Seed dispersal effectiveness and plant-bird interaction networks in the Tehuacan Valley

The maintenance of biodiversity in communities is mediated by interactions that influence community structure, including seed dispersal. The aim of this study was to evaluate the seed dispersal effectiveness of fruit-eating bird species in the Tehuacan Valley and assess the extinction risk of both bird and plant species through interaction networks. From June 2022 to July 2024, we conducted monthly observations of bird foraging on 12 plant species in San Juan Raya and 13 plant species in Zapotitlan Salinas. We calculated the seed dispersal effectiveness and constructed quantitative and qualitative interaction networks for both locations. For both sites, we found that few birds were effective seed dispersers. The most effective dispersers in San Juan Raya were Melanerpes hypopolius, Toxostoma curvirostre, and Phainopepla nitens, while in Zapotitlan Salinas, the main dispersers were Mimus polyglottos, T. curvirostre, and P. nitens. Through qualitative analysis of the interaction networks, we determined that plant communities in both locations are moderately fragile. Quantitative network analyses revealed that plants in Zapotitlan Salinas are particularly vulnerable, as most species could face local extinction if they lose their disperser species, potentially disrupting the community structure. In contrast, bird species exhibited a lower degree of specialization. Thus, even if certain plant species are lost, birds could continue to interact with other species or migrate to areas with a greater availability of resources. The extraction of plant species, many of which are used for firewood, could negatively impact seed dispersal, as these plants serve as facilitators for many of the species studied. This could reduce the number of available sites where birds can deposit seeds, decreasing the likelihood of seed germination and the establishment of new individuals, which, in turn, may compromise community structure.