Plant-disperser mutualistic networks

Understanding the role of hornbills in plant-disperser networks

This project aims to understand the relative importance of hornbills and other frugivores as seed dispersers for tree species across a gradient of seed sizes and fruit types using the network approach.

  • Great Hornbill. Picture by Malyasri Bhattacharya/Eastern Himalaya Program

  • Rufous-necked Hornbill with a Lauraceae fruit! Painting by Sartaj Ghuman

  • A sample of seeds that are dispersed by hornbills in Pakke

  • Arillate dehiscent capsular fruit of Chisocheton cumingianus whose seeds are dispersed widely by hornbills

  • Small-seeded fruits of Ilex which are eaten by hornbills

  • Great Hornbill feeding on arillate fruit of Dysoxylum binectariferum. Picture by Aakanksha Rathore/Eastern Himalaya Program

  • Hornbills are often driven locally extinct by high hunting pressures for their meat and other body parts!

  • Our understanding of the impacts of hornbill loss on plants is limited! A freshly shot Rufous-necked Hornbill.

  • Great Hornbill regurgitating seed of Horsfieldia kingii

Coming soon.

People

Partners

  • Hari Sridhar

Funding

  • International Foundation for Science (Sweden)

Publications

  • Journal Article
    2019
    Large frugivores matter: insights from network and seed dispersal effectiveness approaches
    Journal of Animal Ecology https://doi.org/10.1111/1365-2656.13005
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    PDF, 1.15 MB

    We evaluated the role of large avian frugivores in a plant‐disperser community by a) determining whether the plant‐disperser community was modular, with a distinct community of large frugivores (thereby highlighting their importance), b) determining relative qualitative and quantitative roles played by large‐bodied frugivores vis‐à‐vis other frugivores and c) determining impacts of large‐bodied frugivore loss on the plant‐disperser community. The study was carried at a tropical forest site in north‐east India which is part of the Eastern Himalaya Biodiversity Hotspot. We collected tree watch data (2055 h) from 46 tree species, which represented 85% of tree species that are predominantly bird‐dispersed in the area. We found that the plant‐disperser community was modular, with a distinct module of large‐seeded tree species and large frugivores. Intermediate‐sized frugivores such as barbets and bulbuls were the most connected, while large‐sized frugivores, such as hornbills and imperial‐pigeons were moderately well‐connected. Qualitative and quantitative roles played by different dispersers varied across the gradient of frugivore body size. Hornbills, the largest avian frugivores, consumed a significantly greater number of fruits and swallowed larger proportions of fruits compared to other avian groups. In comparison to similar‐sized frugivores, imperial‐pigeons fed on larger‐sized fruits, highlighting their importance for dispersal of large‐seeded plants. Under simulated extinction scenarios, larger extinction cascades weren't necessarily caused by larger frugivores, however, extinctions of certain large‐bodied frugivores (hornbills, imperial‐pigeons) caused extinction cascades. Integrating information from networks and seed dispersal effectiveness approaches enabled a better understanding of large frugivore role in a plant‐disperser community. While large‐bodied frugivores may not be playing a central role in plant‐disperser communities, they are crucial as seed dispersal service providers for large‐seeded plants. In conjunction with the reported local extinctions of large frugivores like hornbills from the south Asian region, this study's findings highlight the irreplaceable quantitative and qualitative impacts that tropical plant communities are likely to experience in the future.

  • Report
    2018
    Understanding impacts of hornbill loss on plants
    Final report submitted to Arunachal Pradesh Forest Department, Itanagar, Arunachal Pradesh towards completion of the research project titled “Understanding Impacts of Hornbill Loss on Plants”.
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    PDF, 21.2 MB

    While large avian frugivores are known to be key dispersers for large-seeded plants, their role in the wider plant-disperser networks is still poorly known. In this study, we evaluate the role of large avian frugivores in plant-disperser communities using network and seed dispersal effectiveness approaches in a tropical forest site in north-east India. We systematically-collected tree watch data from 46 plant species, representing 85 percent of typically bird-dispersed plant species, spanning over 2055 h. We found that the plant-disperser community was modular with a distinct community of large-sized seed plants and frugivores. While intermediate-sized birds such as barbets and bulbuls were the most connected, large-sized dispersers such as hornbills and Imperial-pigeons were moderately well-connected. Imperial-pigeons consistently fed on large-sized fruits, highlighting their importance for dispersal of large-seeded plants. In addition to frugivore-fruit size matching, frugivore dietary choices might play an important role in governing the organization of modules. There was a gradient in qualitative and quantitative roles played by different dispersers, with hornbills removing significantly larger number of fruits and consistently swallowing larger proportions of fruits as compared to other avian groups. Under simulated extinction scenarios, observed networks were far less resilient to disperser loss along a gradient of body size from large to small as compared to extinctions that were random or based on rarity. Given the paucity of information on plant-disperser networks from the South Asian region and reported local extinctions of large frugivores like hornbills, this study is important in highlighting that loss of large avian frugivores might have irreplaceable quantitative and qualitative damages to plant communities.

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