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1.
Habitat fragmentation is globally one of the most important drivers of change in biodiversity. Seed dispersal by birds is crucial for tree regeneration in remnant patchy forests, yet how bird traits affect seed dispersal pattern is still poorly understood. We studied the extent to which bird traits affect seed‐removal networks and whether these traits affect seed deposition and seedling recruitment for 3 co‐fruiting tree species (Taxus chinensis, Cinnamomum bodinieri and Machilus thunbergii) in a patchy forest. A total of 17, 18 and 10 bird species were recorded foraging for seeds of T. chinensis, M. thunbergii and C. bodinieri, respectively. Frequency of bird visitation increased with tail length, wing length and body length. Furthermore, bird body length, bill length, body weight and wing length were important in the strength of the seed removal network. During foraging, 6 bird species exhibited different patterns of microhabitat utilization and their perching frequency increased with bird weight and tarsus length. As a consequence, frequency of habitat use, bird length and tarsus length were important in determining the number of deposited seeds. For seedling recruitment, seedling number increased with bird tarsus length and weight, but decreased with wing length. Overall, our results showed that various bird traits not only affected seed removal, but also influenced the subsequent processes of seed deposition and seedling distribution in a patchy forest. These results thus highlight the importance of large‐bodied birds for plant recruitment and point out the need to prioritize the protection and conservation of these birds in remnant patchy forests.  相似文献   

2.
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.  相似文献   

3.
Masting is an evolutionary strategy used by plants to promote seed survival and/or seed dispersal under animal predation, but its effects on seedling establishment in field condition are rarely tested by long-term experiments incorporating combined effects of seed and animal abundance. Here, we tracked seed production, rodent-mediated seed dispersal, and seedling establishment in Armeniaca sibirica from 2005 to 2014 in a warm-temperate forest in northern China, and examined the effects of seed abundance and per capita seed availability on seed fate and seedling recruitment rate. Our results showed that seed abundance or per capita seed availability generally benefited the seedling recruitment of A. sibirica through increasing dispersal intensity, supporting predator dispersal hypothesis. However, seedling recruitment showed satiated or even dome-shaped association with per capita seed availability, suggesting the benefit to trees would be decreased when seed abundance were too high as compared to rodent abundance (a satiated effect). Our results suggest that the predator dispersal and satiation effects of masting on seedling recruitment can operate together in one system and conditionally change with seed and animal abundance.  相似文献   

4.
Although seed dispersal is a key process determining the regeneration and spread of invasive plant populations, few studies have explicitly addressed the link between dispersal vector behavior and seedling recruitment to gain insight into the invasion process within an urban garden context. We evaluated the role of bird vectors in the dispersal of pokeweed (Phytolacca americana), a North American herb that is invasive in urban gardens in China. Fruiting P. americana attracted both generalist and specialist bird species that fed on and dispersed its seeds. The generalist species Pycnonotus sinensis and Urocissa erythrorhyncha were the most frequent dispersers. Seedling numbers of P. americana were strongly associated with the perching behavior of frugivorous birds. If newly recruited bird species use seedling‐safe perching sites, the P. americana will regenerate faster, which would enhance its invasive potential. Based on our observations, we conclude that the 2 main bird vectors, P. sinensis and U. erythrorhyncha, provide potential effective dispersal agents for P. americana. Our results highlight the role of native birds in seed dispersal of invasive plants in urban gardens.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
Plants produce nutritious, fleshy fruits that attract various animals to facilitate seed dispersal and recruitment dynamic. Species-specific differential selection of seed size by multiple frugivorous disperser assemblages may affect the subsequent germination of the ingested seeds. However, there is little empirical evidence supporting this association. In the present study, we documented conflicting selection pressures exerted on seed size and germination by five frugivorous carnivores on a mammal-dispersed pioneer tree, the date-plum persimmon (Diospyros lotus), in a subtropical forest. Fecal analyses revealed that these carnivores acted as primary seed dispersers of D. lotus. We also observed that seed sizes were selected based on body mass and were species-specific, confirming the “gape limitation” hypothesis; three small carnivores (the masked palm civet Paguma larvata, yellow-throated marten Martes flavigula, and Chinese ferret-badger Melogale moschata) significantly preferred to disperse smaller seeds in comparison with control seeds obtained directly from wild plants whereas the largest Asiatic black bears (Ursus thibetanus) ingested larger seeds. Seeds dispersed by medium-sized hog badgers (Arctonyx albogularis) were not significantly different from control seeds. However, regarding the influence of gut passage on seed germination, three arboreal dispersal agents (martens, civets, and bears) enhanced germination success whereas terrestrial species (ferret-badgers and hog badgers) inhibited the germination process compared with undigested control seeds. These conflicting selection pressures on seed size and germination may enhance the heterogeneity of germination dynamics and thus increase species fitness through diversification of the regeneration niche. Our results advance our understanding of seed dispersal mechanisms and have important implications for forest recruitment and ecosystem dynamics.  相似文献   

8.
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.  相似文献   

9.
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.  相似文献   

10.
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.  相似文献   

11.
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.  相似文献   

12.
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.  相似文献   

13.
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.  相似文献   

14.
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.  相似文献   

15.
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.  相似文献   

16.
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.  相似文献   

17.
Seed and seedling predation by small mammals, thought to be significant factors controlling the recruitment of Proteaceae in fynbos shrublands, were studied in a fynbos shrubland before and after a fire in March 1987. Seeds of Protea neriifolia R.Br. were planted inside and outside 14 mm mesh exclosures. The abundance of small mammals was recorded at two fynbos and five forest sites before the fire and at an additional forest and fynbos site after the fire. Seed predation reduced seedling recruitment from seeds planted in March 1986 in mature fynbos, but the reduction was significant only at the site with the highest abundance of small mammals. Seed predation did not significantly reduce seedling recruitment from seed planted in July, August and September 1986 in mature fynbos. The primary cause of seedling mortality before the fire was wilting, presumably owing to moisture stress. After the fire small mammal abundance decreased in burnt fynbos and increased in unburnt forest refuges until eight months after the fire when it increased again in the fynbos to a maximum of 41 animals per 100 trapnights two years after the fire. Seedling predation by small mammals had a limited impact after the fire probably because their numbers dropped soon after the fire. The effects of seed predation did not decrease with increasing distance from a forest refuge. Fungal pathogens and herbivory by insects were the primary causes of seedling mortality after the fire. Small mammal abundance in mature fynbos 25–30 years after a fire may have been too low to prevent the recruitment of a second cohort of P. neriifolia seedlings.  相似文献   

18.
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.  相似文献   

19.
The shrub Osteospermum sinuatum, an important fodder plant in Karoo rangelands, flowered after heavy rain in autumn, winter and spring. The number of flowers produced per bush was positively conelated with basal stem diameter and rainfall in the 12 weeks before anthesis. Flowering increased when neighbouring plants of all species were removed. Grazing during flowering and seed set, by sheep stocked at recommended densities, reduced potential seed set by as much as 90%. Birds, hares and small antelope consumed 10–50% of the flowers. Size‐class distributions indicated that little recent recruitment had taken place on a ranch where palatable plants were scarce and where O. sinuatum flower production was severely depressed by grazing sheep.  相似文献   

20.
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.  相似文献   

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