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1. Nectar robbers and simulated robbing differ in their effects on nectar microbial communities

   https://doi.org/10.1111/1442-1984.12446  

   Luizzi, Victoria J. ; Harrington, Alison H. ; Bronstein, Judith L. ; Arnold, A. Elizabeth ( January 2024 , Plant Species Biology)

   Floral nectar contains microbes that can influence nectar chemistry and pollinator visitation, and these microbial communities can be affected by pollinators in turn. Some flowers are also visited by nectar robbers, which feed on nectar through holes cut in floral tissue. If nectar robbers alter nectar microbial communities, they might have unexpected impacts on pollinator visitation. We investigated whether robbing could affect nectar microbial communities directly, by introducing microbes, or indirectly, by triggering a plant response to floral damage. We applied four treatments to flowers ofTecoma× “Orange Jubilee” (Bignoniaceae) in an arboretum setting: flowers were (1) covered to exclude all visitors; (2) available to both pollinators and nectar robbers and robbed naturally by carpenter bees; (3) available to pollinators only but cut at the base to simulate nectar robbing damage; or (4) available to pollinators only. We found that nectar in flowers accessible to any visitors was more likely to contain culturable microbes than flowers from which visitors were excluded. Microbial community composition and beta diversity were similar across treatments. Among flowers containing culturable microbes, flowers available to pollinators and nectar robbers had higher microbial abundance than flowers with simulated robbing, but there were no differences between flowers available to pollinators and robbers and unwounded flowers from which robbers were excluded. Overall, our results suggest that floral damage can affect some features of nectar microbial communities, but specific effects of nectar robbing are limited compared with the influence of visitation in general.

    

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2. Biotic and abiotic drivers of plant–pollinator community assembly across wildfire gradients

   https://doi.org/10.1111/1365-2745.13530  

   LaManna, Joseph A. ; Burkle, Laura A. ; Belote, R. Travis ; Myers, Jonathan A. ; Bartomeus, ed., Ignasi ( November 2020 , Journal of Ecology)

   Understanding how abiotic disturbance and biotic interactions determine pollinator and flowering‐plant diversity is critically important given global climate change and widespread pollinator declines. To predict responses of pollinators and flowering‐plant communities to changes in wildfire disturbance, a mechanistic understanding of how these two trophic levels respond to wildfire severity is needed.

   We compared site‐to‐site variation in community composition (β‐diversity), species richness and abundances of pollinators and flowering plants among landscapes with no recent wildfire (unburned), mixed‐severity wildfire and high‐severity wildfire in three sites across the Northern Rockies Ecoregion, USA. We used variation partitioning to assess the relative contributions of wildfire, other abiotic variables (climate, soils and topography) and biotic associations among plant and pollinator composition to community assembly of both trophic levels.

   Wildfire disturbance generally increased species richness and total abundance, but decreasedβ‐diversity, of both pollinators and flowering plants. However, reductions inβ‐diversity from wildfire appeared to result from increased abundances following fires, resulting in higher local species richness of pollinators and flowers in burned than unburned landscapes. After accounting for differences in abundance, standardized effect sizes ofβ‐diversity were higher in burned than unburned landscapes, suggesting that wildfire enhances non‐random assortment of pollinator and flowering‐plant species among local communities.

   Wildfire disturbance mediated the relative importance of mutualistic associations toβ‐diversity of pollinators and flowering plants. The influence of pollinatorβ‐diversity on flowering‐plantβ‐diversity increased with wildfire severity, whereas the influence of flowering‐plantβ‐diversity on pollinatorβ‐diversity was greater in mixed‐severity than high‐severity wildfire or unburned landscapes. Moreover, biotic associations among pollinator and plant species explained substantial variation inβ‐diversity of both trophic levels beyond what could be explained by wildfire and all other abiotic and spatial factors combined.

   Synthesis. Wildfire disturbance and plant–pollinator interactions both strongly influenced the assembly of pollinator and flowering‐plant communities at local and regional scales. However, biotic interactions were generally more important drivers of community assembly in disturbed than undisturbed landscapes. As wildfire regimes continue to change globally, predicting its effects on biodiversity will require a deeper understanding of the ecological processes that mediate biotic interactions among linked trophic levels.

    

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3. The dispersal of microbes among and within flowers by butterflies

   https://doi.org/10.1111/een.13239  

   Olson, Malia M. ; Ravikanthachari, Nitin ; Blackwell, Meredith ; Boggs, Carol L. ( March 2023 , Ecological Entomology)

   Floral microbes, including bacteria and fungi, alter nectar quality, thus changing pollinator visitation. Conversely, pollinator visitation can change the floral microbial community.

   Most studies on dispersal of floral microbes have focused on bees, ants or hummingbirds, yet Lepidoptera are important pollinators.

   We asked (a) where are microbes present on the butterfly body, (b) do butterflies transfer microbes while foraging, and (c) how does butterfly foraging affect microbial abundance on different floret structures.

   The tarsi and proboscis had significantly more microbes than the thorax in wild‐caughtGlaucopsyche lygdamus(Lepidoptera: Lycaenidae) andSpeyeria mormonia(Lepidoptera: Nymphalidae).Glaucopsyche lygdamus, a smaller‐bodied species, had fewer microbes thanS. mormonia.

   As a marker for microbes, we used a bacterium (Rhodococcus fascians,near NCBI Y11196) isolated from aS. mormoniathat was foraging for nectar, and examined its dispersal byG. lygdamusandS. mormoniavisiting florets ofPyrrocoma crocea(Asteraceae). Microbial dispersal among florets correlated positively with bacterial abundance in the donor floret. Dispersal also depended on butterfly species, age, and bacterial load carried by the butterfly.

   Recipient florets had less bacteria than donor florets. The nectaries had more bacteria than the anthers or the stigmas, while anthers and stigmas did not differ from each other. There was no differential transmission among floral organs.

   Lepidoptera thus act as vectors of floral microbes. Including Lepidoptera is thus crucial to an understanding of plant–pollinator–microbe interactions. Future studies should consider the role of vectored microbes in lepidopteran ecology and fitness.

    

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4. Pollen transfer networks reveal alien species as main heterospecific pollen donors with fitness consequences for natives

   https://doi.org/10.1111/1365-2745.13520  

   Parra‐Tabla, Víctor ; Alonso, Conchita ; Ashman, Tia‐Lynn ; Raguso, Robert A. ; Albor, Cristopher ; Sosenski, Paula ; Carmona, Diego ; Arceo‐Gómez, Gerardo ; Heard, ed., Matthew ( October 2020 , Journal of Ecology)

   The ecological dynamics of co‐flowering communities are largely mediated by pollinators. However, current understanding of pollinator‐mediated interactions primarily relies on how co‐flowering plants influence attraction of shared pollinators, and much less is known about plant–plant interactions that occur via heterospecific pollen (HP) transfer. Invaded communities in particular can be highly affected by the transfer of alien pollen, but the strength, drivers and fitness consequences of these interactions at a community scale are not well understood.

   Here we analyse HP transfer networks in nine coastal communities in the Yucatan Mexico that vary in the relative abundance of invasive flowers to evaluate how HP donation and receipt varies between native and alien plants. We further evaluate whether HP donation and receipt are mediated by floral traits (e.g. display, flower size) or pollinator visitation rate. Finally, we evaluated whether post‐pollination success (proportion of pollen tubes produced) was affected by alien HP receipt and whether the effect varied between native and alien recipients.

   HP transfer networks exhibit relatively high connectance (c. 15%), suggesting high HP transfer within the studied communities. Significant network nestedness further suggests the existence of species that predominantly act as HP donors or recipients in the community. Species‐level analyses showed that natives receive 80% more HP compared to alien species, and that alien plants donate 40% more HP than natives. HP receipt and donation were mediated by different floral traits and such effects were independent of plant origin (native or alien). The proportion of alien HP received significantly affected conspecific pollen tube success in natives, but not that of alien species.

   Synthesis. Our results suggest that HP transfer in invaded communities is widespread, and that native and alien species play different roles within HP transfer networks, which are mediated by a different suite of floral traits. Alien species, in particular, play a central role as HP donors and are more tolerant to HP receipt than natives—a finding that points to two overlooked mechanisms facilitating alien plant invasion and success within native co‐flowering communities.

    

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5. Nectar compounds impact bacterial and fungal growth and shift community dynamics in a nectar analog

   https://doi.org/10.1111/1758-2229.13139  

   Mueller, Tobias G. ; Francis, Jacob S. ; Vannette, Rachel L. ( February 2023 , Environmental Microbiology Reports)

   Floral nectar is frequently colonised by microbes. However, nectar microbial communities are typically species‐poor and dominated by few cosmopolitan genera. One hypothesis is that nectar constituents may act as environmental filters. We tested how five non‐sugar nectar compounds as well as elevated sugar impacted the growth of 12 fungal and bacterial species isolated from nectar, pollinators, and the environment. We hypothesised that nectar isolated microbes would have the least growth suppression. Additionally, to test if nectar compounds could affect the outcome of competition between microbes, we grew a subset of microbes in co‐culture across a subset of treatments. We found that some compounds such as H₂O₂suppressed microbial growth across many but not all microbes tested. Other compounds were more specialised in the microbes they impacted. As hypothesised, the nectar specialist yeastMetschnikowia reukaufiiwas unaffected by most nectar compounds assayed. However, many non‐nectar specialist microbes remained unaffected by nectar compounds thought to reduce microbial growth. Our results show that nectar chemistry can influence microbial communities but that microbe‐specific responses to nectar compounds are common. Nectar chemistry also affected the outcome of species interactions among microbial taxa, suggesting that non‐sugar compounds can affect microbial community assembly in flowers.

    

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