Fruit–frugivore interactions in two southern hemisphere forests: allometry,phylogeny and body size

The size of fleshy fruits spans several orders of magnitude. However, the evolution of fruit size diversity is poorly understood. Fruit size diversity is hypothesised to result from several potential processes. The frugivore hypothesis postulates that different‐sized animal fruit consumers select for different‐sized fruits. The correlated selection hypothesis postulates that fruit size is allometrically related to other plant traits (e.g. leaf size, plant height); therefore differences in fruit size result from correlated evolution with other plant traits. We tested the frugivore and correlated selection hypotheses as potential explanations for fruit size diversity in two New Zealand study sites. We observed birds foraging for fruits over two fruiting seasons at each site and measured fruit size, leaf size and plant height in a total of 32 plant species. Relationships between average fruit size, leaf size, plant size and the average size of birds consuming each fruit species were then evaluated using phylogenetically independent contrasts. Similar results were obtained in both study sites. Fruit size was correlated with the size of avian fruit consumers, but was unrelated to leaf size or plant height. Therefore, results falsified the correlated selection hypothesis but failed to falsify the frugivore hypothesis. Although results suggest that frugivores may have influenced the evolution of fruit size in New Zealand, further study is needed to generate a mechanistic understanding of how frugivores may have selected for interspecific variation in fruit size.     

The role of fruit traits of bird-dispersed plants in invasiveness and weed risk assessment

Aim  Birds play a major role in the dispersal of seeds of many fleshy-fruited invasive plants. The fruits that birds choose to consume are influenced by fruit traits. However, little is known of how the traits of invasive plant fruits contribute to invasiveness or to their use by frugivores. We aim to gain a greater understanding of these relationships to improve invasive plant management.
Location  South-east Queensland, Australia.
Methods  We measure a variety of fruit morphology, pulp nutrient and phenology traits of a suite of bird-dispersed alien plants. Frugivore richness of these aliens was derived from the literature. Using regressions and multivariate methods, we investigate relationships between fruit traits, frugivore richness and invasiveness.
Results  Plant invasiveness was negatively correlated to fruit size, and all highly invasive species had quite similar fruit morphology [smaller fruits, seeds of intermediate size and few (< 10) seeds per fruit]. Lower pulp water was the only pulp nutrient trait associated with invasiveness. There were strong positive relationships between the diversity of bird frugivores and plant invasiveness, and in the diversity of bird frugivores in the study region and another part of the plants' alien range.
Main conclusions  Our results suggest that weed risk assessments (WRA) and predictions of invasive success for bird-dispersed plants can be improved. Scoring criteria for WRA regarding fruit size would need to be system-specific, depending on the fruit-processing capabilities of local frugivores. Frugivore richness could be quantified in the plant's natural range, its invasive range elsewhere, or predictions made based on functionally similar fruits.     

Influence of type of avian frugivory on the fitness ofPistacia terebinthus L.

Summary The fruits ofPistacia terebinthus, a circum-Mediterranean tree/shrub, are consumed by an array of bird species that differ in feeding methods and in relative frequencies of visits to plants. In this study I document interindividual variation in the proportion of fruits consumed by three types of frugivores: legitimate dispersers, pulp-consumers and seed predators. The results show that the relative frequencies of each kind of frugivore notably influence the final reproductive output (absolute number of viable seeds dispersed) and in fact prevail over the effects of pre-dispersal factors acting on plant fitness. Those relative frequencies are not associated with any of the plant traits related to fitness, such as fruit crop size and the number of viable seeds produced, suggesting that the type of avian frugivory exerts a negligible, if not null, selective pressure on such plant attributes. Plant specialization to attract the most effective seed dispersers seems to be precluded, given the small scale at which the high variation in seed dispersal success takes place.     

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.     

Can Functional Traits Predict Ecological Interactions? A Case Study Using Rain forest Frugivores and Plants in Australia

In rain forest, the large numbers of species of fleshy-fruited plants and frugivorous animals result in a large number of potential fruit–frugivore interactions, which are challenging to survey in the field. Yet, knowledge of these relationships is needed to predict consequences of changes in the frugivore assemblage for seed dispersal. In the absence of comprehensive dietary information, it may be possible to delineate between frugivores that disperse different plants using ‘functional traits,’ or morphological and behavioral attributes of frugivores that interact with differences in salient characteristics of plant species. Here we use data on the consumption of 244 Australian rain forest plant species by 38 bird species to test for associations between patterns of frugivory and birds': (1) degree of frugivory, (2) gape width, and (3) seed treatment (seed crushing or seed dispersing). Degree of frugivory and gape width explain 74 percent of the variation in the sizes of fruits consumed by frugivorous birds. Among birds that consume a substantial dietary proportion of fruit, birds with wider gapes consume larger fruits. In contrast, this relationship was not shown by birds for which fruit is only a minor dietary component. Degree of frugivory and gape width, together with seed treatment, also strongly predict the overall taxonomic composition and diversity of plants consumed by bird species. Functional classifications of frugivore species may prove useful in developing a predictive understanding of fruit–frugivore interactions in other rain forest regions where detailed dietary information is not available for most frugivores.     

Plant-disperser mutualisms in a semi-arid habitat invaded by <Emphasis Type="Italic">Lantana camara</Emphasis> L.

Dispersal is an important ecological process that affects plant population structure and community composition. Invasive plants with fleshy fruits rapidly form associations with native and invasive dispersers, and may affect existing native plant-disperser associations. We asked whether frugivore visitation rate and fruit removal was associated with plant characteristics in a community of fleshy-fruited plants and whether an invasive plant receives more visitation and greater fruit removal than native plants in a semi-arid habitat of Andhra Pradesh, India. Tree-watches were undertaken at individuals of nine native and one invasive shrub species to assess the identity, number and fruit removal by avian frugivores. Network analyses and generalised linear mixed-effects models were used to understand species and community-level patterns. All plants received most number of visits from abundant, generalist avian frugivores. Number of frugivore visits and time spent by frugivores at individual plants was positively associated with fruit crop size, while fruit removal was positively associated with number of frugivore visits and their mean foraging time at individual plants. The invasive shrub, Lantana camara L. (Lantana), had lower average frugivore visit rate than the community of fleshy-fruited plants and received similar average frugivore visits but greater average per-hour fruit removal than two other concurrently fruiting native species. Based on the results of our study, we infer that there is little evidence of competition between native plants and Lantana for the dispersal services of native frugivores and that more data are required to assess the nature of these interactions over the long term. We speculate that plant associations with generalist frugivores may increase the functional redundancy of this frugivory network, buffering it against loss of participating species.     

Frugivore gape size and the evolution of fruit size and shape in southern hemisphere floras

Abstract The present study uses differences among frugivore faunas of the southern hemisphere landmasses to test whether frugivore characteristics have influenced the evolution of fruit traits. Strong floristic similarities exist among southern landmasses; for example, 75% of New Zealand vascular plant genera also have species in Australia. However, plants in Australia and South America have evolved in the presence of a range of mammalian frugivores, whereas those in New Zealand, New Caledonia and the Pacific Islands have not. In addition, the avian frugivores in New Zealand and New Caledonia are generally smaller than those of Australia. If frugivore characteristics have influenced the evolution of fruit traits, predictable differences should exist between southern hemisphere fruits, particularly fruit size and shape. Fruit dimensions were measured for 77 New Zealand species and 31 Australian species in trans‐Tasman genera. New Zealand fruits became significantly more ellipsoid in shape with increasing size. This is consistent with frugivore gape size imposing a selective pressure on fruit ingestability. This result is not a product of phylogenetic correlates, as fruit length and width scaled isometrically for Australian species in genera shared with New Zealand. Within‐genus contrasts between New Zealand and Australian species in 20 trans‐Tasman genera showed that New Zealand species have significantly smaller fruits than their Australian counterparts. Within‐genus contrasts between New Zealand and South American species in nine genera gave the same result; New Zealand species had significantly smaller fruits than their South American counterparts. No difference was found in fruit size or shape between New Zealand and New Caledonia congeneric species from 12 genera. These results are consistent with the broad characteristics of the frugivore assemblage influencing the evolution of fruit size and shape in related species. The smaller‐sized New Zealand frugivore assemblage has apparently influenced the evolution of fruit size of colonizing taxa sometimes within a relatively short evolutionary timeframe.     

Vertically stratified frugivore community composition and interaction frequency in a liana fruiting across forest strata

Vertical stratification is a key feature of tropical forests and structures plant–frugivore interactions. However, it is unclear whether vertical differences in plant-frugivore interactions are due to differences among strata in plant community composition or inherent preferences of frugivores for specific strata. To test this, we observed fruit removal of a diverse frugivore community on the liana Marcgravia longifolia in a Peruvian rain forest. Unlike most other plants, Marcgravia longifolia produces fruits across forest strata. This enabled us to study effects of vertical stratification on fruit removal without confounding effects of plant species and stratum. We found a high number of visits of a few frugivore species in the understorey and a low number of visits of many different frugivores in the canopy and midstorey. Whereas partial and opportunistic frugivores foraged across strata with differing frequencies, obligate frugivores were only found eating fruits in the higher strata. Avian frugivores foraging in the canopy were mainly large species with pointed wings, whereas under- and midstorey avian foragers were smaller with rounded wings. Our findings suggest a continuous shift in the frugivore community composition along the vertical gradient, from a few generalized frugivores in the understorey to a diverse set of specialized frugivores in the canopy. This shift in the frugivore community leads to correlated, reciprocal changes from specialized to generalized plant-frugivore interactions. Thus, we conclude that vertical niche differentiation between species in tropical forests persists even when food resources are available across strata. This highlights its role for promoting biodiversity and ecosystem functioning.     

Fruit preferences by fishes in a Neotropical floodplain

The diets of frugivorous animals result from the interaction between feeding preference and ecological factors such as availability of alternative resources and interactions with other frugivores. A better understanding of frugivore diets will enable predictions about the vulnerability of plant populations to anthropogenic or natural environmental changes. In addition, frugivores with greater variation in diet (generalists) are potentially more resilient to habitat changes than specialists. Here, we combined data on diets of frugivorous fishes with visual censuses on fruit availability to evaluate if fishes are selective or opportunistic in their use of fruits in floodplain habitats. We found a high diversity of fruit species (74 species) frequently consumed by four common species of frugivorous fishes during the flooding season. The identity of preferred fruits, rather than their availability, had a stronger effect on the patterns of fruit consumed by fishes in this system. Fruit preferences by fish may influence the long-term persistence and the maintenance of plant diversity in floodplain habitats. Possible disturbances of fish populations with selective consumption and the plant populations on which they depend could increase the vulnerability of both populations involved. Thus, selectivity may affect ecological and evolutionary processes associated with frugivory by fish.     

High Conservation Value of Forest Fragments for Plant and Frugivore Communities in a Fragmented Forest Landscape in South Africa

Fragmentation is a major threat factor for plant–frugivore communities in tropical and subtropical forests. Resulting changes in the distribution of traits within these communities, e.g., a loss in large‐bodied frugivores, may lead to strong changes in plant–frugivore interactions in fragmented forests. Yet, we still lack a thorough understanding of the interplay between forest fragmentation, the trait‐composition of communities and resulting plant–frugivore interactions on a community‐scale. In a fragmented South African landscape comprising different forest categories—i.e., continuous natural forest, forest fragments surrounded by natural grassland, and forest fragments surrounded by sugarcane—we investigated the relationship between communities of fruiting plants and their frugivore visitors in response to forest fragmentation, as well as the interactive effects of forest fragmentation and fruit size of the plants on the number of frugivore visitors and their body size. Neither the fruit size of plant nor the body mass of frugivore communities differed between natural forest sites and forest fragments. Moreover, in‐depth analyses of frugivore assemblages visiting plant species revealed no effect of forest category on the number of frugivore visits or their mean body mass. The number of visits and body mass of frugivores were merely determined by the crop and fruit size of the focal plant species. Overall, our results suggest that frugivory of plant species with differently sized fruits was not reduced in forest fragments. Thus, fragments with high fruit availability may be key elements maintaining the functional connectivity of a heterogeneous forest landscape.     

Bird Assemblage and Visitation Pattern at Fruiting Elmerrillia tsiampaca (Magnoliaceae) Trees in Papua New Guinea

Most tropical trees produce fleshy fruits that attract frugivores that disperse their seeds. Early demography and distribution for these tree species depend on the effects of frugivores and their behavior. Anthropogenic changes that affect frugivore communities could ultimately result in changes in tree distribution and population demography. We studied the frugivore assemblage at 38 fruiting Elmerrillia tsiampaca, a rain forest canopy tree species in Papua New Guinea. Elmerrillia tsiampaca is an important resource for frugivorous birds at our study site because it produces abundant lipid-rich fruits at a time of low fruit availability. We classified avian frugivores into functional disperser groups and quantified visitation rates and behavior at trees during 56 canopy and 35 ground observation periods. We tested predictions derived from other studies of plant–frugivore interactions with this little-studied frugivore assemblage in an undisturbed rain forest. Elmerrillia tsiampaca fruits were consumed by 26 bird species, but most seeds were removed by eight species. The most important visitors (Columbidae, Paradisaeidae and Rhyticeros plicatus) were of a larger size than predicted based on diaspore size. Columbidae efficiently exploited the structurally protected fruit, which was inconsistent with other studies in New Guinea where structurally protected fruits were predominantly consumed by Paradisaeidae. Birds vulnerable to predation foraged for short time periods, consistent with the hypothesis that predator avoidance enhances seed dispersal. We identified seven functional disperser groups, indicating there is little redundancy in disperser groups among the regular and frequent visitors to this tropical rain forest tree species.     

Fruit removal rate depends on neighborhood fruit density,frugivore abundance,and spatial context

Fleshy-fruited plants depend fundamentally on interactions with frugivores for effective seed dispersal. Recent models of frugivory within spatially explicit networks make two general predictions regarding these interactions: rate of fruit removal increases (i.e., is facilitated) as densities of conspecific neighborhood fruits increase, and fruit removal rate varies positively with frugivore abundance. We conducted a field experiment that constitutes the first empirical and simultaneous test of these two primary predictions. We manipulated neighborhood abundances of arrowwood (Viburnum recognitum and Viburnum dentatum) fruits in southern New England’s maritime shrub community and monitored removal rates by autumn-migrating birds. Focal arrowwood plants in neighborhoods with high conspecific fruit density sustained moderately decreased fruit removal rates (i.e., competition) relative to those in low-density neighborhoods, a result that agrees with most field research to date but contrasts with theoretical expectation. We suggest the spatial contexts that favor competition (i.e., high-abundance neighborhoods and highly aggregated landscapes) are considerably more common than the relatively uniform, low-aggregation fruiting landscapes that promote facilitation. Patterns of arrowwood removal by avian frugivores generally varied positively with, and apparently in response to, seasonal changes in migratory frugivore abundance. However, we suggest that dense stands of arrowwood concentrated frugivore activity at the neighborhood scale, thus counteracting geographic patterns of frugivore abundance. Our results underscore the importance of considering spatial context (e.g., fruit distribution and aggregation, frugivory hubs) in plant-avian frugivore interactions.     

Avian fruit preferences across a Puerto Rican forested landscape: pattern consistency and implications for seed removal

Avian fruit consumption may ensure plant reproductive success when frugivores show consistent preference patterns and effectively remove and disperse seeds. In this study we examined avian fruit preferences and their seed-removal services at five study sites in north-central Puerto Rico. At each site, we documented the diet of seven common fruit-eating avian species from February to September 1998. Using foraging observations and area-based estimates of fruit abundance, we examined preference patterns of birds. We found that 7 out of 68 fleshy-fruited plant species were responsible for most of the fruit diet of birds. Seventeen plant species were preferred and four of them were repeatedly preferred across several study sites and times by at least one avian species. Preferred plant species comprised a small percentage of fleshy fruits at each site (<15% in four out of five study sites), but showed extended phenology patterns. The quantity of seeds removed by frugivore species was not strictly related to preferences. Some frugivores showing no preference could effectively remove more seeds from plants at some locations than species exhibiting constancy in their patterns of preference. Only two frugivores, Euphonia musica and Vireo altiloquous, removed most of the seeds of plants for which they exhibited repeated preference across the landscape. Preference patterns, particularly those exhibiting consistency in space and time for plant species having prolonged fruiting periods, may have important mechanistic consequences for the persistence, succession, and regeneration of tropical plant communities.     

Food plant diversity as broad-scale determinant of avian frugivore richness

The causes of variation in animal species richness at large spatial scales are intensively debated. Here, we examine whether the diversity of food plants, contemporary climate and energy, or habitat heterogeneity determine species richness patterns of avian frugivores across sub-Saharan Africa. Path models indicate that species richness of Ficus (their fruits being one of the major food resources for frugivores in the tropics) has the strongest direct effect on richness of avian frugivores, whereas the influences of variables related to water-energy and habitat heterogeneity are mainly indirect. The importance of Ficus richness for richness of avian frugivores diminishes with decreasing specialization of birds on fruit eating, but is retained when accounting for spatial autocorrelation. We suggest that a positive relationship between food plant and frugivore species richness could result from niche assembly mechanisms (e.g. coevolutionary adaptations to fruit size, fruit colour or vertical stratification of fruit presentation) or, alternatively, from stochastic speciation-extinction processes. In any case, the close relationship between species richness of Ficus and avian frugivores suggests that figs are keystone resources for animal consumers, even at continental scales.     

Functional heterogeneity in a plant–frugivore assemblage enhances seed dispersal resilience to habitat loss

The ability of ecosystems to maintain their functions after disturbance (ecological resilience) depends on heterogeneity in the functional capabilities among species within assemblages. Functional heterogeneity may affect resilience by determining multiplicity between species in the provision of functions (redundancy) and complementarity between species in their ability to respond to disturbances (response diversity), but also by promoting the maintenance of biological information that enables ecosystems to reorganize themselves (ecological memory). Here, we assess the role of the components of the functional heterogeneity of a plant–frugivore assemblage on the resilience of seed dispersal to habitat loss. For three years, we quantified the distributions of fruits, frugivorous thrushes (Turdus spp.) and dispersed seeds, as well as frugivore diet and movement, along a gradient of forest cover in N Spain. The abundances and the spatial distributions of fruits and birds varied between years. The different thrushes showed similar diets but differed in spatial behavior and response to habitat loss, suggesting the occurrence of both functional redundancy and response diversity. Forest cover and fruit availability affected the spatial distribution of the whole frugivore assemblage. Fruit tracking was stronger in years when fruits were scarcer but more widespread across the whole fragmented landscape, entailing larger proportions of seeds dispersed to areas of low forest cover and open microhabitats. Rather than depending on redundancy and/or response diversity, seed dispersal resilience mostly emerged from the ecological memory conferred by the inter‐annual variability in fruit production and the ability of thrushes to track fruit resources across the fragmented landscape. Ecological memory also derived from the interaction of plants and frugivores as source organisms (trees in undisturbed forest), mobile links (birds able to disperse seeds into the disturbed habitat), and biological legacies (remnant trees and small forest patches offering scattered fruit resources across the landscape).     

Do frugivores enhance germination success of plant species? An experimental approach

Frugivorous birds are among the most important consumers of fleshy fruits particularly in sub-tropical and tropical forest ecosystems. Whether or not such plant–frugivore interactions contribute to germination enhancement is still a subject of much debate. We tested the effect of gut treatment by four captive species of avian frugivores in comparison to manually depulped seeds and whole fruits on seedling emergence and germination probability of seeds from sixteen plant species in South Africa. Moreover, we determined whether fruit weight of each plant species affected germination patterns. Across plant species, a total of 2795 seeds were planted, of which 50% germinated. Both seedling emergence and germination probability neither differed among the bird species nor in comparison to manually depulped seeds or whole fruits. Further, seedling emergence and germination probability were both unaffected by fruit weight. However, the germination probability of all treatments increased similarly with increasing number of weeks after planting. Overall, these results suggest that seed depulping, neither by gut treatment nor manually improved germination of seeds, irrespective of their fruit weights. Thus, the major contribution of frugivores to forest regeneration may be more confined in transporting seeds away from the mother plant than in germination enhancement per se.     

Fruit tracking,frugivore satiation,and their consequences for seed dispersal

Vertebrate frugivore communities are easily satiated by abundant fruit supplies and, contrary to abiotic dispersal agents, typically disperse only part of the available seed pool. This frugivore satiation is likely to be a widespread phenomenon and should be an influential predictor of plants’ ability to disperse their offspring to suitable establishment sites; yet it has never been systematically quantified. Here I investigate patterns of fruit abundance, frugivore activity and frugivore satiation, and their consequences for seed dispersal in the fleshy-fruited tree Frangula alnus. Based on constant-effort seed trapping conducted over 3 years, I assess densities of total and frugivore-consumed seedfall across two spatial (within/between populations) and two temporal (within/between ripening seasons) scales. Furthermore, I examine relationships between fruit abundance and the amount of seeds that are actually dispersed away from fruiting trees. Frugivore activity tightly matched fruit abundance, although some differences existed between scales. This marked fruit tracking did not prevent a significant frugivore satiation, however, and only 53% of the available fruit crops were actually consumed. The extent of satiation varied most at the within-population level, likely due to the territorial behaviour of important frugivore species. In contrast, levels of satiation remained remarkably invariable through time, suggesting that frugivores behave as opportunists and closely adjust the composition of their diet to the available food supply. Overall, greater fruit abundance resulted in a higher proportion of seeds falling beneath fruiting trees, but it also helped increase the (absolute) number of seeds dispersed. This study shows that frugivore satiation can be an important phenomenon even when frugivores tightly track fruit abundance. Its negative effects on recruitment may be attenuated, however, if greater fruit crops help increase population-wide frugivore activity and the amount of seeds being dispersed to suitable establishment sites.     

Does fire affect the temporal pattern of trophic resource supply to pollinators and seed-dispersing frugivores in a Brazilian savanna community?

In tropical savannas, such as the campo cerrado in Brazil, fire plays an important role, affecting plant species’ life history. Since fire has the potential to modify the structure of savanna communities as a whole, it is expected that it may influence the resource supply for mutualists by altering the pattern of investment in sexual reproduction. We used an experimental approach to test if fire alters trophic resource availability to pollinators (nectar, pollen, and oil) and seed-dispersing frugivores (fleshy fruits) by altering the seasonality of reproductive phenophases in a savanna community. We sampled all individuals of 60 species that were common to both control and experimental fire treatments. Each month we recorded the number of reproductive individuals to test whether fire affected the temporal resource offered by the plant assemblage as a whole, and by each specific plant group supporting distinct groups of pollinators and seed-dispersing frugivores. We noticed that fire advanced the nectar, pollen, and fleshy fruit offered by the whole assemblage. Additionally, fire affected the temporal pattern of nectar and pollen available to various pollinator groups, and of fleshy fruits available to all seed-dispersing frugivores. In general, fire seems to have a neutral or even a positive effect on resource availability to mutualists. Nevertheless, there were differences in the availability of the resource utilized by each guild of mutualists.     

Can network metrics predict vulnerability and species roles in bird‐dispersed plant communities? Not without behaviour

Network metrics are widely used to infer the roles of mutualistic animals in plant communities and to predict the effect of species' loss. However, their empirical validation is scarce. Here we parameterized a joint species model of frugivory and seed dispersal with bird movement and foraging data from tropical and temperate communities. With this model, we investigate the effect of frugivore loss on seed rain, and compare our predictions to those of standard coextinction models and network metrics. Topological coextinction models underestimated species loss after the removal of highly linked frugivores with unique foraging behaviours. Network metrics informed about changes in seed rain quantity after frugivore loss. However, changes in seed rain composition were only predicted by partner diversity. Nestedness, closeness, and d’ specialisation could not anticipate the effects of rearrangements in plant–frugivore communities following species loss. Accounting for behavioural differences among mutualists is critical to improve predictions from network models.     

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.