Effects of fragmentation on the seed predation and dispersal by rodents differ among species with different seed size

Fragmentation influences the population dynamics and community composition of vertebrate animals. Fragmentation effects on rodent species in forests may, in turn, affect seed predation and dispersal of many plant species. Previous studies have usually addressed this question by monitoring a single species, and their results are contradictory. Very few studies have discussed the fragmentation effect on rodent–seed interaction among tree species with different seed sizes, which can significantly influence rodent foraging preference and seed fate. Given that fruiting periods for many coexisting plant species overlap, the changing foraging preference of rodents may substantially alter plant communities. In this study, we monitored the dispersal and predation by rodents of 9600 seeds, belonging to 4 Fagaceae species with great variation in seed size, in both the edge and interior areas of 12 tropical forest fragments ranging in area from 6.3 to 13872.9 ha in Southwest China. The results showed that forest fragmentation altered the seed fates of all the species, but the intensity and even the direction of fragmentation effect differed between species with large versus small seeds. For the seeds harvested, fragment size showed negative effects in forest interiors but positive effects at edges for the 2 large‐seeded species, but showed little effect for the 2 small‐seeded species. For the seeds removed, negative effects of fragment size only existed among the small‐seeded species. The different fragmentation effect on seed dispersal and predation among plant species may, in turn, translate into the composition differences of the regeneration of the whole fragmented forest.     

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.     

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.     

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.     

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.     

Rodent abundance triggered switch between the relative mutualism and predation in a rodent–seed system of the subtropical island forest

Density-dependent non-monotonic species interactions are important in maintaining ecosystem stability and function, but empirical evidences are still rare. Rodents, as both seed dispersers and seed predators, have dual effects on plant regeneration and may result in non-monotonic rodent-plant interactions. According to the non-monotonic models, the relative positive or negative effects of rodents on seedling establishment can be measured based on the positive or negative association of seedling recruitment rate and rodent abundance. In this study, we investigated the fates of acorns of Quercus serrata by tracking tagged seeds on 21 fragmented subtropical islands in the Thousand Island Lake, China. We found that the proportion of germinated seeds of all released seeds showed a dome-shaped association with rodent abundance per seed. The proportion of removed seeds and cached seeds showed a saturated- and a weak dome-shaped association with rodent abundance per seed, respectively. Our results demonstrated a clear empirical evidence that rodent abundance per seed triggered a switch between the relative mutualism and predation in a rodent–seed system. Our study implied that the observed non-monotonic interactions between plants and animals may play a significant role in maintaining biodiversity and ecosystem function. We appeal for more investigations of the complex non-monotonic interactions in various ecosystems.     

High rodent abundance increases seed removal but decreases scatter-hoarding and seedling recruitment along an elevational gradient

The distributions of small rodents in mountainous environments across different elevations can provide important information regarding the effects of climate change on the dispersal of plant species. However, few studies of oak forest ecosystems have compared the elevational patterns of sympatric rodent diversity, seed dispersal, seed bank, and seedling abundance. Thus, we tested the differences in the seed disperser composition and abundance, seed dispersal, seed bank abundance, and seedling recruitment for Quercus wutaishanica along 10 elevation levels in the Taihang Mountains, China. Our results provide strong evidence that complex asymmetric seed dispersal and seedling regeneration exist along an elevational gradient. The abundance of rodents had a significant negative correlation with the elevation and the seed removal rates peaked and then declined with increasing elevation. The seed removal rates were higher at middle and lower elevations than higher elevations but acorns were predated by 5 species of seed predators at middle and lower elevations, and thus, there was a lower likelihood of recruitment compared with those dropped beneath mother oaks at higher elevations. More importantly, the number of individual seeds in the seed bank and seedlings increased with the elevation, although dispersal services were reduced at sites lacking rodents. As conditional mutualists, the rodents could possibly act as antagonistic seed predators rather than mutualistic seed dispersers at low and middle elevations, thereby resulting in the asymmetric pattern of rodent and seedling abundance with increasing elevation to affect the community assembly and ecosystem functions on a large spatial scale.     

高寒草甸8种植物种子内生细菌和真菌群落的多样性

种子是微生物从母本植物到子代植物的传播介质,将有益微生物代代相传。种子传播的微生物存在于植物不同部位,为寄主植物提供了一系列的益处。以往种子微生物研究主要集中于农作物,鲜有关于草地植物的研究。本研究利用Illumina-Miseq DNA测序技术,对青藏高原高山草甸8种优势植物的种子微生物群进行多样性分析。结果表明:8种草地植物的种子中有多种细菌和真菌(115个细菌属和135个真菌属),且细菌和真菌群落均存在显著差异(P<0.05)。8种草地植物的优势种细菌门和真菌门分别为Proteobacteria和Ascomycota。在8种草地植物的种子中均发现了细菌属Pseudomonas、Pantoea和Ochrobactrum及真菌属Botrytis、Bullera和Didymella。另外,在8种草地植物的种子中有其独特的细菌和真菌属。本研究表明,植物的个体特征是塑造种子微生物群落的重要因素,同时还发现了一些有利于寄主植物生长且可用于未来种子微生物组调控的微生物。     

Seed handling by primary frugivores differentially influence post‐dispersal seed removal of Chinese yew by ground‐dwelling animals

Seed handling by primary frugivores can influence secondary dispersal and/or predation of post‐dispersal seeds by attracting different guilds of ground‐dwelling animals. Many studies have focused on seeds embedded in feces of mammals or birds; however, less is known about how ground‐dwelling animals treat seeds regurgitated by birds (without pulp and not embedded in feces). To compare the effect of differential seed handling by primary dispersers on secondary seed removal of Chinese yew (Taxus chinensis var. mairei), we conducted a series of exclosure experiments to determine the relative impact of animals on the removal of defecated seeds (handled by masked palm civet), regurgitated seeds (handled by birds) and intact fruits. All types of yew seeds were consistently removed at a higher rate by rodents than by ants. Regurgitated seeds had the highest removal percentage and were only removed by rodents. These seeds were probably eaten in situ without being secondarily dispersed. Defecated seeds were removed by both rodents and ants; only ants might act as secondary dispersers of defecated seeds, whereas rodents ate most of them. We inferred that seeds regurgitated by birds were subjected to the highest rates of predation, whereas those dispersed in the feces of masked palm civets probably had a higher likelihood of secondary dispersal. Seeds from feces attracted ants, which were likely to transport seeds and potentially provided a means by which the seeds could escape predation by rodents. Our study highlighted that primary dispersal by birds might not always facilitate secondary dispersal and establishment of plant populations.     

Spatial and temporal effects on seed dispersal and seed predation of Musa acuminata in southern Yunnan, China

Wild bananas are abundant in tropical areas and many ecologists have observed that the succession process is quicker following increased disturbance. This study was conducted to analyze animal-seed interactions and their effects on the seed fate of a wild banana species (Musa acuminata) in tropical southern Yunnan (China) through experiments considering spatial (site and habitat) and temporal (seasons) variation. The largest proportion of fruits (81%) was removed by frugivorous seed dispersers, especially by bats at nighttime. Only 13% of the fruits were removed by climbing seed predators (different species of rats). In the exclosure treatment, rodents accounted for a significantly higher total artificially exposed seed removal number than ants, but with spatial and temporal differences. The highest seed predation rate by rodents (70%) was found in forest with wild banana stands, corresponding with the highest rodent diversity (species numbers and abundance) among the habitat types. In contrast, the seed removal number by ants (57%) was highest in the open land habitats, but there was no close correlation with ant diversity. Seed removal numbers by ants were significantly higher in the dry compared to the rainy season, but rodent activity showed no differences between seasons. The overall results suggest that the largest proportion of seeds produced by wild banana are primarily dispersed by bats. Primary seed dispersal by bats at nighttime is essential for wild banana seeds to escape seed predation.     

科尔沁沙地75种植物结种量种子形态和植物生活型关系研究

研究了科尔沁沙地75种植物的结种量、种子形态、植物生活型关系.结果表明,灌木和半灌木(小半灌木)的结种量比草本植物的大;就草本植物而言,多年生植物的结种量较一、二年生植物的小;植物结种量和种子重量之间存在显著负相关;植物结种量和种子形状之间存在显著负相关,即种子越接近圆球形,结种量越大;占绝大多数的草甸植物结种量相对较小;而在物种数占总物种数的百分数相近时,草原植物的结种量最小,沙生植物的最大,杂草植物居中.     

How seed defense and seed abundance predict dispersal and survival patterns in Camellia

Little is known about how seed defense and seed abundance interact with behavioral responses of seed dispersers to predict dispersal and survival dynamics in animal‐dispersed plants. By tracking the fate of individual seeds in Camellia stands with high and low seed abundance in Southwest China in 2007, we investigated the dispersal and survival of 2 high‐saponin Camellia species (Camellia oleifera and Camellia sinensis and 1 non‐saponin species (peanut Arachis hypogaea) as a control. Saponins in Camellia seeds are chemical compounds that act as seed defense. Our results were most consistent with the predictions based on the predator satiation hypothesis and the plant defense hypothesis. At the abundant Camellia stand (predators and dispersers were satiated), more Camellia seeds survived at the source but fewer were hoarded and survived at cache sites. At the sparse Camellia stand (predators and dispersers were not satiated), no Camellia seeds survived at the source, but more Camellia seeds were hoarded and survived at cache sites. Unlike Camellia seeds, no peanuts survived at the source at both stands, while more peanuts were hoarded and then survived at cache sites in the abundant Camellia stand compared to none at the sparse Camellia stand. In addition, the 2 Camellia species showed similar trends for seed fates across different dispersal stages. Our study indicates that the combined effects of seed abundance and seed defense, compared to their separate effects, provide a more accurate prediction for dispersal and survival patterns in animal‐dispersed Camellia species.     

绢蒿荒漠植物种子大小、形状变异及其生态适应特征

广布于北疆地区的绢蒿荒漠草地作为重要牧场蕴含着丰富的生物多样性。收集了绢蒿荒漠的88种植物种子,对种子大小、形状及物种生活型进行了测定和分析,利用系统比较的方法对不同种子的大小和形状两个主要性状进行了谱系信号分析,并对不同种子对荒漠、半荒漠环境条件的适应类型进行了归纳分类。结果表明,88种种子大小可划分为A型(0.01~0.10 mg)、B型(0.10~1.00 mg)、C型(1.00~10.00 mg)和D型(10.00~50.00 mg) 4种类型,其中B和C型种子在数量上占优势地位。所涉及物种可分为6种生活型,以一年生、多年生及短命植物为主。种子形状指数为0.00~0.20,细长或扁平种子有42种,球形或接近球形种子有46种。种子大小和形状在不同科间、科内种间以及同种植物异型种子间均具有极显著差异。种子大小无明显的谱系信号,存在一定的可塑性。种子形状具有明显的谱系信号,表现出较强的稳定性。绝大多数植物种子能够通过种子多型性、产生种子粘液、具有助力传播结构、特殊生活型以及动物消化道传播等适应对策对特殊环境产生很强的适应性。     

Secondary seed dispersal by dung beetles in an Amazonian forest fragment of Colombia: influence of dung type and edge effect

Seeds of many plant species are secondarily dispersed by dung beetles, but the outcome of this interaction is highly context‐specific. Little is known about how certain anthropogenic disturbances affect this plant–animal interaction. The aims of this study were to assess the effect of dung type on secondary dispersal by dung beetles in a forest fragment, and to determine whether this interaction is affected by edge effects. Using pitfall traps, we captured dung beetles attracted to dung of 2 frugivorous mammals: woolly monkeys and howler monkeys. We found differences between both dung beetle assemblages, but these differences were not consistent in time. Using seeds surrounded by both dung types, we carried out a field experiment using seeds of 2 plant species. We found that the probability of secondary dispersal by dung beetles was higher for seeds placed in woolly monkey dung. Finally, we carried out a field experiment using plastic beads as seed mimics to assess edge effects. We found that secondary seed dispersal by dung beetles was negatively affected by edges. The disruption of plant–animal interactions along anthropogenic forest edges could have long‐term negative effects on forest dynamics by affecting processes of regeneration.     

Endozoochorous seed dispersal by golden snub-nosed monkeys in a temperate forest

Seed dispersal is essential for plant recruitment and the maintenance of biodiversity. Colobine monkeys are primarily folivorous, but they also consume fruits and are often assumed to be seed predators. Although they are known to be epizoochorous seed dispersers, their role as endozoochorous seed dispersers needs reassessment. We examined potential endozoochory in golden snub-nosed monkeys (Rhinopithecus roxellana) at Dalongtan in Shennongjia National Park, central China, by assessing potential germination of ingested seeds (n = 1806, 9 species) from fecal samples. Intact seeds were in almost all fecal samples (ranging from 5–130 seeds), and ingested seeds were from small seeded species (seed width <4.5 mm). The 2 most abundant species were Actinidia arguta (73%) and Rosa caudata (15%). The fruits of A. arguta were unripe when ingested (i.e. effective seed predation) and the ingested seeds did not germinate in the trials. Therefore, ingestion of unripe seeds does not lead to effective seed dispersal. However, germination rates of defecated R. caudata (9%) were greater than control seeds (6% and 0%), demonstrating potential endozoochorous seed dispersal. Thus, colobine monkeys do indeed disperse mainly small-seeded from multi-seeded fruits through potential endozoochory and this process enhances the recruitment of seedlings.     

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.     

围栏封育对青藏高原东缘高寒草甸种子雨的影响

围栏封育是一种常见的退化草地恢复措施,其改变了草地植物生长繁殖的小环境。在青藏高原东缘高寒草甸中,采用定点监测的方法研究了封育8年之后围栏内外植被与种子雨的差异。结果表明,围栏封育显著降低了植被中物种丰富度、Shannon Wiener指数以及植株个体密度,但显著提高了种子雨中物种丰富度和种子雨密度,种子雨密度增加主要由禾本科植物种子数量增加所致;种子雨中物种多度等级分布模式在封育地中符合生态位优先占据模型,而在放牧地中符合对数正态模型。围栏封育对种子雨的季节动态没有明显影响,表现为放牧地与封育地的种子雨均为单峰模式。封育地中种子雨与植被相似性略高于放牧地,但封育地与放牧地中种子雨具有极高相似性。     

种子 科技浅析AOSCA种子认证体系在草种子生产中的应用

以北美官方种子认证机构协会（AOSCA）所制订的种子认证体系为基础,比较在野生植物种子采集或生产和栽培植物品种种子生产认证过程的具体应用。表明野生植物或栽培植物种子生产均需按照相应的认证程序,根据实际利用状况和培育目的具有不同的认证级别,并且各级别的认证种子均有明确的标签标识,保证植物材料或品种的遗传一致性。通过分析该体系在保证植物种子遗传稳定性和一致性方面的优越性和特点,为我国野生植物资源的收集利用、牧草种子的生产提供实践指导和借鉴经验,以促进我国草地生态建设和牧草种子生产的国产化。     

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.     

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.