@article{Voulgari‐KokotaAnkenbrandGrimmeretal.2019,
  author    = {Voulgari-Kokota, Anna and Ankenbrand, Markus J. and Grimmer, Gudrun and Steffan-Dewenter, Ingolf and Keller, Alexander},
  title     = {Linking pollen foraging of megachilid bees to their nest bacterial microbiota},
  series = {Ecology and Evolution},
  volume    = {2019},
  journal   = {Ecology and Evolution},
  number    = {9},
  issn      = {00},
  doi       = {10.1002/ece3.5599},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-201749},
  pages     = {10788-10800},
  year      = {2019},
  abstract  = {Solitary bees build their nests by modifying the interior of natural cavities, and they provision them with food by importing collected pollen. As a result, the microbiota of the solitary bee nests may be highly dependent on introduced materials. In order to investigate how the collected pollen is associated with the nest microbiota, we used metabarcoding of the ITS2 rDNA and the 16S rDNA to simultaneously characterize the pollen composition and the bacterial communities of 100 solitary bee nest chambers belonging to seven megachilid species. We found a weak correlation between bacterial and pollen alpha diversity and significant associations between the composition of pollen and that of the nest microbiota, contributing to the understanding of the link between foraging and bacteria acquisition for solitary bees. Since solitary bees cannot establish bacterial transmission routes through eusociality, this link could be essential for obtaining bacterial symbionts for this group of valuable pollinators.},
  language  = {en}
}
@article{SponslerRequierKallniketal.2022,
  author    = {Sponsler, Douglas B. and Requier, Fabrice and Kallnik, Katharina and Classen, Alice and Maihoff, Fabienne and Sieger, Johanna and Steffan-Dewenter, Ingolf},
  title     = {Contrasting patterns of richness, abundance, and turnover in mountain bumble bees and their floral hosts},
  series = {Ecology},
  volume    = {103},
  journal   = {Ecology},
  number    = {7},
  doi       = {10.1002/ecy.3712},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-287199},
  year      = {2022},
  abstract  = {Environmental gradients generate and maintain biodiversity on Earth. Mountain slopes are among the most pronounced terrestrial environmental gradients, and the elevational structure of species and their interactions can provide unique insight into the processes that govern community assembly and function in mountain ecosystems. We recorded bumble bee-flower interactions over 3 years along a 1400-m elevational gradient in the German Alps. Using nonlinear modeling techniques, we analyzed elevational patterns at the levels of abundance, species richness, species β-diversity, and interaction β-diversity. Though floral richness exhibited a midelevation peak, bumble bee richness increased with elevation before leveling off at the highest sites, demonstrating the exceptional adaptation of these bees to cold temperatures and short growing seasons. In terms of abundance, though, bumble bees exhibited divergent species-level responses to elevation, with a clear separation between species preferring low versus high elevations. Overall interaction β-diversity was mainly caused by strong turnover in the floral community, which exhibited a well-defined threshold of β-diversity rate at the tree line ecotone. Interaction β-diversity increased sharply at the upper extreme of the elevation gradient (1800-2000 m), an interval over which we also saw steep decline in floral richness and abundance. Turnover of bumble bees along the elevation gradient was modest, with the highest rate of β-diversity occurring over the interval from low- to mid-elevation sites. The contrast between the relative robustness bumble bee communities and sensitivity of plant communities to the elevational gradient in our study suggests that the strongest effects of climate change on mountain bumble bees may be indirect effects mediated by the responses of their floral hosts, though bumble bee species that specialize in high-elevation habitats may also experience significant direct effects of warming.},
  language  = {en}
}
@article{RequierJowanowitschKallniketal.2020,
  author    = {Requier, Fabrice and Jowanowitsch, Kim K. and Kallnik, Katharina and Steffan-Dewenter, Ingolf},
  title     = {Limitation of complementary resources affects colony growth, foraging behavior, and reproduction in bumble bees},
  series = {Ecology},
  volume    = {101},
  journal   = {Ecology},
  number    = {3},
  doi       = {10.1002/ecy.2946},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-211891},
  pages     = {e02946},
  year      = {2020},
  abstract  = {Resource availability in agricultural landscapes has been disturbed for many organisms, including pollinator species. Abundance and diversity in flower availability benefit bee populations; however, little is known about which of protein or carbohydrate resources may limit their growth and reproductive performance. Here, we test the hypothesis of complementary resource limitation using a supplemental feeding approach. We applied this assumption with bumble bees (Bombus terrestris), assuming that colony growth and reproductive performance should depend on the continuous supply of carbohydrates and proteins, through the foraging for nectar and pollen, respectively. We placed wild-caught bumble bee colonies along a landscape gradient of seminatural habitats, and monitored the colonies' weight, foraging activity, and reproductive performance during the whole colony cycle. We performed supplemental feeding as an indicator of landscape resource limitation, using a factorial design consisting of the addition of sugar water (carbohydrate, supplemented or not) crossed by pollen (protein, supplemented or not). Bumble bee colony dynamics showed a clear seasonal pattern with a period of growth followed by a period of stagnation. Higher abundance of seminatural habitats resulted in reducing the proportion of pollen foragers relative to all foragers in both periods, and in improving the reproductive performance of bumble bees. Interestingly, the supplemental feeding of sugar water positively affected the colony weight during the stagnation period, and the supplemental feeding of pollen mitigated the landscape effect on pollen collection investment. Single and combined supplementation of sugar water and pollen increased the positive effect of seminatural habitats on reproductive performance. This study reveals a potential colimitation in pollen and nectar resources affecting foraging behavior and reproductive performance in bumble bees, and indicates that even in mixed agricultural landscapes with higher proportions of seminatural habitats, bumble bee populations face resource limitations. We conclude that the seasonal management of floral resources must be considered in conservation to support bumble bee populations and pollination services in farmlands.},
  language  = {en}
}
@article{RedlichZhangBenjaminetal.2022,
  author    = {Redlich, Sarah and Zhang, Jie and Benjamin, Caryl and Dhillon, Maninder Singh and Englmeier, Jana and Ewald, J{\"o}rg and Fricke, Ute and Ganuza, Cristina and Haensel, Maria and Hovestadt, Thomas and Kollmann, Johannes and Koellner, Thomas and K{\"u}bert-Flock, Carina and Kunstmann, Harald and Menzel, Annette and Moning, Christoph and Peters, Wibke and Riebl, Rebekka and Rummler, Thomas and Rojas-Botero, Sandra and Tobisch, Cynthia and Uhler, Johannes and Uphus, Lars and M{\"u}ller, J{\"o}rg and Steffan-Dewenter, Ingolf},
  title     = {Disentangling effects of climate and land use on biodiversity and ecosystem services—A multi-scale experimental design},
  series = {Methods in Ecology and Evolution},
  volume    = {13},
  journal   = {Methods in Ecology and Evolution},
  number    = {2},
  doi       = {10.1111/2041-210X.13759},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-258270},
  pages     = {514-527},
  year      = {2022},
  abstract  = {Climate and land-use change are key drivers of environmental degradation in the Anthropocene, but too little is known about their interactive effects on biodiversity and ecosystem services. Long-term data on biodiversity trends are currently lacking. Furthermore, previous ecological studies have rarely considered climate and land use in a joint design, did not achieve variable independence or lost statistical power by not covering the full range of environmental gradients. Here, we introduce a multi-scale space-for-time study design to disentangle effects of climate and land use on biodiversity and ecosystem services. The site selection approach coupled extensive GIS-based exploration (i.e. using a Geographic information system) and correlation heatmaps with a crossed and nested design covering regional, landscape and local scales. Its implementation in Bavaria (Germany) resulted in a set of study plots that maximise the potential range and independence of environmental variables at different spatial scales. Stratifying the state of Bavaria into five climate zones (reference period 1981-2010) and three prevailing land-use types, that is, near-natural, agriculture and urban, resulted in 60 study regions (5.8 × 5.8 km quadrants) covering a mean annual temperature gradient of 5.6-9.8°C and a spatial extent of ~310 × 310 km. Within these regions, we nested 180 study plots located in contrasting local land-use types, that is, forests, grasslands, arable land or settlement (local climate gradient 4.5-10°C). This approach achieved low correlations between climate and land use (proportional cover) at the regional and landscape scale with |r ≤ 0.33| and |r ≤ 0.29| respectively. Furthermore, using correlation heatmaps for local plot selection reduced potentially confounding relationships between landscape composition and configuration for plots located in forests, arable land and settlements. The suggested design expands upon previous research in covering a significant range of environmental gradients and including a diversity of dominant land-use types at different scales within different climatic contexts. It allows independent assessment of the relative contribution of multi-scale climate and land use on biodiversity and ecosystem services. Understanding potential interdependencies among global change drivers is essential to develop effective restoration and mitigation strategies against biodiversity decline, especially in expectation of future climatic changes. Importantly, this study also provides a baseline for long-term ecological monitoring programs.},
  language  = {en}
}
@article{RedlichMartinSteffan‐Dewenter2021,
  author    = {Redlich, Sarah and Martin, Emily A. and Steffan-Dewenter, Ingolf},
  title     = {Sustainable landscape, soil and crop management practices enhance biodiversity and yield in conventional cereal systems},
  series = {Journal of Applied Ecology},
  volume    = {58},
  journal   = {Journal of Applied Ecology},
  number    = {3},
  doi       = {10.1111/1365-2664.13821},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-228345},
  pages     = {507 -- 517},
  year      = {2021},
  abstract  = {Input-driven, modern agriculture is commonly associated with large-scale threats to biodiversity, the disruption of ecosystem services and long-term risks to food security and human health. A switch to more sustainable yet highly productive farming practices seems unavoidable. However, an integrative evaluation of targeted management schemes at field and landscape scales is currently lacking. Furthermore, the often-disproportionate influence of soil conditions and agrochemicals on yields may mask the benefits of biodiversity-driven ecosystem services. Here, we used a real-world ecosystem approach to identify sustainable management practices for enhanced functional biodiversity and yield on 28 temperate wheat fields. Using path analysis, we assessed direct and indirect links between soil, crop and landscape management with natural enemies and pests, as well as follow-on effects on yield quantity and quality. A paired-field design with a crossed insecticide-fertilizer experiment allowed us to control for the relative influence of soil characteristics and agrochemical inputs. We demonstrate that biodiversity-enhancing management options such as reduced tillage, crop rotation diversity and small field size can enhance natural enemies without relying on agrochemical inputs. Similarly, we show that in this system controlling pests and weeds by agrochemical means is less relevant than expected for final crop productivity. Synthesis and applications. Our study highlights soil, crop and landscape management practices that can enhance beneficial biodiversity while reducing agrochemical usage and negative environmental impacts of conventional agriculture. The diversification of cropping systems and conservation tillage are practical measures most farmers can implement without productivity losses. Combining local measures with improved landscape management may also strengthen the sustainability and resilience of cropping systems in light of future global change.},
  language  = {en}
}
@article{MayrKellerPetersetal.2021,
  author    = {Mayr, Antonia V. and Keller, Alexander and Peters, Marcell K. and Grimmer, Gudrun and Krischke, Beate and Geyer, Mareen and Schmitt, Thomas and Steffan-Dewenter, Ingolf},
  title     = {Cryptic species and hidden ecological interactions of halictine bees along an elevational gradient},
  series = {Ecology and Evolution},
  volume    = {11},
  journal   = {Ecology and Evolution},
  number    = {12},
  doi       = {10.1002/ece3.7605},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-238853},
  pages     = {7700 -- 7712},
  year      = {2021},
  abstract  = {Changes of abiotic and biotic conditions along elevational gradients represent serious challenges to organisms which may promote the turnover of species, traits and biotic interaction partners. Here, we used molecular methods to study cuticular hydrocarbon (CHC) profiles, biotic interactions and phylogenetic relationships of halictid bees of the genus Lasioglossum along a 2,900 m elevational gradient at Mt. Kilimanjaro, Tanzania. We detected a strong species turnover of morphologically indistinguishable taxa with phylogenetically clustered cryptic species at high elevations, changes in CHC profiles, pollen resource diversity, and a turnover in the gut and body surface microbiome of bees. At high elevations, increased proportions of saturated compounds in CHC profiles indicate physiological adaptations to prevent desiccation. More specialized diets with higher proportions of low-quality Asteraceae pollen imply constraints in the availability of food resources. Interactive effects of climatic conditions on gut and surface microbiomes, CHC profiles, and pollen diet suggest complex feedbacks among abiotic conditions, ecological interactions, physiological adaptations, and phylogenetic constraints as drivers of halictid bee communities at Mt. Kilimanjaro.},
  language  = {en}
}
@article{LaswayPetersNjovuetal.2022,
  author    = {Lasway, Julius V. and Peters, Marcell K. and Njovu, Henry K. and Eardley, Connal and Pauly, Alain and Steffan-Dewenter, Ingolf},
  title     = {Agricultural intensification with seasonal fallow land promotes high bee diversity in Afrotropical drylands},
  series = {Journal of Applied Ecology},
  volume    = {59},
  journal   = {Journal of Applied Ecology},
  number    = {12},
  doi       = {10.1111/1365-2664.14296},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-311877},
  pages     = {3014 -- 3026},
  year      = {2022},
  abstract  = {The exponential increase in the human population in tandem with increased food demand has caused agriculture to be the global-dominant form of land use. Afrotropical drylands are currently facing the loss of natural savannah habitats and agricultural intensification with largely unknown consequences for bees. Here we investigate the effects of agricultural intensification on bee assemblages in the Afrotropical drylands of northern Tanzania. We disentangled the direct effects of agricultural intensification and temperature on bee richness from indirect effects mediated by changes in floral resources. We collected data from 24 study sites representing three levels of management intensity (natural savannah, moderate intensive and highly intensive agriculture) spanning an extensive gradient of mean annual temperature (MAT) in northern Tanzania. We used ordinary linear models and path analysis to test the effects of agricultural intensity and MAT on bee species richness, bee species composition and body-size variation of bee communities. We found that bee species richness increased with agricultural intensity and with increasing temperature. The effects of agricultural intensity and temperature on bee species richness were mediated by the positive effects of agriculture and temperature on the richness of floral resources used by bees. During the off-growing season, agricultural land was characterized by an extensive period of fallow land holding a very high density of flowering plants with unique bee species composition. The increase in bee diversity in agricultural habitats paralleled an increasing variation of bee body sizes with agricultural intensification that, however, diminished in environments with higher temperatures. Synthesis and applications. Our study reveals that bee assemblages in Afrotropical drylands benefit from agricultural intensification in the way it is currently practiced. However, further land-use intensification, including year-round irrigated crop monocultures and excessive use of agrochemicals, is likely to exert a negative impact on bee diversity and pollination services, as reported in temperate regions. Moreover, several bee species were restricted to natural savannah habitats. To conserve bee communities and guarantee pollination services in the region, a mixture of savannah and agriculture, with long periods of fallow land should be maintained.},
  language  = {en}
}
@article{KoenigKraussKelleretal.2022,
  author    = {K{\"o}nig, Sebastian and Krauss, Jochen and Keller, Alexander and Bofinger, Lukas and Steffan-Dewenter, Ingolf},
  title     = {Phylogenetic relatedness of food plants reveals highest insect herbivore specialization at intermediate temperatures along a broad climatic gradient},
  series = {Global Change Biology},
  volume    = {28},
  journal   = {Global Change Biology},
  number    = {13},
  doi       = {10.1111/gcb.16199},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-276441},
  pages     = {4027 -- 4040},
  year      = {2022},
  abstract  = {The composition and richness of herbivore and plant assemblages change along climatic gradients, but knowledge about associated shifts in specialization is scarce and lacks controlling for the abundance and phylogeny of interaction partners. Thus, we aimed to test whether the specialization of phytophagous insects in insect-plant interaction networks decreases toward cold habitats as predicted by the 'altitude niche-breadth hypothesis' to forecast possible consequences of interaction rewiring under climate change. We used a non-invasive, standardized metabarcoding approach to reconstruct dietary relationships of Orthoptera species as a major insect herbivore taxon along a broad temperature gradient (~12°C) in Southern Germany. Based on Orthoptera surveys, feeding observations, collection of fecal pellets from >3,000 individuals of 54 species, and parallel vegetation surveys on 41 grassland sites, we quantified plant resource availability and its use by herbivores. Herbivore assemblages were richer in species and individuals at sites with high summer temperatures, while plant richness peaked at intermediate temperatures. Corresponding interaction networks were most specialized in warm habitats. Considering phylogenetic relationships of plant resources, however, the specialization pattern was not linear but peaked at intermediate temperatures, mediated by herbivores feeding on a narrow range of phylogenetically related resources. Our study provides empirical evidence of resource specialization of insect herbivores along a climatic gradient, demonstrating that resource phylogeny, availability, and temperature interactively shape the specialization of herbivore assemblages. Instead of low specialization levels only in cold, harsh habitats, our results suggest increased generalist feeding due to intraspecific changes and compositional differences at both ends of the microclimatic gradient. We conclude that this nonlinear change of phylogeny-based resource specialization questions predictions derived from the 'altitude-niche breadth hypothesis' and highlights the currently limited understanding of how plant-herbivore interactions will change under future climatic conditions.},
  language  = {en}
}
@article{KrimmerMartinHolzschuhetal.2022,
  author    = {Krimmer, Elena and Martin, Emily A. and Holzschuh, Andrea and Krauss, Jochen and Steffan-Dewenter, Ingolf},
  title     = {Flower fields and pesticide use interactively shape pollen beetle infestation and parasitism in oilseed rape fields},
  series = {Journal of Applied Ecology},
  volume    = {59},
  journal   = {Journal of Applied Ecology},
  number    = {1},
  doi       = {10.1111/1365-2664.14051},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-258037},
  pages     = {263-273},
  year      = {2022},
  abstract  = {Pollen beetles (Brassicogethes spp.) are the main pests of oilseed rape (OSR, Brassica napus) in Europe and responsible for massive yield losses. Upcoming pesticide resistances highlight the need for other means of crop protection, such as natural pest control. Sown flower fields aim to counteract the decrease of insect biodiversity in agricultural landscapes by providing resources to ecosystem service providers. However, the optimal age and size of flower fields to increase natural pest control is still unclear. We conducted experiments on 31 OSR fields located along a gradient of landscape-scale semi-natural habitat (SNH). OSR fields were located adjacent to flower fields which differed in age, continuity and size, or adjacent to crop fields or calcareous grasslands. Pesticide-free areas were established to examine interactive effects of pesticide use and flower field characteristics. The abundance of pollen beetle adults and larvae, parasitism and superparasitism rates in OSR were recorded at increasing distances to the adjacent sites. Flower fields and calcareous grasslands increased pollen beetle parasitism when compared to OSR fields neighbouring crop fields. The threshold for effective natural pest control of 35\% could be reached in the pesticide-free areas of OSR fields adjacent to calcareous grasslands and flower fields maintained continuously for at least 6 years. In pesticide-sprayed areas, pollen beetle parasitism and superparasitism declined with increasing distance to the adjacent field. Furthermore, flower fields larger than 1.5 ha were able to improve pollen beetle parasitism more than smaller fields. Synthesis and applications. To promote natural pest control in oilseed rape (OSR), large flower fields should be maintained for several years, to create stable habitats for natural enemies. The continuous maintenance of flower fields should be preferred, as ploughing and resowing after 5-6 years decreased the positive effects of the flower fields on natural pest control in adjacent OSR fields. However, pesticide use can abrogate positive effects of flower fields on pollen beetle parasitism. This study highlights that sown flower fields have the potential to increase natural pest control in OSR, but this potential is depending on its age, continuity and size and can be hindered by pesticide use.},
  language  = {en}
}
@article{KohlSteffan‐Dewenter2022,
  author    = {Kohl, Patrick L. and Steffan-Dewenter, Ingolf},
  title     = {Nectar robbing rather than pollinator availability constrains reproduction of a bee-flowered plant at high elevations},
  series = {Ecosphere},
  volume    = {13},
  journal   = {Ecosphere},
  number    = {6},
  doi       = {10.1002/ecs2.4077},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-287141},
  year      = {2022},
  abstract  = {Abiotic factors are generally assumed to determine whether species can exist at the extreme ends of environmental gradients, for example, at high elevations, whereas the role of biotic interactions is less clear. On temperate mountains, insect-pollinated plant species with bilaterally symmetrical flowers exhibit a parallel elevational decline in species richness and abundance with bees. This suggests that the lack of mutualistic interaction partners sets the elevational range limits of plants via a reduction in reproductive success. We used the bee-pollinated mountain plant Clinopodium alpinum (Lamiaceae), which blooms along a continuous 1000-m elevational gradient and has bilaterally symmetrical flowers, as a model to test the predicted parallel elevational decline in flower visitation and seed production. Although the community of flower visitors changed with elevation, the flower visitation rate by the most frequent visitors, bumble bees (33.8\% of legitimate visits), and the overall rate of flower visitation by potential pollinators did not vary significantly with elevation. However, we discovered that nectar robbing by bumble bees and nectar theft by ants, two interactions with potentially negative effects on flowers, sharply increased with elevation. Seed set depended on pollinators across elevations and followed a weak hump-shaped pattern, peaking at mid-elevations and decreasing by about 20\% toward both elevational range edges. Considering the mid- and high elevations, elevational variation in seed production could not be explained by legitimate bee visitation rates but was inversely correlated with the frequency of nectar robbing. Our observations challenge the hypothesis that a decrease in the availability of pollinators limits seed production of bee-flowered plants at high elevations but suggest that an increase in negative interactions (nectar robbing and larceny) constrains reproductive success.},
  language  = {en}
}