Megafaunal Fruit Research Articles

Seed dispersal effectiveness by greater one-horned rhinos and domestic bovids of a megafaunal fruit

The extinction of megafauna, such as rhinos, from tropical Asian forests may have detrimental effects on the regeneration of plant species that rely heavily on their dispersal services. Understanding the potential of other animals to substitute the ecological function of megafauna is important for predicting ecosystem change following declines or extirpation of megafauna. Anthropogenic activities have led to the presence of domestic bovids in many tropical habitats, and these animals could be capable of substituting seed dispersal roles of megafauna. Here, we conducted feeding trials, germination tests, and collected movement data on greater one-horned rhino (Rhinoceros unicornis) and domestic bovids (Bos primigenius; Bubalus bubalis) in the national parks of Chitwan and Shuklaphanta, Nepal. Our aim was to investigate whether domestic bovids can serve as effective substitutes for rhinos in dispersing the megafaunal-fruited Mallotus nudiflorus, which are specialized for rhino dispersal. Specifically, we assessed the long-distance seed dispersal capabilities of rhinos and bovids by combining gut passage times and movement patterns. Additionally, we compared the seed germination success rates among rhinos, bovids and other dispersal modes (e.g., deer and water dispersal). We found that rhinos dispersed 80 percent of seeds over distances greater than 1 km, with potential dispersal distances of up to approximately 5.4 km within their maximum gut passage time. In contrast, cattle dispersed 20 percent of seeds over 1 km, with a maximum distance of around 2.2 km, while buffaloes dispersed 15 percent of seeds over 1 km, with a maximum distance of around 1.4 km. Seeds consumed by rhinos exhibited similar or better germination rates compared to seeds retrieved from cattle and buffalo dung, as well as other dispersal modes. These findings indicate that rhinos provide a functionally unique dispersal service for this megafaunal fruit, especially in long-distance dispersal. While domestic bovids can partially substitute the seed dispersal functions of rhinos, they cannot fully compensate for the loss of seed dispersal that occurs with the disappearance of rhinos.

Could foxes be surrogate seed dispersers of a megafaunal fruit vine in southern South America?

AbstractPlants that bear oversized fruits, but do not co‐occur with present‐day large‐bodied frugivores to disperse their seeds, are considered to represent seed dispersal anachronisms. It is hypothesized that these plants were originally dispersed by the megafauna that became extinct at the end of the Pleistocene. Accordingly, many plant species in South America bearing the so‐called megafaunal fruits occur in ecosystems lacking native modern megafauna. In Chile, Lardizabala biternata is an endemic vine that produces a large edible fruit, with a morphology suggesting a megafaunal seed dispersal syndrome. This species grows across the Chilean Winter Rainfall‐Valdivian Forests and has a rather wide distribution, along which there are currently no large native vertebrates that could ingest its fruits and disperse the seeds. We hypothesized that foxes may be its present‐day surrogate dispersers, because they are the only remnant mesofauna across L. biternata's range that include fruits in their diet. We collected fox scats periodically for 1 year and analyzed their contents, which revealed the presence of intact L. biternata seeds. These results suggest that foxes may be acting as present‐day dispersers of this vine; however, it is unknown whether they provide effective dispersal. Our findings stress the fragmentary state of the knowledge of ecological interactions among species in Chilean ecosystems, opening new perspectives in terms of the role of terrestrial fauna in maintaining ecosystem functions.

Seed ecophysiology of Elephant Apple (Dillenia indica)—An important tree species of the Indomalayan realm

AbstractDillenia indica produces mucilaginous seeds embedded in hard, fibrous, megafaunal fruits, and little is known about the ecological function of mucilage in its regeneration. Using standard laboratory protocols, we investigated the role of mucilage on seed dispersal (buoyancy), chemical defense (antibiotic, antifungal, antioxidant, and allelopathic activities), and seed germination. Further, we characterized seed germination, dormancy, and storage physiology of D. indica. Results revealed that mucilage associated with seed‐coat assists seeds in floating on water for a longer duration, acts as an antimicrobial agent without hampering the overall seed germination. It was noticed that fresh mature seeds possess an underdeveloped embryo that grows within the seed before radicle emergence (a sign of morphological dormancy; MD), and seeds took ~70 days to achieve 95% germination (a sign of physiological dormancy; PD). However, the rate of germination increased when seeds were treated with gibberellin or subjected to 1‐month dry‐storage (confirmation of PD). Seeds disperse with ~12% moisture and retain high viability even after ultra‐drying over silica gel, indicating an orthodox seed storage physiology. Study concludes that mucilage plays a crucial ecophysiological function in dispersal‐defense mechanism of D. indica seeds, by enhancing seed buoyancy, helping seeds to disperse long‐distance, and protecting the seeds from soil pathogens through antimicrobial activity. Our study confirmed that seeds of D. indica possess morphophysiological dormancy (MPD), unlike the MD reported in an earlier study from North India. Possible ecophysiological function of mucilage on seed dispersal‐defense mechanism and production of morphophysiological dormant and orthodox seeds in D. indica are discussed.

The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms.

The Cretaceous–Palaeogene (K-Pg) extinction of the non-avian dinosaurs (66 Ma) led to a 25 million year gap of megaherbivores (>1000 kg) before the evolution of megaherbivorous mammals in the Late Eocene (40 Ma). The botanical consequences of this ‘Palaeocene megaherbivore gap’ (PMHG) remain poorly explored. We hypothesize that the absence of megaherbivores should result in changes in the diversification and trait evolution of associated plant lineages. We used phylogenetic time- and trait-dependent diversification models with palms (Arecaceae) and show that the PMHG was characterized by speciation slowdowns, decreased evolution of armature and increased evolution of megafaunal (≥4 cm) fruits. This suggests that the absence of browsing by megaherbivores during the PMHG may have led to a loss of defence traits, but the absence of megaherbivorous seed dispersers did not lead to a loss of megafaunal fruits. Instead, increases in PMHG fruit sizes may be explained by simultaneously rising temperatures, rainforest expansion, and the subsequent radiation of seed-dispersing birds and mammals. We show that the profound impact of the PMHG on plant diversification can be detected even with the overwriting of adaptations by the subsequent Late Eocene opening up of megaherbivore-associated ecological opportunities. Our study provides a quantitative, comparative framework to assess diversification and adaptation during one of the most enigmatic periods in angiosperm history.

Anachronic Fruit Traits and Natural History Suggest Extinct Megafauna Herbivores as the Dispersers of an Endangered Tree.

Megafaunal seed dispersal syndrome refers to a group of traits attributed to the evolution of plants in the presence of large mammals. Present-day plants that bear these traits in areas where megafauna are absent are presumed to represent anachronic dispersal systems. Gomortega keule is an endangered tree species from a monotypic family (Gomortegaceae), endemic to Chile. Its fruit traits suggest adaptation to seed dispersal by large vertebrates; however, none are present today along its area of distribution. Here, we conducted a detailed revision on the fruit morphology of G. keule to examine whether its fruit traits fit a megafaunal dispersal syndrome. Additionally, we examined the fruit processing behavior of large domestic and captive wild animals fed with G. keule fruits, and its effect on germination. G. keule fruits had traits consistent with those of a Type 1 megafaunal fruit. Compared to intact, whole stones, seed germination probabilities decreased when fruits were handled by animals, suggesting that the seed was damaged during mastication and/or ingestion. Moreover, results from our feeding trials with elephants may also imply low efficiency of extinct gomphotheres as seed dispersers of this species. Our results also suggest that although domestic animals may disperse G. keule, it is unlikely that at present they can substitute the services of its original dispersers. Further investigation on seedling survival, local livestock management and forest management practices may help reinstate sexual regeneration in G. keule. Finally, integrating observations on fruit ecology and local people’s knowledge with experimental data enriches our species-centered approach and may help to address regeneration problems in other endangered plants.

Predators and dispersers: Context-dependent outcomes of the interactions between rodents and a megafaunal fruit plant

Many plant species bear fruits that suggest adaptation to seed dispersal by extinct megafauna. Present-day seed dispersal of these megafaunal plants is carried out by rodents, which can act as predators or dispersers; whether this interaction is primarily positive or negative can depend on the context. Here, we parameterized a stochastic model using data from the field and experimental arenas to estimate the effect of rodents on the recruitment of Myrcianthes coquimbensis -an Atacama Desert shrub with megafaunal fruits- and examine whether environmental conditions can alter the sign and strength of these rodent-plant interactions. We show that the outcome of these interactions is context-dependent: in wet conditions seed removal by rodents negatively impacts the recruitment probability of M. coquimbensis; in contrast, in dry conditions, the interaction with rodents increases recruitment success. In all cases, the strength of the effect of rodents on the recruitment success was determined mainly by their role as dispersers, which could be positive or negative. This study demonstrates that by caching seeds, rodents can be effective dispersers of a megafaunal fruit plant, but that the sign and magnitude of their effect on recruitment changes as a function of the environmental context in which the interaction occurs.

The historical distribution of megaherbivores does not determine the distribution of megafaunal fruit in southern Africa

Abstract Large specialized fruit (megafaunal fruit) have evolved alongside megaherbivores to take advantage of their unparalleled seed dispersal service. Megaherbivores were widespread and abundant in the Pleistocene but due to multiple extinction events have been extirpated from all continents except Africa and small pockets of South East Asia. In Africa, we are in the unique position of being able to study megafaunal fruits where there are still areas with a largely intact megaherbivore community. The megafaunal fruits of the African forests have been examined but those of the African savannas have been largely overlooked. We use an operational definition of megafaunal fruit developed in the Neotropics to identify megafaunal fruit in the South African tree flora. Thirty-one species were identified as megafaunal fruit-bearers, representing only 3% of the tree flora. Megafaunal tree species are well represented in the families Mimosoideae, Arecaceae, Strychnaceae and Caesalpinoideae. We explored the factors underlying the distribution of these megafaunal tree species. We found that the historical distribution of megaherbivores in South Africa does not explain the distribution of these fruit. Megaherbivores have historically been found throughout South Africa while megafaunal fruit tree species occur almost exclusively in the northern tropical reaches of the country. Abiotic factors such as precipitation and temperature appear to best explain the distribution of megafaunal fruit species in the region. We conclude that megafaunal fruit are a tropical phenomenon and their tropical origins now limit their distribution.

To adapt or go extinct? The fate of megafaunal palm fruits under past global change.

Past global change may have forced animal-dispersed plants with megafaunal fruits to adapt or go extinct, but these processes have remained unexplored at broad spatio-temporal scales. Here, we combine phylogenetic, distributional and fruit size data for more than 2500 palm (Arecaceae) species in a time-slice diversification analysis to quantify how extinction and adaptation have changed over deep time. Our results indicate that extinction rates of palms with megafaunal fruits have increased in the New World since the onset of the Quaternary (2.6 million years ago). In contrast, Old World palms show a Quaternary increase in transition rates towards evolving small fruits from megafaunal fruits. We suggest that Quaternary climate oscillations and concurrent habitat fragmentation and defaunation of megafaunal frugivores in the New World have reduced seed dispersal distances and geographical ranges of palms with megafaunal fruits, resulting in their extinction. The increasing adaptation to smaller fruits in the Old World could reflect selection for seed dispersal by ocean-crossing frugivores (e.g. medium-sized birds and bats) to colonize Indo-Pacific islands against a background of Quaternary sea-level fluctuations. Our macro-evolutionary results suggest that megafaunal fruits are increasingly being lost from tropical ecosystems, either due to extinctions or by adapting to smaller fruit sizes.

Seed dispersal kernel of the largest surviving megaherbivore—the African savanna elephant

AbstractOwing to the late Pleistocene extinctions, the megafauna of Europe, Australia and the Americas disappeared, and with them the dispersal service they offered megafaunal fruit. The African savanna elephant, the largest remaining megaherbivore, offers valuable insights into the seed dispersal services provided by extinct megafauna in prehistoric times. Elephant seed dispersal studies have for the most part concentrated on African and Asian forest elephants. African savanna elephants are morphologically distinct from their forest counterparts. Like the forest elephants they consume large quantities of fruit from a large number of tree species. Despite this little is known of the savanna trees that rely on elephants for their dispersal or the spatial scale at which these seeds are dispersed. We combined information from feeding trials conducted on four park elephants with field telemetry data from 38 collared elephants collected over an 8‐year period in APNR/Kruger National Park to assess the seed dispersal service provided by savanna elephants. This study provides the first detailed account of the spatial scale at which African savanna elephants disperse seeds. Our mechanistic model predicts that 50 percent of seeds are carried over 2.5 km, and distances up to 65 km are achievable in maximum gut passage time. These findings suggest the savanna elephant as the longest distance terrestrial vertebrate disperser yet investigated. Maintaining their ecological role as a seed disperser may prove a significant factor in the conservation of large‐fruited tree diversity within the savannas. These results suggest that extinct megafauna offered a functionally unique dispersal service to megafaunal fruit.

Effectiveness of primate seed dispersers for an “oversized” fruit, Garcinia benthamii

The largest fruits found in tropical forests may depend on complementary seed dispersal strategies. These fruits are dispersed most effectively by megafauna, but populations can persist where megafauna are absent or erratic visitors. Smaller animals often consume these large fruits, but their capacity to disperse these seeds effectively has rarely been assessed. We evaluated the contributions of gibbons (Hylobates lar) and other frugivores in the seed dispersal of the megafaunal fruit Garcinia benthamii, using the SDE (seed dispersal effectiveness) landscape. Gibbons preferentially consumed G. benthamii fruits and were the main seed disperser that we observed. However, gibbons became satiated when availability was high, with 57% of fruits falling to the ground unhandled. Recruitment of seedlings from gibbon-dispersed seeds was also very low. Elephants consumed G. benthamii fruit, but occurred at low density and were rare visitors to the trees. We suggest that gibbons might complement the seed dispersal role of elephants for G. benthamii, allowing limited recruitment in areas (such as the study site) where elephants occur at low density. Fruit availability varied between years; when availability was low, gibbons reliably consumed most of the crop and dispersed some seeds that established seedlings, albeit at low numbers (2.5 seedlings per crop). When fruit availability was high, the fruit supply overwhelmed the gibbons and other arboreal frugivores, ensuring a large abundance of fruit available to terrestrial seed dispersers. Although gibbons effectively dispersed more seeds at these times (20.7 seedlings per crop), there was the potential for elephants to move many more seeds. Complementary seed dispersal strategies may be important for megafaunal fruit, because they ensure that very large fruits are able to benefit from megafaunal dispersal but also persist where this dispersal becomes erratic. However, our data suggest that smaller seed dispersers might not be capable of replacing large dispersers, leading to potential changes in landscape-scale dispersal patterns where megafauna are absent.

The anomalous Kentucky coffeetree: megafaunal fruit sinking to extinction?

The Kentucky coffeetree (Gymnocladus dioicus, Fabaceae) is an ecological paradox. A rare tree in nature in eastern and central North America, G. dioicus produces legumes that are only known to be dispersed by water, but appear similar to fruits consumed and dispersed by elephants and rhinoceros. One would expect the pods to be consumed by livestock, but the pulp and seeds are toxic to cattle and sheep. We examine the puzzle of G. dioicus dispersal in light of its other reproductive and life history characteristics and find that it probably is a botanical anachronism, in terms of both a set of dispersal agents long extinct and habitats, including what we term megafaunal disclimaxes, which have disappeared. Large seeds, the megafaunal gestault of the fruit, a dioecious mating system, and shade-intolerance combined with vigorous cloning suggest a widely dispersed pioneer of Miocene through Pleistocene habitats profoundly altered by large-mammal herbivory. As to what ate it, we can only say there were once many candidates. We hypothesize that the plant is an ecological anachronism, sinking to extinction in the wild.

Seed Dispersal Anachronisms: Rethinking the Fruits Extinct Megafauna Ate

BackgroundSome neotropical, fleshy-fruited plants have fruits structurally similar to paleotropical fruits dispersed by megafauna (mammals >103 kg), yet these dispersers were extinct in South America 10–15 Kyr BP. Anachronic dispersal systems are best explained by interactions with extinct animals and show impaired dispersal resulting in altered seed dispersal dynamics.Methodology/Principal FindingsWe introduce an operational definition of megafaunal fruits and perform a comparative analysis of 103 Neotropical fruit species fitting this dispersal mode. We define two megafaunal fruit types based on previous analyses of elephant fruits: fruits 4–10 cm in diameter with up to five large seeds, and fruits >10 cm diameter with numerous small seeds. Megafaunal fruits are well represented in unrelated families such as Sapotaceae, Fabaceae, Solanaceae, Apocynaceae, Malvaceae, Caryocaraceae, and Arecaceae and combine an overbuilt design (large fruit mass and size) with either a single or few (<3 seeds) extremely large seeds or many small seeds (usually >100 seeds). Within-family and within-genus contrasts between megafaunal and non-megafaunal groups of species indicate a marked difference in fruit diameter and fruit mass but less so for individual seed mass, with a significant trend for megafaunal fruits to have larger seeds and seediness.Conclusions/SignificanceMegafaunal fruits allow plants to circumvent the trade-off between seed size and dispersal by relying on frugivores able to disperse enormous seed loads over long-distances. Present-day seed dispersal by scatter-hoarding rodents, introduced livestock, runoff, flooding, gravity, and human-mediated dispersal allowed survival of megafauna-dependent fruit species after extinction of the major seed dispersers. Megafauna extinction had several potential consequences, such as a scale shift reducing the seed dispersal distances, increasingly clumped spatial patterns, reduced geographic ranges and limited genetic variation and increased among-population structuring. These effects could be extended to other plant species dispersed by large vertebrates in present-day, defaunated communities.

Gomphothere Fruits: A Critique

The hypothesis that giant Pleistocene mammals shaped reproductive traits of many tropical plants could help explain anomalous fruits which appear adapted for animal consumption, but which lack contemporary dispersal agents. The fruit syndrome, however, is not yet a useful tool. It lacks consistent criteria, depends upon precarious ecological assumptions, and does not give adequate attention to the likelihood that megafaunal plants actually have effective contemporary dispersal agents in protected forests. If qualities of living animals are sufficient to explain dispersal adaptations of common tropical trees, guesswork about horses and ground sloths of the Pleistocene is superfluous. Even the scanty literature now available shows that nearly half of the megafaunal fruits have living dispersal agents, that seeds of some of these plants suffer catastrophic mortality if they are not dispersed, and that many megafaunal species are common in Central and South America where horses and cattle (though...

Some Unique Examples of Dispersion of Seeds and Fruits

Previous articleNext article FreeSome Unique Examples of Dispersion of Seeds and FruitsW. J. BealW. J. Beal Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 32, Number 383Nov., 1898 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/277045 Views: 139Total views on this site Citations: 2Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:David N. Zaya, Henry F. Howe The anomalous Kentucky coffeetree: megafaunal fruit sinking to extinction?, Oecologia 161, no.22 (Jun 2009): 221–226.https://doi.org/10.1007/s00442-009-1372-3Roland M. Harper A PHYTOGEOGRAPHICAL SKETCH OF THE ALTAMAHA GRIT REGION OF THE COASTAL PLAIN OF GEORGIA., Annals of the New York Academy of Sciences 17, no.11 (Mar 1906): 1–414.https://doi.org/10.1111/j.1749-6632.1906.tb56903.x