus mongolica and hoard them for future use. Such caches may deteriorate due to the early germination of the acorns in autumn, which can be inhibited by radicle pruning or embryo excision. Siberian chipmunks are found to frequently prune the radicles of germinated acorns of Q. mongolica; however, whether this behavior is a kind of cache management tactic remains unclear. Here, we performed semi-natural enclosure and field experiments to test the role of radicle pruning in cache management of T. sibiricus. We found that T. sibiricus preferred non-germinated acorns and tended to prune radicles of germinating acorns when scatter-hoarding them, but did not perform the behavior of embryo excision by squirrels. Both semi-natural enclosure and field experiments showed that T. sibiricus not only pruned radicles repeatedly but removed radicles varied in length from acorns, which significantly postponed acorn germination and radicle growth. These observations suggest that radicle pruning would be an evolutionary tactic for cache management of Siberian chipmunks.