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

Background

Defaunation, primarily caused by overhunting, is known to disrupt critical plant-animal interactions such as seed dispersal and seed predation. This can have cascading effects on plant regeneration, species composition, and even carbon storage. While previous studies have focused on the negative consequences of losing vertebrate seed dispersers and predators, it remains unclear whether other organisms, such as fungi and insects, can compensate for these losses. This study explores whether the decline of large vertebrate seed predators in a tropical rainforest is offset by increased seed predation from non-vertebrate sources, specifically insects and fungi.

Goals and Methods

The study aimed to determine whether fungi, insects, or smaller vertebrates compensate for the loss of large hunted seed predators. Researchers conducted a nested exclusion experiment in a lowland rainforest in Borneo, using fenced plots to isolate the effects of different seed predators. They tested five native tree species, four of which belonged to the dominant Dipterocarpaceae family. The experimental design included: (1) open control plots accessible to all predators, (2) fenced plots excluding large vertebrates, (3) smaller cages to exclude rodents, and (4) additional treatments where insecticide and fungicide were applied to evaluate the independent effects of insects and fungi. By tracking seed fate over time, the researchers assessed whether seed predation rates changed when large vertebrates were removed.

Conclusion

The results showed that large vertebrates were significant seed predators, preying on 13-66% of seeds depending on the species. However, when these large animals were excluded, seed mortality from insects and fungi fully compensated for the lost vertebrate predation. As a result, overall seed survival and seedling recruitment remained unchanged between defaunated and intact plots. These findings challenge previous assumptions that defaunation would necessarily lead to reduced seed predation and increased seedling survival. Instead, the shift from vertebrate to non-vertebrate seed predators suggests that complex ecological interactions can buffer against the direct effects of defaunation.