Dispersal In Tropical Forests Research Articles

Climate and microhabitat shape the prevalence of endozoochory in the seed rain of tropical montane forests

AbstractEndozoochory, the dispersal of seeds by animal ingestion, is the most dominant mode of seed dispersal in tropical forests and is a key process shaping current and future forest dynamics. However, it remains largely unknown how endozoochory is associated with environmental conditions at regional and local scales. Here, we investigated the effects of elevation, climate, and microhabitat conditions on the proportion of endozoochorous plant species in the seed rain of the tropical Andes of southern Ecuador. Over 1 year, we measured seed rain in 162 seed traps on nine 1‐ha forest plots located at 1000, 2000, and 3000 m a.s.l. We recorded climatic conditions (mean annual temperature and rainfall) in each plot and microhabitat conditions (leaf area index and soil moisture) adjacent to each seed trap. In total, we recorded 331,838 seeds belonging to 323 morphospecies. Overall, the proportion of endozoochorous species in the seed rain decreased with elevation. The relative biomass of endozoochorous species decreased with increasing rainfall, whereas the relative seed richness of endozoochorous species increased with increasing temperature and leaf area index. These findings suggest an interplay between climate factors and microhabitat conditions in shaping the importance of endozoochorous plant species in the seed rain of tropical montane forests. We conclude that changing climatic and microhabitat conditions are likely to cause changes in the dominant dispersal modes of plant communities which may trigger changes in the current and future dynamics of tropical forests.Abstract in Spanish is available with online material.

Intraspecific Variation of Samara Dispersal Traits in the Endangered Tropical Tree Hopea hainanensis (Dipterocarpaceae).

Propagule dispersal is a crucial life history stage, which affects population recruitment and regeneration as well as community structure and functions. The windborne process of samara dispersal is affected not only by samara traits and other plant traits, but also by environmental factors. Therefore, studying samara traits related to its dispersal and intraspecific variation in relation to other plant traits and environmental factors could help to understand population distribution and dynamics. Hopea hainanensis, a Dipterocarpaceae tree species dominant in lowland rainforests in Hainan (China) but endangered due to anthropogenic disturbances, is dispersed mainly by wind because of its sepal-winged samara. Here, we measured dispersal-related intraspecific samara traits of H. hainanensis, and analyzed their variation and correlation in relation to plant height, DBH (diameter at breast height), and elevation plant location. Great variations in the samara traits existed, and the variations were larger within than among individuals, which indicated a “bet-hedging” strategy of this species. Plant height, DBH, and elevation explained slight variation in the samara traits. Samara dispersal potential is mainly affected by the samara mass and morphological traits. Samara settling velocity was significantly positively correlated with fruit mass, seed mass, length and width, as well as samara wing loading, and negatively correlated with wing mass ratio, wing area, and wing aspect ratio. Substantial proportions of intraspecific variation in samara dispersal are explained by the samara mass and morphological traits. Natural regeneration with human-aided dispersal is necessary for recovering the H. hainanensis population. This finding contributes to the generalization of trait-based plant ecology, modeling of seed dispersal in tropical forests, and conservation and recovery of rare and endangered species such as H. hainanensis.

Climate niche mismatch and the collapse of primate seed dispersal services in the Amazon

Animal-plant interactions are threatened by ongoing climate change, deforestation, and defaunation. The disruption of biotic interactions leads to loss of ecosystem services but estimates of the magnitude of reductions are rarely available. Using a seed disperser primate community in the Amazon as study case, we forecast the magnitude of seed dispersal services to be lost as function of the future redistribution of species. In the most likely scenario, our projections indicate average contractions of 56% (23 to 100% reduction) on the suitable areas for the studied primates. As result, we found billions of seeds of a model tree (Manilkara bidentata) might fail to be dispersed by this primate community on each fruiting season. Primate contribution to seed dispersal was, however, uneven among species, highlighting the endangered large-bodied woolly monkey Lagothrix cana as a keystone disperser. That species alone was responsible for about 64% of all Manilkara seeds dispersed in the present and up to 71% in the future. Niche mismatch will, however, lead to 37% of the future plant distribution not being able to host its second top disperser (the tufted capuchin Sapajus apella), exacerbating losses on potential seed dispersal. Our projections indicate that seed dispersal in tropical forests might be hampered by global changes, even if defaunation by poaching is controlled. The forecasted magnitude of loss in seed dispersal services is alarming and may have been overlooked in conservation assessments. In a similar manner, niche mismatch and disruption of biotic interactions will likely impair ecosystems functions and resilience worldwide.

Impacts of habitat on butterfly dispersal in tropical forests, parks and grassland patches embedded in an urban landscape

AbstractDispersal distances of 17 species of butterflies in tropical Singapore were significantly greater in forest than in urban habitat. Butterflies in urban plots frequently moved within suitable habitat (park/grassland) patches but rarely crossed non‐habitat patches suggesting potential isolation and a need for urban corridors.

Chemical compounds in Neotropical fruit bat-plant interactions

Fruit-eating bats are important seed dispersers in tropical forests. Olfaction seems to be the main sense used by these bats to locate and select food. Previous studies have demonstrated that they identify and select volatile organic compounds, being able to track essential oils of their preferred fruits. However, the specific role played by different compounds in this attraction is largely unknown. Here, we used chromatographic analysis and attraction trials to investigate the molecular basis of foraging in two Neotropical bat species. Both were able to discriminate two classes of compounds, monoterpenes and sesquiterpenes. We suggest that the first class provide the initial signal as they are released only in early stages and the second group is formed by less volatile compounds released in later stages and responsible for maintaining bat interest even in the absence of monoterpenes. These findings provide a unique molecular perspective for this mutualistic interaction with important implications in forest restoration. Specifically, simple mixtures of commercially available terpenes could act as attractants to seed-dispersing bats into degraded landscapes.

Forest disturbance and seasonal food availability influence a conditional seed dispersal mutualism

AbstractThe interaction between granivorous scatterhoarding mammals and plants is a conditional mutualism: scatterhoarders consume seeds (acting as predators), but the movement of seed by scatterhoarders may contribute to dispersal (acting as mutualists). Understanding the ecological factors that shape this relationship is highly relevant in anthropogenically disturbed tropical forests where large‐bodied frugivores are extirpated. In such forests, large‐seeded trees that once depended on these frugivores for dispersal may now only have scatterhoarders as prospective dispersers. We studied Carapa oreophila (Meliaceae) in an Afromontane forest, to test the hypotheses that the proportion of seeds immediately consumed or hoarded (dispersed) would vary over a disturbance gradient. Temporal replication also afforded exploration of how habitat effects might vary with food availability. Using a Bayesian framework, we demonstrate that seeds were more likely to be hoarded in less disturbed forest, irrespective of temporal variation in food abundance. In contrast, forest disturbance only appeared to increase seed predation in temporal replicates that coincided with sustained food availability. These results highlight the potential variability in the dynamics between plants and scatterhoarders over fine temporal scales, elucidating possible ecological scenarios where scatterhoarders might act as mutualists (contributing positively to plant recruitment). Our study also fills important knowledge gaps about the importance of scatterhoarders as dispersers in tropical forests depleted of large‐bodied frugivores, particularly in Africa where scatterhoarding mutualisms have not been extensively studied.

Habitat fragmentation narrows the distribution of avian functional traits associated with seed dispersal in tropical forest

Land-use change influences biodiversity in non-random ways, affecting some species and functional groups more than others, with potential implications for the loss or degradation of important ecological processes, such as seed dispersal. Here we investigate the effect of patch-size reduction on the composition and functional richness (FRic) of avian communities in Atlantic Forest fragments, focusing on morphological traits associated with seed dispersal in frugivorous birds. We found that FRic of three key traits—hand-wing index, body mass and gape width—decreased with patch size reduction, because species with larger values for morphological traits were lost through local extinction. The relative absence of large-gaped and more-dispersive frugivores in small forest fragments has important implications because these species play a pivotal role in seed dispersal, carrying higher seed loads for longer distances, and consuming larger-sized seeds that cannot be dispersed by smaller-gaped frugivores. Our results highlight the importance of preserving large or interconnected habitat patches, and promoting habitat restoration of cleared areas, to ensure that sufficient avian functional diversity is maintained to supply the full range of seed dispersal services required by tropical forests, both currently and in future.

The role of Lithodoras dorsalis (Siluriformes: Doradidae) as seed disperser in Eastern Amazon

ABSTRACT Ichthyochory is an important process responsible for the high diversity of plant species in tropical flooded forests. Thus, this study aimed to investigate the role of a catfish species, Lithodoras dorsalis, as seed disperser in the flooded forests at the Amazon River mouth, Brazil. Analyzing the stomach contents of 371 individuals of Lithodoras dorsalis, the Germination Potential (GP%) and Germination Speed Index (GSI) of seeds that were removed intact were investigated. This allowed us to evaluate the germination performance of two important species of plants in Amazonia, Euterpe oleracea (Açaí) and Montrichardia linifera (Aninga), after passage through the digestive tract of this catfish species. Given that digestion by L. dorsalis reduced the germination viability of M. linifera and that seeds were often destroyed during consumption, we suggest that L. dorsalis may have a limited role as seed disperser of M. linifera and instead mostly act as seed predator. However, for the species E. oleracea, L. dorsalis was a potential disperser, since the performance of germination of these seeds was improved after digestion. In addition, the number of seeds consumed was directly proportional to the catfish’s body size, reinforcing the role of doradids as potential seed dispersers in tropical forests.

Possible implications of seed dispersal by the howler monkey for the early recruitment of a legume tree in small rain-forest fragments in Mexico

Abstract:Primates are important seed dispersers in tropical forests, but they are being lost due to forest fragmentation. We compared post-dispersal seed fate and seedling density for the tree Dialium guianense, in forest fragments in which its main seed disperser, the mantled howler monkey (Alouatta palliata) is present, and in fragments in which it is absent. We also carried out a germination experiment to assess gut-passage effect. Seeds extracted from fruits had very low germination (2%) compared with defecated seeds (70%). Seeds in monkey faeces had a lower probability of being attacked by predators, but a higher probability of being attacked by fungus, when compared with seeds inside fruits. Seed fate was similar in fragments with vs. without monkeys, and in sites under parent trees vs. under monkey sleeping sites. Seedling density was highest under sleeping sites in fragments with monkeys, followed by sites under parent trees in fragments with monkeys, and it was lowest in uninhabited fragments, regardless of deposition site. Our study adds to an increasing line of evidence suggesting that loss of frugivores can have strong consequences for plant recruitment.

How do primates affect seed germination? A meta‐analysis of gut passage effects on neotropical plants

Biotic seed dispersal is a key process maintaining biodiversity in tropical forests where most trees produce vertebrate‐dispersed seeds. Existing meta‐analyses suggest an overall positive effect of vertebrate gut passage on seed germination, but no significant effects for non‐flying mammals. However, previous meta‐analyses combined rodents (seed predators) and primates (seed dispersers) into the non‐flying mammals category, which may confound specific effects of each group on seed germination. However positive effects of monkeys on germination had previously been found in some studies. Here we disentangle the role of Neotropical primates as contributors to seed dispersal in tropical forests by running a meta‐analysis to determine the overall magnitude of gut passage effects on seed germination percentage and mean time to germination. We also compare effect sizes as a function of different feeding guilds, gut complexities, and seed size. Our results show a strong, positive effect of primates on seed germination percentage and on the number of days to first germination. Strictly frugivorous monkeys, the group most threatened by extinction, showed the highest dispersal quality, increasing germination percentage by 75%. Primates that include insects in their diets had no average effect on germination percentage or time. Gut passage had different outcomes on seeds with different sizes; both large and small seeds showed similar increases in germination percentages after gut passage, but only large seeds germinated faster than control seeds after gut passage. Our results show a relevant role for primates in providing high seed dispersal quality and as drivers of forest regeneration. The combined effects of defaunation and forest fragmentation may result in decreased regeneration of trees, which has the potential to affect negatively both forest structure and ecosystem processes. Finally, we provide general guidelines for standardizing research on seed dispersal by primates.SynthesisConsuming fleshy fruits and dispersing seeds is the main ecological service provided by vertebrates to plants. Vertebrate increases seed germination due to treatment given during digestive system passage. Previous meta‐analyses suggest an overall positive effect of vertebrate gut passage on germination, but no insights are available on its variation among different functional groups of mammals. Our analyses indicated that gut passage by Neotropical primates increased seed germination. Strict frugivores, the ones most threatened by extinction, were the most efficient. Our results show a relevant role for primates in providing high seed dispersal quality and as drivers of forest regeneration, which can be meaningful for conservation in a community scale.

Seed Dispersal of Vitex Glabrata and Prunus Ceylanica by Civets (Viverridae) in Pakke Tiger Reserve, North-East India: Spatial Patterns and Post-Dispersal Seed Fates

Civets are considered potentially important seed dispersers in tropical forests of Asia, but relatively little is known about spatial patterns of dispersal and post-dispersal fates of civet-dispersed seeds. We explored these aspects of civet seed dispersal for two tree species Vitex glabrata (Lamiaceae), also known as smooth chaste tree and Prunus ceylanica (Rosaceae), in Pakke Tiger Reserve, a tropical forest reserve in north-east India. Pakke has five known species of viverrids: small Indian civet ( Viverricula indica), large Indian civet ( Viverra zibetha), common palm civet ( Paradoxurus hermaphroditus), masked palm civet ( Paguma larvata) and the binturong ( Arctictis binturong). For both tree species, civets as a group dispersed seeds (100% of scats that we found) within 50 meters from fruiting trees and deposited seeds onto multiple substrates including tree branches, forest floor, and fallen logs. However, the distribution of seeds among substrates differed for the two tree species: while most seeds of V. glabrata (> 90%) were deposited onto canopy branches and fallen logs, the majority of P. ceylanica seeds (> 70%) were deposited on the forest floor. For both tree species, seeds deposited on logs experienced higher seed predation than seeds on the forest floor, especially when local seed densities (number of seeds in 1m2 area around the scat and in the scat) were high. Further, seed viability of P. ceylanica was significantly lower on logs (~35%) than on the forest floor (~65%). For both tree species, civets neither dispersed seeds far from fruiting trees nor to sites where seeds experienced either low predation or high survival, suggesting that while civets were legitimate dispersers, they were not especially effective.

Size-class effect contributes to tree species assembly through influencing dispersal in tropical forests.

We have investigated the processes of community assembly using size classes of trees. Specifically our work examined (1) whether point process models incorporating an effect of size-class produce more realistic summary outcomes than do models without this effect; (2) which of three selected models incorporating, respectively environmental effects, dispersal and the joint-effect of both of these, is most useful in explaining species-area relationships (SARs) and point dispersion patterns. For this evaluation we used tree species data from the 50-ha forest dynamics plot in Barro Colorado Island, Panama and the comparable 20 ha plot at Bubeng, Southwest China. Our results demonstrated that incorporating an size-class effect dramatically improved the SAR estimation at both the plots when the dispersal only model was used. The joint effect model produced similar improvement but only for the 50-ha plot in Panama. The point patterns results were not improved by incorporation of size-class effects using any of the three models. Our results indicate that dispersal is likely to be a key process determining both SARs and point patterns. The environment-only model and joint-effects model were effective at the species level and the community level, respectively. We conclude that it is critical to use multiple summary characteristics when modelling spatial patterns at the species and community levels if a comprehensive understanding of the ecological processes that shape species’ distributions is sought; without this results may have inherent biases. By influencing dispersal, the effect of size-class contributes to species assembly and enhances our understanding of species coexistence.

Seed dispersal by rhesus macaques Macaca mulatta in Northern India.

Frugivorous primates are important seed dispersers and their absence from forest patches is predicted to be detrimental to tropical forest regeneration and recruitment. With the reduction of primate populations globally, ecologically resilient primate species, characterized by dietary flexibility and the ability to thrive in a variety of habitats, assume new importance as seed dispersers. The most widely distributed non-human primate, the rhesus macaque Macaca mulatta has been intensively studied but little is known about its role in maintaining ecosystem structure and functions. Due to their frugivorous diet, large group sizes, large home ranges and tolerance to disturbance, rhesus macaques may be effective seed dispersers. We studied seed dispersal by rhesus macaques at the Buxa Tiger Reserve, India, through a combination of behavioural observations and germination experiments. Rhesus macaques dispersed 84% of the 49 species they fed on either through spitting or defecation. Nearly 96% of the handled seeds were undamaged and 61% of the species for which germination tests were performed had enhanced germination. Almost 50% of the monitored seeds among those deposited in situ germinated and 22% established seedlings, suggesting that rhesus macaques are important seed dispersers in tropical forests. Due to their widespread distribution and large populations, rhesus macaques are perceived as common and are categorized as Least Concern on the IUCN Red List, effectively excluding them from any conservation plans. Based on the results of our study, we argue that rhesus macaques fulfill critical ecological functions in their habitat and that this parameter must be taken into consideration when they are reviewed for conservation priorities.

Interactions between ants and non-myrmecochorous diaspores in a tropical wet forest in southern Bahia, Brazil

Abstract:Interactions between ants and non-myrmecochorous diaspores occur frequently on the forest floor and the results of these interactions (e.g. diaspore cleaning or removal) will often depend on the morpho-chemical characteristics of the diaspores. We conducted two different experiments with seven plant species in the north-eastern Atlantic forest, Brazil. To evaluate whether ant interactions decrease diaspore persistence time on the forest floor, we established sample stations by placing five diaspores of each species spaced every 10 m along a transect and monitored ant interactions over a 24-h period. We also compared diaspore removal by ants and vertebrates through a paired experiment. We monitored removal of the seven plant species in treatments where ants were excluded and treatments where vertebrates were excluded. We recorded 332 ant–diaspore interactions, most resulting in ants cleaning diaspores in situ. Persistence of diaspores on the forest floor varied greatly among studied species and was less than 50% for three species. Ants also removed more diaspores than did vertebrates. Number of diaspores removed by ants was greater for small diaspores and with high lipid concentration. Ant–diaspore interactions may not always exert a positive influence on plant recruitment for diaspores with poor nutrient concentration. Consequently, ants may play a disproportionately important role as secondary dispersers in tropical forests.

Diet and Fruit Choice of the Brown Palm Civet Paradoxurus Jerdoni, a Viverrid Endemic to the Western Ghats Rainforest, India

Brown palm civet diet was assessed by examining 1,013 scats between May 1996 and December 1999 in Kalakad-Mundanthurai Tiger Reserve, Western Ghats, India. The brown palm civet is predominantly frugivorous, with fruits of 53 native species and four species of introduced plants comprising 97% of its diet. There was high intra- and inter-annual variation in the diet of brown palm civets. Civets adapted to fluctuations in fruit resources by feeding on a diverse range of species and supplementing their year-round, primarily frugivorous, diet with invertebrates and vertebrates. Civets mainly ate fruits of trees and lianas, rarely those of herbs or shrubs. Fruits eaten by civets were mostly small (<1 cm diameter), multi-seeded, pulpy berries, and drupes with moderate to high water content, along with several large (>2 cm) fruits like Palaquium ellipticum, Elaeocarpus serratus, Holigarna nigra, and Knema attenuata. The brown palm civet is a key mammalian seed disperser in the Western Ghats rainforest by being predominantly frugivorous and dispersing a diverse array of plant species. As brown palm civets can persist in fragmented rainforest, they can play a major role in restoration of degraded fragments in these landscapes. The results emphasize the need to recognize the importance of small carnivores as seed dispersers in tropical forests.

The role of timber tree species in the nutritional ecology of spider monkeys in a certified logging concession, Bolivia

Selective harvesting of timber can lead to population declines in some primate species. As frugivorous primates are important seed dispersers in tropical forests, the reduction of their populations may affect the ecological sustainability of selectively logged forests. This paper is the first to quantify the importance of timber tree species in the diet and nutritional ecology of a primate species. We studied spider monkeys ( Ateles chamek) inhabiting a certified forestry concession in Bolivia where post-logging population declines of this species have been recorded. We show that spider monkeys occupying unlogged areas obtained approximately 50% of their total intake of macro-nutrients from timber tree species and exhibited a distinct preference for foraging within trees that were of harvestable size. Timber tree species dominated the spider monkeys’ diet both during peak fruiting periods and during periods of fruit scarcity. We estimate that under current timber extraction intensities spider monkeys lose significant proportions of their food sources. Our results indicate that further extraction limits could be considered for Ficus boliviana, Spondias mombin and Pouteria nemorosa. We suggest that to ensure long-term ecological sustainability of certified forestry concessions, the importance of timber tree species in the ecology of seed dispersers needs to be taken into account.

Are tortoises important seed dispersers in Amazonian forests?

According to most studies on seed dispersal in tropical forests, mammals and birds are considered the main dispersal agents and the role played by other animal groups remains poorly explored. We investigate qualitative and quantitative components of the role played by the tortoise Chelonoidis denticulata in seed dispersal in southeastern Amazon, and the influence of seasonal variation in tortoise movement patterns on resulting seed shadows. Seed shadows produced by this tortoise were estimated by combining information on seed passage times through their digestive tract, which varied from 3 to 17 days, with a robust dataset on movements obtained from 18 adult C. denticulata monitored with radio transmitters and spoon-and-line tracking devices. A total of 4,206 seeds were found in 94 collected feces, belonging to 50 seed morphotypes of, at least, 25 plant genera. Very low rates of damage to the external structure of the ingested seeds were observed. Additionally, results of germination trials suggested that passage of seeds through C. denticulata's digestive tract does not seem to negatively affect seed germination. The estimated seed shadows are likely to contribute significantly to the dispersal of seeds away from parent plants. During the dry season seeds were dispersed, on average, 174.1 m away from the location of fruit ingestion; during the rainy season, this mean dispersal distance increased to 276.7 m. Our results suggest that C. denticulata plays an important role in seed dispersal in Amazonian forests and highlight the influence of seasonal changes in movements on the resulting seed shadows.

High-quality seed dispersal by fruit-eating fishes in Amazonian floodplain habitats

Seed dispersal is a critical stage in the life history of plants. It determines the initial pattern of juvenile distribution, and can influence community dynamics and the evolutionary trajectories of individual species. Vertebrate frugivores are the primary vector of seed dispersal in tropical forests; however, most studies of seed dispersal focus on birds, bats and monkeys. Nevertheless, South America harbors at least 200 species of frugivorous fishes, which move into temporarily flooded habitats during lengthy flood seasons and consume fruits that fall into the water; and yet, we know remarkably little about the quality of seed dispersal they effect. We investigated the seed dispersal activities of two species of large-bodied, commercially important fishes (Colossoma macropomum and Piaractus brachypomus, Characidae) over 3 years in Pacaya-Samiria National Reserve (Peru). We assessed the diet of these fishes during the flood season, conducted germination trials with seeds collected from digestive tracts, and quantified fruit availability. In the laboratory, we fed fruits to captive Colossoma, quantified the proportion of seeds defecated by adult and juvenile fish, and used these seeds in additional germination experiments. Our results indicate that Colossoma and Piaractus disperse large quantities of seeds from up to 35% of the trees and lianas that fruit during the flood season. Additionally, these seeds can germinate after floodwaters recede. Overexploitation has reduced the abundance of our focal fish species, as well as changed the age structure of populations. Moreover, older fish are more effective seed dispersers than smaller, juvenile fish. Overfishing, therefore, likely selects for the poorest seed dispersers, thus disrupting an ancient interaction between seeds and their dispersal agents.

Interspecific variation in primary seed dispersal in a tropical forest

SummaryWe investigated the relationships of seed size, dispersal mode and other species characteristics to interspecific variation in mean primary seed dispersal distances, mean annual seed production per unit basal area, and clumping of seed deposition among 41 tropical tree species on Barro Colorado Island, Panama.A hierarchical Bayesian model incorporating interannual variation in seed production was used to estimate seed dispersal, seed production, and clumping of seed rain for each species from 19 years of data for 188 seed traps on a 50‐ha plot in which all adult trees were censused every 5 years.Seed dispersal was modelled as a two‐dimensional Student'sTdistribution with the degrees of freedom parameter fixed at 3, interannual variation in seed production per basal area was modelled as a lognormal, and the clumping of seed rain around its expected value was modelled as a negative binomial distribution.There was wide variation in seed dispersal distances among species sharing the same mode of seed dispersal. Seed dispersal mode did not explain significant variation in seed dispersal distances, but did explain significant variation in clumping: animal‐dispersed species showed higher clumping of seed deposition.Among nine wind‐dispersed species, the combination of diaspore terminal velocity, tree height and wind speed in the season of peak dispersal explained 40% of variation in dispersal distances. Among 31 animal‐dispersed species, 20% of interspecific variation in dispersal distances was explained by seed mass (a negative effect) and tree height (a positive effect).Among all species, seed mass, tree height and dispersal syndrome explained 28% of the variation in mean dispersal distance and seed mass alone explained 45% of the variation in estimated seed production per basal area.Synthesis. There is wide variation in patterns of primary seed rain among tropical tree species. Substantial proportions of interspecific variation in seed production, seed dispersal distances, and clumping of seed deposition are explained by relatively easily measured plant traits, especially dispersal mode, seed mass, and tree height. This provides hope for trait‐based generalization and modelling of seed dispersal in tropical forests.

Aggregated seed dispersal by wreathed hornbills at a roost site in a moist evergreen forest of Thailand

AbstractHornbills (Bucerotidae) are widely regarded as important seed dispersers in tropical forests in Africa and Asia. We investigated how the roosting behavior of wreathed hornbills (Aceros undulatus) influences seed deposition and seedling survival at a roost site in a moist evergreen forest of Khao Yai National Park, Thailand. Fallen fruits and seeds were collected in traps that were placed around a roosting site for 14 months, and seedlings were monitored in adjacent quadrats for 3 years. Seedfall and seedlings of species represented in the hornbill diet occurred at significantly higher densities in the traps and quadrats located beneath the crown of the roosting tree than in those located beyond the crown. With the exception of Cinnamomum subavenium, the seeds and seedlings of most diet species rarely survived beyond the first year. The quality of hornbill dispersal to this roosting site may be poor due to the highly concentrated seedfall, which results in high seed and seedling mortality. However, the number of seeds deposited by each hornbill each day at roosting sites is relatively low. Wreathed hornbills are primarily scatter dispersers during the day and probably serve as agents of seed dispersal in the moist evergreen forest of Khao Yai.