Basin-Wide Effects of Game Harvest on Vertebrate Population Densities in Amazonian Forests: Implications for Animal-Mediated Seed Dispersal

Background

Tropical forest ecosystems rely heavily on animal-plant interactions, especially seed dispersal by vertebrates. In the Amazon, widespread hunting significantly reduces populations of many vertebrate species, particularly large-bodied frugivores that play a key role in dispersing seeds of large-seeded plants. Although some species show greater sensitivity to hunting than others, the overall impact of hunting across the Amazon basin remains poorly quantified. This study aims to understand how subsistence hunting affects vertebrate populations and, in turn, the ecological services they provide—most notably seed dispersal.

Goals and Methods

This study quantifies the effects of subsistence hunting on the population densities of 30 mid-sized to large-bodied vertebrate species in the Amazon and evaluates the consequences for seed dispersal services. The authors conduct a large-scale meta-analysis using data from 101 Neotropical forest sites, comparing vertebrate population densities in hunted and non-hunted areas. They apply both “unnested” (broad comparisons without controlling for habitat variation) and “nested” (paired comparisons within similar habitats) analyses to assess species abundance relative to hunting pressure. They categorize species as seed dispersers or seed predators and analyze how body size and dietary habits influence vulnerability to hunting.

Conclusion

The study reveals that 22 out of 30 species suffer significant population declines in areas with intense hunting pressure. Large-bodied frugivores—such as woolly monkeys, spider monkeys, and forest tortoises—decline by 90–96% in these areas. Body size emerges as the strongest predictor of population decline, with larger species facing the greatest losses. As a result, heavily hunted forests lose critical seed dispersal services, especially for large-seeded plants. The findings underscore the widespread ecological impact of hunting across the Amazon, showing that many forests, though structurally intact, suffer functional degradation due to defaunation.