Cascading effects of contemporaneous defaunation on tropical forest communities

• Defaunation is associated with lower diversity.
• Defaunation leads to lower seed dispersal, seed predation, and herbivory rates.
• Potential for functional compensation among vertebrates appears limited.

Defaunation, driven by hunting and habitat fragmentation, poses a threat to wildlife in tropical forests worldwide and is expected to have cascading effects on other organisms, particularly plant communities. This review summarizes empirical evidence from 42 studies on the indirect effects of defaunation on plants, focusing on altered plant–animal interactions, the resulting effects on plant population demography, and finally, community-level changes in plant composition and diversity. This review confirms, as previously documented, that larger-seeded species consistently experience reduced primary seed dispersal, and increased seedling aggregation around parent trees, as a result of defaunation. Reduced seed predation and herbivory are also associated with defaunation, in some cases countering the negative effects of reduced dispersal. The net effects of these changes led to either higher or lower seedling recruitment, depending on plant species. Defaunated plant communities show consistent shifts toward lower species richness, higher species dominance, and lower diversity. More research integrating effects of defaunation on all processes from seed dispersal through plant recruitment is required to mechanistically link altered species interactions to changes in recruitment and community composition.