Abstract
Figs (Ficus spp.) are a diverse taxon of woody plants that play keystone ecological roles. They provide nutritional and aseasonal fruit crops that are consumed by many frugivores, often in times of fruit scarcity. In a mutually beneficial relationship, the plants also benefit from seed dispersal by birds and mammals away from the parent plants enhancing germination and plant recruitment. Here, we assessed the effect of ingestion of Ficus fruit by avian frugivores, compared with manually de-pulped fruit and whole fruits, on seedling emergence and cumulative germination of three Ficus spp. (F. sur, F. lutea and F. natalensis). Fruits of Ficus spp. were fed to Dark-capped Bulbuls Pycnonotus tricolor, Knysna Turacos Tauraco corythaix, Purple-crested Turaco Gallirex porphyreolophus, Red-winged Starlings Onychognathus morio, Speckled Mousebirds Colius striatus and invasive Rose-ringed Parakeets Psittacula krameri. We recorded seed retention time as the time from the ingestion of seeds to the first appearance when excreted by the birds. Seeds removed from excreta, manually de-pulped seeds, and whole fruit were planted concurrently in soil trays in a greenhouse. Seedling emergence was recorded daily, and the proportion of seed germinated was calculated as germination success. Germination success of avian ingested seeds increased significantly compared with seeds in whole fruit and manually de-pulped seeds, except seed germination for F. sur seeds ingested by Dark-capped Bulbuls. Ingested seeds germinated the fastest, followed by seeds in whole fruits and lastly, de-pulped seeds. Ficus sur and F. lutea ingested seeds had higher germination percentages than F. natalensis. Our results showed that ingestion by birds typically improved Ficus seed germination as well as the additional positive effects of seed movement such as long-distance seed dispersal. These findings have important implications with the potential to improve Ficus seed dispersal, promote regeneration and sustain populations of the many vertebrates that depend on fig fruit.
Zusammenfassung
Die Rolle frugivorer Vögel bei Keimung und Verbreitung von Ficus -Arten mit fleischigen Früchten in KwaZulu-Natal, Südafrika
Feigen (Ficus spp.) sind ein diverses Taxon von Gehölzpflanzen, die ökologische Schlüsselrollen innehaben. Sie liefern ein nahrhaftes und jahreszeitübergreifendes Angebot an Früchten, die von zahlreichen Frugivoren verzehrt werden, häufig in Zeiten, in denen es sonst wenige Früchte gibt. Es ist ein Verhältnis zum gegenseitigen Vorteil, denn die Pflanzen profitieren von der Samenverbreitung durch Vögel und Säugetiere fort von den Elternpflanzen, wodurch Keimung und Entwicklung der Jungpflanzen begünstigt werden. Hier untersuchten wir den Effekt des Fruchtverzehrs durch frugivore Vögel auf Saatauflauf und die kumulative Keimrate dreier Ficus-Arten (F. sur, F. lutea und F. natalensis), verglichen mit von Hand entfernten Samen sowie mit ganzen Früchten. Die Früchte diverser Ficus-Arten wurden an Rußkopfbülbüls Pycnonotus tricolor, Helmturakos Tauraco corythaix, Glanzhaubenturakos Gallirex porphyreolophus, Rotschwingenstare Onychognathus morio, Braunflügel-Mausvögel Colius striatus sowie invasive Halsbandsittiche Psittacula krameri verfüttert. Wir erfassten die Darmpassagezeit, das heißt die Zeitspanne zwischen dem Verzehr der Samen bis zum ersten Wiedererscheinen beim Ausscheiden durch die Vögel. Die Samen aus den Ausscheidungen, von Hand vom Fruchtfleisch befreite Samen sowie ganze Früchte wurden zeitgleich in Pflanzschalen in einem Gewächshaus ausgebracht. Das Auflaufen von Keimlingen wurde täglich erfasst und der Anteil gekeimter Samen als Keimerfolg berechnet. Mit Ausnahme von Ficus sur-Samen, welche von Rußkopfbülbüls verzehrt worden waren, stieg der Keimerfolg bei den von Vögeln verzehrten Samen verglichen mit ganzen Früchten und den von Hand vom Fruchtfleisch befreiten Samen signifikant an. Verzehrte Samen keimten am schnellsten, gefolgt von den Samen aus ganzen Früchten und schließlich den aus dem Fruchtfleisch freigelegten Samen. Verzehrte Samen von Ficus sur und F. lutea wiesen höhere Keimraten auf als F. natalensis. Unsere Ergebnisse konnten zeigen, dass der Verzehr durch Vögel die Keimung von Ficus-Samen typischerweise verbesserte, abgesehen vom zusätzlichen Nutzen der Samenverbreitung über weitere Strecken. Diese Erkenntnisse sind von weitreichender Konsequenz durch ihr Potenzial zur Verbesserung der Verbreitung von Ficus-Samen sowie zur Förderung der Regeneration und des Erhalts von Populationen der zahlreichen Wirbeltiere, die von Feigenfrüchten abhängig sind.
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Data availability
Data for this study are available on reasonable request from the authors but belong to the University of KwaZulu-Natal.
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Acknowledgements
Thanks to T. Mjara, E. Ally and M. Nkomo for assisting with experimental setup and data collection.
Funding
We would like to thank the University of KwaZulu-Natal (ZA) and the National Research Foundation (NRF, ZA, Grant 98404) for financial support, especially IAR with a NRF-TWAS African Renaissance bursary. We thank the Ford Wildlife Foundation (ZA) for vehicle support.
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All authors conceived the research idea. CTD sort funding. IAR collected and analysed the data. IAR drafted the manuscript. All authors provided comments and revisions to the manuscript.
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Raji, I.A., Thabethe, V. & Downs, C.T. The role of avian frugivores in the germination and dispersal of fleshy-fruited Ficus species in KwaZulu-Natal, South Africa. J Ornithol 163, 395–404 (2022). https://doi.org/10.1007/s10336-022-01963-8
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DOI: https://doi.org/10.1007/s10336-022-01963-8