Animal-mediated seed dispersal is a key ecological process that enhances plant fitness and diversity in tropical forest ecosystems. Large-bodied dispersers, many of which are endangered, are particularly important owing to their ability to disperse large-sized seeds via endozoochory (seed dispersal through defecation following ingestion). In contrast, some small vertebrates, mainly rodents, may also play a crucial role in seed dispersal networks because they disperse small- and large-sized seeds via synzoochory (seed dispersal through scatter-hoarding). Despite their potential importance, few studies have evaluated the role of synzoochrous dispersers in the community-level seed dispersal interactions. Here, we (a) used multiple sampling methods to collect seed dispersal information, (b) described the community-wide seed dispersal network including both endo- and syn-zoochory to assess the relative importance of synzoochory, and (c) examined the contribution of these dispersers to the network robustness.
Field surveys were conducted in Ankarafantsika National Park, northwestern Madagascar, from November 2023 to February 2025. We studied plant-animal interactions by combining the follow four complementary methods: (1) identification of intact seeds in bird and mammal feces, (2) recording videos of interactions captured by motion-triggered cameras, (3) interviews of local residents and (4) literature survey of interaction records. We evaluated how three disperser traits (body mass, the largest seed size that can be handled, and extinction risk) would explain the relative importance of dispersers in the network. We then simulated plant extinction risks based on multiple scenarios of specific-disperser extinction to analyze the effect of extinction on network robustness for original network including both endo- and syn-zoochory, only endozoochory network, and null network.
We found that all disperser traits were relevant to the relative importance of dispersers, whereas the maximum-seed size had the greatest influence on this importance rather than body mass and extinction risk. Simulations of disperser extinction based on body mass showed that the endozoochory network showed lower robustness compared with the original and null networks. These results suggest that synzoochory is critical in maintaining network structure and robustness. Synzoochrous rodents, frugivorous lemurs, and endangered dispersers that could disperse large-sized and various plant seeds play important role in the network. Furthermore, synzoochrous rodents can contribute to maintaining plant diversity after extinction of large-bodied frugivores.