Potential for ants and vertebrate predators to shape seed-dispersal dynamics of the invasive thistles <Emphasis Type="Italic">Cirsium arvense</Emphasis> and <Emphasis Type="Italic">Carduus nutans</Emphasis> in their introduced range (North America)

The population dynamics of invasive plants are influenced by positive and negative associations formed with members of the fauna present in the introduced range. For example, mutualistic associations formed with pollinators or seed dispersers may facilitate invasion, but reduced fitness from attack by native herbivores can also suppress it. Since population expansion depends on effective seed dispersal, interactions with seed dispersers and predators in a plant species introduced range may be of particular importance. We explored the relative contributions of potential seed dispersers (ants) and vertebrate predators (rodents and birds) to seed removal of two diplochorous (i.e., wind- and ant-dispersed), invasive thistles, Cirsium arvense and Carduus nutans, in Colorado, USA. We also conducted behavior trials to explore the potential of different ant species to disperse seeds, and we quantified which potential ant dispersers were prevalent at our study locations. Both ants and vertebrate predators removed significant amounts of C. arvense and C. nutans seed, with the relative proportion of seed removed by each guild varying by location. The behavior trials revealed clear seed preferences among three ant species as well as differences in the foragers’ abilities to move seeds. In addition, two ant species that acted as potential dispersal agents were dominant at the study locations. Since local conditions in part determined whether dispersers or predators removed more seed, it is possible that some thistle populations benefit from a net dispersal effect, while others suffer proportionally more predation. Additionally, because the effectiveness of potential ant dispersers is taxon-specific, changes in ant community composition could affect the seed-dispersal dynamics of these thistles. Until now, most studies describing dispersal dynamics in C. arvense and C. nutans have focused on primary dispersal by wind or pre-dispersal seed predation by insects. Our findings suggest that animal-mediated dispersal and post-dispersal seed predation deserve further consideration.     

Unexpected relationships and valuable mistakes: non‐myrmecochorous Prosopis dispersed by messy leafcutting ants in harvesting their seeds

Abstract Ants generally disperse seeds while feeding on fruits or structures attached to the seed. Seed dispersal as a by‐product of seed predation (dyszoochory) was recognized in specialized harvester ants, but not in ants predating seeds opportunistically. Leafcutting ants are the main herbivores in much of the Neotropics, and they have been reported to remove fruits and seeds, but their role as seed predators and dispersers has not been acknowledged. Prosopis flexuosa D.C. (Fabaceae, Mimosoideae) is the most abundant tree species in the central Monte Desert, Argentina, and it is likely to depend on secondary animal dispersal. Mammalian frugivores are usually considered its main dispersers, but the opportunity for dispersal may be small since the removal of fruits and seeds by seed predators is very intense. The objective of this study was to identify which ant species interact with P. flexuosa fruits and to evaluate their relative importance as seed predators and dispersers. In a field experiment, whole and segmented pods were offered and several ant species exploiting the fruits were identified. Additionally, all pod segments remaining around nests of the three ant species able to remove them (the leafcutters Acromyrmex lobicornis Emery and Acromyrmex striatus Roger, and Pheidole bergi Mayr) were examined during and after the P. flexuosa primary dispersal season. Up to 753 pod segments and 90 sound seeds were found accumulated in a circle of 1 m radius over nests of A. lobicornis, and even more in an examined trail. Acromyrmex striatus left a smaller proportion of sound seeds and P. bergi left a smaller number of pod segments. All tendencies were similar during shorter known periods of accumulation. Leafcutting ants are acting as important seed predators, and ‘by mistake’ may be dispersing a key non‐myrmecochorous tree. This is an unexplored path in the seed dispersal cycle of P. flexuosa that challenges the tendency to predict interactions based on classifications made with other goals.     

Responses of pre‐dispersal seed predators to sequential flowering of Dipterocarps in Malaysia

Many species of Dipterocarpaceae and other plant families reproduce synchronously at irregular, multi‐year intervals in Southeast Asian forests. These community‐wide general flowering events are thought to facilitate seed survival through satiation of generalist seed predators. During a general flowering event, closely related Shorea species (Dipterocarpaceae) stagger their flowering times by several weeks, which may minimize cross pollination and interspecific competition for pollinators. Generalist, pre‐dispersal seed predators might also track flowering hosts and influence predator satiation. We addressed the question of whether pre‐dispersal seed predation differed between early and late flowering Shorea species by monitoring flowering, fruiting and seed predation intensity over two general flowering events at the Pasoh Research Forest, Malaysia. Pre‐dispersal insect seed predators killed up to 63 percent of developing seeds, with Nanophyes shoreae, a weevil that feeds on immature seeds being the most important predator for all Shorea species. This weevil caused significantly greater pre‐dispersal seed predation in earlier flowering species. Long larval development time precluded oviposition by adults that emerged from the earliest flowering Shorea on the final flowering Shorea. In contrast, larvae of weevils that feed on mature seeds before seed dispersal (Alcidodes spp.), appeared in seeds of all Shorea species almost simultaneously. We conclude that general flowering events have the potential to satiate post‐dispersal seed predators and pre‐dispersal seed predators of mature fruit, but are less effective at satiating pre‐dispersal predators of immature fruit attacking early flowering species.     

DUAL FUNCTION OF THE ELAIOSOME OF CORYDALIS AUREA (FUMARIACEAE): ATTRACTION OF DISPERSAL AGENTS AND REPULSION OF PEROMYSCUS MANICULATUS,A SEED PREDATOR

It has been suggested that one of the selective advantages of ant dispersal is the burial of seeds in ant nests where predators such as small rodents cannot find them. The elaiosomes of Corydalis aurea (Fumariaceae) are extremely attractive to ants, which assiduously gather the seeds and take them to nests. However, seed production commonly exceeds the gathering capacity of ants so that seeds accumulate beneath the parent plants. In spite of this, no signs of rodent predation are evident. Experiments with a major seed predator, the deer mouse Peromyscus maniculatus, show that when given the choice of seeds with and without elaiosomes, the mice consume significantly more seeds without elaiosomes. This remains true whether or not the intact seeds bear fresh, moist elaiosomes or dry, withered ones. Our experiments strongly suggest that the elaiosome has a dual function, the attraction of the ant seed dispersers and the repulsion of seed predators.     

Post-dispersal seed predation and the establishment of vertebrate dispersed plants in Mediterranean scrublands

The post-dispersal fate of seeds and fruit (diaspores) of three vertebrate-dispersed trees, Crataegus monogyna, Prunus mahaleb and Taxus baccata, was studied in the Andalusian highlands, south-eastern Spain. Exclosures were used to quantify separately the impact of vertebrates and invertebrates on seed removal in relation to diaspore density and microhabitat. The three plant species showed marked differences in the percentage of diaspores removed, ranging from only 5% for C. monogyna to 87% for T. baccata. Although chaffinches (Fringilla coelebs) fed on diaspores, rodents (Apodemus sylvaticus) were the main vertebrate removers of seed and fruit. Two species of ant (Cataglyphis velox and Aphaenogaster iberica) were the only invertebrates observed to remove diaspores. However, the impact of ants was strongly seasonal and they only removed P. mahaleb fruit to any significant extent. While removal of seed by rodents was equivalent to predation, ants were responsible for secondary dispersal. However, their role was limited to infrequent, small-scale redistribution of fruit in the vicinity of parent trees. Rodents and ants differed in their use of different microhabitats. Rodents foraged mostly beneath trees and low shrubs and avoided open areas while the reverse was true of ants. Thus, patterns of post-dispersal seed removal will be contigent on the relative abundance and distribution of ants and rodents. Studies which neglect to quantify separately the impacts of these two guilds of seed removers may fail to elucidate the mechanisms underlying patterns of post-dispersal seed removal. The coincidence of both increased seed deposition by the main avian dispersers (Turdus spp.) and increased seed predation with increasing vegetation height suggested that selection pressures other than post-dispersal seed predation shape the spatial pattern of seed dispersal. Rather than providing a means of escaping post-dispersal seed predators, dispersal appears to direct seeds to microhabitats most suitable for seedling survival. Nevertheless, the reliance of most vertebrate-dispersed trees on regeneration by seed and the absence of persistent soil seed banks imply that post-dispersal seed predators may exert a strong influence on the demography of the plants whose seeds they consume. Even where microsites are limited, the coincidence of the most suitable microhabitats for seedling establishment with those where seed predation is highest provide a means by which selective seed predators can influence community composition. Received: 19 August 1996 / Accepted: 25 January 1997     

Mammal Abundances and Seed Traits Control the Seed Dispersal and Predation Roles of Terrestrial Mammals in a Costa Rican Forest

In Neotropical forests, mammals act as seed dispersers and predators. To prevent seed predation and promote dispersal, seeds exhibit physical or chemical defenses. Collared peccaries (Pecari tajacu) cannot eat some hard seeds, but can digest chemically defended seeds. Central American agoutis (Dasyprocta punctata) gnaw through hard‐walled seeds, but cannot consume chemically defended seeds. The objectives of this study were to determine relative peccary and agouti abundances within a lowland forest in Costa Rica and to assess how these two mammals affect the survival of large seeds that have no defenses (Iriartea deltoidea, Socratea exorrhiza), physical defenses (Astrocaryum alatum, Dipteryx panamensis), or chemical defenses (Mucuna holtonii) against seed predators. Mammal abundances were determined over 3 yrs from open‐access motion‐detecting camera trap photos. Using semi‐permeable mammal exclosures and thread‐marked seeds, predation and dispersal by mammals for each seed species were quantified. Abundances of peccaries were up to six times higher than those of agoutis over 3 yrs, but neither peccary nor agouti abundances differed across years. Seeds of A. alatum were predominantly dispersed by peccaries, which did not eat A. alatum seeds, whereas non‐defended and chemically defended seeds suffered high levels of predation, mostly by peccaries. Agoutis did not eat M. holtonii seeds. Peccaries and agoutis did not differ in the distances they dispersed seeds. This study shows that seed fates are contingent upon many factors such as seed defenses, frugivore–granivore abundances, and seed‐handling capabilities. Mammal–seed interactions are complex; the outcomes of these interactions depend on the inherent characteristics of seeds and their potential dispersers.     

How much Dillenia indica seed predation occurs from Asian elephant dung?

Elephants are thought to be effective seed dispersers, but research on whether elephant dung effectively protects seeds from seed predation is lacking. Quantifying rates of seed predation from elephant dung will facilitate comparisons between elephants and alternative dispersers, helping us understand the functional role of megaherbivores in ecosystems. We conducted an experiment to quantify the predation of Dillenia indica seeds from elephant dung in Buxa Reserve, India from December 2012 to April 2013. Using dung boluses from the same dung pile, we compared the number of seeds in boluses that are a) opened immediately upon detection (control boluses), b) made available only to small seed predators (<3 mm wide) for 1–4 months, and c) made available to all seed predators and secondary dispersers for 1–4 months. Using a model built on this experiment, we estimated that seed predation by small seed predators (most likely ants and termites) destroys between 82.9% and 96.4% of seeds in elephant dung between the time of defecation and the median germination date for D. indica. Exposure to larger seed predators and secondary dispersers did not lead to a significant additional reduction in the number of seeds per dung bolus. Our findings suggest that post-dispersal seed predation by small insects (<3 mm) substantially reduces but does not eliminate the success of elephants as dispersers of D. indica in a tropical moist forest habitat.     

Seed predator deterrence by seed-carrying ants in a dyszoochorous plant, <Emphasis Type="Italic">Chamaesyce maculata</Emphasis> L. Small (Euphorbiaceae)

Seeds are often carried by omnivorous ants even if they do not carry elaiosomes. Although many seeds carried by ants are consumed, both seeds abandoned during the seed carrying and leftover seeds are consequently dispersed (dyszoochory). These non-myrmecochorous seeds do not necessarily attract ants quickly. Therefore, these seeds often seem to be exposed to the danger of consumption by pre-dispersal seed predators. We propose the hypotheses, “seed predator deterrence hypothesis” that plants may benefit from seed-carrying ants if they deter seed predators from visiting plants, and seed-carrying ants may play additional roles in plant reproductive success, besides dyszoochory by ants. To test the hypotheses, we investigated the abundance of seed-carrying ants of the species Tetramorium tsushimae Linnaeus and Pheidole noda Smith F., and of the seed predatory stinkbug, Nysius plebeius Distat, on the spotted sandmat, Chamaesyce maculata L. Small, of which the seeds have no elaiosomes but are consumed by both ants and bugs. In the field, ants and stinkbugs seldom encountered each other on the plant. The number of stinkbugs beneath the plants with ants was smaller than that beneath the plants without ants. In laboratory experiments, the number of stinkbugs on the shoot was smaller when ants were present than when they were absent. These results might support the seed predator deterrence hypothesis: the probability of seed predation by stinkbugs seems to be reduced by the ant visits on plants and/or the existence of ants beneath the plants. This study highlights a new ant–plant interaction in seed dispersal by ants.     

The role of avian ‘seed predators’ as seed dispersers

Seed dispersal is a central process in plant ecology with consequences for species composition and habitat structure. Some bird species are known to disperse the seeds they ingest, whereas others, termed ‘seed predators’, digest them and apparently play no part in dispersal, but it is not clear if these are discrete strategies or simply the ends of a continuum. We assessed dispersal effectiveness by combining analysis of faecal samples and bird density. The droppings of seed dispersers contained more entire seeds than those of typical seed predators, but over a quarter of the droppings of seed predators contained whole seeds. This effect was further magnified when bird density was taken into account, and was driven largely by one frequent interaction: the Chaffinch Fringilla coelebs, a typical seed predator and the most abundant bird species in the area and dispersed seeds of Leycesteria formosa, a non‐native plant with berry‐like fruits. These results suggest the existence of a continuum between seed predators and seed dispersers.     

Geographical variation in the potential of mice to constrain an ant-seed dispersal mutualism

Pre‐ and post‐dispersal Helleborus foetidus (Ranunculaceae) seed predation by mice Apodemus sylvaticus as well as post‐dispersal seed removal by ants was studied, during two years, in six plant populations within three geographical regions (Caurel, Cazorla and Mágina) of the Iberian Peninsula. An observational approach revealed strong interregional differences in seed predation by mice during the pre‐dispersal phase, with high and similar rates of predation in Cazorla and Mágina and much lower rates in Caurel. There were also significant inter‐annual variations on pre‐dispersal seed predation by mice, while the existing habitat‐related differences (of lower magnitude) were not consistent across regions. Field experiments based on seed‐offering exclosures, showed that, despite some interregional variation, post‐dispersal seed removal by ants was consistently high through all spatial and temporal scales considered, with most seeds being removed within 48 h. Conversely, post‐dispersal seed predation by mice was highly variable among regions, being very high in Cazorla and minimal or absent in Caurel and Mágina. Interestingly, in Cazorla, in presence of mice, the number of seeds removed was rather independent of the presence/absence of ants, while under mice exclusion, it was determined by the presence/absence of ants. Conversely, in Caurel, the number of seeds removed by each remover agent (ants or mice) was independent of the presence/absence of the other agent. Thus, though uniquely in Cazorla, mice limited the number of seeds available to ants and, therefore, in this region could potentially have interfered on the development of seed traits that enable ants to efficiently harvest them. Our results support the notion that geographical variation over the Iberian Peninsula of mice seed predation may have promoted a mosaic of well‐matching and mismatching situations between H. foetidus diaspore traits and the characteristics of ant communities, which is consistent with some recent theories on the geographical structure of interactions.     

Vertebrate Fruit Removal and Ant Seed Dispersal in the Neotropical Ginger Renealmia alpinia (Zingiberaceae)*

Plants frequently display fruit characteristics that support multiple seed‐dispersal syndromes. These ambiguous characteristics may reflect the fact that seed dispersal is usually a complex process involving multiple dispersers. This is the case for the Neotropical ginger Renealmia alpinia (Zingiberaceae). It was originally suggested that the aromatic fruits of R. alpinia located at the base of the plant are adapted for terrestrial mammal seed dispersal. However, the dark‐purple coloration of the fruits and bright orange aril surrounding the seeds suggest that birds may play a role in R. alpinia seed dispersal. At La Selva Biological Station, Costa Rica, we used camera traps to record vertebrate visits to infructescences of R. alpinia. Most visitors were toucans and aracaris (Ramphastidae). However fruits were also removed by terrestrial mammals (coatis and armadillos). In addition to vertebrate fruit removal, some of the fruits dehisce and the seeds that fall on the ground are dispersed by ants. Fruitfall traps showed that 77 percent of fruits are removed by vertebrates. However, 15 percent of fruits fall to the base of parent plants to be potentially dispersed by ants. Experiments using a laboratory ant colony showed that ants are effective seed dispersers of R. alpinia. Ant seed manipulation increased germination success and reduced time to germination. In conclusion, primary seed dispersal in the Neotropical ginger R. alpinia is mostly performed by birds, additionally ants are effective dispersers at short distances. Seed dispersal in R. alpinia is a complex process involving a diverse array of dispersal agents.     

Impact of seed abundance on seed processing and dispersal by the red ant Myrmica rubra

1. Myrmecochory sensu stricto is an ant–plant mutualism in which non‐granivorous ants disperse plant diaspores after feeding on their nutrient‐rich seed appendage, the elaiosome. Phenological traits associated with the diaspore can influence the behaviour of ants and thus their ultimate efficiency as seed dispersers. 2. This study investigated how a contrasting availability of seeds (20 vs. 200 seeds) from the diplochorous Chelidonium majus (Papaveraceae, Linnaeus) plant species influences the behaviour of Myrmica rubra (Formicidae, Linnaeus) ants, from the retrieval of seeds until their dispersal outside the ant nest. 3. Regardless of seed abundance, the ants collected the first diaspores at similar rates. Then, seed retrieval sped up over time for large seed sources until satiation took place with only one‐third of the tested colonies wholly depleting abundant seed sources. 4. No active recruitment by trail‐laying ants was triggered, even to an abundant seed source 5. In both conditions of seed abundance, the majority of the diaspores retrieved inside the nest were discarded with the elaiosome removed and were dispersed at similar distances from the nest. 6. The paper concludes with a discussion of how the quantity of seeds released by a plant with a dual mode of dispersal can potentially influence the behaviour of ant dispersers and hence the dispersal efficiency derived from myrmecochory.     

Interaction between ungulates and bruchid beetles and its effect on <Emphasis Type="Italic">Acacia</Emphasis> trees: modeling the costs and benefits of seed dispersal to plant demography

Integrative studies of plant–animal interactions that incorporate the multiple effects of interactions are important for discerning the importance of each factor within the population dynamics of a plant species. The low regeneration capacity of many Acacia species in arid savannas is a consequence of a combination of reduction in seed dispersal and high seed predation. Here we studied how ungulates (acting as both seed dispersers and herbivores) and bruchid beetles (post-dispersal seed predators) modulate the population dynamics of A. raddiana, a keystone species in the Middle East. We developed two simulation models of plant demography: the first included seed ingestion by ungulates and seed predation by bruchids, whereas the second model additionally incorporated herbivory by ungulates. We also included the interacting effects of seed removal and body mass, because larger ungulates destroy proportionally fewer seeds and enhance seed germination. Simulations showed that the negative effect of seed predation on acacia population size was compensated for by the positive effect of seed ingestion at 50 and 30% seed removal under scenarios with and without herbivory, respectively. Smaller ungulates (e.g., <35 kg) must necessarily remove tenfold more seeds than larger ungulates (e.g., >250 kg) to compensate for the negative effect of seed predation. Seedling proportion increased with seed removal in the model with herbivory. Managing and restoring acacia seed dispersers is key to conserving acacia populations, because low-to-medium seed removal could quickly restore their regeneration capacity.     

Introduction of mammalian seed predators and the loss of an endemic flightless bird impair seed dispersal of the New Zealand tree Elaeocarpus dentatus

Understanding the mutualistic services provided by species is critical when considering both the consequences of their loss or the benefits of their reintroduction. Like many other Pacific islands, New Zealand seed dispersal networks have been changed by both significant losses of large frugivorous birds and the introduction of invasive mammals. These changes are particularly concerning when important dispersers remain unidentified. We tested the impact of frugivore declines and invasive seed predators on seed dispersal for an endemic tree, hinau Elaeocarpus dentatus, by comparing seed dispersal and predation rates on the mainland of New Zealand with offshore sanctuary islands with higher bird and lower mammal numbers. We used cameras and seed traps to measure predation and dispersal from the ground and canopy, respectively. We found that canopy fruit handling rates (an index of dispersal quantity) were poor even on island sanctuaries (only 14% of seeds captured below parent trees on islands had passed through a bird), which suggests that hinau may be adapted for ground‐based dispersal by flightless birds. Ground‐based dispersal of hinau was low on the New Zealand mainland compared to sanctuary islands (4% of seeds dispersed on the mainland vs. 76% dispersed on islands), due to low frugivore numbers. A flightless endemic rail (Gallirallus australis) conducted the majority of ground‐based fruit removal on islands. Despite being threatened, this rail is controversial in restoration projects because of its predatory impacts on native fauna. Our study demonstrates the importance of testing which species perform important mutualistic services, rather than simply relying on logical assumptions.     

Persistence of the effect of frugivore identity on post‐dispersal seed fate: consequences for the assessment of functional redundancy

Large frugivores play an important role as seed dispersers and their extinction may affect plant regeneration. The consequences of such extinctions depend on the likelihood of other species being functionally redundant and on how post‐dispersal events are affected. We assess the functional redundancy of two seed dispersers of the Atlantic Forest, the muriqui (Brachyteles arachnoides) and the tapir (Tapirus terrestris) through the comparison of their seed dispersal quality, taking into account post‐dispersal events. We compare tapirs and muriquis for: (1) the dung beetle community associated with their feces; (2) the seed burial probability and burial depth by dung beetles; and (3) the seed mortality due to predators or other causes according to burial depth. We determine how seed burial affects seed dispersal effectiveness (SDE) and compare the dispersal quality of four plant species dispersed by these frugivores. Muriqui feces attract 16‐fold more dung beetles per gram of fecal matter and seeds experience 10.5‐fold more burial than seeds in tapir feces. In both feces types, seed mortality due to predation decreases with burial depth but seed mortality due to other causes increases. Total seed mortality differ within plant species according to the primary disperser. Therefore, the effect of seed burial on SDE varies according to the plant species, burial depth, and primary disperser. As tapirs and muriquis differently affect the seed fate, they are not functionally redundant. Since the effect of the primary disperser persists into the post‐dispersal events, we should consider the cascading effects of these processes when assessing functional redundancy.     

The timing of seed dispersal in Viooa nuttallii: attraction of dispersers and avoidance of predators

Summary Elaiosomes attract rodent predators, as well as ant dispersers (Myrmica discontinua and Formica podzolica), to Viola nuttallii seeds. Seed removal by ants and rodents was studied over 24 h and over two separate 4-h periods. Experimental treatments included i) ants and rodents having access to seeds, ii) only ants having access, iii) only rodents having access, and iv) neither ants nor rodents having access. Seed dehiscence was monitored for 3 days. A simple model is used to determine the relative importance of ants and rodents in removing seeds, and these frequencies are related to the time when most seeds were released. The data show that most seeds are shed from capsules between 9 AM and 1 PM and are immediately removed by ants. Ants, on the average, remove 88% of the seeds. The timing of seed dehiscence increases the probability of seeds being dispersed by ants. The results are discussed with respect to the hypothesis that a sychrony of the time of seed dispersal and the period when most ants (mutualists) and least rodents (predators) are active would be advantageous to the plant species.     

Increased Productivity and Reduced Seed Predation Favor a Large‐seeded Palm in Small Atlantic Forest Fragments

Large‐seeded plants are especially vulnerable to the loss of seed dispersers in small forest fragments. The palm Attalea humilis goes against this trend by reaching high abundances in small remnants. Productivity, seed dispersal and seed predation of A. humilis were investigated in two large (2400 and 3500 ha) and three small (19, 26 and 57 ha) Atlantic Forest fragments in southeastern Brazil. Palms in the small fragments produced more female inflorescences, resulting in a higher fruit production in these places. Seed dispersal rates were higher in the large fragments, where scatter hoarding was more frequent. Scolytine beetles were the main seed predators and damaged a larger number of seeds in small fragments, but predation by rodents and bruchine beetles was low irrespective of fragment size. As scolytines do not necessarily kill the seeds, low predation by bruchines and rodents, together with its own high productivity, allow A. humilis to be more abundant in small fragments despite the scarcity of its main dispersers. This increased abundance, by its turn, can increase competitive interactions between A. humilis and other plants in small fragments. Thus, abundance patterns of A. humilis are a good example of fragmentation affecting the balance of ecological interactions in a complex way, emphasizing the role of preserving ecological processes for conserving biodiversity in fragmented tropical landscapes. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .     

动物对花楸树种实的取食与传播

花楸树是我国东北林区重要的非木质资源树种,其种实既有自然散布方式,也有动物散布方式.本文通过对花楸树种实散布过程中动物活动特点的研究,探索动物取食和传播花楸树种实的规律及其对花楸树天然更新的影响.在2008和2009年花楸树果实成熟期,通过定期观察取食花楸树果实的鸟类及其取食方式,确定对花楸树果实有拜访行为的鸟类有8种,其中食果肉鸟类斑鸫、灰喜鹊和白背啄木鸟对花楸树种实有传播作用,它们对花楸树果实的拜访频率分别为54%、12%和7%,取食后第一落点集中于距离母树5～10 m之间（占68.2%）,其次为距离母树5 m以内（占27.3%）,距离母树10 m以外的比例很小（占4.5%）.果实在鸟类消化道内的滞留时间可达20 min,表明潜在传播距离会很长.人工摆放果实和种子试验表明,在不同生境地面摆放的果实6～7 d内全部消失,果实的取食者主要是啮齿类和地面取食的鸟类,取食率均较高（50%～70%）;种子的取食者为啮齿类、地面取食的鸟类和蚁类,取食率均较低（1%～5%）.花楸树为多种动物提供食物,而动物为花楸树传播种子,动物的取食对花楸树的天然更新有重要影响.     

Consequences of the timing of seed release of Erythronium americanum (Liliaceae), a deciduous forest myrmecochore

Myrmecochores are plants with seeds adapted for ant dispersal. This specialized dispersal syndrome may provide Erythronium americanum seeds with protection from predators within the eastern deciduous forests. To determine the adaptive significance of myrmecochory in E. americanum, seed removal rates and seed predation in relation to seed release date and location along the Potomac River in Langley, Virginia, were examined. The number of seeds removed from four exclosure treatments were monitored two times in 1992 and three times in 1993 within floodplain and hilltop populations of E. americanum. Overall, seed removal was greatest from control depots, and E. americanum seeds were removed at nearly the same rate from predator-exclusion depots, indicating that removal from open depots is largely due to ant removal. Ants removed significantly more seeds than predators in the first 48 h of seed exposure and could potentially remove all E. americanum seeds before nightfall. Aphaenogaster rudis was identified as the primary disperser of E. americanum. Seeds placed in depots after the natural seed release period were discovered more quickly and removed by ants at a significantly higher rate than seeds released at the natural date. These results suggest that ant dispersal of E. americanum seeds reduces the likelihood of seed predation.     

How intraspecific variation in seed‐dispersing animals matters for plants

Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context‐dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed‐dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed‐dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex‐specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best‐documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed‐dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed‐dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal‐mediated seed dispersal.