Synergistic Effects of Seed Disperser and Predator Loss on Recruitment Success and Long-Term Consequences for Carbon Stocks in Tropical Rainforests

Background

Defaunation—the loss of animal species due to hunting, habitat destruction, and other anthropogenic activities—has far-reaching consequences for tropical forests. Large frugivores play a crucial role in seed dispersal, while seed predators influence recruitment success and plant population dynamics. Previous studies have primarily focused on how defaunation affects seed dispersal, often overlooking the role of seed predators and potential compensatory effects within ecosystems. This study examines how the simultaneous loss of seed dispersers and seed predators affects tree recruitment and long-term carbon storage in tropical forests.

Goals and Methods

The researchers investigated the recruitment success of the large-seeded tree Cryptocarya mandioccana (Lauraceae) across a gradient of defaunation in the Atlantic Forest of Brazil. They studied three sites with varying levels of seed disperser and predator loss: (1) an intact forest with a full community of dispersers and predators, (2) a moderately defaunated forest missing some large-bodied species, and (3) a heavily defaunated forest where only small seed dispersers and predators remained.  Researchers also simulated defaunation scenarios to estimate potential long-term effects on tree populations and carbon stocks.

Conclusion

The results demonstrated that defaunation increased both seed dispersal limitation and seed predation, leading to a dramatic reduction in plant recruitment. Depending on the level of seed predator loss, tree recruitment decreased by 70.7% to 94.9% due to the absence of seed dispersers. While some smaller frugivores (such as howler monkeys and jacutingas) compensated for the loss of larger dispersers (like muriquis), this compensation was insufficient to fully maintain seed dispersal services. Additionally, the loss of large seed predators such as peccaries led to a rise in small rodent populations, increasing net seed mortality by 7% to 30%.