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 human activities—affects tropical forests profoundly. Large frugivores play a key role in seed dispersal, while seed predators influence recruitment success and plant population dynamics. Previous studies focus mainly on how defaunation impacts seed dispersal but often overlook the role of seed predators and potential compensatory ecosystem effects. This study examines how losing both seed dispersers and seed predators simultaneously affects tree recruitment and long-term carbon storage in tropical forests.

Goals and Methods

The researchers investigate recruitment success of the large-seeded tree Cryptocarya mandioccana (Lauraceae) along a defaunation gradient in Brazil’s Atlantic Forest. They study three sites with differing levels of disperser and predator loss: (1) intact forest with full communities of dispersers and predators, (2) moderately defaunated forest missing some large-bodied species, and (3) heavily defaunated forest where only small seed dispersers and predators remain. They also simulate defaunation scenarios to estimate potential long-term effects on tree populations and carbon stocks.

Conclusion

The results show that defaunation increases both seed dispersal limitation and seed predation, causing a dramatic drop in plant recruitment. Tree recruitment decreases by 70.7% to 94.9% due to missing seed dispersers, depending on seed predator loss. Some smaller frugivores—such as howler monkeys and jacutingas—partially compensate for the loss of larger dispersers like muriquis, but this compensation fails to fully sustain seed dispersal services. Furthermore, losing large seed predators such as peccaries allows small rodent populations to rise, increasing net seed mortality by 7% to 30%.