Size-Related Differential Seed Predation in a Heavily Defaunated Neotropical Rain Forest

Background

Defaunation, driven by hunting and habitat loss, disproportionately affects medium and large mammals, often leaving behind a residual community dominated by small rodents. This shift in mammal communities can alter seed predation dynamics and impact forest regeneration. In heavily defaunated areas like Los Tuxtlas, Mexico, small rodents have become the primary seed predators. This study investigates whether seed predation patterns differ based on seed size in a highly defaunated forest. Specifically, it examines whether small rodents preferentially consume small seeds while large-seeded species escape predation, potentially influencing seed germination and plant recruitment.

Goals and Methods

The researchers aimed to determine how defaunation alters seed predation and subsequent plant recruitment based on seed size. To test this, they conducted two experiments. First, they used caged rodents (Heteromys desmarestianus) in laboratory conditions to evaluate their seed size preferences. Second, they carried out a field experiment comparing seed predation rates between small-seeded and large-seeded species. Seeds were placed in two treatments: one accessible to predators and one protected by wire mesh exclosures. The effects of predation on germination were also monitored.

Conclusion

The study found that small rodents strongly preferred small seeds, both in laboratory and field conditions. In the field experiment, small, unprotected seeds experienced predation rates 30 times higher than protected ones, while large seeds showed no significant difference between protected and exposed treatments. As a result, small-seeded species had much lower germination rates in exposed conditions, whereas large-seeded species had similar germination regardless of predation exposure. These findings suggest that in heavily defaunated forests, small-seeded plants face increased seed predation pressure, while large-seeded species escape predation and may become more dominant in the seedling layer.