Frugivore Behavioural Details Matter for Seed Dispersal: A Multi-Species Model for Cantabrian Thrushes and Trees

Animal movement and behaviour is fundamental for ecosystem functioning. The process of seed dispersal by frugivorous animals is a showcase for this paradigm since their behaviour shapes the spatial patterns of the earliest stage of plant regeneration. However, we still lack a general understanding of how intrinsic (frugivore and plant species traits) and extrinsic (landscape features) factors interact to determine how seeds of a given species are more likely to be deposited in some places more than in others. We develop a multi-species mechanistic model of seed dispersal based on frugivore behavioural responses to landscape heterogeneity. The model was fitted to data from three-years of spatially-explicit field observations on the behaviour of six frugivorous thrushes and the fruiting patterns of three fleshy-fruited trees in a secondary forest of the Cantabrian range (N Spain). With such model we explore how seed rain patterns arise from the interaction between animal behaviour and landscape heterogeneity. We show that different species of thrushes respond differently to landscape heterogeneity even though they belong to the same genus, and that provide complementary seed dispersal functions. Simulated seed rain patterns are only realistic when at least some landscape heterogeneity (forest cover and fruit abundance) is taken into account. The common and simple approach of re-sampling movement data to quantify seed dispersal produces biases in both the distance and the habitat at which seeds arrive. Movement behaviour not only affects dispersal distance and seed rain patterns but also can affect frugivore diet composition even if there is no built-in preference for fruiting species. In summary, the fate of seeds produced by a given plant species is strongly affected by both the composition of the frugivore assemblage and the landscape-scale context of the plant location, including the presence of fruits from other plants (from the same or different species).     

Exploring the interaction of avian frugivory and plant spatial heterogeneity and its effect on seed dispersal kernels using a simulation model

Seed dispersal by avian frugivores is one of the key processes influencing plant spatial patterns, but may fail if there is disruption of plant–frugivore mutualisms, such as decline in abundance of dispersers, fragmentation of habitat, or isolation of individual trees. We used simulation model experiments to examine the interaction between frugivore density and behaviour and the spatial arrangement of fruiting plants and its effect on seed dispersal kernels. We focussed on two New Zealand canopy tree species that produce large fruits and are dispersed predominantly by one avian frugivore (Hemiphaga novaeseelandiae). Although the mean seed dispersal distance decreased when trees became more aggregated, there were more frugivore flights between tree clusters, consequently stretching the tails of the dispersal kernels. Conversely, when trees were less aggregated in the landscape, mean dispersal distances increased because seeds were deposited over larger areas, but the kernels had shorter tails. While there were no statistically meaningful changes in kernel parameters when frugivore density changed, decreases in density did cause a proportional reduction in the total number of dispersed seeds. However, birds were forced to move further when fruit availability and fruit ripening were low. Sensitivity analysis showed that dispersal kernels were primarily influenced by the model parameters relating to disperser behaviour, especially those determining attractiveness based on distance to candidate fruiting trees. Our results suggest that the spatial arrangement of plants plays an important role in seed dispersal processes – although tree aggregation curbed the mean seed dispersal distance, it was accompanied by occasional long distance events, and tree dispersion caused an increase in mean dispersal distance, both potentially increasing the probability of seeds finding suitable habitats for germination and growth. Even though low frugivore densities did not cause dispersal failure, there were negative effects on the quantity of seed dispersal because fewer seeds were dispersed.     

Fragmentation, habitat composition and the dispersal/predation balance in interactions between the Mediterranean myrtle and avian frugivores

Human‐induced fragmentation and disturbance of natural habitats can shift abundance and composition of frugivore assemblages, which may alter patterns of frugivory and seed dispersal. However, despite their relevance to the functioning of ecosystems, plant‐frugivore interactions in fragmented areas have been to date poorly studied. I investigated spatial variation of avian frugivore assemblages and fruit removal by dispersers and predators from Mediterranean myrtle shrubs (Myrtus communis) in relation to the degree of fragmentation and habitat features of nine woodland patches (72 plants). The study was conducted within the chronically fragmented landscape of the Guadalquivir Valley (SW Spain), characterized by ~1% of woodland cover. Results showed that the abundance and composition of the disperser guild was not affected by fragmentation, habitat features or geographical location. However, individual species and groups of resident/migrant birds responded differently: whereas resident dispersers were more abundant in large patches, wintering dispersers were more abundant in fruit‐rich patches. Predator abundances were similar between patches, although the guild composition shifted with fragmentation. The proportion of myrtle fruits consumed by dispersers and predators varied greatly between patches, but did not depend on bird abundances. The geographical location of patches determined the presence or absence of interactions between myrtles and seed predators (six predated and three non‐predated patches), a fact that greatly influenced fruit dispersal success. Moreover, predation rates were lower (and dispersal rates higher) in large patches with fruit‐poor heterospecific environments (i.e. dominated by myrtle). Predator satiation and a higher preference for heterospecific fruits by dispersers may explain these patterns. These results show that 1) the frugivore assemblage in warm Mediterranean lowlands is mostly composed of fragmentation‐tolerant species that respond differently to landscape changes; and 2) that the feeding behaviour of both dispersers and predators influenced by local fruit availability may be of great importance for interpreting patterns of frugivory throughout the study area.     

Unravelling seed dispersal through fragmented landscapes: Frugivore species operate unevenly as mobile links

Seed dispersal constitutes a pivotal process in an increasingly fragmented world, promoting population connectivity, colonization and range shifts in plants. Unveiling how multiple frugivore species disperse seeds through fragmented landscapes, operating as mobile links, has remained elusive owing to methodological constraints for monitoring seed dispersal events. We combine for the first time DNA barcoding and DNA microsatellites to identify, respectively, the frugivore species and the source trees of animal‐dispersed seeds in forest and matrix of a fragmented landscape. We found a high functional complementarity among frugivores in terms of seed deposition at different habitats (forest vs. matrix), perches (isolated trees vs. electricity pylons) and matrix sectors (close vs. far from the forest edge), cross‐habitat seed fluxes, dispersal distances and canopy‐cover dependency. Seed rain at the landscape‐scale, from forest to distant matrix sectors, was characterized by turnovers in the contribution of frugivores and source‐tree habitats: open‐habitat frugivores replaced forest‐dependent frugivores, whereas matrix trees replaced forest trees. As a result of such turnovers, the magnitude of seed rain was evenly distributed between habitats and landscape sectors. We thus uncover key mechanisms behind “biodiversity–ecosystem function” relationships, in this case, the relationship between frugivore diversity and landscape‐scale seed dispersal. Our results reveal the importance of open‐habitat frugivores, isolated fruiting trees and anthropogenic perching sites (infrastructures) in generating seed dispersal events far from the remnant forest, highlighting their potential to drive regeneration dynamics through the matrix. This study helps to broaden the “mobile‐link” concept in seed dispersal studies by providing a comprehensive and integrative view of the way in which multiple frugivore species disseminate seeds through real‐world landscapes.     

Inter‐group variability in seed dispersal by white‐handed gibbons in mosaic forest

Seed dispersers, like white‐handed gibbons (Hylobates lar), can display wide inter‐group variability in response to distribution and abundance of resources in their habitat. In different home ranges, they can modify their movement patterns along with the shape and scale of seed shadow produced. However, the effect of inter‐group variability on the destination of dispersed seeds is still poorly explained. In this study, we evaluate how seed dispersal patterns of this arboreal territorial frugivore varies between two neighboring groups, one inhabiting high quality evergreen forest and one inhabiting low quality mosaic forest. We predicted a difference in seed dispersal distance between the two groups (longer in the poor quality forest). We hypothesized that this difference would be explained by differences in home range size, daily path length, and ranging tortuosity. After 6 months of data collection, the evergreen group had a smaller home range (12.4 ha) than the mosaic group (20.9 ha), significantly longer daily path lengths (1507 m vs. 1114 m respectively) and greater tortuosity (39.1 vs. 16.1 respectively). Using gut passage times and displacement rates, we estimated the median seed dispersal distance as 163 m for the evergreen group (high quality forest) and of 116 m for the mosaic group (low quality forest). This contradiction with our initial prediction can be explained in term of social context, resource distribution, and habitat quality. Our results indicate that gibbons are dispersers of seeds between habitats and that dispersal distances provided by gibbons are influenced by a range of factors, including habitat and social context.     

Forest cover,hunting pressure,and fruit availability influence seed dispersal in a forest‐savanna mosaic in the Congo Basin

Forest fragmentation, reduced forest cover, and hunting pressure are the main threats affecting animal‐mediated seed dispersal. However, their combined effects on seed dispersal rates have been simultaneously investigated only rarely, and never in Africa. We aimed to disentangle the effects of forest cover, hunting pressure, frugivore abundance, and fruit availability at the local and landscape scales on the seed dispersal rates of Staudtia kamerunensis (Myristicaceae). To estimate the percentages of seed dispersal failure (undispersed seeds), we quantitated fruit remains below fruiting trees distributed across five contrasting sites in a semi‐natural forest‐savanna mosaic in the Democratic Republic of Congo. We used statistical analyses accounting for spatial autocorrelation and found that forest cover in the surrounding landscape, hunting level, the associated abundance of dispersers, and fruit availability all had significant effects on the percentage of seed dispersal failure. The combination of high fruit availability and reduced abundance of seed dispersers could accelerate seed disperser satiation, causing the seed dispersal system to be saturated. Our study highlights how two major factors associated with anthropogenic activities, forest cover and hunting, affect seed dispersal by animals. These findings could have far‐reaching implications for our understanding of tree‐frugivore interactions and the conservation of tropical communities.     

Variation in seed dispersal effectiveness: the redundancy of consequences in diversified tropical frugivore assemblages

Plant–frugivore mutualistic assemblages frequently combine multiple, complementary or not (i.e. redundant), distinct effects of animal species. To a large extent, the outcomes of these interactions crucially depend on the delayed consequences of frugivore effectiveness on plant recruitment. We evaluated seed dispersal effectiveness for three plant species in a Brazilian Atlantic forest with a marked habitat heterogeneity defined by bamboo and non‐bamboo patches. Twenty one, 23 and 14 bird species ate fruits of Euterpe edulis, Sloanea guianensis and Virola bicuhyba trees, respectively. For both Euterpe and Virola, visitation rate was the variable contributing for most variance across frugivore species in the quantitative component of effectiveness (QC, which depends on the combined effects of interaction frequency and per‐interaction effect), while the number of fruits manipulated/visit had the greatest contribution in Sloanea. By combining observational data and experimental seed addition for Euterpe we tested for consistent functional patterns among species in the frugivore assemblage, extending beyond the fruit removal stage. Rankings of QC across Euterpe frugivores remained consistent with their relative contributions to fruit removal and, importantly, with their contributions to seedling establishment. Yet, QC of effectiveness across Euterpe frugivores were more homogeneous at the fruit removal and dispersal stages (contribution to seed dispersal) than for the delayed, dissemination and post‐dispersal effects on recruitment. High complementarity of diversified frugivore assemblages may increase through added variance in their delayed effects related to qualitative components of effectiveness. Our results underscore the importance of assessing how dispersal services provided by mutualistic frugivores play complementary, rather than redundant, roles in seed dispersal within heterogeneous landscapes. Such ecological outcomes highlight the value of combining observational and experimental field designs to assess functional diversity patterns of tropical frugivore assemblages and delayed effects of their interactions with plants.     

Integrating frugivory and animal movement: a review of the evidence and implications for scaling seed dispersal

General principles about the consequences of seed dispersal by animals for the structure and dynamics of plant populations and communities remain elusive. This is in part because seed deposition patterns emerge from interactions between frugivore behaviour and the distribution of food resources, both of which can vary over space and time. Here we advocate a frugivore‐centred, process‐based, synthetic approach to seed dispersal research that integrates seed dispersal ecology and animal movement across multiple spatio‐temporal scales. To guide this synthesis, we survey existing literature using paradigms from seed dispersal and animal movement. Specifically, studies are discussed with respect to five criteria: selection of focal organisms (animal or plant); measurement of animal movement; characterization of seed shadow; animal, plant and environmental factors included in the study; and scales of the study. Most studies focused on either frugivores or plants and characterized seed shadows directly by combining gut retention time with animal movement data or indirectly by conducting maternity analysis of seeds. Although organismal traits and environmental factors were often measured, they were seldom used to characterize seed shadows. Multi‐scale analyses were rare, with seed shadows mostly characterized at fine spatial scales, over single fruiting seasons, and for individual dispersers. Novel animal‐ and seed‐tracking technologies, remote environmental monitoring tools, and advances in analytical methods can enable effective implementation of a hierarchical mechanistic approach to the study of seed dispersal. This kind of mechanistic approach will provide novel insights regarding the complex interplay between the factors that modulate animal behaviour and subsequently influence seed dispersal patterns across spatial and temporal scales.     

Plant–frugivore networks are less specialized and more robust at forest–farmland edges than in the interior of a tropical forest

Forest fragmentation and local disturbance are prevailing threats to tropical forest ecosystems and affect frugivore communities and animal seed dispersal in different ways. However, very little is known about the effects of anthropogenic forest edges and of local disturbance on the structure and robustness of plant–frugivore networks. We carried out focal tree observations to record the frugivore species feeding on eight canopy tree species in the forest interior and at forest–farmland edges in a little and a highly disturbed part of a Kenyan rain forest. For each frugivore species, we recorded its body mass and its forest dependence. We examined how forest edge and local disturbance affected the abundance, the richness and the composition of the frugivore community and tested whether forest edge and local disturbance affected plant frugivore networks. Abundance and species richness of frugivores were higher at edges than in the forest interior. Forest visitors and small‐bodied frugivores increased, while forest specialists decreased in abundance at forest edges. The changes in frugivore community composition resulted in plant–frugivore networks that were more connected, more nested and more robust against species extinctions at forest–farmland edges than in the forest interior. Network specialization was lower at forest edges than in the forest interior because at the edges plant specialization on frugivores was very low in small‐fruited species. In contrast, small‐fruited plants were more specialized than large‐fruited plants in the forest interior. Our findings suggest that forest‐visiting birds may stabilize seed‐dispersal services for small‐fruited plant species at rain forest margins, while seed‐dispersal services for large‐fruited plant species may be disrupted at forest edges due to the decrease of large‐bodied frugviores. To assess the ultimate consequences of bird movements from farmland to forest edges for ecosystem functioning, future studies are required to investigate the seed‐dispersal qualities provided by forest‐visiting bird species in the tropics.     

Frugivore diversity increases frugivory rates along a large elevational gradient

The effect of biodiversity on ecosystem functioning is increasingly well understood, but it has mainly been studied in small‐scale experiments of plant‐based ecosystem functions. In contrast, the relevance of biodiversity for animal‐mediated ecosystem functions like seed dispersal still poses an important gap in ecological knowledge. In particular, it is little understood how avian diversity affects frugivory rates, one of the most important parameters of seed dispersal rates, along large environmental gradients. Even less is known about the environmental context dependence of the frugivore–frugivory relationship. We used artificial fruits to analyze experimentally how the abundance and richness of three avian frugivore guilds (with incrementally more stringent classifications of frugivory) contributed to frugivory rates across 13 different habitat types along an elevational gradient from 870 to 4550 m a.s.l. at Mt Kilimanjaro, Tanzania. We further investigated how environmental context, in terms of local vegetation structure and natural fruit availability, modified the relationship between frugivores and frugivory rates. Our results demonstrate that the positive effect of avian diversity on frugivory rates holds along a large elevational gradient. We found marked differences in frugivory rates among the 13 habitat types, which were strongly related to the abundance and richness of obligate frugivorous birds. Vegetation structure had no significant effect on frugivory rates. An intermediate abundance of natural fruits enhanced frugivory rates, but this effect did not alter the positive frugivore–frugivory relationship. These results emphasize the fundamental importance of obligate frugivore diversity for frugivory rates and suggest that the positive effect of biodiversity on ecosystem functioning holds along large environmental gradients.     

Resources determine frugivore assemblages and fruit removal along an elevational gradient

Geographic variation in the diversity, abundance or composition of plant and frugivore assemblages may have consequences for seed dispersal processes. Such variations may be related to climatic conditions as well as habitat characteristics such as fruit availability and forest complexity. Studying frugivore assemblages and seed dispersal processes along an elevational gradient can help to elucidate the interplay between the extent of dispersal services provided by frugivores and the geographic variability of the food resources. We studied frugivore assemblages on and fruit removal from 28 rowan trees (Sorbus aucuparia) along an elevational gradient in the Bavarian Forest, Germany. Both, the number of frugivore species and the number of frugivore individuals were significantly enhanced by high fruit availability. In both cases we found a slight interaction between elevation and fruit availability indicating a higher attractiveness of fruits for frugivores at lower than at higher elevations. A high number of frugivore individuals in turn significantly increased fruit removal from rowan trees. Here, we found a significant interaction between elevation and the number of frugivore individuals suggesting that the number of frugivores is of major importance for fruit removal particularly at lower elevations. Path analysis corroborated that the number of frugivore individuals indirectly mediated the effect of fruit availability on fruit removal. These findings suggest that fruit removal is rather influenced by changes in habitat characteristics than in climatic conditions across space.     

Negative density dependence of seed dispersal and seedling recruitment in a Neotropical palm

Negative density dependence (NDD) of recruitment is pervasive in tropical tree species. We tested the hypotheses that seed dispersal is NDD, due to intraspecific competition for dispersers, and that this contributes to NDD of recruitment. We compared dispersal in the palm Attalea butyracea across a wide range of population density on Barro Colorado Island in Panama and assessed its consequences for seed distributions. We found that frugivore visitation, seed removal and dispersal distance all declined with population density of A. butyracea, demonstrating NDD of seed dispersal due to competition for dispersers. Furthermore, as population density increased, the distances of seeds from the nearest adult decreased, conspecific seed crowding increased and seedling recruitment success decreased, all patterns expected under poorer dispersal. Unexpectedly, however, our analyses showed that NDD of dispersal did not contribute substantially to these changes in the quality of the seed distribution; patterns with population density were dominated by effects due solely to increasing adult and seed density.     

Seed dispersal effectiveness by a large‐bodied invasive species in defaunated landscapes

Animal‐dispersed plants are increasingly reliant on effective seed dispersal provided by small‐bodied frugivores in defaunated habitats. In the Neotropical region, the non‐native wild pig (Sus scrofa) is expanding its distribution and we hypothesized that they can be a surrogate for seed dispersal services lost by defaunation. We performed a thorough analysis of their interaction patterns, interaction frequencies, seed viability, and characteristics of the seed shadows they produce. We found 15,087 intact seeds in 56% of the stomachs and 5,186 intact seeds in 90% of the scats analyzed, 95% of which were smaller than 10 mm in diameter. Wild pigs were the third most effective disperser among 21 extant frugivore species in a feeding trail experiment in terms of quantity of seeds removed. Gut retention time was 70 ± 23 hr, indicating wild pigs can promote long‐distance seed dispersal. Seed survival after seed handling and gut passage by wild pigs was positively related with seed size, but large seeds were spat out and only smaller seeds were defecated intact, for which we observed a positive or neutral effect on germination relative to manually de‐pulped seeds. Finally, deposition of seeds was four times more frequent in unsuitable than suitable sites for seedling recruitment and establishment. Seed dispersal effectiveness by wild pigs is high in terms of the quantity of seeds dispersed but variable in terms of the quality of the service provided. Our study highlights that negative and positive effects delivered by non‐native species should be examined in a case by case scenario. Abstract in Portuguese is available with online material.     

What causes conspecific plant aggregation? Disentangling the role of dispersal,habitat heterogeneity and plant–plant interactions

Spatial patterns of plant species are determined by an array of ecologica factors including biotic and abiotic environmental constraints and intrinsic species traits. Thus, an observed aggregated pattern may be the result of short‐distance dispersal, the presence of habitat heterogeneity, plant–plant interactions or a combination of the above. Here, we studied the spatial pattern of Mediterranean alpine plant Silene ciliata (Caryophyllaceae) in five populations and assessed the contribution of dispersal, habitat heterogeneity and conspecific plant interactions to observed patterns. For this purpose, we used spatial point pattern analysis combined with specific a priori hypotheses linked to spatial pattern creation. The spatial pattern of S. ciliata recruits was not homogeneous and showed small‐scale aggregation. This is consistent with the species’ short‐distance seed dispersal and the heterogeneous distribution of suitable sites for germination and establishment. Furthermore, the spatial pattern of recruits was independent of the spatial pattern of adults. This suggests a low relevance of adult‐recruits interactions in the spatial pattern creation. The difference in aggregation between recruits and adults suggests that once established, recruits are subjected to self‐thinning. However, seedling mortality did not erase the spatial pattern generated by seed dispersal, as S. ciliata adults were still aggregated. Thus, the spatial aggregation of adults is probably due to seed dispersal limitation and the heterogeneous distribution of suitable sites at seedling establishment rather than the presence of positive plant–plant interactions at the adult stage. In fact, a negative density‐dependent effect of the conspecific neighbourhood was found on adult reproductive performance. Overall, results provide empirical evidence of the lack of a simple and direct relationship between the spatial structure of plant populations and the sign of plant–plant interactions and outline the importance of considering dispersal and habitat heterogeneity when performing spatial analysis assessments.     

The relative contributions of seed and pollen dispersal to gene flow and genetic diversity in seedlings of a tropical palm

Seed and pollen dispersal shape patterns of gene flow and genetic diversity in plants. Pollen is generally thought to travel longer distances than seeds, but seeds determine the ultimate location of gametes. Resolving how interactions between these two dispersal processes shape microevolutionary processes is a long‐standing research priority. We unambiguously isolated the separate and combined contributions of these two dispersal processes in seedlings of the animal‐dispersed palm Oenocarpus bataua to address two questions. First, what is the spatial extent of pollen versus seed movement in a system characterized by long‐distance seed dispersal? Second, how does seed dispersal mediate seedling genetic diversity? Despite evidence of frequent long‐distance seed dispersal, we found that pollen moves much further than seeds. Nonetheless, seed dispersal ultimately mediates genetic diversity and fine‐scale spatial genetic structure. Compared to undispersed seedlings, seedlings dispersed by vertebrates were characterized by higher female gametic and diploid seedling diversity and weaker fine‐scale spatial genetic structure for female gametes, male gametes and diploid seedlings. Interestingly, the diversity of maternal seed sources at seed deposition sites (N _em) was associated with higher effective number of pollen sources (N _ep), higher effective number of parents (N _e) and weaker spatial genetic structure, whereas seed dispersal distance had little impact on these or other parameters we measured. These findings highlight the importance maternal seed source diversity (N _em) at frugivore seed deposition sites in driving emergent patterns of fine‐scale genetic diversity and structure.     

Seeds tend to disperse further in the tropics

Despite the importance of seed dispersal in a plant's life cycle, global patterns in seed dispersal distance have seldom been studied. This paper presents the first geographically and taxonomically broad quantification of the latitudinal gradient in seed dispersal distance. Although there is substantial variation in the seed dispersal distances of different species at a given latitude, seeds disperse on average more than an order of magnitude further at the equator than towards the poles. This pattern is partially explained by plant life‐history traits that simultaneously associate with seed dispersal distance and latitude, including dispersal mode and plant height. The extended seed shadow of tropical plants could increase the distance between conspecific individuals. This could facilitate species coexistence and contribute to the maintenance of high plant diversity in tropical communities. The latitudinal gradient in dispersal distance also has implications for species’ persistence in the face of habitat fragmentation and climate change.     

Seed Dispersal by Avian Frugivores: Non‐random Heterogeneity at Fine Scales

Seed dispersal studies have primarily examined dispersal as a function of distance from the parent tree and/or heterogeneity in dispersal due to animal use of nesting, roosting and sleeping sites. However, non‐random heterogeneity in seed dispersal is also likely to result from the post‐foraging behavior and movement of frugivores which prefer certain trees. To characterize variation in seed rain at fine scales, we studied the dispersal curve of Prunus ceylanica, a primarily bird‐dispersed species. We compared seed rain at conspecifics, heterospecific fruiting trees with similar frugivore assemblages, emergent trees, and the landscape surrounding these trees. Seed rain of P. ceylanica was found to peak globally under the canopy of conspecifics but to peak locally under the canopy and immediate neighborhood of heterospecific fruiting trees. Our results demonstrate that seed rain is highly clumped even at fine spatial scales. A large proportion of seeds are dispersed in specific, localized regions. This variation can have important implications for plant population dynamics and might significantly alter the impact of post‐dispersal processes. Seed dispersal models may need to incorporate this heterogeneity to explain manifestations of spatially explicit dynamics like mixed species ‘orchards’.     

An invasive tree alters the structure of seed dispersal networks between birds and plants in French Polynesia

Aim We studied how the abundance of the highly invasive fruit‐bearing tree Miconia calvescens DC. influences seed dispersal networks and the foraging patterns of three avian frugivores. Location Tahiti and Moorea, French Polynesia. Methods Our study was conducted at six sites which vary in the abundance of M. calvescens. We used dietary data from three frugivores (two introduced, one endemic) to determine whether patterns of fruit consumption are related to invasive tree abundance. We constructed seed dispersal networks for each island to evaluate how patterns of interaction between frugivores and plants shift at highly invaded sites. Results Two frugivores increased consumption of M. calvescens fruit at highly invaded sites and decreased consumption of other dietary items. The endemic fruit dove, Ptilinopus purpuratus, consumed more native fruit than either of the two introduced frugivores (the red‐vented bulbul, Pycnonotus cafer, and the silvereye, Zosterops lateralis), and introduced frugivores showed a low potential to act as dispersers of native plants. Network patterns on the highly invaded island of Tahiti were dominated by introduced plants and birds, which were responsible for the majority of plant–frugivore interactions. Main conclusions Shifts in the diet of introduced birds, coupled with reduced populations of endemic frugivores, caused differences in properties of the seed dispersal network on the island of Tahiti compared to the less invaded island of Moorea. These results demonstrate that the presence of invasive fruit‐bearing plants and introduced frugivores can alter seed dispersal networks, and that the patterns of alteration depend both on the frugivore community and on the relative abundance of available fruit.     

The key role of the largest extant Neotropical frugivore (Tapirus terrestris) in promoting admixture of plant genotypes across the landscape

The historical and contemporary loss of large‐bodied frugivores has disrupted many plant‐disperser mutualisms, with potentially profound consequences for plants. Although several aspects of seed dispersal by megafrugivores have already been examined, the role of these species in promoting seed‐mediated gene flow has remained unexplored. We evaluated the role of the Amazonian tapir (Tapirus terrestris), the largest Neotropical frugivore, in shaping plant genetic structure through seed‐mediated gene flow. We used microsatellites to analyze the genetic patterns of Syagrus romanzoffiana seedlings recruited in tapir latrines and around conspecific adult palms, the two sites where seeds and seedlings are most frequently found in this species. While the genetic diversity of seedlings was rather similar in both sites, the kinship structure was substantially weaker in latrines. Most seedlings recruited around adult palms were half‐ or full‐sibs originating from those adults. In contrast, seedlings recruited in latrines came from several (>5, on average) contributing mothers other than the nearest adult (95%) and were mostly non‐sibs (72%). Kinship patterns indicated that tapir‐mediated dispersal promotes the admixture of genotypes across space. Also, our results suggested that genetic diversity and the number of contributing mothers in latrines increase with the number of fruiting adults visited by tapirs before defecating and with the accumulation of feces over time. We provide evidence of the relevance of tapirs in mobilizing maternal progenies (and genotypes) across the landscape and recruiting clusters of unrelated seedlings. This study suggests a key role for plant–megafrugivore interactions in seed‐mediated gene flow and emphasizes the importance of preserving such mutualisms.     

Antelope mating strategies facilitate invasion of grasslands by a woody weed

Intra and interspecific variation in frugivore behaviour can have important consequences for seed dispersal outcomes. However, most information comes from among‐species comparisons, and within‐species variation is relatively poorly understood. We examined how large intraspecific differences in the behaviour of a native disperser, blackbuck antelope Antilope cervicapra, influence dispersal of a woody invasive, Prosopis juliflora, in a grassland ecosystem. Blackbuck disperse P. juliflora seeds through their dung. In lekking blackbuck populations, males defend clustered or dispersed mating territories. Territorial male movement is restricted, and within their territories males defecate on dung‐piles. In contrast, mixed‐sex herds range over large areas and do not create dung‐piles. We expected territorial males to shape seed dispersal patterns, and seed deposition and seedling recruitment to be spatially localized. Territorial males had a disproportionately large influence on seed dispersal. Adult males removed twice as much fruit as females, and seed arrival was disproportionately high on territories. Also, because lek‐territories are clustered, seed arrival was spatially highly concentrated. Seedling recruitment was also substantially higher on territories compared with random sites, indicating that the local concentration of seeds created by territorial males continued into high local recruitment of seedlings. Territorial male behaviour may, thus, result in a distinct spatial pattern of invasion of grasslands by the woody P. juliflora. An ex situ experiment showed no beneficial effect of dung and a negative effect of light on seed germination. We conclude that large intraspecific behavioural differences within frugivore populations can result in significant variation in their effectiveness as seed dispersers. Mating strategies in a disperser could shape seed dispersal, seedling recruitment and potentially plant distribution patterns. These mating strategies may aid in the spread of invasives, such as P. juliflora, which could, in turn, negatively influence the behaviour and ecology of native dispersers.