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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, 2017Co-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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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.
Jason M. Tylianakis - One of the best experts on this subject based on the ideXlab platform.
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exotic birds increase generalization and compensate for native bird decline in plant frugivore assemblages
Journal of Animal Ecology, 2014Co-Authors: Daniel Garcia, Daniel B. Stouffer, Jason M. Tylianakis, Daniel MartinezAbstract:Summary 1. Exotic species are thought to alter the structure of natural communities and disrupt ecosystem functioning through invasion. Nevertheless, exotic species may also provide ecological insurance when they contribute to maintain ecosystem functions after the decline of native species following anthropogenic disturbance. 2. Here, this hypothesis is tested with the assemblage of frugivorous birds and fleshy-fruited plants of New Zealand, which has suffered strong historical declines in native birds while simultaneously gaining new Frugivores introduced by European settlers. 3. We studied the plant–frugivore assemblage from measures of fruit and bird abundances and fruit consumption in nine forest patches, and tested how this changed across a gradient of relative abundance of exotic birds. We then examined how each bird species’ role in the assemblage (the proportion of fruits and the number of plant species consumed) varied with their relative abundance, body size and native/exotic status. 4. The more abundant and, to a lesser extent, larger birds species consumed a higher proportion of fruits from more plant species. Exotic birds consumed fruits less selectively and more proportionate to the local availability than did native species. Interaction networks in which exotic birds had a stronger role as Frugivores had higher generalization, higher nestedness and higher redundancy of plants. 5. Exotic birds maintained frugivory when native birds became rarer, and diversified the local spectrum of Frugivores for co-occurring native plants. These effects seemed related to the fact that species abundances, rather than trait-matching constraints, ultimately determined the patterns of interactions between birds and plants. By altering the structure of plant–frugivore assemblages, exotic birds likely enhance the stability of the community-wide seed dispersal in the face of continued anthropogenic impact.
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Exotic birds increase generalization and compensate for native bird decline in plant–frugivore assemblages
Journal of Animal Ecology, 2014Co-Authors: Daniel Garcia, Daniel B. Stouffer, Daniel Martinez, Jason M. TylianakisAbstract:Summary 1. Exotic species are thought to alter the structure of natural communities and disrupt ecosystem functioning through invasion. Nevertheless, exotic species may also provide ecological insurance when they contribute to maintain ecosystem functions after the decline of native species following anthropogenic disturbance. 2. Here, this hypothesis is tested with the assemblage of frugivorous birds and fleshy-fruited plants of New Zealand, which has suffered strong historical declines in native birds while simultaneously gaining new Frugivores introduced by European settlers. 3. We studied the plant–frugivore assemblage from measures of fruit and bird abundances and fruit consumption in nine forest patches, and tested how this changed across a gradient of relative abundance of exotic birds. We then examined how each bird species’ role in the assemblage (the proportion of fruits and the number of plant species consumed) varied with their relative abundance, body size and native/exotic status. 4. The more abundant and, to a lesser extent, larger birds species consumed a higher proportion of fruits from more plant species. Exotic birds consumed fruits less selectively and more proportionate to the local availability than did native species. Interaction networks in which exotic birds had a stronger role as Frugivores had higher generalization, higher nestedness and higher redundancy of plants. 5. Exotic birds maintained frugivory when native birds became rarer, and diversified the local spectrum of Frugivores for co-occurring native plants. These effects seemed related to the fact that species abundances, rather than trait-matching constraints, ultimately determined the patterns of interactions between birds and plants. By altering the structure of plant–frugivore assemblages, exotic birds likely enhance the stability of the community-wide seed dispersal in the face of continued anthropogenic impact.
K C Burns - One of the best experts on this subject based on the ideXlab platform.
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Evaluating Frugivore-fruit Interactions Using Avian Eye Modelling.
tropical life sciences research, 2013Co-Authors: Nik Fadzly, K C Burns, Wan Fatma ZuharahAbstract:Fruit phenotypes are often hypothesised to be affected by selection by Frugivores. Here, we tested two hypotheses concerning frugivore-fruit interactions from the perspective of fruit colours. We measured the spectral properties of 26 fruits and the associated leaves of plants from 2 islands in New Zealand. Visual observations were also performed to record the birds that fed on the fruits. First, we tested the fruit-foliage hypothesis, where fruit colours are assumed to be evolutionarily constrained by their own leaf colour to maximise colour contrast and fruit conspicuousness. We ran a null model analysis comparing fruit colour contrast using an avian eye model. Second, we tested the frugivore specificity hypothesis, where specific fruit colours are thought to be connected with a specific bird frugivore. We performed a regression on the number of bird visits against the fruit colour in tetrahedral colour space based on an avian eye calculation using Mantel’s test. The results show that fruit colours are not constrained by their own leaf colours. There is also no relationship or pattern suggesting a link between a specific fruit colour and specific bird visitors. We suggest that although fruit colour is one of the most highly discussed components, it is not the most important single deciding factor in frugivore fruit selection.
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what causes size coupling in fruit frugivore interaction webs
Ecology, 2013Co-Authors: K C BurnsAbstract:The simplest and arguably the most ubiquitous pattern in seed dispersal mutualisms is size coupling: large Frugivores tend to consume larger fruits and small Frugivores tend to consume smaller fruits. Despite the simplicity of this pattern, the potential mechanisms responsible for fruit–frugivore size coupling are mechanistically divergent and poorly resolved. Size coupling could arise deterministically, if large Frugivores actively seek out larger fruits to maximize their foraging efficiency. Alternatively, size coupling could also arise passively, if Frugivores forage randomly, but are able to consume only those fruit species that are smaller than their gape width. I observed birds forage for fruits in a New Zealand forest reserve at approximately five-day intervals for six years to test for fruit–frugivore size coupling. I then derived a suite of network analyses to establish whether fruit–frugivore size coupling was best explained by active or passive foraging by Frugivores. Results showed a strikingl...
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What causes size coupling in fruit–frugivore interaction webs?
Ecology, 2013Co-Authors: K C BurnsAbstract:The simplest and arguably the most ubiquitous pattern in seed dispersal mutualisms is size coupling: large Frugivores tend to consume larger fruits and small Frugivores tend to consume smaller fruits. Despite the simplicity of this pattern, the potential mechanisms responsible for fruit–frugivore size coupling are mechanistically divergent and poorly resolved. Size coupling could arise deterministically, if large Frugivores actively seek out larger fruits to maximize their foraging efficiency. Alternatively, size coupling could also arise passively, if Frugivores forage randomly, but are able to consume only those fruit species that are smaller than their gape width. I observed birds forage for fruits in a New Zealand forest reserve at approximately five-day intervals for six years to test for fruit–frugivore size coupling. I then derived a suite of network analyses to establish whether fruit–frugivore size coupling was best explained by active or passive foraging by Frugivores. Results showed a strikingl...
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Fruit-frugivore interactions in two southern hemisphere forests: allometry, phylogeny and body size.
Oikos, 2009Co-Authors: K C Burns, Babs LakeAbstract: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.
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a simple null model predicts fruit frugivore interactions in a temperate rainforest
Oikos, 2006Co-Authors: K C BurnsAbstract:Studies of seed dispersal mutualisms typically test for adaptive relationships between fruits and Frugivores. Here, I take the opposite approach, and ask what relationships would be expected based on chance encounters between mutualists. 1 derived a simple null model to predict pair-wise relationships between fruit and frugivore species. I assumed that all Frugivores had identical fruit preferences, but allowed for interspecific variation in plant abundances, frugivore abundances and fruit phenologies. Under these conditions, the number of visits each frugivore species makes to each plant species results from the product of plant abundances and frugivore abundances when each plant species produces fruit. I then tested null model predictions with observations in a temperate rainforest in British Columbia, Canada. I measured the abundance and phenology of seven bird-dispersed plant species, seasonal changes in the abundances of six avian frugivore species and 212 interactions between them. Empirical results were generally consistent with predictions, suggesting that relationships between birds and fruits are structured randomly. However, some variation in relationships between observations and predictions was observed, suggesting deterministic processes may also be important. Overall results illustrate that predictable relationships between fruit and frugivore species can result from random encounters between mutualists.
Daniel Garcia - One of the best experts on this subject based on the ideXlab platform.
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from structure to function in mutualistic interaction networks topologically important Frugivores have greater potential as seed dispersers
Journal of Animal Ecology, 2020Co-Authors: Juan Fernando Acevedoquintero, Joan Gaston Zamoraabrego, Daniel GarciaAbstract:Networks of mutualistic interactions between animals and plants are considered a pivotal part of ecological communities. However, mutualistic networks are rarely studied from the perspective of species-specific roles, and it remains to be established whether those animal species more relevant for network structure also contribute more to the ecological functions derived from interactions. Here, we relate the contribution to seed dispersal of vertebrate species with their topological role in frugivore-plant interaction networks. For one year in two localities with remnant patches of Colombian tropical dry forest, we sampled abundance, morphology, behaviour and fruit consumption from fleshy-fruited plants of various frugivore species. We assessed the network topological role of each frugivore species by integrating their degree of generalization in interactions with plants with their contributions to network nestedness and modularity. We estimated the potential contribution of each frugivore species to community-wide seed dispersal, on the basis of a set of frugivore ecological, morphological and behavioural characteristics important for seed dispersal, together with frugivore abundance and frugivory degree. The various frugivore species showed strong differences in their network structural roles, with generalist species contributing the most to network modularity and nestedness. Frugivores also showed strong variability in terms of potential contribution to seed dispersal, depending on the specific combinations of frugivore abundance, frugivory degree and the different traits and behaviours. For both localities, the seed dispersal potential of a frugivore species responded positively to its contribution to network structure, evidencing that the most important frugivore species in the network topology were also those making the strongest contribution as seed dispersers. Contribution to network structure was correlated with frugivore abundance, diet and behavioural characteristics. This suggests that the species-level link between structure and function is due to the fact that the occurrence of frugivore-plant interactions depends largely on the characteristics of the frugivore involved, which also condition its ultimate role in seed dispersal.
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exotic birds increase generalization and compensate for native bird decline in plant frugivore assemblages
Journal of Animal Ecology, 2014Co-Authors: Daniel Garcia, Daniel B. Stouffer, Jason M. Tylianakis, Daniel MartinezAbstract:Summary 1. Exotic species are thought to alter the structure of natural communities and disrupt ecosystem functioning through invasion. Nevertheless, exotic species may also provide ecological insurance when they contribute to maintain ecosystem functions after the decline of native species following anthropogenic disturbance. 2. Here, this hypothesis is tested with the assemblage of frugivorous birds and fleshy-fruited plants of New Zealand, which has suffered strong historical declines in native birds while simultaneously gaining new Frugivores introduced by European settlers. 3. We studied the plant–frugivore assemblage from measures of fruit and bird abundances and fruit consumption in nine forest patches, and tested how this changed across a gradient of relative abundance of exotic birds. We then examined how each bird species’ role in the assemblage (the proportion of fruits and the number of plant species consumed) varied with their relative abundance, body size and native/exotic status. 4. The more abundant and, to a lesser extent, larger birds species consumed a higher proportion of fruits from more plant species. Exotic birds consumed fruits less selectively and more proportionate to the local availability than did native species. Interaction networks in which exotic birds had a stronger role as Frugivores had higher generalization, higher nestedness and higher redundancy of plants. 5. Exotic birds maintained frugivory when native birds became rarer, and diversified the local spectrum of Frugivores for co-occurring native plants. These effects seemed related to the fact that species abundances, rather than trait-matching constraints, ultimately determined the patterns of interactions between birds and plants. By altering the structure of plant–frugivore assemblages, exotic birds likely enhance the stability of the community-wide seed dispersal in the face of continued anthropogenic impact.
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Exotic birds increase generalization and compensate for native bird decline in plant–frugivore assemblages
Journal of Animal Ecology, 2014Co-Authors: Daniel Garcia, Daniel B. Stouffer, Daniel Martinez, Jason M. TylianakisAbstract:Summary 1. Exotic species are thought to alter the structure of natural communities and disrupt ecosystem functioning through invasion. Nevertheless, exotic species may also provide ecological insurance when they contribute to maintain ecosystem functions after the decline of native species following anthropogenic disturbance. 2. Here, this hypothesis is tested with the assemblage of frugivorous birds and fleshy-fruited plants of New Zealand, which has suffered strong historical declines in native birds while simultaneously gaining new Frugivores introduced by European settlers. 3. We studied the plant–frugivore assemblage from measures of fruit and bird abundances and fruit consumption in nine forest patches, and tested how this changed across a gradient of relative abundance of exotic birds. We then examined how each bird species’ role in the assemblage (the proportion of fruits and the number of plant species consumed) varied with their relative abundance, body size and native/exotic status. 4. The more abundant and, to a lesser extent, larger birds species consumed a higher proportion of fruits from more plant species. Exotic birds consumed fruits less selectively and more proportionate to the local availability than did native species. Interaction networks in which exotic birds had a stronger role as Frugivores had higher generalization, higher nestedness and higher redundancy of plants. 5. Exotic birds maintained frugivory when native birds became rarer, and diversified the local spectrum of Frugivores for co-occurring native plants. These effects seemed related to the fact that species abundances, rather than trait-matching constraints, ultimately determined the patterns of interactions between birds and plants. By altering the structure of plant–frugivore assemblages, exotic birds likely enhance the stability of the community-wide seed dispersal in the face of continued anthropogenic impact.
Katrin Bohninggaese - One of the best experts on this subject based on the ideXlab platform.
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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, Martina Florchinger, Julius Braun, Martin H Schaefer, Nico Bluthgen, 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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effects of local disturbance of tropical forests on Frugivores and seed removal of a small seeded afrotropical tree
Conservation Biology, 2008Co-Authors: Jasper Mbae Kirika, Nina Farwig, Katrin BohninggaeseAbstract:Small-scale, local disturbance of tropical forests, for example from selective logging, is widespread, but its effects on biodiversity and ecosystem function have rarely been studied. In 3 East African tropical rainforests, we investigated the effect of different levels of local forest disturbance on the frugivore community and on tree visitation and fruit removal rates of the small-seeded tree Celtis durandii. We quantified birds and primates in little and heavily disturbed sites, distinguishing between forest specialists, forest generalists, and forest visitors. We quantified frugivorous tree visitors and seed removal rates of C. durandii trees in the same sites. Forest disturbance reduced the species richness and density of the frugivore community and of forest specialists. Frugivorous species and individuals visiting the study trees were reduced significantly, which led to a marginally significant decline in fruit removal by all Frugivores and a significant reduction in removal by forest specialists. Reduction in fruit removal by forest specialists was not compensated for by increases in removal by forest generalists or visitors. Results did not differ among the 3 rainforests, which suggests they were consistent at a regional scale. So local forest disturbance led to a loss of Frugivores and their seed removal services. This suggests that large-seeded tree species and trees with small fruits are losing seed dispersers. Thus, local forest disturbance appears to have a more general negative impact on Frugivores and their seed dispersal services than anticipated previously.
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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.
