Recent studies on mutualistic networks have highlighted the importance of plant–animal interactions in shaping biodiversity, and have prompted calls to focus on the conservation of the structure of interactions. Animal-mediated seed dispersal is an important ecological function in many ecosystems, and the complexity of these interactions at the community level is a good example of species interaction networks. Here, we evaluate the virtually intact seed dispersal network (SDN) of Aldabra Atoll, and use it as a functional baseline for guiding restoration and conservation efforts of plant–frugivore interactions on Rodrigues; both in the Western Indian Ocean. Aldabra is one of the few islands with an almost intact vertebrate fauna, comprising lizards, birds, fruit bats, and giant tortoises. In contrast, Rodrigues has suffered high levels of anthropogenic-mediated vertebrate extinctions, including the majority of its frugivores and several plant species. To construct the SDN of Aldabra, we employed three field methodologies to sample plant–frugivore interactions (“focused approach”): observations, camera traps, and faecal analysis. In addition, we surveyed published and grey literature on plant–frugivore interactions on Aldabra (“literature approach”), and compared it to our focused network. We investigated structural parameters and identified potential drivers and hub species of the SDNs.
Results/Conclusions
We recorded a total of 80 interactions in the field, with 9 frugivores and 29 fleshy-fruited plant species. The focused Aldabra SDN had a connectance of 0.30, was nested (NODF = 64.76, z = 7.06, p < 0.001), and did not show modularity (QB = 0.29, p = 0.88). There was a 40% overlap between the focused- and the literature-derived SDNs, with 40 interactions only recorded in the field, and 22 interactions only recovered from the literature. Notably, the literature increased the number of interactions to 102, highlighting the utility of including such sources when constructing SDNs. Moreover, the literature-derived SDN and the SDN derived from combining both approaches, exhibited structural characteristics similar to the focused SDN. Blue pigeons and Aldabra giant tortoises were the two most central species in the SDNs, and thus, potential drivers of its structure. Closely related species of these two animals have gone extinct on Rodrigues, and we discuss conservation implications for the functional resurrection of biotic interactions in the Rodrigues SDN. Overall, we believe the Aldabra SDN has a great potential as a functional baseline to inform restoration and conservation efforts at the community level on highly degraded islands in the Western Indian Ocean.