@article{HornBecherJohstetal.2020,
  author    = {Horn, Juliane and Becher, Matthias A. and Johst, Karin and Kennedy, Peter J. and Osborne, Juliet L. and Radchuk, Viktoriia and Grimm, Volker},
  title     = {Honey bee colony performance affected by crop diversity and farmland structure},
  series = {Ecological applications},
  volume    = {31},
  journal   = {Ecological applications},
  number    = {1},
  publisher = {Wiley Periodicals LLC},
  address   = {Washington DC},
  issn      = {1939-5582},
  doi       = {10.1002/eap.2216},
  pages     = {1 -- 22},
  year      = {2020},
  abstract  = {Forage availability has been suggested as one driver of the observed decline in honey bees. However, little is known about the effects of its spatiotemporal variation on colony success. We present a modeling framework for assessing honey bee colony viability in cropping systems. Based on two real farmland structures, we developed a landscape generator to design cropping systems varying in crop species identity, diversity, and relative abundance. The landscape scenarios generated were evaluated using the existing honey bee colony model BEEHAVE, which links foraging to in-hive dynamics. We thereby explored how different cropping systems determine spatiotemporal forage availability and, in turn, honey bee colony viability (e.g., time to extinction, TTE) and resilience (indicated by, e.g., brood mortality). To assess overall colony viability, we developed metrics,P(H)andP(P,)which quantified how much nectar and pollen provided by a cropping system per year was converted into a colony's adult worker population. Both crop species identity and diversity determined the temporal continuity in nectar and pollen supply and thus colony viability. Overall farmland structure and relative crop abundance were less important, but details mattered. For monocultures and for four-crop species systems composed of cereals, oilseed rape, maize, and sunflower,P(H)andP(P)were below the viability threshold. Such cropping systems showed frequent, badly timed, and prolonged forage gaps leading to detrimental cascading effects on life stages and in-hive work force, which critically reduced colony resilience. Four-crop systems composed of rye-grass-dandelion pasture, trefoil-grass pasture, sunflower, and phacelia ensured continuous nectar and pollen supply resulting in TTE > 5 yr, andP(H)(269.5 kg) andP(P)(108 kg) being above viability thresholds for 5 yr. Overall, trefoil-grass pasture, oilseed rape, buckwheat, and phacelia improved the temporal continuity in forage supply and colony's viability. Our results are hypothetical as they are obtained from simplified landscape settings, but they nevertheless match empirical observations, in particular the viability threshold. Our framework can be used to assess the effects of cropping systems on honey bee viability and to develop land-use strategies that help maintain pollination services by avoiding prolonged and badly timed forage gaps.},
  language  = {en}
}
@article{LachmuthHenrichmannHornetal.2017,
  author    = {Lachmuth, Susanne and Henrichmann, Colette and Horn, Juliane and Pagel, J{\"o}rn and Schurr, Frank M.},
  title     = {Neighbourhood effects on plant reproduction},
  series = {The journal of ecology},
  volume    = {106},
  journal   = {The journal of ecology},
  number    = {2},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0022-0477},
  doi       = {10.1111/1365-2745.12816},
  pages     = {761 -- 773},
  year      = {2017},
  abstract  = {Density dependence is of fundamental importance for population and range dynamics. Density-dependent reproduction of plants arises from competitive and facilitative plant-plant interactions that can be pollination independent or pollination mediated. In small and sparse populations, conspecific density dependence often turns from negative to positive and causes Allee effects. Reproduction may also increase with heterospecific density (community-level Allee effect), but the underlying mechanisms are poorly understood and the consequences for community dynamics can be complex. Allee effects have crucial consequences for the conservation of declining species, but also the dynamics of range edge populations. In invasive species, Allee effects may slow or stop range expansion. Observational studies in natural plant communities cannot distinguish whether reproduction is limited by pollination-mediated interactions among plants or by other neighbourhood effects (e.g. competition for abiotic resources). Even experimental pollen supply cannot distinguish whether variation in reproduction is caused by direct density effects or by plant traits correlated with density. Finally, it is unknown over which spatial scales pollination-mediated interactions occur. To circumvent these problems, we introduce a comprehensive experimental and analytical framework which simultaneously (1) manipulates pollen availability and quality by hand pollination and pollinator exclusion, (2) manipulates neighbourhoods by transplanting target plants, and (3) analyses the effects of con- and heterospecific neighbourhoods on reproduction with spatially explicit trait-based neighbourhood models. Synthesis. By manipulating both pollen availability and target plant locations within neighbourhoods, we can comprehensively analyse spatially explicit density dependence of plant reproduction. This experimental approach enhances our ability to understand the dynamics of sparse populations and of species geographical ranges.},
  language  = {en}
}
@article{HornBecherKennedyetal.2016,
  author    = {Horn, Juliane and Becher, Matthias A. and Kennedy, Peter J. and Osborne, Juliet L. and Grimm, Volker},
  title     = {Multiple stressors: using the honeybee model BEEHAVE to explore how spatial and temporal forage stress affects colony resilience},
  series = {Oikos},
  volume    = {125},
  journal   = {Oikos},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0030-1299},
  doi       = {10.1111/oik.02636},
  pages     = {1001 -- 1016},
  year      = {2016},
  abstract  = {The causes underlying the increased mortality of honeybee Apis mellifera colonies observed over the past decade remain unclear. Since so far the evidence for monocausal explanations is equivocal, involvement of multiple stressors is generally assumed. We here focus on various aspects of forage availability, which have received less attention than other stressors because it is virtually impossible to explore them empirically. We applied the colony model BEEHAVE, which links within-hive dynamics and foraging, to stylized landscape settings to explore how foraging distance, forage supply, and "forage gaps", i.e. periods in which honeybees cannot find any nectar and pollen, affect colony resilience and the mechanisms behind. We found that colony extinction was mainly driven by foraging distance, but the timing of forage gaps had strongest effects on time to extinction. Sensitivity to forage gaps of 15 days was highest in June or July even if otherwise forage availability was sufficient to survive. Forage availability affected colonies via cascading effects on queen's egg-laying rate, reduction of new-emerging brood stages developing into adult workers, pollen debt, lack of workforce for nursing, and reduced foraging activity. Forage gaps in July led to reduction in egg-laying and increased mortality of brood stages at a time when the queen's seasonal egg-laying rate is at its maximum, leading to colony failure over time. Our results demonstrate that badly timed forage gaps interacting with poor overall forage supply reduce honeybee colony resilience. Existing regulation mechanisms which in principle enable colonies to cope with varying forage supply in a given landscape and year, such as a reduction in egg-laying, have only a certain capacity. Our results are hypothetical, as they are obtained from simplified landscape settings, but they are consistent with existing empirical knowledge. They offer ample opportunities for testing the predicted effects of forage stress in controlled experiments.},
  language  = {en}
}
@article{BecherGrimmThorbeketal.2014,
  author    = {Becher, Matthias A. and Grimm, Volker and Thorbek, Pernille and Horn, Juliane and Kennedy, Peter J. and Osborne, Juliet L.},
  title     = {BEEHAVE: a systems model of honeybee colony dynamics and foraging to explore multifactorial causes of colony failure},
  series = {Journal of applied ecology : an official journal of the British Ecological Society},
  volume    = {51},
  journal   = {Journal of applied ecology : an official journal of the British Ecological Society},
  number    = {2},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0021-8901},
  doi       = {10.1111/1365-2664.12222},
  pages     = {470 -- 482},
  year      = {2014},
  abstract  = {BEEHAVE offers a valuable tool for researchers to design and focus field experiments, for regulators to explore the relative importance of stressors to devise management and policy advice and for beekeepers to understand and predict varroa dynamics and effects of management interventions. We expect that scientists and stakeholders will find a variety of applications for BEEHAVE, stimulating further model development and the possible inclusion of other stressors of potential importance to honeybee colony dynamics.},
  language  = {en}
}