Megafaunal frugivores can consume large amounts of fruits whose seeds may be dispersed over long distances, thus, affecting plant regeneration processes and ecosystem functioning. We investigated the ...role of brown bears (Ursus arctos) as legitimate megafaunal seed dispersers. We assessed the quantity component of seed dispersal by brown bears across its entire distribution based on information about both the relative frequency of occurrence and species composition of fleshy fruits in the diet of brown bears extracted from the literature. We assessed the quality component of seed dispersal based on germination experiments for 11 fleshy-fruited plant species common in temperate and boreal regions and frequently eaten by brown bears. Across its distribution, fleshy fruits, on average, represented 24% of the bear food items and 26% of the total volume consumed. Brown bears consumed seeds from at least 101 fleshy-fruited plant species belonging to 24 families and 42 genera, of which Rubus (Rosaceae) and Vaccinium (Ericaceae) were most commonly eaten. Brown bears inhabiting Mediterranean forests relied the most on fleshy fruits and consumed the largest number of species per study area. Seeds ingested by bears germinated at higher percentages than those from whole fruits, and at similar percentages than manually depulped seeds. We conclude that brown bears are legitimate seed dispersers as they consume large quantities of seeds that remain viable after gut passage. The decline of these megafaunal frugivores may compromise seed dispersal services and plant regeneration processes.
Mutualistic interactions form the basis for many ecological processes and are often analyzed within the framework of ecological networks. These interactions can be sampled with a range of methods and ...first analyses of pollination networks sampled with different methods showed differences in common network metrics. However, it is yet unknown if metrics of seed dispersal networks are similarly affected by the sampling method and if different methods detect a complementary set of frugivores. This is necessary to better understand the (dis‐)advantages of each method and to identify the role of each frugivore for the seed dispersal process.
Here, we compare seed removal networks based on the observation of 2189 frugivore visits on ten focal plant species with seed deposition networks constructed by DNA barcoding of plant seeds in 3094 frugivore scats. We were interested in whether both methods identify the same disperser species and if species‐level network metrics of plant species were correlated between network types.
Both methods identified the same avian super‐generalist frugivores, which accounted for the highest number of dispersed seeds. However, only with DNA barcoding, we detected elusive but frequent mammalian seed dispersers. The overall networks created by both methods were congruent but the plant species' degree, their interaction frequency and their specialization index (d′) differed.
Our study suggests that DNA barcoding of defecated and regurgitated seeds can be used to construct quantitative seed deposition networks similar to those constructed by focal observations. To improve the overall completeness of seed dispersal networks it might be useful to combine both methods to detect interactions by both birds and mammals. Most importantly, the DNA barcoding method provides information on the post‐dispersal stage and thus on the qualitative contribution of each frugivore for the plant community thereby linking species interactions to regeneration dynamics of fleshy‐fruited plant species.
Impacts of climate change on individual species are increasingly well documented, but we lack understanding of how these effects propagate through ecological communities. Here we combine species ...distribution models with ecological network analyses to test potential impacts of climate change on >700 plant and animal species in pollination and seed-dispersal networks from central Europe. We discover that animal species that interact with a low diversity of plant species have narrow climatic niches and are most vulnerable to climate change. In contrast, biotic specialization of plants is not related to climatic niche breadth and vulnerability. A simulation model incorporating different scenarios of species coextinction and capacities for partner switches shows that projected plant extinctions under climate change are more likely to trigger animal coextinctions than vice versa. This result demonstrates that impacts of climate change on biodiversity can be amplified via extinction cascades from plants to animals in ecological networks.
1. 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. 2. Here, we studied the effects of habitat fragmentation on the seed removal by frugivorous birds and mammals from nine fleshy-fruited plant species in Białowieża 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. 3. 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. 4. 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. 5. 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.
Theory assumes that fair trade among mutualists requires highly reliable communication. In plant-animal mutualisms the reliability of cues that indicate reward quality is often low. Therefore, it is ...controversial whether communication allows animal mutualists to regulate their reward intake. Here we show that even loose relationships between fruit brightness and nutritional rewards (r
= 0.11-0.35) allow birds to regulate their nutrient intake across distinct European plant-frugivore networks. Resident, over-wintering generalist frugivores that interact with diverse plant species select bright, lipid-rich fruits, whereas migratory birds select dark, sugar- and antioxidant-rich fruits. Both nutritional strategies are consistent with previous physiological experiments suggesting that over-wintering generalists aim to maximize their energy intake, whereas migrants aim to enhance the build-up of body fat, their immune response and oxidative status during migration. Our results suggest that animal mutualists require only weak cues to regulate their reward intake according to specific nutritional strategies.
•75% of all insect flower visitor species on wildflower plantings were neither bees nor hoverflies.•Even low levels of flower richness were sufficient to support high visitor richness.•With the ...exception of wild bees, visitor richness was high also in simple landscapes.•Specialist taxa benefit most from establishing multiple locally connected plantings.
One goal of wildflower plantings is to promote biodiversity in intensively managed agricultural landscapes. Flower visitors of wildflower plantings encompass many ecologically and economically important species. However, most studies on flower visitors of wildflower plantings have focused on single or few prominent taxa (e.g., wild bees and hoverflies). In contrast, it remains largely unresolved how non-prominent flower visitors of the community are affected by wildflower resources, landscape context and time of the flowering season. We studied highly diverse flower-visitor communities on 14 wildflower plantings varying in flower abundance and richness and their surrounding landscape context within a 500m radius (percentage arable land, presence of additional wildflower plantings). Flower visitors were sampled in the early (May–June) and late (June–July) flowering season and grouped as follows: managed honeybees, wild bees, hoverflies, all other flower visitors. Strikingly, only 81 (25.1%) of all 322 visiting species (<50.0% of individuals) were bees or hoverflies, and 241 non-prominent ‘other’ visitor taxa were sampled, encompassing many ecologically and economically important species, e.g., parasitic wasps and non-syrphid Diptera. With the exception of honeybee abundance that was positively related to flower abundance, flower abundance and richness of wildflower plantings affected neither abundance nor richness of any visitor group. While a high amount of surrounding arable land decreased species richness of wild bees, richness of all other groups was unaffected. In contrast to the relatively weak abundance and richness responses at the group-level, we found strong species-specific responses to landscape context, resulting in substantial spatial and temporal turnover in community composition. In the early flowering season, wildflower plantings that were accompanied by additional local plantings and embedded within complex landscapes supported the highest abundances of habitat specialists (e.g. Bombus spp.), whereas isolated plantings were predominantly visited by agricultural generalists (e.g. predatory hoverflies and pollen beetles). These compositional differences diminished towards the end of the flowering season. Our study highlights the great conservation potential of wildflower plantings in agricultural landscapes. With the exception of wild bees, wildflower plantings support a high diversity of functionally complementary flower-visitor species from complex to structurally simple agricultural landscapes. These so-far overlooked flower visitors may have the potential to provide complementary ecosystem services and to step-in in agricultural settings where prominent providers have been lost. Assessments of the value of wildflower plantings to biodiversity conservation and agriculture require a shift away from solely focusing on prominent taxa and towards a more holistic appreciation of the entire flower-visitor community.
Species' functional traits set the blueprint for pair-wise interactions in ecological networks. Yet, it is unknown to what extent the functional diversity of plant and animal communities controls ...network assembly along environmental gradients in real-world ecosystems. Here we address this question with a unique dataset of mutualistic bird-fruit, bird-flower and insect-flower interaction networks and associated functional traits of 200 plant and 282 animal species sampled along broad climate and land-use gradients on Mt. Kilimanjaro. We show that plant functional diversity is mainly limited by precipitation, while animal functional diversity is primarily limited by temperature. Furthermore, shifts in plant and animal functional diversity along the elevational gradient control the niche breadth and partitioning of the respective other trophic level. These findings reveal that climatic constraints on the functional diversity of either plants or animals determine the relative importance of bottom-up and top-down control in plant-animal interaction networks.
Diet studies are essential to understand animal ecology and ecosystem dynamics, especially in the case of large omnivores. These studies are particularly relevant in areas where human disturbance is ...intense and, thus, species dietary patterns might change due to the easy accessibility of food resources of human origin, which may hinder the ecosystem services these species provide. We assessed the diet of brown bears (Ursus arctos) by DNA metabarcoding in Tatra National Park (southern Poland), a highly touristic protected area. Brown bears' diet showed a marked seasonality, a characteristic feature of brown bear populations relying on natural foods. Graminoids represented the main food during spring, while fleshy-fruited plants became more important from mid-summer. Fleshy-fruited plants were present in 56% of faeces and during the entire activity period of bears, revealing that fruits play a pivotal role in the feeding ecology of Tatra brown bears. Two berry species, Vaccinium myrtillus and Rubus idaeus, were the most frequently detected (in 42% and 20% of faeces, respectively). The large consumption of fleshy-fruited plants, and particularly of berries, suggests that, despite high levels of human disturbance in the area, brown bears still play a key role as seed dispersers. Management strategies focused on an effective waste management, control of berry picking, strict regulations about human activities in specific areas during sensitive periods in the feeding ecology of bears, and the lack of artificial food provisioning are crucial to ensure the seed dispersal processes and associated ecosystem services that bears and other frugivores provide.
•Human disturbance may disrupt ecosystem services provided by wildlife.•We analyzed brown bears' diet in a highly touristic protected area.•Bears relied mostly on natural foods and fleshy fruits were especially important.•Bears can still be effective seed dispersers in anthropogenic landscapes.•An effective and well-informed management may be key to ensure ecosystem services.
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