Changes of community composition at multiple trophic levels due to hunting in Nigerian tropical forests

Hunting in tropical forests decimates large mammals, and this may have direct and indirect effects on other trophic levels and lead to trophic cascades. We compared replicated sites of hunted and protected forests in southeastern Nigeria, with respect to community composition of primates, other mammals, birds, plant seedlings, and mature trees. We make predictions regarding the community composition at the different trophic levels. In forests where large primates are rare, we hypothesize that their ecological role will not be fully compensated for by small frugivores. We apply multivariate methods to assess changes in community composition of mammals, birds, and seedlings, controlling for any differences between sites in the other groups, including mature trees. Medium and large (4–180 kg) primates were much rarer in hunted sites, while porcupine and rock hyrax increased in abundance with hunting. In contrast, the community composition of birds was similar in both types of forests. Seedling communities were significantly related to the community composition of mammals, and thus strongly affected by hunting. In protected forests primate dispersed plant seedling species dominated, whereas in hunted forests the seedling community was shifted towards one dominated by abiotically dispersed species. This was probably both a consequence of reduced seed dispersal by primates, and increased seed predation by rodents and hyrax. Hence we found no evidence for buffering effects on tree regeneration through functional compensation by non‐hunted animals (such as birds). Our results highlight how seedling communities are changed by the complex plant–animal intera ctions, triggered by the loss of seed dispersers. The results predict a rarity of primate‐dispersed trees in future tropical forest canopies; a forest less diverse in timber and non‐timber resources.     

Differential Effects of Hunting on Pre-Dispersal Seed Predation and Primary and Secondary Seed Removal of Two Neotropical Tree Species

Many of the mammals undergoing drastic declines in tropical forests worldwide are important seed dispersers and seed predators, and thus changes in mammal communities due to hunting will affect plant recruitment. It has been hypothesized that larger-seeded species will suffer greater reductions in seed removal and thus greater increases in predispersal seed predation than smaller-seeded species. We compared primary and secondary seed removal and predispersal seed predation of two tree species between hunted and nonhunted sites in Central Panama. Seeds of Oenocarpus mapora (Arecaceae) are 16-times greater in size than those of Cordia bicolor (Boraginaceae). We quantified primary seed removal and predispersal seed predation using seed traps, and we assessed secondary seed removal using seed removal plots. Primary removal of C. bicolor was 43 percent lower in the hunted sites, while primary removal of O. mapora was not significantly different. Secondary removal of unprotected O. mapora seeds on the ground was 59 percent lower in hunted sites, while secondary removal of C. bicolor was not significantly different. Predispersal seed predation of O. mapora by mammals was significantly lower in hunted sites, while predispersal seed predation by insects was not significantly different in either species. In combination with other studies, our results suggest that seed size is not a reliable predictor of the impacts of hunting. Mammal defaunation differentially affects stages and modes of seed dispersal and seed predation of different plant species, suggesting that these influences are complex and related to multiple plant traits.     

Positive relationship between fruit removal by animals and seedling recruitment in a tropical forest

Fleshy-fruited plants rely on animal frugivores to disperse their seeds, and seed removal by frugivores may leave an imprint on seedling recruitment. However, to what extent plant–frugivore interactions are related to seedling recruitment has rarely been quantified at the community level, especially in species-rich tropical forests. In this study, we tested the effect of different plant traits on fruit removal by frugivores and tested the relative importance of fruit removal, plant traits and abiotic factors for seedling recruitment. We quantified plant–frugivore interactions of 22 fleshy-fruited plant species consumed by 56 diurnal frugivore species, and counted the number of seedlings that emerged along an elevational gradient in the Colombian Andes. We measured a set of plant traits (i.e., crop size; fruit size; seed load and mass; fruit nutritional contents), estimated the density of adult plants and recorded relevant abiotic factors (light, temperature and humidity). We found that fruit removal by frugivores was positively associated with crop size, but negatively associated with fruit length and unrelated to seed load and fruit nutritional content. Seedling densities were positively related to the density of adult plants, seed mass and fruit removal by animals. We found no relationship between abiotic factors and seedling recruitment. Our results indicate that fruit abundance and morphology are important determinants of fruit removal and that fruit removal is positively associated with seedling recruitment accounting for effects of species abundance and plant traits. We conclude that plant traits shape fruit removal and seedling recruitment at the community level, while these two crucial processes of forest regeneration are directly linked by seed dispersal of animals.     

Large herbivores regulate the spatial recruitment of a hyperdominant Neotropical palm

Large mammalian herbivores play an important role in shaping the diversity of tropical forests by affecting the survival of seedlings and saplings beneath parent plants. The white‐lipped peccary (Tayassu pecari) accounts for the largest herbivore biomass that controls seed and seedling survival in Neotropical ecosystems. However, hunting and habitat loss has driven peccaries to local extinction for most of their original distribution, so it is likely that their absence will affect plant recruitment dynamics. We tested the effects of peccary local extinction on the density and spatial distribution of the hyperdominant palm Euterpe edulis by performing a fine‐scale characterization of its spatial recruitment in six forest sites in the Brazilian Atlantic forest. We compared the age structure and the spatial patterns of seedlings, saplings, and adults as well as the relationship between them. We found that while under the presence of peccaries there was a decrease in recruitment rates under adults, the local extinction of these large mammals led to a more clumped process of spatial recruitment. Despite such contrasting spatial patterns of recruitment dynamics, neither age structure nor the random spatial distribution of adults was affected by the presence or absence of peccaries, indicating that their early effects on these palm populations are mitigated as recruitment advances. Our findings highlight the role of large‐bodied forest‐dwelling herbivores in regulating the fine‐scale spatial recruitment of plants and advance our understanding on the effects of defaunation in tropical forests. Abstract in Portuguese is available with online material.     

Bushmeat hunting changes regeneration of African rainforests

To assess ecological consequences of bushmeat hunting in African lowland rainforests, we compared paired sites, with high and low hunting pressure, in three areas of southeastern Nigeria. In hunted sites, populations of important seed dispersers—both small and large primates (including the Cross River gorilla, Gorilla gorilla diehli)—were drastically reduced. Large rodents were more abundant in hunted sites, even though they are hunted. Hunted and protected sites had similar mature tree communities dominated by primate-dispersed species. In protected sites, seedling communities were similar in composition to the mature trees, but in hunted sites species with other dispersal modes dominated among seedlings. Seedlings emerging 1 year after clearing of all vegetation in experimental plots showed a similar pattern to the standing seedlings. This study thus verifies the transforming effects of bushmeat hunting on plant communities of tropical forests and is one of the first studies to do so for the African continent.     

Frugivore loss limits recruitment of large-seeded trees

Although global declines in frugivores may disrupt seed dispersal mutualisms and inhibit plant recruitment, quantifying the likely reduction in plant regeneration has been difficult and rarely attempted. We use a manipulative factorial experiment to quantify dependence of recruitment on dispersal (i.e. fruit pulp removal and movement of seed away from parental area) in two large-seeded New Zealand tree species. Complete dispersal failure would cause a 66 to 81 per cent reduction in recruitment to the 2-year-old seedling stage, and synergistic interactions with introduced mammalian seed and seedling predators increase the reduction to 92 to 94 per cent. Dispersal failure reduced regeneration through effects on seed predation, germination and (especially) seedling survival, including distance- and density-dependent (Janzen-Connell) effects. Dispersal of both species is currently largely dependent on a single frugivore, and many fruits today remain uneaten. Present-day levels of frugivore loss and mammal seed and seedling predators result in 57 to 84 per cent fewer seedlings after 2 years. Our study demonstrates the importance of seed dispersal for local plant population persistence, and validates concerns about the community consequences of frugivore declines.     

Seed size: a key trait determining species distribution and diversity of dry tropical forest in northern India

The study examined the relationships among seed size, plant distribution and abundance in a dry tropical forest of northern India. Results indicated that small-seeded species, which were generally wind-dispersed, were more widely distributed, at this local scale, compared to large-seeded species. However, the proportional abundance and basal cover of seed size categories indicated that the structure of the dry forest was largely determined by the medium- to large-seeded species. There was a considerable amount of redundancy within each seed size group, which added to the species diversity. Variability in seed size and the variable degree of shade-tolerance permit the species to occupy the full range of the gradient of light environments of the forest floor. This study revealed that in little to moderately disturbed locations seedlings of large-seeded species increased in abundance, whereas in extremely perturbed locations seedlings of species with medium-sized to small seeds were more abundant.     

Seed-spitting Primates and the Conservation and Dispersion of Large-seeded Trees

Primate frugivory may reduce density-dependent predation on seeds and seedlings via effective seed dispersal. Accordingly, the tendency of cercopithecines to spit and scatter seeds > 4 mm wide could represent a prominent means of dispersal. However, the importance of seed-spitting may vary according to the life history adaptations of plants. Indeed, the actions of cercopithecines may be incongruent with the reproductive biology of plants that rely on large frugivores to swallow and defecate their seeds. This possibility raises conservation concerns because large frugivores are often susceptible to extirpation or extinction from hunting and habitat fragmentation. It is therefore important to determine if cercopithecines have a compensatory effect; that is, whether or not seed-spitting effectively conveys large seeds to recruitment sites. To test this concept, we used geospatial techniques to measure and analyze the dispersion of tree species dispersed by elephants, chimpanzees, and cercopithecines to different spatial extents. We studied adult trees of Balanites wilsoniana, Chrysophyllum gorungosanum, and Uvariopsis congensis in a 2.2-ha plot in Kibale National Park, Uganda. Despite the tendency of cercopithecines to spit the seeds of Uvariopsis congensis, adult trees were highly clumped, with a modal nearest-neighbor distance of < 5 m and a crown overlap of 1.5 m. Virtually identical results for Balanites wilsoniana and Chrysophyllum gorungosanum, the seeds of which are not spat, suggest that seed-spitting may be a poor mechanism of dispersal for some large-seeded plants.     

Fig-eating by vertebrate frugivores: a global review

The consumption of figs (the fruit of Ficus spp.: Moraceae) by vertebrates is reviewed using data from the literature, unpublished accounts and new field data from Borneo and Hong Kong. Records of frugivory from over 75 countries are presented for 260 Ficus species (approximately 30% of described species). Explanations are presented for geographical and taxonomic gaps in the otherwise extensive literature. In addition to a small number of reptiles and fishes, 1274 bird and mammal species in 523 genera and 92 families are known to eat figs. In terms of the number of species and genera of fig-eaters and the number of fig species eaten we identify the avian families interacting most with Ficus to be Columbidae, Psittacidae, Pycnonotidae, Bucerotidae, Sturnidae and Lybiidae. Among mammals, the major fig-eating families are Pteropodidae, Cercopithecidae, Sciuridae, Phyllostomidae and Cebidae. We assess the role these and other frugivores play in Ficus seed dispersal and identify fig-specialists. In most, but not all, cases fig specialists provide effective seed dispersal services to the Ficus species on which they feed. The diversity of fig-eaters is explained with respect to fig design and nutrient content, phenology of fig ripening and the diversity of fig presentation. Whilst at a gross level there exists considerable overlap between birds, arboreal mammals and fruit bats with regard to the fig species they consume, closer analysis, based on evidence from across the tropics, suggests that discrete guilds of Ficus species differentially attract subsets of sympatric frugivore communities. This dispersal guild structure is determined by interspecific differences in fig design and presentation. Throughout our examination of the fig-frugivore interaction we consider phylogenetic factors and make comparisons between large-scale biogeographical regions. Our dataset supports previous claims that Ficus is the most important plant genus for tropical frugivores. We explore the concept of figs as keystone resources and suggest criteria for future investigations of their dietary importance. Finally, fully referenced lists of frugivores recorded at each Ficus species and of Ficus species in the diet of each frugivore are presented as online appendices. In situations where ecological information is incomplete or its retrieval is impractical, this valuable resource will assist conservationists in evaluating the role of figs or their frugivores in tropical forest sites.     

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

The 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.     

Reduced Hornbill Abundance Associated with Low Seed Arrival and Altered Recruitment in a Hunted and Logged Tropical Forest

Logging and hunting are two key direct threats to the survival of wildlife in the tropics, and also disrupt important ecosystem processes. We investigated the impacts of these two factors on the different stages of the seed dispersal cycle, including abundance of plants and their dispersers and dispersal of seeds and recruitment, in a tropical forest in north-east India. We focused on hornbills, which are important seed dispersers in these forests, and their food tree species. We compared abundances of hornbill food tree species in a site with high logging and hunting pressures (heavily disturbed) with a site that had no logging and relatively low levels of hunting (less disturbed) to understand logging impacts on hornbill food tree abundance. We compared hornbill abundances across these two sites. We, then, compared the scatter-dispersed seed arrival of five large-seeded tree species and the recruitment of four of those species. Abundances of hornbill food trees that are preferentially targeted by logging were two times higher in the less disturbed site as compared to the heavily disturbed site while that of hornbills was 22 times higher. The arrival of scatter-dispersed seeds was seven times higher in the less disturbed site. Abundances of recruits of two tree species were significantly higher in the less disturbed site. For another species, abundances of younger recruits were significantly lower while that of older recruits were higher in the heavily disturbed site. Our findings suggest that logging reduces food plant abundance for an important frugivore-seed disperser group, while hunting diminishes disperser abundances, with an associated reduction in seed arrival and altered recruitment of animal-dispersed tree species in the disturbed site. Based on our results, we present a conceptual model depicting the relationships and pathways between vertebrate-dispersed trees, their dispersers, and the impacts of hunting and logging on these pathways.     

The Role of Mammals in Creating and Modifying Seedshadows in Tropical Forests and Some Possible Consequences of Their Elimination

Mammal populations are increasingly hunted, yet the consequences of their disappearance from tropical forests have only recently been explored. Here, we summarize current research on the role of mammals in seed dispersal and postdispersal processes, such as seed predation and secondary dispersal, in different tropical regions. We evaluate how mammal features influence seedshadows and ultimately forest regeneration. Finally, we discuss the potential effect of changes in seedshadows caused by the elimination of many medium- and large-sized mammals. The complex role that mammals play in creating and modifying seedshadows in tropical forests cannot be easily quantified, and in this review we emphasize the variation that exists both within and among mammal taxa and across continents. To bridge this gap in information, we suggest that more studies should evaluate the relative importance of the disappearance of both seed dispersers and seed predators for particular plant species so that we may begin to understand the balance between these two influences. We also suggest that future studies identify ecological redundancy in nonhunted vertebrates within any particular community to evaluate compensatory behavior that may help ameliorate some of the negative effects of hunting of large and medium mammals.     

Bushmeat and the Fate of Trees with Seeds Dispersed by Large Primates in a Lowland Rain Forest in Western Amazonia

In Neotropical forests, large fruit-eating primates play important ecological roles as dispersal agents of large seeds. Bushmeat hunting threatens to disrupt populations of primates and large-seeded trees. We test the hypothesis that otherwise intact Neotropical forests with depressed populations of large primates experience decline in recruitment of large-seeded trees. We quantify the proportion of small juveniles (> 0.5 m tall–1 cm diameter at breast height, DBH) of large primate-dispersed tree species found underneath heterospecifc trees that are also dispersed by large primates at two protected sites in Manu National Park and one hunted site outside Manu N.P. in southeastern Peru. The forests are comparable in edaphic and climatic qualities, successional stage, and adult tree species composition. We found that hunting locally exterminates populations of large primates, and reduced primates of intermediate body size (hereafter "medium primates") by 80 percent. Moreover, tree species richness was 55 percent lower and density of species dispersed by large and medium-bodied primates 60 percent lower in hunted than in protected sites. In addition, richness and density of abiotically dispersed species and plants dispersed by non-game animals are greater in hunted sites. Overhunting threatens to disrupt the ecological interactions between primates and the plants that rely on them for seed dispersal and recruitment. Sustainable wildlife management plans are urgently needed, because protected areas are at risk of becoming "island" parks if buffer zones become empty of animals and have impoverished flora.     

Potential Effects of Ateline Extinction and Forest Fragmentation on Plant Diversity and Composition in the Western Orinoco Basin,Colombia

Cattle and agricultural farming in the western Orinoco Basin began in 1555, and since then fragmentation of continuous forest has occurred. We evaluated the effects of the disturbances and the absence of large primates on plant community composition, diversity, and regeneration patterns. Atelines (Lagothrix and Ateles) inhabited the lowlands close to the Andean mountains, but no longer live in fragmented habitats. Their absence may have negative effects on plant populations because atelines play important roles as seed dispersers in neotropical forests, especially for large-seeded plants, which are rarely swallowed by other seed dispersers. We compared 2 1-ha vegetation plots in forest fragments north of the La Macarena Mountains with 7 plots in continuous forest in Tinigua National Park. Both sites share the same climatic conditions and have similar geological origins. There is floristic affinity between forests with similar ecological characteristics; the fragmented forests are also less diverse than the continuous forests. As predicted, the forest fragments have fewer individuals with large seeds. The results suggest that forest fragmentation and local ateline extinctions affect plant communities, reducing diversity and affecting large-seeded plants.     

Effect of seed passage through vertebrate frugivores'' guts on germination: a review

The capacity of seeds to germinate after ingestion by frugivores is important for the population dynamics of some plant species and significant for the evolution of plant-frugivore interactions. In this paper the effects of different vertebrates on seed germination of nearly 200 plant species are reviewed, searching for patterns that predict the circumstances in which germination of seeds is enhanced, inhibited, or unaffected by the passage through the digestive tract of a seed disperser. It was found that seed dispersers commonly have an effect on the germinability of seeds, or on the rate of germination, or both, in about 50% of the plants they consume, although the diversity of animal species tested so far is still rather low (42 bird species, 28 non-flying mammals, 10–15 bats, 12 reptiles, 2 fishes). Enhancement of germination occurred about twice as often as inhibition.

In spite of the morphological and physiological differences in their digestive tracts, the different animal groups tested have similar effects on seed germination, although non-flying mammals tend to influence germination slightly more often than the other groups. Data on fishes are still too scarce for any generalization. Seed retention time in the dispersers' digestive tract is one factor affecting germination, and helps to explain the variation in seed responses observed among plant species, and even within a species. However other factors are also important; for example, the type of food ingested along with the fruits may affect germination through its influence on chemical or mechanical abrasion of the seed coat. Seed traits such as coat structure or thickness may themselves be responsible for some of the variation in seed retention times. Seeds of different sizes, which usually have different transit times through frugivores, and seeds of either fleshy or dry fruits, show often similar germination response to gut passage.

Seeds of different plants species differ strongly in their germination response after ingestion, even by the same frugivore species. Congeneric plants often show little consistency in their response. Even within a species variation is found which can be related to factors such as the environmental conditions under which germination takes place, seed morphology, seed age, and the season when the seeds are produced.

The effect of gut passage on germination differs between tropical and temperate zones. Seed germination of both shrubs and trees (data on herbaceous species are still scarce) in the temperate zone is more frequently enhanced than in the tropics. This result supports the hypothesis that enhanced germination may be more advantageous in unpredictable or less constant environments. Significant differences in frugivore-mediated germination are also found among different life forms. In both tropical and temperate zones, trees appear to be consistently more affected than shrubs or herbs. This might be due to an overall higher thickness of the seed coats, or to a higher frequency of seed-coat dormancy in tree species.

The influence of frugivory upon the population dynamics of a species has to be evaluated relative to other factors that influence germination and seedling recruitment at a particular site. Whether seed ingestion by dispersers is really advantageous to a plant (as has commonly been assumed) can only be assessed if we also determine the fate of the ingested seeds under natural conditions, and compare it to the fate of seeds that have not been ingested.     

Consequences of Lemur Loss for Above-Ground Carbon Stocks in a Malagasy Rainforest

Anthropogenic disturbances have resulted in declines of seed-dispersing primate frugivores in tropical forests. Previous work has suggested that loss of seed dispersal by large frugivores may have a negative impact on ecosystem carbon storage by reducing tree biomass. However, we know little about the potential impacts of losing frugivores in Madagascar’s diverse rainforest ecosystem. Understanding the effects of frugivore extinction on carbon loss is relevant in Madagascar, where threatened lemur taxa are the only dispersers of many large-seeded plant species. Using a dataset of tree species composition and traits from the southeastern rainforests of Ranomafana National Park, we examined whether seed size and lemur-dependent dispersal are positively associated with above-ground tree biomass. We then simulated different scenarios of population declines of large-seeded trees (>10 mm seed length) dependent on lemur-mediated seed dispersal, to examine potential directional changes in carbon storage capacity of Malagasy forests under lemur loss. Lemur-dispersed tree species, which have large seeds, had higher above-ground biomass than other species. Our simulations showed that the loss of large frugivorous primates in Madagascar may decrease the forest’s potential to store carbon. These results demonstrate the importance of primate conservation for maintaining functioning ecosystems and forest carbon stocks in one of the world’s hottest hotspots of biodiversity.     

Importance of animal and plant traits for fruit removal and seedling recruitment in a tropical forest

The traits of animals and plants influence their interaction networks, but the significance of species' traits for the resulting ecosystem functions is poorly understood. A crucial ecosystem function in the tropics is seed dispersal by animals. While the importance of species' traits for structuring plant–frugivore networks is supported by a number of studies, no study has so far identified the functional traits determining the subsequent processes of fruit removal and seedling recruitment. Here, we conducted a comprehensive field study on fruit removal by frugivorous birds and seedling recruitment along an elevational gradient in the Colombian Andes. We measured morphological traits of birds (body mass, bill width, Kipp's index) and plants (plant height, crop mass, fruit width and seed mass) which we expected to be related to fruit removal and seedling recruitment. We tested 1) which bird and plant traits influence fruit removal, and 2) whether network metrics at plant species level, functional identities of frugivores (community‐based mean trait values) and/or plant traits were the main determinants of seedling recruitment. We found that large‐bodied bird species contributed more to fruit removal than small‐bodied bird species and that small‐sized fruits were more frequently removed than large‐sized fruits. Small plant species and plants with heavy seeds recruited more seedlings than did large plants and plants with light seeds. Network metrics and functional identities of seed dispersers were unrelated to seedling recruitment. Our findings have two important implications. First, large birds are functionally more important than small birds in tropical seed‐removal networks. Second, the detected tradeoff between fruit size and seed mass in subsequent recruitment processes suggests that the adaptability of forest plant communities to a loss of large frugivores is limited by life‐history constraints. Hence, the protection of large‐bodied frugivores is of primary importance for the maintenance of diverse tropical plant communities.     

The Abundance of Large Ateline Monkeys is Positively Associated with the Diversity of Plants Regenerating in Neotropical Forests

Ateline monkeys, the largest primates in the Neotropics, may disperse more than one million seeds/km²/d at sites where they are abundant, but it is unclear whether a reduction in their populations can alter plant diversity patterns. The species richness and composition of regenerating plants as a proxy of future plant communities were studied by comparing 16 sites with different ateline abundance in three countries in northwestern South America. A total of 3658 plots included 94,340 regenerating plants, which were assigned to species or morphospecies. Paired t‐tests comparing sites in the same region but with different densities of atelines, and regression analyses showed a consistent positive relationship between ateline density and plant diversity. These results were due to the larger number of stems per area and higher evenness at sites with more atelines, suggesting higher recruitment rates for dispersed seeds. Differences were also found in plant composition, as canopy, endozoochorous, and medium seed size plants were consistently more abundant in sites with more ateline monkeys than in sites with less atelines. The findings of this study suggest that these primates play a key role in plant regeneration. In order to maintain the diversity and plant composition of tropical forests for future generations, conservation of these large frugivores and other key game species is imperative.     

Sowing forests: a synthesis of seed dispersal and predation by agoutis and their influence on plant communities

Granivorous rodents have been traditionally regarded as antagonistic seed predators. Agoutis (Dasyprocta spp.), however, have also been recognized as mutualistic dispersers of plants because of their role as scatter-hoarders of seeds, especially for large-seeded species. A closer look shows that such definitions are too simplistic for these Neotropical animals because agoutis can influence plant communities not only through seed dispersal of large seeds but also through predation of small seeds and seedlings, evidencing their dual role. Herein, we summarize the literature on plant–agouti interactions, decompose agouti seed dispersal into its quantitative and qualitative components, and discuss how environmental factors and plant traits determine whether these interactions result in mutualisms or antagonisms. We also look at the role of agoutis in a community context, assessing their effectiveness as substitutes for extinct megafaunal frugivores and comparing their ecological functions to those of other extant dispersers of large seeds. We also discuss how our conclusions can be extended to the single other genus in the Dasyproctidae family (Myoprocta). Finally, we examine agoutis’ contribution to carbon stocks and summarize current conservation threats and efforts. We recorded 164 interactions between agoutis and plants, which were widespread across the plant phylogeny, confirming that agoutis are generalist frugivores. Seed mass was a main factor determining seed hoarding probability of plant species and agoutis were found to disperse larger seeds than other large-bodied frugivores. Agoutis positively contributed to carbon storage by preying upon seeds of plants with lower carbon biomass and by dispersing species with higher biomass. This synthesis of plant–agouti interactions shows that ecological services provided by agoutis to plant populations and communities go beyond seed dispersal and predation, and we identify still unanswered questions. We hope to emphasise the importance of agoutis in Neotropical forests.     

Relative Importance of Seed-Bank and Post-Disturbance Seed Dispersal on Early Gap Regeneration in a Colombian Amazon Forest

Early forest gap regeneration may be generated by postdisturbance seed rain and by seed, seedling or bud banks (i.e., resprouting). The relative importance of each process may depend on several factors (e.g., fruit/seed production, abundance and behavior of seed dispersers, gap characteristics, etc.). We experimentally compared the importance of seed-bank and seed-rain affecting early recruitment of seedlings in an Amazonian forest (Zafire Biological Station, Colombia), using soil transplants from forests to gaps and seed rain enclosures. We found that, during the 8-mo study, the seed-bank contributed with a larger number of individuals and species than seed-rain. The low seedling recruitment rates may be associated with reduced populations of animal seed-dispersers due to hunting and/or low levels of forest fruit production.