Seed Dispersal Research Articles

The Distinct Fruit Size and Physical Defense Promote Divergent Secondary Seed Dispersal Strategies of Three Oak Species

The Distinct Fruit Size and Physical Defense Promote Divergent Secondary Seed Dispersal Strategies of Three Oak Species

Dispersal of Dioon edule cycad seeds by rodents in a tropical oak forest in Mexico

Predation of seeds of the cycad Dioon edule Lindl. by Peromyscus mexicanus (Saussure, 1860) has been previously documented, demonstrating that the seeds’ toxins are not harmful when combined with a varied diet. However, there is scarce evidence of P. mexicanus as a seed disperser. In a tropical oak forest in San Luis Potosí, Mexico, we experimented with seeds of D. edule and Quercus polymorpha Schltdl. & Cham., evaluating predators’ preference and recording it with photo-trapping. Burrows were sampled in concentric circles around a D. edule mother plant, and the types of burrows and condition of the seeds inside were identified with a borescope without destroying the burrows. The structure and composition of the forest were evaluated. The primary dispersion of D. edule seeds is by barochory. The rodents predate on seeds and prefer Q. polymorpha over D. edule (survival: 48.9% and 78.5%, respectively). There are more escape and multiple burrows at 3–6 m with mature oaks. Rodents forget or abandon D. edule seeds in the burrows, and such seeds germinate at 3–6 m. Peromyscus leucopus (Rafinesque, 1818) is a short-distance secondary disperser and predator of Dioon edule seeds.

Native seed dispersal by rodents is negatively influenced by an invasive shrub

Refuge–mediated apparent competition is the mechanism by which invasive plants increase pressure on native plants by providing refuge for generalist consumers. In the UK, the invasive Rhododendron ponticum does not provide food for generalist seed consumers like rodents, but evergreen canopy provides refuge from rodent predators, and predation and pilferage risk are key factors affecting rodent foraging and caching behaviour. Here we used a seed removal/ seed fate experiment to understand how invasion by an evergreen shrub can alter seed dispersal, seed fate and early recruitment of native trees. We used seeds of four species, small and wind–dispersed (sycamore maple Acer pseudoplatanus and European ash Fraxinus excelsior) and large and animal–dispersed (pedunculate oak Quercus robur and common hazel Corylus avellana), and monitored seed predation and caching in open woodland, edge habitats, and under Rhododendron. In the open woodland, wind–dispersed seeds had a higher probability of being eaten in situ than cached seeds, while the opposite occurred with animal–dispersed seeds. The latter were removed from the open woodland and edge habitats and cached under Rhododendron. This pattern was expected if predation risk was the main factor influencing the decision to eat or to cach a seed. Enhanced dispersal towards Rhododendron cover did not increase the prospects for seed survival, as density of hazel and oak saplings under its cover was close to zero as compared to open woodland, possibly due to increased cache pilferage or low seedling survival under dense shade, or both. Enhanced seed predation of ash and sycamore seeds close to Rhododendron cover also decreased recruitment of these trees. Rhododendron patches biased rodent foraging behaviour towards the negative (net predation) side of the conditional rodent / tree interaction. This effect will potentially impact native woodland regeneration and further facilitate Rhododendron spread due to refuge–mediated apparent competition.

High-throughput sequencing of faeces provides evidence for dispersal of parasites and pathogens by migratory waterbirds.

Examination of faecal material has demonstrated how a broad range of organisms are distributed by bird movements. Such research has largely focused on dispersal of plant seeds by frugivores and of freshwater organisms by waterbirds. However, with few exceptions (e.g. avian influenza, Ebola virus), there is a dearth of evidence for transport of parasites and pathogens. High-throughput sequencing methods now provide a powerful means of addressing this knowledge gap by elucidating faecal contents in unprecedented detail. We collected faeces excreted by a range of migratory waterbirds in south-west Spain and pooled faecal DNA to create libraries reflective of feeding behavior. We created sets of libraries using high-throughput metagenomic and amplicon sequencing. For the latter we employed two sets of primers to broadly target the V4 region of the 18S rRNA gene (one set amplifying the region across all eukaryotes, the other excluding amplification of metazoans). Libraries revealed a wide diversity of eukaryotes, including parasites of the faecal producers themselves, parasites of food items, or those incidentally ingested. We also detected novel microbial eukaryotic taxa and found that parasite assemblage profiles were relatively distinct. Comparing the performance of the methods used supports their joint use for future studies of diversity and abundance. Because viable stages of many parasites are likely to be present in faeces, our results suggest significant levels of bird-mediated dispersal of parasites (both from avian and other hosts). Our methods revealed much hidden biodiversity, and allowed identification of the individuals who produced the faecal samples to species level, facilitating the study of interaction networks.

The effects of human‐altered habitat spatial pattern on frugivory and seed dispersal: a global meta‐analysis

Seed dispersal by frugivorous animals is important for plant mobility, regeneration and persistence. Human‐caused landscape change is thought to disrupt seed dispersal, but evidence is scarce. We performed a comprehensive meta‐analysis on the effects of habitat spatial pattern on frugivory and seed dispersal. We found 233 effects from 71 studies. At a patch or local scale, altered habitat spatial pattern was measured as declining patch size, increasing patch isolation or habitat edge (versus interior). At a landscape scale it was measured as declining amount of habitat, increasing mean patch isolation, increasing number of patches or increasing habitat edge in the landscape. We found overall negative effects of altered habitat spatial pattern on: 1) the quantity of frugivory or seed dispersal, 2) the number of species involved in a plant–frugivore interaction and 3) seed dispersal distance. Moderator variable analysis was only possible for the first of these. It revealed negative responses of the quantity of frugivory or seed dispersal to habitat loss at both the local scale (declining patch size), and the landscape scale (declining habitat amount), but little evidence for a response to habitat edge at either scale. In addition, altered habitat spatial pattern reduced the quantity of frugivory or seed dispersal more strongly in temperate than tropical areas. Finally, the few‐recorded effects of landscape‐scale fragmentation per se (increasing patch density or edge density) on the quantity of frugivory or seed dispersal were mixed and weak. Our meta‐analysis reinforces the notion that habitat loss is a major threat to frugivory and seed dispersal by animals, and reveals an insufficiency of studies of the effects of habitat fragmentation per se. Thus, based on the current literature, we conclude that maintaining and increasing habitat amount is vital for maintaining seed dispersal by frugivorous animals.

Long Distance Seed Dispersal by Forest Elephants

By dispersing seeds long distances, large, fruit-eating animals influence plant population spread and community dynamics. After fruit consumption, animal gut passage time and movement determine seed dispersal patterns and distances. These, in turn, are influenced by extrinsic, environmental variables and intrinsic, individual-level variables. We simulated seed dispersal by forest elephants (Loxodonta cyclotis) by integrating gut passage data from wild elephants with movement data from 96 individuals. On average, elephants dispersed seeds 5.3 km, with 89% of seeds dispersed farther than 1 km. The longest simulated seed dispersal distance was 101 km, with an average maximum dispersal distance of 40.1 km. Seed dispersal distances varied among national parks, perhaps due to unmeasured environmental differences such as habitat heterogeneity and configuration, but not with human disturbance or habitat openness. On average, male elephants dispersed seeds farther than females. Elephant behavioral traits strongly influenced dispersal distances, with bold, exploratory elephants dispersing seeds 1.1 km farther than shy, idler elephants. Protection of forest elephants, particularly males and highly mobile, exploratory individuals, is critical to maintaining long distance seed dispersal services that shape plant communities and tropical forest habitat.

Fire Occurrence Mediates Small-Mammal Seed Removal of Native Tree Species in a Neotropical Savanna

Seed dispersal and predation are critical processes for plant recruitment which can be affected by fire events. We investigated community composition of small mammals in gallery forests with distinct burning histories (burned or not burned ∼3 years before) in the Cerrado (neotropical savanna). We evaluated the role of these animals as seed removers of six native tree species, potentially mediated by the occurrence of fire. We sampled four previously burned sites and four unburned ones. Seed removal was assessed using two exclusion treatments: exclusive access of small rodents and access of all seed-removing vertebrates. The previous burning changed the structural characteristics of the forests, increasing the density of the understory vegetation and herbaceous cover, which determined differences in species composition, richness, and abundance of small rodents (abundance in the burned forests was 1/6 of the abundance in the unburnt ones). Seed removal rates across the six species were reduced in burnt forests in both treatments and were higher for the “all vertebrates” treatment. Other vertebrates, larger than small rodents, played a significant role as seed removers for five of the six species. The effects of fire were consistent across species, but for the two species with the largest seeds (Hymenaea courbaril and Mauritia flexuosa) removal rates for both treatments were extremely low in the burned forests (≦5%). The observed decline in small rodent seed predation in the burned forests may have medium to long-term consequences on plant communities in gallery forests, potentially affecting community composition and species coexistence in these forests. Moreover, fire caused a sharp decline in seed removal by large mammals, indicating that the maintenance of dispersal services provided by these mammals (mainly the agouti Dasyprota azarae) for the large-seeded species may be jeopardized by the burning of gallery forests. This burning would also affect several small mammal species that occur in the surrounding typical savanna habitats but also use these forests. Fire events have been increasing in frequency and intensity because of human activities and climate changing. This current scenario poses a serious threat considering that these forests are fire-sensitive ecosystems within the Cerrado.

Epizoochorous seed dispersal by an Afroalpine savanna primate

AbstractPrimates are prolific dispersers of seeds via endozoochory (i.e., defecation and spitting). In contrast, epizoochorous seed dispersal (i.e., via adhesion to fur) has rarely been observed in primates. On the Guassa Plateau in north‐central Ethiopia, grass‐eating geladas (Theropithecus gelada) regularly carry on their fur the barbed seeds of a commonly eaten plant, a low‐lying herbaceous forb called Agrocharis melanantha [Apiaceae]. Here, we describe the basic ecology of this plant–primate relationship. For 24 months (November 2017–December 2019), we monitored the number and location of A. melanantha seeds on the fur of geladas (n = 225 individuals) from four age‐sex classes: adult males, adult females, juveniles, and infants. Seed accumulation (n = 12649 seeds in total) was seasonal and closely tracked patterns of landscape vegetation phenology, peaking in September near the end of the rainy season. During seasonal periods of heavy seed accumulation, larger animals carried more seeds, which accumulated most often on the hindlimbs and on the long‐haired “cape” (a secondary sexual characteristic) of adult males. Geladas almost never removed seeds during self‐ or social grooming. Rather, data on seed gain and loss from focal follows indicate that geladas gain and lose seeds every few minutes as they walk and sit in an upright feeding position amidst terrestrial vegetation. We estimate that, on average, geladas disperse seeds roughly 80 m from their parent plants. Geladas appear to exert negative and positive fitness impacts on A. melanantha by regularly consuming its herbaceous and underground tissues and dispersing its seeds.Abstract in Amharic is available with online material.

Persistence of Seed Dispersal in Agroecosystems: Effects of Landscape Modification and Intensive Soil Management Practices in Avian Frugivores, Frugivory and Seed Deposition in Olive Croplands

Farming impacts animal-mediated seed dispersal through mechanisms operating on at least two spatial scales. First, at the landscape scale, through habitat loss and land conversion to agriculture/livestock grazing, and second, at the farm scale, via a local intensification of agricultural practices. These two scales of farming impact seed dispersal function but have rarely been integrated. In particular, studies evaluating the effect of agriculture on the seed dispersal function of frugivorous birds in Mediterranean ecosystems are lacking. This study evaluates the role of landscape transformation, from fruit-rich woodland habitats to olive grove landscapes, together with local intensive practices of soil management on the persistence of the seed dispersal function for Mediterranean fleshy-fruited plants in olive landscapes of south Spain. We used bird censuses, mist-nets, and seed traps to characterize avian frugivore assemblages, frugivory, and seed deposition in the seminatural woodland habitat (SNWH) patches and olive fields of 40 olives farms spanning 20 localities distributed across the whole range of olive cultivation in Andalusia (southern Spain). We found that despite the remarkable dispersal function of olive grove landscapes, avian frugivore abundance and diversity, frugivory, and seed arrival decreased in olive fields compared to SNWH patches. Likewise, SNWH cover loss and/or olive growing expansion decreased avian frugivory and seed arrival. Interestingly, the habitat effects in the olive farms often depended on the landscape context. In particular, less diverse fruit-eating bird assemblages pooled in SNWH patches as olive grove cover increased or SNWH decreased in the landscape, while remaining relatively invariant in the olive fields. Finally, compared to conventional intensive agriculture, low-intensity management increased frugivory and seed deposition. We conclude that olive fields are less permeable to frugivores than expected due to the agroforest-like nature of these landscapes and that the presence of SNWH patches is crucial for the maintenance of frugivory and seed dispersal in agricultural landscapes. These results evidence that woodland habitat loss by olive expansion and intensive practices seriously threaten the dispersal service in olive-dominated landscapes. Maintenance, restoration, and promotion of woodland patches should be prioritized for the conservation of seed dispersal service and for enhancing the functional connectivity in human-shaped olive landscapes.

Multiple Anthropogenic Pressures Lead to Seed Dispersal Collapse of the Southernmost Palm Jubaea chilensis

Seed dispersal is a critical process for plant reproduction and regeneration. Successful recruitment depends on pre- and post-dispersal processes that complete a seed’s journey until becoming a new plant. However, anthropogenic stressors may disrupt the seed dispersal process at some stages, collapsing plant regeneration and hampering its long-term persistence. The Chilean palm tree Jubaea chilensis is the southernmost and the only non-tropical palm species, which currently relies on the scatter-hoarding rodent Octodon degus for seed dispersal. We assessed seed fate by measuring predation and dispersal rates through experimental fieldwork in the Palmar de Ocoa site (located within La Campana National Park) and the Palmar El Salto. We also used previous reports on seed harvest and seedling herbivory to depict the whole J. chilensis seed dispersal process and assess the relative importance of different anthropogenic pressures. We asked the following questions: (1) What is the effect of human harvesting on J. chilensis recruitment? (2) Do native and exotic rodents predate J. chilensis seeds in the same way? and (3) Does post-dispersal herbivory matter? We found that J. chilensis fruits are harvested for human consumption, reducing pre-dispersal available seeds by removing about 23 tons per season. Then, post-dispersal seeds at the Ocoa palm grove are heavily predated by exotic (Rattus rattus) and native (Octodon spp.) rodents; only 8.7% of the seeds are effectively dispersed by Octodon degus. At Palmar El Salto, 100% of the seeds were predated by Rattus rattus, precluding further analysis. Finally, 70% of the seedlings were consumed by exotic herbivores (mainly rabbits), resulting in a success rate of 1.81%. Only 7.9% of the surviving seedlings become infantile plants (4 year-old). Our assessment suggests that J. chilensis has aging populations with very few young individuals in disturbed sites to replace the old ones. For those reasons, we suggest increasing its conservation category to critically endangered as land-use change is rapidly fragmenting and shrinking the extant J. chilensis populations. We urge to take urgent actions to protect this relict palm, which otherwise may go extinct in the next decades.

Linking howler monkey ranging and defecation patterns to primary and secondary seed dispersal.

To define the chances of a dispersed seed to produce a new recruit, it is essential to consider all stages of the dispersal process. Howler monkeys are recognized to have positive impacts on forest regeneration, acting as primary dispersers. Furthermore, dung beetles attracted to their feces protect the seeds against predators, and provide a better microenvironment for germination due to the removal of fecal matter, to seed burial, and/or by reducing the spatial aggregation of seeds in fecal clumps. Despite the recognized positive effects of primary seed dispersal through defecation by howler monkeys for plant recruitment, there are some important aspects of their behavior, such as the habit of defecating in latrines, that remain to be explored. Here, we investigated the fate of Campomanesia xanthocarpa seeds defecated by brown howlers, Alouatta guariba clamitans, and the secondary seed dispersal by dung beetles, considering how this process is affected by the monkey's defecation patterns. We found that brown howler monkeys dispersed seeds from several species away from fruit-feeding trees, partly because defecation under the canopy of such trees was not very frequent. Instead, most defecations were associated with latrines under overnight sleeping trees. Despite a very similar dung beetle community attracted to howler feces in latrines and fruit-feeding sites, seeds were more likely to be buried when deposited in latrines. In addition, C. xanthocarpa seeds showed higher germination and establishment success in latrines, but this positive effect was not due to the presence of fecal matter surrounding seeds. Our results highlight that A. guariba clamitans acts as a legitimate seed disperser of C. xanthocarpa seeds in a preserved context of the Brazilian Atlantic Forest and that defecations in latrines increase the dispersal effectiveness.

Seed predation by macaws favors fruits with less seeds and thicker endocarps in the palm Attalea phalerata

When foraging on a specific range of fruits or seeds, animals can represent a natural selection force, affecting plant population realized fecundity. Most studies have focused on characteristics of dispersed seeds, but the higher predation of seeds of specific size or shape is also an important force that influences the populations’ realized fecundity and can help to understand patterns of plants genetic variability. In the Brazilian Pantanal, we investigated the predation of Acuri (Attalea phalerata) palm fruits by macaws, whose seeds go intact through tapirs digestive tract and then are deposited on latrines, where they are often consumed by seed predators. We found 251 fruits, containing between 1 and 5 seeds per fruit; 170 were intact and 81 had been partially damaged by macaws, mostly those containing 3 or 4 seeds per fruit and with thin endocarps. We argue that the higher consumption of fruits with these traits reflects a trade-off in the energy spent by macaws to open the fruits and the energy provided by them. Higher predation on 3-4 seeded fruits favors the selection of 1-2 seeded fruits, revealing a selection force opposed to the one exerted by bruchids and small rodents, which favors multi-seeded palm fruits.

Horsenettle (Solanum carolinense) fruit bacterial communities are not variable across fine spatial scales.

Fruit house microbial communities that are unique from the rest of the plant. While symbiotic microbial communities complete important functions for their hosts, the fruit microbiome is often understudied compared to other plant organs. Fruits are reproductive tissues that house, protect, and facilitate the dispersal of seeds, and thus they are directly tied to plant fitness. Fruit microbial communities may, therefore, also impact plant fitness. In this study, we assessed how bacterial communities associated with fruit of Solanum carolinense, a native herbaceous perennial weed, vary at fine spatial scales (<0.5 km). A majority of the studies conducted on plant microbial communities have been done at large spatial scales and have observed microbial community variation across these large spatial scales. However, both the environment and pollinators play a role in shaping plant microbial communities and likely have impacts on the plant microbiome at fine scales. We collected fruit samples from eight sampling locations, ranging from 2 to 450 m apart, and assessed the fruit bacterial communities using 16S rRNA gene amplicon sequencing. Overall, we found no differences in observed richness or microbial community composition among sampling locations. Bacterial community structure of fruits collected near one another were not more different than those that were farther apart at the scales we examined. These fine spatial scales are important to obligate out-crossing plant species such as S. carolinense because they are ecologically relevant to pollinators. Thus, our results could imply that pollinators serve to homogenize fruit bacterial communities across these smaller scales.

The mutualism-antagonism continuum in Neotropical palm-frugivore interactions: from interaction outcomes to ecosystem dynamics.

ABSTRACTFrugivory, that is feeding on fruits, pulp or seeds by animals, is usually considered a mutualism when interactions involve seed dispersal, and an antagonism when it results in the predation and destruction of seeds. Nevertheless, most frugivory interactions involve both benefits and disadvantages for plants, and the net interaction outcomes thus tend to vary along a continuum from mutualism to antagonism. Quantifying outcome variation is challenging and the ecological contribution of frugivorous animals to plant demography thus remains little explored. This is particularly true for interactions in which animals do not ingest entire fruits, that is in seed‐eating and pulp‐eating. Here, we provide a comprehensive review of Neotropical palm–frugivore interactions, with a focus on how frugivore consumption behaviour (i.e. digestive processing, fruit‐handling ability and caching behaviour) and feeding types (fruit‐eating, pulp‐eating and seed‐eating) influence interaction outcomes at different demographic stages of palms. We compiled a total of 1043 species‐level palm–frugivore interaction records that explicitly captured information on which parts of palm fruits are eaten by animals. These records showed consumption of fruits of 106 Neotropical palm species by 273 vertebrate species, especially birds (50%) and mammals (45%), but also fish (3%) and reptiles (2%). Fruit‐eating involved all four taxonomic vertebrate classes whereas seed‐eating and pulp‐eating were only recorded among birds and mammals. Most fruit‐eating interactions (77%) resulted in positive interaction outcomes for plants (e.g. gut‐passed seeds are viable or seeds are successfully dispersed), regardless of the digestive processing type of vertebrate consumers (seed defecation versus regurgitation). The majority of pulp‐eating interactions (91%) also resulted in positive interaction outcomes, for instance via pulp removal that promoted seed germination or via dispersal of intact palm seeds by external transport, especially if animals have a good fruit‐handling ability (e.g. primates, and some parrots). By contrast, seed‐eating interactions mostly resulted in dual outcomes (60%), where interactions had both negative effects on seed survival and positive outcomes through seed caching and external (non‐digestive) seed dispersal. A detailed synthesis of available field studies with qualitative and quantitative information provided evidence that 12 families and 27 species of mammals and birds are predominantly on the mutualistic side of the continuum whereas five mammalian families, six mammal and one reptile species are on the antagonistic side. The synthesis also revealed that most species can act as partial mutualists, even if they are typically considered antagonists. Our review demonstrates how different consumption behaviours and feeding types of vertebrate fruit consumers can influence seed dispersal and regeneration of palms, and thus ultimately affect the structure and functioning of tropical ecosystems. Variation in feeding types of animal consumers will influence ecosystem dynamics via effects on plant population dynamics and differences in long‐distance seed dispersal, and may subsequently affect ecosystem functions such as carbon storage. The quantification of intra‐ and inter‐specific variation in outcomes of plant–frugivore interactions – and their positive and negative effects on the seed‐to‐seedling transition of animal‐dispersed plants – should be a key research focus to understand better the mutualism–antagonism continuum and its importance for ecosystem dynamics.

Trophic and spatial complementarity on seed dispersal services by birds, wild mammals, and cattle in a Mediterranean woodland pasture

Most earth surfaces have undergone intensive land-use changes, creating habitat mosaics. Seed dispersal by animals is a crucial process in such mosaics, but community-wide studies comparing the functional complementarity and response to man-imposed habitat heterogeneity are rare. Here, we investigate the trophic and spatial seed dispersal networks underpinning a strong, woody vegetation expansion over a pastureland inside the largest forest remnant in western Sicily, Italy. Over two fruiting seasons, we surveyed transects in three distinct biomes within our study area: forest, pastureland, and unpaved road. In total, we collected 659 feces and tested for differences in defecation patterns and seed rain density of birds, wild mammals, and cattle. We also tested the degree of trophic and spatial specialization and modularity using a network approach. Overall, birds dispersed 1208 seeds/ha of nine plant species, including six exclusive. Mammals dispersed 679 seeds/ha from four wild species, three of which also dispersed by birds, and 38 seeds/ha of three cultivated species. In turn, mammals dispersed exclusively the seeds of wild pear ( Pyrus amygdaliformis ), the most abundant tree in the woodland pasture. Cattle only dispersed wild pear, but accounting for 56% of the dispersed seeds. Seed rain densities were significantly higher in woodland pastures than in forests. However, almost of half the seeds dispersed by cattle and red fox were deposited on unpaved roads. While both trophic and spatial networks were more specialized than expected, we did detect distinct modules. Our study demonstrated the magnitude of the effects of man-made habitat heterogeneity on seed dispersal services, giving baseline information for restoration programs as well as high nature value pastureland management strategies. • Birds and mammals are complementary in their seed dispersal services and key for vegetation dynamics. • Rewilding with cattle can just partially compensate this services, but not replace wild mammals role. • Fruit-rich woodland pasture was more relevant than fruit poor managed forest for seed dispersal networks. • Soft linear developments may act both as seed dispersal corridors or as seed dispersal sinks. • Seed dispersal networks can be good indicators to define high nature value agroforestry systems.

Bird-plant interaction networks in native forests and eucalyptus plantations within a protected area

Frugivory is a plant-animal mutualistic interaction carried out mostly by birds. It consists in the bird consumption of fruits with later dispersion of the plants' seeds, helping in the vegetation regeneration. Frugivory can be affected by the habitat fragmentation and introduction of exotic species, which may alter the species interaction by extinction or competitor introduction. This study aimed to compare the structure of the network of frugivorous interactions between birds and plants in native forest and eucalyptus plantation. Birds were captured by mist nets and had their feces collected. Later, the seeds were identified in laboratory. The records of fruit consumption by birds in the zoochoric plant species present in the study area were also conducted. The data collected was used to build a network of interactions and identify the most important network metrics, species, and ecological functional groups in the studied environments. The results showed that the species composition, the connectivity of the relationships, the importance of the species for the interaction networks and the number of subgroups within the networks were highly similar between the native forest and the eucalyptus plantation. This could be explained by the favorable conditions that the studied eucalyptus plantations presented, such as the lack of anthropogenic activities, well-developed understory, and the presence of native surrounding vegetation, allowing practically the same seed dispersal capacity in both types of environments.

The environmental adaptation strategy of seed germination, and roles of the seed pappus on dispersal and hypocotyl hairs on seedling anchorage in Tamarix ramosissima.

Seed dispersal, germination and seedling establishment are affected by various ecological factors in desert plant species. Tamarix ramosissima has evolved multiple strategies to facilitate its survival in harsh environments during the early stages of development. In this study, we investigated the effects of different ecological factors on seed germination and seedling growth, the function of the seed pappus in seed dispersal, as well as the function of the hypocotyl hairs in seedling establishment. We found that the seed germination of T. ramosissima was rapid and could occur under a wide range of temperatures (5–30 °C), after long periods of storage (at least 12 months on dispersal), under high concentrations of salts (700–900 mmol·L−1) and polyethylene glycol (PEG) 6000 (500 g·L−1) and under medium concentrations of alkalis (300–500 mmol·L−1). Lower concentrations of salts and PEG promoted seedling growth. The seed pappus had no effect on seed germination, but it might function as an accessory structure that provides a buoyancy force and promotes long-distance seed dispersal. The hypocotyl hairs located on the edge of the hypocotyl end might aid the upright positioning of the seedlings during early development, especially when seed germination occurs under floating or flooding conditions. In conclusion, the germination of T. ramosissima seeds and seedling development can occur under diverse types of abiotic stress, and the seed pappus and hypocotyl hairs played an important role in seed dispersal and seedling establishment.

Gardeners of the forest: hornbills govern the spatial distribution of large seeds

Seed dispersal by frugivores is vital to the maintenance of tree diversity in tropical forests. However, determining the influence of different frugivores over the distribution of their food plants is difficult, given the complexity of these interactions in the tropics. Consequently, most studies have been restricted to small scales, examining seed dispersal and establishment associated with nests, roosts or fruiting trees. Here, we evaluate the role of frugivorous hornbills in dispersing seeds at spatial scales of 1 ha. We monitored hornbills and seed rain at a tropical forest site in north‐east India. We quantified the abundance of hornbill food plants and recruits of large‐seeded plants. We estimated removal rates of dispersed, large seeds to determine post‐dispersal seed fate. We found that the distribution of large‐seeded canopy food plants influenced the distribution of the relatively abundant Rhyticeros undulatus. The overall distribution of hornbills resulted in spatially contagious seed rain patterns for the large‐seeded plant species. Patches with canopy food plants had a higher recruit diversity. Our results show positive feedback between distribution of rare but important hornbill food plants, hornbills and distribution of seeds and saplings of large‐seeded plants in the landscape. Widespread loss of hornbills due to hunting and habitat loss in the region have likely disrupted these feedback mechanisms that are critical for tree species regeneration.

Valuing the economic impacts of seed dispersal loss on voluntary carbon markets

Seed dispersal is an ecosystem service strongly affected by the loss of mutualist dispersers, with economic consequences in terms of carbon sequestration and climate change mitigation policies. Especially, large frugivores are important contributors to carbon sequestration because they are the main disperser of large-seeded trees, which store a high amount of carbon. The effect of seed dispersers defaunation on carbon sequestration is particularly significant in tropical forests, where frugivores disperse 70–94% of the woody plant species and where ∼59% of the world’s forest carbon above ground is stored. However, the economic impacts of the defaunation of large frugivores on ecosystem services, such as seed dispersal and carbon sequestration, are poorly valued. Here, we simulate the effects of the loss of three large frugivores (Brachyteles arachnoides, Alouatta guariba, and Pipile jacutinga) on the recruitment of hardwood tree species and its economic impact on carbon markets. We found that the combined loss of the large frugivores would reduce the standing carbon sequestration by 2.5%. However, defaunation also affects seed predator communities, which influences the contribution of the frugivores. By adding the loss of large seed predators, the reduction in carbon sequestration would rise to 3.5%. In summary, the potential economic contribution of the seed dispersal services provided by our target dispersers ranges from US$3.94 ha−1 year−1 to US$15.42 ha−1 year−1. We highlight the importance of conserving seed disperser and predator communities to guarantee the long-term viability of forest carbon sequestration. We argue that knowledge of the economic consequences of defaunation should be included in carbon mitigation policies and encourage animal conservation and forest restoration.

Landscape configuration and frugivore identity affect seed rain during restoration

Seed dispersal is a critical ecological function provided largely by vertebrate frugivores in tropical forests. The seed dispersal events mediated by a frugivore species depend on the interaction between the frugivore's traits and landscape structure. Managers seeking to restore seed dispersal to degraded areas to facilitate passive regeneration must consider these interactions. We explore how the relationship between disperser traits and landscape configuration affects seed rain patterns by assessing two restoration goals: 1) high native seed dispersal into degraded areas and 2) low non‐native seed dispersal into intact areas. We developed an individual‐based, spatially‐explicit model, ‘Estimating Seed‐Animal‐Landscape Interactions' (eSALI), and applied it to the case study of Guam, a tropical island that experienced near‐total loss of animal‐mediated seed dispersal following extirpation of its vertebrate frugivores. We focus on two frugivorous bird species, såli Aplonis opaca and totot Ptilinopus roseicapilla, both candidates for rewilding on Guam but differ in their movement distances, gut passage times and habitat use. We simulated populations of both species in seven theoretical landscapes. These landscapes varied in the spatial configuration of intact and degraded forest patches, hosting native and non‐native plant species, respectively. Our results showed that seed rain pattern of the two frugivore species differed across scenarios. A clear tradeoff appeared between both restoration goals in all scenarios: while Såli moved overall more native seeds into degraded areas, they also moved more non‐native seeds into intact areas. Totot on the contrary minimized non‐native seed into intact areas at the expense of moving overall fewer native seeds in degraded areas. This tradeoff was also correlated to landscape configuration: lower heterogeneity minimized non‐native seed rain into intact patches while higher heterogeneity maximized native seed rain into degraded patches. Land managers should explore the interactions between dispersers and landscape configuration to identify ideal candidates for restoring ecological functions.