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Nina Farwig - One of the best experts on this subject based on the ideXlab platform.
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Trait‐associated loss of Frugivores in fragmented forest does not affect seed removal rates
Journal of Ecology, 2016Co-Authors: Nina Farwig, Dana G. Schabo, Jorg AlbrechtAbstract:Summary Seed dispersal by frugivorous animals forms the basis for regeneration of numerous plant species. Habitat fragmentation has been found to be one major factor perturbing Frugivore communities and dependent plant species. Yet, community-wide consequences of fragmentation for both Frugivore and plant communities are still hardly understood. Here, we studied the effects of habitat fragmentation on the seed removal by frugivorous birds and mammals from nine fleshy-fruited plant species in Bialowieza Forest (Eastern Poland). This last relict of old-growth lowland forest in Europe poses an exceptional reference site for studying the impact of habitat fragmentation on seed dispersal processes in temperate forest ecosystems. In particular, (i) we tested for associations between forest fragmentation and response traits of Frugivores, that is forest specialization and body mass; (ii) we studied the relationship between Frugivore response and effect traits, that is centrality (number of consumed plant species) and interaction type (mutualistic vs. antagonistic); and (iii) we assessed the feedback of fragmentation-induced changes on plant–Frugivore interactions and seed removal rates. We found that fragmentation led to shifts in the Frugivore community, associated with the response traits forest specialization and body mass, with fewer forest specialists and large-bodied Frugivores in fragmented than in continuous forests. However, forest generalists and small-bodied Frugivores were more central in the plant–Frugivore associations than forest specialists and large-bodied Frugivores. Therefore, the loss of vulnerable species did not result in reduced seed removal rates in fragmented compared with continuous forest. Synthesis. These results indicate that seed removal may be relatively robust in spite of shifts in the Frugivore community in forest fragments. The correlation between response and effect traits of Frugivores highlights the importance of forest generalists and small-bodied Frugivores for maintaining dispersal processes in fragmented forests in temperate regions. Yet, future studies should aim at quantifying the consequences of seed disperser loss on other aspects of dispersal, such as long-distance dispersal, spatial patterns of seed deposition, seed germination and plant regeneration.
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variation in neighbourhood context shapes Frugivore mediated facilitation and competition among co dispersed plant species
Journal of Ecology, 2015Co-Authors: Jorg Albrecht, Dana G Berens, Bogdan Jaroszewicz, Nuria Selva, Victoria Bohle, Nina FarwigAbstract:Summary1. Co-occurring and simultaneously fruiting plant species may either compete for dispersal byshared Frugivores or enhance each other’s dispersal through joint attraction of Frugivores. Whilecompetitive plant–plant interactions are expected to cause the evolutionary divergence of fruit phe-nologies, facilitative interactions are assumed to promote their convergence. To which extent com-petitive and facilitative interactions among plant species with similar phenological niches arecontrolled by spatial variation in their local abundance and co-occurrence is poorly understood.2. Here, we test the hypotheses that when a plant species fruits in high densities, large phenologicaloverlap with other plant species causes competition for seed dispersers owing to Frugivore satiation.Conversely, we expect large phenological overlap to enhance the dispersal of a plant species fruitingin low densities through attraction of Frugivores by other species in its local neighbourhood.3. We test these predictions on plant–Frugivore networks based on seed removal from 15 woody,fleshy-fruited plant species by 30 avian and 4 mammalian Frugivore species across 13 study sites inBialowieza Forest, Poland._4. A null model indicated that fruit phenologies of the regional plant assemblage were more differ-entiated than expected by chance. In the local networks, the tendency of plants to share Frugivoresincreased with phenological overlap. High phenological overlap reduced the seed removal rates,interaction strength (proportion of interactions) and the number of partners of plant species fruitingin high densities. Conversely, plant species fruiting in low densities mainly profited from high phe-nological overlap with other species. Importantly, the sharing of mutualistic partners among co-fruiting plant species was also reflected in their co-occurrence.5. Synthesis. Our study highlights that, in spite of the overall signal of competition, Frugivore-medi-ated interactions among cofruiting plant species may consistently promote the establishment and per-sistence of rare species through facilitation. In addition, our results suggest that, among otherfactors, indirect coupling of species through shared mutualistic partners might be an important deter-minant of plant community assembly. The coupling through shared mutualists may cause the forma-tion of associations among co-dispersed plant species and might contribute to the coexistence ofspecies in plant–animal mutualistic communities.Key-words: Bialowieza Forest, interaction networks, limiting similarity, niche differentiation, phe-_nological overlap, plant–animal mutualism, plant–plant interactions, seed dispersalIntroduction
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high conservation value of forest fragments for plant and Frugivore communities in a fragmented forest landscape in south africa
Biotropica, 2014Co-Authors: Dana G Berens, Lackson Chama, Jorg Albrecht, Nina FarwigAbstract: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.
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Guild-specific shifts in visitation rates of Frugivores with habitat loss and plant invasion
Oikos, 2013Co-Authors: Ingo Grass, Dana G Berens, Nina FarwigAbstract:Habitat loss and plant invasions are two major drivers of global change in subtropical and tropical ecosystems. Both lead to a loss of biodiversity and alter species interactions, which may imperil vital ecosystem processes such as seed dispersal by Frugivores. Reponses of Frugivores to disturbance are often linked to their specialization on certain habitats or resources. Yet, it is poorly understood how habitat loss and plant invasion structure interactions between plants and different habitat or feeding guilds. Here we investigated whether visitation rates of Frugivores change guild-specifically with increasing habitat loss and invasion level in a heterogeneous subtropical landscape. In 756 h of observations, we recorded 1446 plant–Frugivore interactions among 18 plant species and 42 avian Frugivore species. Visitation rates of forest specialists decreased with increasing habitat loss, but not with changes in invasion level. In contrast forest generalists and forest visitors were unaffected by either driver. Similarly, obligate Frugivores that overall showed a generalized fruit choice were unaffected by habitat loss and changes in invasion level. Contrary, visitation rates of specialized partial and opportunistic Frugivores decreased with higher invasion level. Importantly, the negative effect of plant invasion on partial Frugivores was more pronounced as habitat loss in the same study site increased, indicating a synergistic effect of the two drivers. The implications of our study are twofold: first, Frugivores respond guild-specifically to habitat loss and plant invasion. Thereby forest dependency is mainly related to habitat loss, and degree of frugivory mainly related to plant invasion. Forest generalists and obligate Frugivores in turn may play a key-role for forest regeneration in disturbed forest landscapes. Second, particularly Frugivores with a specialized fruit choice may be threatened by synergistic effects between habitat loss and plant invasion.
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Resources determine Frugivore assemblages and fruit removal along an elevational gradient
Acta Oecologica-international Journal of Ecology, 2013Co-Authors: Alexandra Aparicio, Dana G Berens, Jörg Müller, Nina FarwigAbstract: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.
Jose M Fedriani - One of the best experts on this subject based on the ideXlab platform.
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strong among population variation in frugivory strength by functional diverse Frugivores a reciprocal translocation experiment
Oecologia, 2018Co-Authors: Pedro J Garrote, Gemma Calvo, Magdalena żywiec, Miguel Delibes, Alberto Suarezesteban, Jose M FedrianiAbstract:Fruit–Frugivore interactions are critical for the dynamics and evolution of many plant communities. The strength of the interactions between a given plant species and different Frugivore guilds (e.g., seed dispersers, seed predators) often vary in space due to changes in plant extrinsic factors (e.g., Frugivore abundances) and plant traits (e.g., fruit size and reward). By reciprocally translocating Pyrus bourgaeana ripe fruits representative of five Mediterranean localities during 2 consecutive years, we experimentally quantified guild-specific variations among populations in frugivory strength, while accounted for plant-intrinsic and- extrinsic factors. Though overall fruit removal did not differ among localities, there were strong guild-specific differences in fruit removal strength. Fruit removal by pulp feeders, seed dispersers, and fruit predators varied among populations up to 8.5-, 5.6-, and 4.0-folds, respectively. These strong variations seemed mediated by changes in Frugivore relative abundances rather than on availability of alternative fruits. As expected, all fruit traits considered (e.g., fruit size, pulp amount) markedly varied among tree populations. However, no Frugivore guild showed preference for fruits from any locality, suggesting that fruit traits did not contribute much to differences in frugivory strength among populations. Since the functional diverse Frugivore guilds played contrasting roles in P. bourgaeana dynamics (e.g., seed dispersal vs. seed predation), our study highlights the importance of accounting for functional diversity in Frugivore guilds when estimating spatial variations in the strenght of seed dispersal. This investigation also illustrates a neglected but widely applicable experimental approach to identify the relative importance of extrinsic factors and fruit traits in mediating fruit–Frugivore interactions.
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Strong among population variation in frugivory strength by functional diverse Frugivores: a ‘reciprocal translocation’ experiment
Oecologia, 2018Co-Authors: Pedro J Garrote, Gemma Calvo, Miguel Delibes, Magdalena Żywiec, Alberto Suárez-esteban, Jose M FedrianiAbstract:Fruit–Frugivore interactions are critical for the dynamics and evolution of many plant communities. The strength of the interactions between a given plant species and different Frugivore guilds (e.g., seed dispersers, seed predators) often vary in space due to changes in plant extrinsic factors (e.g., Frugivore abundances) and plant traits (e.g., fruit size and reward). By reciprocally translocating Pyrus bourgaeana ripe fruits representative of five Mediterranean localities during 2 consecutive years, we experimentally quantified guild-specific variations among populations in frugivory strength, while accounted for plant-intrinsic and- extrinsic factors. Though overall fruit removal did not differ among localities, there were strong guild-specific differences in fruit removal strength. Fruit removal by pulp feeders, seed dispersers, and fruit predators varied among populations up to 8.5-, 5.6-, and 4.0-folds, respectively. These strong variations seemed mediated by changes in Frugivore relative abundances rather than on availability of alternative fruits. As expected, all fruit traits considered (e.g., fruit size, pulp amount) markedly varied among tree populations. However, no Frugivore guild showed preference for fruits from any locality, suggesting that fruit traits did not contribute much to differences in frugivory strength among populations. Since the functional diverse Frugivore guilds played contrasting roles in P. bourgaeana dynamics (e.g., seed dispersal vs. seed predation), our study highlights the importance of accounting for functional diversity in Frugivore guilds when estimating spatial variations in the strenght of seed dispersal. This investigation also illustrates a neglected but widely applicable experimental approach to identify the relative importance of extrinsic factors and fruit traits in mediating fruit–Frugivore interactions.
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context dependent fruit Frugivore interactions partner identities and spatio temporal variations
Oikos, 2013Co-Authors: Ramon Perea, Miguel Delibes, Alberto Suarezesteban, Mark Polko, Jose M FedrianiAbstract:Fruit–Frugivore interactions are crucial for the dynamics and regeneration of most forested ecosystems. Still, we lack an understanding of the potential variation in the sign and strength of such interactions in relation to variations in the spatial and temporal ecological context. Here, we evaluated spatial (three sites) and temporal (two fruiting seasons) local variation in the sign (seed predation versus dispersal) and strength (frequency and quantity) of the interactions among six frugivorous mammals and a community of Mediterranean fleshy-fruited shrubs. We examined mammal faecal samples and quantified frequency of seed occurrence, number of seeds per faecal sample, seed species diversity and quality of seed treatment (i.e. percentage of undamaged seeds). The frequency of seed occurrence and number of seeds per faecal sample strongly varied among dispersers, sites, seasons and fruit species. For instance, fox Vulpes vulpes faeces showed between 6 and 40 times more seeds than wild boar Sus scrofa faeces in seasons or sites in which Rubus and Juniperus seeds were dominant. However, in seasons or sites dominated by Corema seeds, wild boar faeces contained up to seven times more seeds than fox faeces. Mammalian carnivores (fox and badger, Meles meles) treated seeds gently, acting mostly as dispersers, whereas deer (Cervus elaphus and Dama dama) acted mainly as seed predators. Interestingly, rabbit Oryctolagus cuniculus acted as either mostly seed disperser or seed predator depending on the plant species. Our results indicated that the sign of fruit–Frugivore interactions depended mainly on the identity of the partners. For a particular fruit–Frugivore pair, however, our surrogate of interaction strength largely varied with the spatio-temporal context (year and habitat), leading to a low specificity across the seed–Frugivore network. The high spatio-temporal variability of seed dispersal (in quantity, quality and seed diversity) by different Frugivores would confer resilience against unpredictable environmental conditions, such as those typical of Mediterranean ecosystems.
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Context‐dependent fruit–Frugivore interactions: partner identities and spatio‐temporal variations
Oikos, 2012Co-Authors: Ramon Perea, Miguel Delibes, Alberto Suárez-esteban, Mark Polko, Jose M FedrianiAbstract:Fruit–Frugivore interactions are crucial for the dynamics and regeneration of most forested ecosystems. Still, we lack an understanding of the potential variation in the sign and strength of such interactions in relation to variations in the spatial and temporal ecological context. Here, we evaluated spatial (three sites) and temporal (two fruiting seasons) local variation in the sign (seed predation versus dispersal) and strength (frequency and quantity) of the interactions among six frugivorous mammals and a community of Mediterranean fleshy-fruited shrubs. We examined mammal faecal samples and quantified frequency of seed occurrence, number of seeds per faecal sample, seed species diversity and quality of seed treatment (i.e. percentage of undamaged seeds). The frequency of seed occurrence and number of seeds per faecal sample strongly varied among dispersers, sites, seasons and fruit species. For instance, fox Vulpes vulpes faeces showed between 6 and 40 times more seeds than wild boar Sus scrofa faeces in seasons or sites in which Rubus and Juniperus seeds were dominant. However, in seasons or sites dominated by Corema seeds, wild boar faeces contained up to seven times more seeds than fox faeces. Mammalian carnivores (fox and badger, Meles meles) treated seeds gently, acting mostly as dispersers, whereas deer (Cervus elaphus and Dama dama) acted mainly as seed predators. Interestingly, rabbit Oryctolagus cuniculus acted as either mostly seed disperser or seed predator depending on the plant species. Our results indicated that the sign of fruit–Frugivore interactions depended mainly on the identity of the partners. For a particular fruit–Frugivore pair, however, our surrogate of interaction strength largely varied with the spatio-temporal context (year and habitat), leading to a low specificity across the seed–Frugivore network. The high spatio-temporal variability of seed dispersal (in quantity, quality and seed diversity) by different Frugivores would confer resilience against unpredictable environmental conditions, such as those typical of Mediterranean ecosystems.
Katrin Bohninggaese - One of the best experts on this subject based on the ideXlab platform.
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Frugivore diversity increases frugivory rates along a large elevational gradient
Oikos, 2016Co-Authors: Stefan W Ferger, Hamadi I Dulle, Matthias Schleuning, Katrin BohninggaeseAbstract: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.
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constant properties of plant Frugivore networks despite fluctuations in fruit and bird communities in space and time
Ecology, 2013Co-Authors: Michaela Plein, Katrin Bohninggaese, Laura Langsfeld, Eike Lena Neuschulz, Christina Schultheis, Lili Ingmann, Till Topfer, Matthias SchleuningAbstract:Human-induced changes in anthropogenic landscapes are a predominant threat to biodiversity and have been documented to affect mutualistic interactions between plants and animals, such as avian seed dispersal. Interactions between fleshy-fruited plants and frugivorous birds are highly seasonal in temperate ecosystems. Nevertheless, combined effects of landscape modification and seasonal variation on plant-Frugivore interactions have never been assessed from a network perspective. Here, we present the first study that simultaneously investigates effects of landscape modification and seasonal variation on plant-Frugivore interactions and on functional and interaction diversity of plant-Frugivore networks. We recorded visitation rates of 39 frugivorous bird species to 28 fruiting-plant species in Central Germany from early summer to late autumn in hedgerows within three landscape types arranged along a gradient of decreasing anthropogenic modification and increasing structural diversity (i.e., farmland, orchard, forest edge). We analyzed how species richness, abundance, and community composition, as well as functional and interaction diversity of fruiting plants and frugivorous birds changed with landscape type, fruit availability, and season. We found that visitation rates of frugivorous birds were lower in farmland, but only in summer. In autumn, visitation rates were similar in all landscape types and strongly increased with increasing local fruit availability. The functional diversity of fruits and frugivorous birds and their interaction diversity remained surprisingly constant in all landscape types. Due to seasonal changes in communities of fruiting plants and frugivorous birds, functional dispersion of fruiting plants was lower in autumn than in summer, whereas functional richness and dispersion of frugivorous birds was higher in autumn than in summer. Our results indicate that seasonal changes in fruit availability influence the abundance of frugivorous birds along gradients of structural diversity at the landscape scale. Although seasonal fluctuations influenced the functional diversity of avian Frugivore communities, we found constant interaction diversity of plant-Frugivore networks in space and time, probably due to the functional redundancy of frugivorous birds. These findings indicate a high robustness of avian frugivory to moderate levels of human-induced landscape modification in temperate ecosystems and call for studies testing the generality of these findings for ultimate avian seed dispersal functions.
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plant Frugivore networks are less specialized and more robust at forest farmland edges than in the interior of a tropical forest
Oikos, 2012Co-Authors: Sebastian Menke, Katrin Bohninggaese, Matthias SchleuningAbstract: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.
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specialization and interaction strength in a tropical plant Frugivore network differ among forest strata
Ecology, 2011Co-Authors: Matthias Schleuning, Nico Bluthgen, Martina Florchinger, Julius Braun, Martin H Schaefer, Katrin BohninggaeseAbstract:The degree of interdependence and potential for shared coevolutionary history of frugivorous animals and fleshy-fruited plants are contentious topics. Recently, network analyses revealed that mutualistic relationships between fleshy-fruited plants and Frugivores are mostly built upon generalized associations. However, little is known about the determinants of network structure, especially from tropical forests where plants' dependence on animal seed dispersal is particularly high. Here, we present an in-depth analysis of specialization and interaction strength in a plant–Frugivore network from a Kenyan rain forest. We recorded fruit removal from 33 plant species in different forest strata (canopy, midstory, understory) and habitats (primary and secondary forest) with a standardized sampling design (3447 interactions in 924 observation hours). We classified the 88 Frugivore species into guilds according to dietary specialization (14 obligate, 28 partial, 46 opportunistic Frugivores) and forest dependence (...
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food plant diversity as broad scale determinant of avian Frugivore richness
Proceedings of The Royal Society B: Biological Sciences, 2007Co-Authors: Daniel W Kissling, Carsten Rahbek, Katrin BohninggaeseAbstract: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.
Matthias Schleuning - One of the best experts on this subject based on the ideXlab platform.
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Frugivore diversity increases frugivory rates along a large elevational gradient
Oikos, 2016Co-Authors: Stefan W Ferger, Hamadi I Dulle, Matthias Schleuning, Katrin BohninggaeseAbstract: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.
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constant properties of plant Frugivore networks despite fluctuations in fruit and bird communities in space and time
Ecology, 2013Co-Authors: Michaela Plein, Katrin Bohninggaese, Laura Langsfeld, Eike Lena Neuschulz, Christina Schultheis, Lili Ingmann, Till Topfer, Matthias SchleuningAbstract:Human-induced changes in anthropogenic landscapes are a predominant threat to biodiversity and have been documented to affect mutualistic interactions between plants and animals, such as avian seed dispersal. Interactions between fleshy-fruited plants and frugivorous birds are highly seasonal in temperate ecosystems. Nevertheless, combined effects of landscape modification and seasonal variation on plant-Frugivore interactions have never been assessed from a network perspective. Here, we present the first study that simultaneously investigates effects of landscape modification and seasonal variation on plant-Frugivore interactions and on functional and interaction diversity of plant-Frugivore networks. We recorded visitation rates of 39 frugivorous bird species to 28 fruiting-plant species in Central Germany from early summer to late autumn in hedgerows within three landscape types arranged along a gradient of decreasing anthropogenic modification and increasing structural diversity (i.e., farmland, orchard, forest edge). We analyzed how species richness, abundance, and community composition, as well as functional and interaction diversity of fruiting plants and frugivorous birds changed with landscape type, fruit availability, and season. We found that visitation rates of frugivorous birds were lower in farmland, but only in summer. In autumn, visitation rates were similar in all landscape types and strongly increased with increasing local fruit availability. The functional diversity of fruits and frugivorous birds and their interaction diversity remained surprisingly constant in all landscape types. Due to seasonal changes in communities of fruiting plants and frugivorous birds, functional dispersion of fruiting plants was lower in autumn than in summer, whereas functional richness and dispersion of frugivorous birds was higher in autumn than in summer. Our results indicate that seasonal changes in fruit availability influence the abundance of frugivorous birds along gradients of structural diversity at the landscape scale. Although seasonal fluctuations influenced the functional diversity of avian Frugivore communities, we found constant interaction diversity of plant-Frugivore networks in space and time, probably due to the functional redundancy of frugivorous birds. These findings indicate a high robustness of avian frugivory to moderate levels of human-induced landscape modification in temperate ecosystems and call for studies testing the generality of these findings for ultimate avian seed dispersal functions.
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plant Frugivore networks are less specialized and more robust at forest farmland edges than in the interior of a tropical forest
Oikos, 2012Co-Authors: Sebastian Menke, Katrin Bohninggaese, Matthias SchleuningAbstract: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.
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specialization and interaction strength in a tropical plant Frugivore network differ among forest strata
Ecology, 2011Co-Authors: Matthias Schleuning, Nico Bluthgen, Martina Florchinger, Julius Braun, Martin H Schaefer, Katrin BohninggaeseAbstract:The degree of interdependence and potential for shared coevolutionary history of frugivorous animals and fleshy-fruited plants are contentious topics. Recently, network analyses revealed that mutualistic relationships between fleshy-fruited plants and Frugivores are mostly built upon generalized associations. However, little is known about the determinants of network structure, especially from tropical forests where plants' dependence on animal seed dispersal is particularly high. Here, we present an in-depth analysis of specialization and interaction strength in a plant–Frugivore network from a Kenyan rain forest. We recorded fruit removal from 33 plant species in different forest strata (canopy, midstory, understory) and habitats (primary and secondary forest) with a standardized sampling design (3447 interactions in 924 observation hours). We classified the 88 Frugivore species into guilds according to dietary specialization (14 obligate, 28 partial, 46 opportunistic Frugivores) and forest dependence (...
Dana G Berens - One of the best experts on this subject based on the ideXlab platform.
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variation in neighbourhood context shapes Frugivore mediated facilitation and competition among co dispersed plant species
Journal of Ecology, 2015Co-Authors: Jorg Albrecht, Dana G Berens, Bogdan Jaroszewicz, Nuria Selva, Victoria Bohle, Nina FarwigAbstract:Summary1. Co-occurring and simultaneously fruiting plant species may either compete for dispersal byshared Frugivores or enhance each other’s dispersal through joint attraction of Frugivores. Whilecompetitive plant–plant interactions are expected to cause the evolutionary divergence of fruit phe-nologies, facilitative interactions are assumed to promote their convergence. To which extent com-petitive and facilitative interactions among plant species with similar phenological niches arecontrolled by spatial variation in their local abundance and co-occurrence is poorly understood.2. Here, we test the hypotheses that when a plant species fruits in high densities, large phenologicaloverlap with other plant species causes competition for seed dispersers owing to Frugivore satiation.Conversely, we expect large phenological overlap to enhance the dispersal of a plant species fruitingin low densities through attraction of Frugivores by other species in its local neighbourhood.3. We test these predictions on plant–Frugivore networks based on seed removal from 15 woody,fleshy-fruited plant species by 30 avian and 4 mammalian Frugivore species across 13 study sites inBialowieza Forest, Poland._4. A null model indicated that fruit phenologies of the regional plant assemblage were more differ-entiated than expected by chance. In the local networks, the tendency of plants to share Frugivoresincreased with phenological overlap. High phenological overlap reduced the seed removal rates,interaction strength (proportion of interactions) and the number of partners of plant species fruitingin high densities. Conversely, plant species fruiting in low densities mainly profited from high phe-nological overlap with other species. Importantly, the sharing of mutualistic partners among co-fruiting plant species was also reflected in their co-occurrence.5. Synthesis. Our study highlights that, in spite of the overall signal of competition, Frugivore-medi-ated interactions among cofruiting plant species may consistently promote the establishment and per-sistence of rare species through facilitation. In addition, our results suggest that, among otherfactors, indirect coupling of species through shared mutualistic partners might be an important deter-minant of plant community assembly. The coupling through shared mutualists may cause the forma-tion of associations among co-dispersed plant species and might contribute to the coexistence ofspecies in plant–animal mutualistic communities.Key-words: Bialowieza Forest, interaction networks, limiting similarity, niche differentiation, phe-_nological overlap, plant–animal mutualism, plant–plant interactions, seed dispersalIntroduction
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high conservation value of forest fragments for plant and Frugivore communities in a fragmented forest landscape in south africa
Biotropica, 2014Co-Authors: Dana G Berens, Lackson Chama, Jorg Albrecht, Nina FarwigAbstract: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.
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Guild-specific shifts in visitation rates of Frugivores with habitat loss and plant invasion
Oikos, 2013Co-Authors: Ingo Grass, Dana G Berens, Nina FarwigAbstract:Habitat loss and plant invasions are two major drivers of global change in subtropical and tropical ecosystems. Both lead to a loss of biodiversity and alter species interactions, which may imperil vital ecosystem processes such as seed dispersal by Frugivores. Reponses of Frugivores to disturbance are often linked to their specialization on certain habitats or resources. Yet, it is poorly understood how habitat loss and plant invasion structure interactions between plants and different habitat or feeding guilds. Here we investigated whether visitation rates of Frugivores change guild-specifically with increasing habitat loss and invasion level in a heterogeneous subtropical landscape. In 756 h of observations, we recorded 1446 plant–Frugivore interactions among 18 plant species and 42 avian Frugivore species. Visitation rates of forest specialists decreased with increasing habitat loss, but not with changes in invasion level. In contrast forest generalists and forest visitors were unaffected by either driver. Similarly, obligate Frugivores that overall showed a generalized fruit choice were unaffected by habitat loss and changes in invasion level. Contrary, visitation rates of specialized partial and opportunistic Frugivores decreased with higher invasion level. Importantly, the negative effect of plant invasion on partial Frugivores was more pronounced as habitat loss in the same study site increased, indicating a synergistic effect of the two drivers. The implications of our study are twofold: first, Frugivores respond guild-specifically to habitat loss and plant invasion. Thereby forest dependency is mainly related to habitat loss, and degree of frugivory mainly related to plant invasion. Forest generalists and obligate Frugivores in turn may play a key-role for forest regeneration in disturbed forest landscapes. Second, particularly Frugivores with a specialized fruit choice may be threatened by synergistic effects between habitat loss and plant invasion.
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Resources determine Frugivore assemblages and fruit removal along an elevational gradient
Acta Oecologica-international Journal of Ecology, 2013Co-Authors: Alexandra Aparicio, Dana G Berens, Jörg Müller, Nina FarwigAbstract: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.
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Do Frugivores enhance germination success of plant species? An experimental approach
South African Journal of Botany, 2013Co-Authors: Lackson Chama, Dana G Berens, Colleen T Downs, Nina FarwigAbstract:Abstract 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 .
