A growing number of frugivorous species in tropical forests are facing heightened extinction risks due to habitat loss, overhunting, and other anthropogenic activities. This threatens the maintenance of seed dispersal services, which are relied upon by the majority of tropical plant species. Interactions between frugivores and the fruiting species they consume create complex mutualistic networks that structure and maintain the diversity and regeneration processes of tropical forest plant communities. Understanding how these networks disassemble following the loss of species currently most in danger of extinction is an important part of understanding how tropical forests may be affected by current global change patterns. However, studies on this are limited and existing knowledge on the vulnerability of seed-dispersal networks to coextinction cascades comes almost exclusively from networks restricted to avian frugivores, despite the importance of a diverse suite of non-avian seed dispersers across the tropics. To address this, we used the most comprehensive and taxonomically-diverse plant-frugivore dataset available (a collation of Atlantic Forest studies) and simulated frugivore extinctions predicted by endangerment status, then analyzed consequences on network robustness through secondary extinctions. Further, we evaluated if the effects of removing species according to extinction risk differ from multiple other loss scenarios.
Results/Conclusions
We found a rapid and disproportionate loss of tree species following the removal of endangered frugivores that surpassed other extinction scenarios (random removal, the sequential removal of the most generalistic species, and the sequential removal of the largest-bodied species). Our results indicate that the mechanism behind this pattern is the fact that a large portion of the specialist plants in the Atlantic Forest seed dispersal network rely on frugivores that are currently endangered. Additionally, we found that interaction compensation by resilient frugivores in the absence of endangered frugivores is unlikely because frugivores with currently growing populations and those categorized as ‘Least Concern’ by the IUCN forage on fewer plant species than frugivores with decreasing populations sizes and endangered IUCN statuses. Therefore, protecting endangered species could be critical for maintaining connectivity in tropical forest plant-frugivore networks and their loss may have higher-than-expected consequences for forest regeneration.
