Differentiation in seed hoarding among three sympatric rodent species in a warm temperate forest

Although seed hoarding by rodents has been extensively studied, differentiation in seed‐hoarding behaviors among sympatric rodent species has not been well investigated. Using semi‐natural enclosures, we demonstrated that three sympatric rodent species showed clear differentiation in food selection, scatter versus larder hoarding behaviors and eating behaviors when offered seeds of four plant species from a warm temperate forest in northern China. The large field mouse Apodemus peninsulae preferred seeds of wild apricot (Prunus armeniaca) and Liaodong oak (Quercus liaotungensis), whereas the Chinese white‐bellied rat Niviventor confucianus preferred seeds of cultivated walnut and Liaodong oak, and the David's rock squirrel Sciurotamias davidianus preferred seeds of cultivated walnut, wild apricot and Liaodong oak. All three rodents showed larder hoarding of seeds from all four plant species, but the large field mouse showed scatter hoarding of wild apricot, and the David's rock squirrel showed scatter hoarding of Liaodong oak and wild walnut. Acorns of Liaodong oak, which have a soft seed hull, were more often eaten in situ, whereas wild walnuts, which have a hard seed hull and more tannin, were less hoarded by all rodent species. Differentiation in the scatter versus larder hoarding behaviors of sympatric rodent species suggests that sympatric rodents play different roles in the regeneration of different sympatric plant species.     

Does scatter‐hoarding of seeds benefit cache owners or pilferers?

The scatter‐hoarding behavior of granivorous rodents plays an important role in seed dispersal and seedling regeneration of trees, as well as the evolution of several well‐known mutualisms between trees and rodents in forest ecosystems. Because it is difficult to identify seed hoarders and pilferers under field conditions by traditional methods, the full costs incurred and benefits accrued by scatter‐hoarding have not been fully evaluated in most systems. By using infrared radiation camera tracking and seed tagging, we investigated the benefits and losses of scatter‐hoarded seeds (Camellia oleifera) for 3 sympatric rodent species (Apodemus draco, Niviventer confucianus and Leopoldamys edwardsi) in a subtropical forest of Southwest China during 2013 to 2015. We established the relationships between the rodents and the seeds at the individual level. For each rodent species, we calculated the cache recovery rate of cache owners, as well as conspecific and interspecific pilferage rates. We found that all 3 sympatric rodent species had a cache recovery advantage with rates that far exceeded average pilferage rates over a 30‐day tracking period. The smallest species (A. draco) showed the highest rate of scatter‐hoarding and the highest recovery advantage compared with the other 2 larger species (N. confucianus and L. edwardsi). Our results suggest that scatter‐hoarding benefits cache owners in food competition, supporting the pilferage avoidance hypothesis. Therefore, scatter‐hoarding behavior should be favored by natural selection, and plays a significant role in species coexistence of rodent community and in the formation of mutualism between seeds and rodents in forest ecosystems.     

Fluctuation in seed abundance has contrasting effects on the fate of seeds from two rapidly germinating tree species in an Asian tropical forest

The seed predator satiation hypothesis states that high seed abundance can satiate seed predators or seed dispersers, thus promoting seed survival. However, for rapidly germinating seeds in tropical forests, high seed abundance may limit dispersal as the seeds usually remain under parent trees for long periods, which may lead to high mortality due to rodent predation or fungal infestations. By tracking 2 species of rapidly germinating seeds (Pittosporopsis kerrii, family Icacinaceae; Camellia kissi, family Theaceae), which depend on dispersal by scatter‐hoarding rodents, we investigated the effects of seed abundance at the community level on predation and seed dispersal in the tropical forest of Xishuangbanna Prefecture, Southwest China. We found that high seed abundance at the community level was associated with delayed and reduced seed removal, decreased dispersal distance and increased pre‐dispersal seed survival for both plant species. High seed abundance was also associated with reduced seed caching of C. kissi, but it showed little effect on seed caching of P. kerrii. However, post‐dispersal seed survival for the 2 plant species followed the reverse pattern. High seed abundance in the community was associated with higher post‐dispersal survival of P. kerrii seeds, but with lower post‐dispersal survival of C. kissi seeds. Our results suggest that different plant species derive benefit from fluctuations in seed production in different ways.     

Scatter‐hoarding rodents as secondary seed dispersers of a frugivore‐dispersed tree Scleropyrum wallichianum in a defaunated Xishuangbanna tropical forest,China

Local extinction or population decline of large frugivorous vertebrates as primary seed dispersers, caused by human disturbance and habitat change, might lead to dispersal limitation of many large‐seeded fruit trees. However, it is not known whether or not scatter‐hoarding rodents as secondary seed dispersers can help maintain natural regeneration (e.g. seed dispersal) of these frugivore‐dispersed trees in the face of the functional reduction or loss of primary seed dispersers. In the present study, we investigated how scatter‐hoarding rodents affect the fate of tagged seeds of a large‐seeded fruit tree (Scleropyrum wallichianum Arnott, 1838, Santalaceae) from seed fall to seedling establishment in a heavily defaunated tropical forest in the Xishuangbanna region of Yunnan Province, in southwest China, in 2007 and 2008. Our results show that: (i) rodents removed nearly all S. wallichianum seeds in both years; (ii) a large proportion (2007, 75%; 2008, 67.5%) of the tagged seeds were cached individually in the surface soil or under leaf litters; (iii) dispersal distance of primary caches was further in 2007 (19.6 ± 14.6 m) than that in 2008 (14.1 ± 11.6 m), and distance increased as rodents recovered and moved seeds from primary caches into subsequent caching sites; and (iv) part of the cached seeds (2007, 3.2%; 2008, 2%) survived to the seedling stage each year. Our study suggests that by taking roles of both primary and secondary seed dispersers, scatter‐hoarding rodents can play a significant role in maintaining seedling establishment of S. wallichianum, and are able to at least partly compensate for the loss of large frugivorous vertebrates in seed dispersal.     

Visual and auditory cues facilitate cache pilferage of Siberian chipmunks (Tamias sibiricus) under indoor conditions

In the struggle for survival, scatter‐hoarding rodents are known to cache food and pilfer the caches of others. The extent to which rodents utilize auditory/visual cues from conspecifics to improve cache‐pilfering is unknown. Here, Siberian chipmunks (Tamias sibiricus) were allowed to search for caches of Corylus heterophylla seeds (man‐made caches and animal‐made caches) after experiencing cues from a conspecific's cache‐searching events. For each type of cache, 3 experimental scenarios were presented: (1) alone (control); (2) auditory/visual (hearing and seeing conspecific's cache‐searching events); and (3) auditory only (hearing conspecific's cache‐searching events only) with random orders. The subjects located man‐made caches faster, harvested more caches, and hoarded more seeds both in the auditory/visual and the auditory only treatments compared to the control, while scatter‐hoarding more seeds in the auditory/visual treatment but larder‐hoarding more seeds in the auditory only treatment. Compared to the control, the animals spent less time locating animal‐made caches, harvested more caches, ate fewer seeds, larder‐hoarded more seeds and hoarded more seeds in total both in the auditory/visual and the auditory only treatments, while eating more seeds and hoarded fewer seeds in total in the auditory only treatment than in the auditory/visual treatment. The results also show that females spent less time locating the animal‐made caches, but they scatter‐hoarded fewer seeds than males in the auditory/visual treatment. To the best of our knowledge, this is the first report that visual and/or auditory cues of conspecifics improve cache‐pilfering and hoarding in rodents.     

Seed value influences cache pilfering rates by desert rodents

Some rodents gather and store seeds. How many seeds they gather and how they treat those seeds is largely determined by seed traits such as mass, nutrient content, hardness of the seed coat, presence of secondary compounds, and germination schedule. Through their consumption and dispersal of seeds, rodents act as agents of natural selection on seed traits, and those traits influence how rodents forage. Many seeds that are scatter‐hoarded by rodents are pilfered, or stolen, by other rodents, and seed traits also likely influence pilfering rates and seed fates of pilfered seeds. To clarify coevolutionary relationships between rodents and the plants that they disperse, one needs to understand the role of seed traits in rodent foraging decisions. We compared how the seeds of 4 species of plants that are dispersed by scatter‐hoarding animals and that differ in value (singleleaf piñon pine, Pinus monophylla; desert peach, Prunus andersonii; antelope bitterbrush, Purshia tridentata; Utah juniper, Juniperus osteosperma) were pilfered and recached by rodents. One hundred artificial caches of the 4 seed species (25 per species) were prepared, and removal by rodents was monitored. Rodents pilfered high‐value seeds more rapidly than the other seeds. Desert peach seeds, which contain toxic secondary compounds, were more frequently recached. Relatively low value seeds like Utah juniper and antelope bitterbrush were pilfered more slowly and were sometimes left at cache sites, and seeds of the latter species were transported shorter distances to new cache sites. The background density of seeds also appeared to influence the relative value of seeds.     

Exclusion of interspecific competition reduces scatter‐hoarding of Siberian chipmunk Tamias sibiricus: A field study

Although food availability and the abundance of seed predators have been postulated to affect seed dispersal, it is not clear how seed‐eating animals modify their scatter‐hoarding strategies in response to different levels of interspecific competition. We placed paired germinated and ungerminated acorns of Quercus mongolica on 30‐cm high platforms to exclude potential interspecific competition of the predominant larder hoarders Apodemus peninsulae and Myodes rufocanus, to investigate seed dispersal by a predominant scatter‐hoarder, Tamias sibiricus, in the field in north‐eastern China. Our results showed that T. sibiricus ate more acorns in situ in the absence of interspecific competition. In the presence of interspecific competition of A. peninsulae and C. rufocanus, however, more acorns were scatter‐hoarded by T. sibiricus. Regardless of interspecific competition, germination of acorns showed no significant effects on seed dispersal patterns, inconsistent with the “seed perishability hypothesis” that animals avoid hoarding seeds with high perishability. Exclusion of interspecific competition, though relatively increasing the per capita seed abundance, appears to reduce seed dispersal, scatter‐hoarding and seedling establishment. Therefore, we propose that moderate interspecific competition rather than competition exclusion may benefit seed scatter‐hoarding and seedling establishment.     

Effects of insect infestation on rodent‐mediated dispersal of Quercus aliena: results from field and enclosure experiments

Rodents influence plant establishment and regeneration by functioning as both seed predators and dispersers. However, these rodent–plant interactions can vary significantly due to various environmental conditions and the activity of other insect seed predators. Here, we use a combination of both field and enclosure (i.e. individual cage and semi‐natural enclosure) experiments, to determine whether rodents can distinguish sound seeds from those infested with insects. We also demonstrate how such responses to insects are influenced by food abundance and other environmental factors. We presented rodents with 2 kinds of Quercus aliena seeds (sound and insect‐infested seeds) in a subtropical forest in the Qinling Mountains, central China, from September to November of 2011 to 2013. The results showed that rodents preferred to hoard and eat sound seeds than infested seeds in the field and semi‐natural enclosure, while they preferred to eat infested seeds over sound seeds in the individual cages. In addition, both hoarding and eating decisions were influenced by food abundance. Rodents hoarded more sound seeds in years of high food abundance while they consumed more acorns in years of food shortage. Compared with field results, rodents reduced scatter‐hoarding behavior in semi‐natural enclosures and ate more insect‐infested seeds in smaller individual cages. These results further confirm that rodents distinguish infested seeds from non‐infested seeds but demonstrate that this behavior varies with conditions (i.e. environment and food abundance). We suggest that such interactions will influence the dispersal and natural regeneration of seeds as well as predation rates on insect larvae.     

Asymmetric competition for seeds between two sympatric food hoarding rodents: implications for coexistence

Asymmetric competition occurs when some species have distinct advantages over their competitors and is common in animals with overlapping habitats and diet. However, the mechanism allowing coexistence between asymmetric competitors is not fully clear. Chinese white-bellied rats (Niviventer confucianus, CWR) and Korean field mice (Apodemus peninsulae, KFM) are common asymmetric competitors in shrublands and forests west of Beijing city. They share similar diet (e.g. plant seeds) and activity (nocturnal), but differ in body size (CWR are bigger than KFM), food hoarding habit (CWR: mainly larder hoarding; KFM: both larder and scatter hoarding), and ability to protect cached food (CWR are more aggressive than KFM). Here, we tested seed competition in 15 CWR–KFM pairs over a 10-day period under semi-natural enclosure conditions to uncover the differences in food hoarding, cache pilferage, and food protection between the 2 rodents, and discuss the implication for coexistence. Prior to pilferage, CWR harvested and ate more seeds than KFM. CWR tended to larder hoard seeds, whereas KFM preferred to scatter hoard seeds. Following pilferage, CWR increased consumption, decreased intensity of hoarding, and pilfered more caches from KFM than they lost, while KFM increased consumption more than they hoarded, and they preferred to hoard seeds in low and medium competition areas. Accordingly, both of the 2 rodent species increased their total energy consumption and hoarding following pilferage. Both rodent species tended to harvest seeds from the source, rather than pilfer caches from each other to compensate for cache loss via pilferage. Compared to CWR, KFM consumed fewer seeds when considering seed number, but hoarded more seeds when considering the seeds’ relative energy (energy of hoarded seeds/rodent body mass^2/3) at the end of the trials. These results suggest that asymmetric competition for food exists between CWR and KFM, but differentiation in hoarding behavior could help the subordinate species (i.e. KFM) hoard more energy than the dominant species (i.e. CWR), and may contribute to their coexistence in the field.     

Context‐dependent responses of food‐hoarding to competitors in Apodemus peninsulae: implications for coexistence among asymmetrical species

Superior species may have distinct advantages over subordinates within asymmetrical interactions among sympatric animals. However, exactly how the subordinate species coexists with superior species is unknown. In the forests west of Beijing City, intense asymmetrical interactions of food competition exist among granivorous rodents (e.g. Apodemus peninsulae, Niviventer confucianus, Sciurotamias davidianus and Tscherskia triton) that have broadly overlapping habitats and diets but have varied body size (range 15–300 g), hoarding habits (scatter vs larder) and/or daily rhythm (diurnal vs nocturnal). The smallest rodent, A. peninsulae, which typically faces high competitive pressure from larger rodents, is an ideal model to explore how subordinate species coexist with superior species. Under semi‐natural enclosure conditions, we tested responses of seed‐hoarding behavior in A. peninsulae to intraspecific and interspecific competitors in the situations of pre‐competition (without competitor), competition (with competitor) and post‐competition (competitor removed). The results showed that for A. peninsulae, the intensity of larder‐hoarding increased and the intensity of scatter‐hoarding declined in the presence of intraspecifics and S. davidianus, whereas A. peninsulae ceased foraging and hoarding in the presence of N. confucianus and T. triton. A. peninsulae reduced intensity of hoarding outside the nest and moved more seeds into the nest for larder‐hoarding under competition from intraspecific individuals and S. davidianus. In most cases, the experimental animals could recover to their original state of pre‐competition when competitors were removed. These results suggest that subordinate species contextually regulate their food‐hoarding strategies according to different competitors, promoting species coexistence among sympatric animals that have asymmetrical food competition.     

Trait‐mediated seed predation,dispersal and survival among frugivore‐dispersed plants in a fragmented subtropical forest,Southwest China

By tracking the fate of individual seeds from 6 frugivore‐dispersed plants with contrasting seed traits in a fragmented subtropical forest in Southwest China, we explored how rodent seed predation and hoarding were influenced by seed traits such as seed size, seed coat hardness and seed profitability. Post‐dispersal seed fates varied significantly among the 6 seed species and 3 patterns were witnessed: large‐seeded species with a hard seed coat (i.e. Choerospoadias axillaries and Diospyros kaki var. silvestris) had more seeds removed, cached and then surviving at caches, and they also had fewer seeds predated but a higher proportion of seeds surviving at the source; medium‐sized species with higher profitability and thinner seed coat (i.e. Phoebe zhennan and Padus braohypoda) were first harvested and had the lowest probability of seeds surviving either at the source or at caches due to higher predation before or after removal; and small‐seeded species with lower profitability (i.e. Elaeocarpus japonicas and Cornus controversa) had the highest probability of seeds surviving at the source but the lowest probability of seeds surviving at caches due to lower predation at the source and lower hoarding at caches. Our study indicates that patterns of seed predation, dispersal and survival among frugivore‐dispersed plants are highly determined by seed traits such as seed size, seed defense and seed profitability due to selective predation and hoarding by seed‐eating rodents. Therefore, trait‐mediated seed predation, dispersal and survival via seed‐eating rodents can largely affect population and community dynamics of frugivore‐dispersed plants in fragmented forests.     

Effects of thinning on scatter‐hoarding by rodents in temperate forest

Deforestation and thinning are human activities that can destabilize the forest ecological system and, consequently, impact significantly on habitat and behavior of forest‐dwelling animals. This hypothesis was tested in Yugong in the Mount Taihangshan area by comparing the tracks of tagged seeds of Armeniaca sibirica. in sites of unthinned and thinned forests. Our results showed that: (i) the diversity of vegetation and rodents drastically reduced in sites with thinned forests, compared to unthinned sites; (ii) the amount of both removed and scatter‐hoarded seeds significantly declined in sites with thinned forests, compared with the unthinned sites; (iii) there was no significant difference observed in the distance of seed dispersal between the thinned and unthinned areas; and (iv) the thinning did not show a significant change to the model of cache size. These results suggested that the thinning of forests negatively influenced the species richness and food‐hoarding behavior of rodents. In addition, the results indicated that the weakened scattered‐hoarding might be disadvantageous to seedling recruitment and forest restoration.     

Visual landmark‐directed scatter‐hoarding of Siberian chipmunks Tamias sibiricus

Spatial memory of cached food items plays an important role in cache recovery by scatter‐hoarding animals. However, whether scatter‐hoarding animals intentionally select cache sites with respect to visual landmarks in the environment and then rely on them to recover their cached seeds for later use has not been extensively explored. Furthermore, there is a lack of evidence on whether there are sex differences in visual landmark‐based food‐hoarding behaviors in small rodents even though male and female animals exhibit different spatial abilities. In the present study, we used a scatter‐hoarding animal, the Siberian chipmunk, Tamias sibiricus to explore these questions in semi‐natural enclosures. Our results showed that T. sibiricus preferred to establish caches in the shallow pits labeled with visual landmarks (branches of Pinus sylvestris, leaves of Athyrium brevifrons and PVC tubes). In addition, visual landmarks of P. sylvestris facilitated cache recovery by T. sibiricus. We also found significant sex differences in visual landmark‐based food‐hoarding strategies in Siberian chipmunks. Males, rather than females, chipmunks tended to establish their caches with respect to the visual landmarks. Our studies show that T. sibiricus rely on visual landmarks to establish and recover their caches, and that sex differences exist in visual landmark‐based food hoarding in Siberian chipmunks.     

Seed traits and taxonomic relationships determine the occurrence of mutualisms versus seed predation in a tropical forest rodent and seed dispersal system

Although many studies have been carried out on plant–animal mutualistic assemblages, the roles of functional traits and taxonomy in determining both whether interactions involve mutualisms or predation and the structure of such assemblages are unclear. We used semi‐natural enclosures to quantitatively assess the interaction strengths between seeds of 8 sympatric tree species and 4 rodent species in a tropical forest in Xishuangbanna, Yunnan, Southwest China. We found 2 clusters of species in the seed–rodent network represented by 2 genera in the Fagaceae (Castanopsis, Lithocarpus). Compared to seeds of 3 Castanopsis species, seeds with heavy weight, hard coat or caloric content (including 3 Lithocarpus species) were eaten less and more frequently hoarded by rodents. In turn, hoarded seeds showed less predation and more mutualism with rodents. Our results suggest that seed traits significantly affected the hoarding behavior of rodents, and, consequently, the occurrence of mutualisms and predation as well as assemblage structure in the plant–animal seed dispersal system. Taxonomically‐related species with similar seed traits as functional groups belong to the same substructures in the assemblage. Our results indicate that both seed traits and taxonomic relationships may simplify thinking about seed dispersal systems by helping to elucidate whether interactions are likely to be dominated by predation or mutualism.     

Does multiple seed loading in Blue Jays result in selective dispersal of smaller acorns?

Studies from both tropical and temperate systems show that scatter‐hoarding rodents selectively disperse larger seeds farther from their source than smaller seeds, potentially increasing seedling establishment in larger‐seeded plants. Size‐biased dispersal is evident in many oaks (Quercus) and is true both across and within species. Here, we predict that intraspecifc variation in seed size also influences acorn dispersal by the Blue Jay (Cyanocitta cristata Linnaeus), but in an opposite manner. Blue Jays are gape‐limited and selectively disperse smaller acorn species (e.g. pin oaks [Quercus palustris Münchh]), but often carry several acorns in their crop during a single dispersal event. We predict that jays foraging on smaller acorns will load more seeds per trip and disperse seeds to greater distances than when single acorns are carried in the bill. To test this, we presented free‐ranging Blue Jays with pin oak acorns of different sizes over a 2‐year period. In each of 16 experimental trials, we monitored the birds at a feeding station with remote cameras and determined the number of acorns removed and the distance acorns were dispersed when cached. Jays were significantly more likely to engage in multiple seed loading with smaller seeds in both years of the study. During the second year, these smaller acorns were dispersed farther than larger acorns, and during the first year, larger acorns were dispersed farther, revealing an inconsistent response to seed size during our study. We suggest that in some circumstances, multiple seed loading by Blue Jays may favor dispersal in some plant species.     

Cultivated walnut trees showed earlier but not final advantage over its wild relatives in competing for seed dispersers

Little is known about seeding regeneration of cultivated trees compared to wild relatives in areas where seed dispersers are shared. Here, we investigated the differences in seed fates of cultivated walnut (Juglans regia) and wild Manchurian walnut (Juglans mandshurica) trees under rodent predation and dispersal. J. regia seeds have higher nutritional value (large size, mass and kernel mass) and lower mechanical defensiveness (thin endocarp) than J. mandshurica seeds. We tracked seeds of J. regia and J. mandshurica under both enclosure and field conditions to assess differences in competing for seed dispersers of the two co‐occurring tree species of the same genus. We found that rodents preferred to harvest, eat and scatter‐hoard seeds of J. regia as compared to those of J. mandshurica. Seeds of J. regia were removed and scatter‐hoarded faster than those of J. mandshurica. Caches of J. regia were more likely to be rediscovered by rodents than those of J. mandshurica. These results suggest that J. regia showed earlier dispersal fitness but not the ultimate dispersal fitness over J. mandshurica in seeding regeneration under rodent mediation, implying that J. regia has little effect on seeding regeneration of J. mandshurica in the field. The effects of seed traits on seed dispersal fitness may vary at different dispersal stages under animal mediation.     

Predation of cassowary dispersed seeds: is the cassowary an effective disperser?

Post‐dispersal predation is a potentially significant modifier of the distribution of recruiting plants and an often unmeasured determinant of the effectiveness of a frugivore's dispersal service. In the wet tropical forests of Australia and New Guinea, the cassowary provides a large volume, long distance dispersal service incorporating beneficial gut processing; however, the resultant clumped deposition might expose seeds to elevated mortality. We examined the contribution of post‐dispersal seed predation to cassowary dispersal effectiveness by monitoring the fate of 11 species in southern cassowary (Casuarius casuarius johnsonii Linnaeus) droppings over a period of 1 year. Across all species, the rate of predation and removal was relatively slow. After 1 month, 70% of seeds remained intact and outwardly viable, while the number fell to 38% after 1 year. The proportion of seeds remaining intact in droppings varied considerably between species: soft‐seeded and large‐seeded species were more likely to escape removal and predation. Importantly, across all species, seeds in droppings were no more likely to be predated than those left undispersed under the parent tree. We speculate that seed predating and scatter‐hoarding rodents are responsible for the vast majority of predation and removal from droppings and that the few seeds which undergo secondary dispersal survive to germination. Our findings reinforce the conclusion that the cassowary is an important seed disperser; however, dispersal effectiveness for particular plant species can be reduced by massive post‐dispersal seed mortality.     

Seed traits and rodent community interact to determine seed fate: evidence from both enclosure and field experiments

Animal-mediated seed dispersal is an important ecological process in which a strong mutualism between animals and plants can arise. However, few studies have examined how a community of potential seed dispersers interacts with sympatric seed trees. We employed a series of experiments in the Qinling Mountains in both semi-natural enclosure and the field to assess the interactions among 3 sympatric rodent species and 3 Fagaceae tree seeds. Seed traits all showed similar tannin levels but markedly different physical traits and nutritional contents. We found that seeds with heavy weight, thick coat, and high nutritional contents were less likely to be eaten in situ but more often to be eaten after dispersal or hoarded by rodents. These results support both the handling time hypothesis and the high nutrition hypothesis. Surprisingly, we also found that rodents, maybe, preferred to consume seeds with low levels of crude fiber in situ, and to harvest and hoard those with high levels of crude fiber for later consumption. The sympatric rodent species, Cansumys canus, the largest rodent in our study, harvested and hoarded more Quercus variabilis seeds with high physical and nutritional traits, while Apodemus draco, the smallest rodent, harvested more Q. serrata seeds with low physical and nutritional traits, and Niviventer confucianus harvested and hoarded more Q. aliena seeds with medium physical and nutritional traits. Our study demonstrates that different seed traits play different roles in influencing the seed fate and the shaping of mutualism and predation interactions within a community of rodent species.     

入侵植物少花蒺藜草异型种子萌发策略及其幼苗生长特性

少花蒺藜草为科尔沁沙地的一种恶性入侵杂草，靠种子进行繁殖，其同一果实刺苞内多包含2粒种子，种子具有异型性（其中一粒相对较大、外形似芒果且有一小部分外露在刺苞中，称为M型种子；另一粒相对较小、外形似李子，称之为P型种子），野外调查发现少花蒺藜草通常以M型种子萌发为主。为探究少花蒺藜草刺苞果皮对异型种子的萌发是否产生影响、M型种子是否对P型种子的萌发产生抑制以及两异型种子的萌发在种群拓展中的作用，在实验室条件下测定少花疾藜草带刺苞（正常条件下）、去刺苞（将果皮解剖取出单独的M型、P型种子）、模拟刺苞（以纱布模拟刺苞果皮将取出的两异型种子进行再次包裹）4种处理下两种异型种子的萌发特征以及正常条件下的刺苞（只萌发M型）、单独的M型、P型及刺苞内P型种子（去除刺苞中已萌发的M型种子形成的幼苗）形成幼苗的生长特征。结果表明：1）刺苞果皮对两种异型种子的萌发均无显著影响；2）M型种子抑制P型种子的萌发，抑制率达到52.5%；3）刺苞内M型种子形成幼苗的地上生物量、地下生物量分别比刺苞内P型种子形成幼苗增加0.1298和0.1068 g·株^-1，M型种子形成幼苗的叶面积、根冠比分别比P型种子形成幼苗显著增加84.3%和356.3%。上述研究表明：刺苞内M型种子比P型种子具有更强的发芽能力，M型种子形成的幼苗具有更好的存活策略，P型种子作为备用种子当年或翌年补充种群数量。     

Do Abrasion- or Temperature-Based Techniques More Effectively Relieve Physical Dormancy in Seeds of Cold Desert Perennials?

Seed dormancy can present a significant barrier to restoration outcomes in dryland systems. Physical and combinational (physical + physiological) dormancy are prevalent among seeds of many herbaceous perennials used in restoration of drylands throughout the western United States. Although many techniques designed to alleviate these dormancy traits exist, their efficacy is species specific, may result in embryo damage, and may have limited large-scale application. To identify the most effective means of dormancy alleviation with the potential to be used on an operational scale, we examined the effects of 16 temperature-based techniques (altering temperature and duration of wet heat, freezing and wet heat, and freeze-thaw cycles) and 6 abrasion-based techniques (altering pneumatic scarification length or using a single duration of manual scarification) on the enhancement of seed permeability among two physically dormant (western prairie clover [Dalea ornata {Douglas} Eaton & Wright] and Munro’s globemallow [Sphaeralcea munroana {Douglas} Spach]) and two combinationally dormant species (basalt milkvetch [Astragalus filipes Torr. ex A. Gray] and longspur lupine [Lupinus arbustus {Douglas} ex Lindl.]). We first assessed seed imbibition following exposure to all temperature- and abrasion-based techniques to identify those most successful at promoting seed permeability and then evaluated the effectiveness of those techniques through a series of germination experiments. For combinationally dormant species, we also tested whether exposure to GA₃ enhanced germination. Abrasion-based techniques were more effective than temperature-based techniques at improving water uptake across all species. Pneumatic scarification significantly improved germination, but optimal treatment durations were species specific. GA₃ did not enhance germination under the tested conditions. We conclude that pneumatic scarification is a fast, safe, and effective method for alleviating physical seed dormancy with a potential to be scaled up for operational use in restoration.