Fungi and Insects Compensate for Lost Vertebrate Seed Predation in an Experimentally Defaunated Tropical Forest

Background

Defaunation disrupts key plant-animal interactions such as seed dispersal and seed predation, triggering cascading effects on plant regeneration, species composition, and carbon storage. While past studies emphasize the negative consequences of losing vertebrate seed dispersers and predators, it remains unclear whether other organisms like fungi and insects can compensate for these losses. This study investigates whether non-vertebrate predators offset the decline of large vertebrate seed predators in a tropical rainforest.

Goals and Methods

The study examines whether fungi, insects, or smaller vertebrates compensate for the absence of large hunted seed predators. Researchers conduct a nested exclusion experiment in a lowland rainforest in Borneo, using fenced plots to isolate the impact of different seed predators. They test five native tree species—four from the dominant Dipterocarpaceae family. The experimental design includes: (1) open control plots accessible to all predators, (2) fenced plots excluding large vertebrates, (3) smaller cages excluding rodents, and (4) treatments with insecticide and fungicide to evaluate the independent effects of insects and fungi. Researchers track seed fate over time to determine how seed predation changes when large vertebrates are absent.

Conclusion

The results show that large vertebrates consume 13–66% of seeds depending on the species, confirming their role as major seed predators. However, when excluded, insects and fungi fully compensate for their absence—maintaining overall seed mortality and keeping seedling recruitment unchanged between defaunated and intact plots. These findings challenge the assumption that defaunation necessarily reduces seed predation and boosts seedling survival. Instead, they reveal that complex ecological interactions can buffer tropical forests against some of the direct impacts of large vertebrate loss.