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

Background

Tropical forest ecosystems depend heavily on animal-plant interactions, particularly seed dispersal by vertebrates. However, widespread hunting in the Amazon has led to a significant decline in populations of many vertebrate species, especially large-bodied frugivores that are crucial for dispersing seeds of large-seeded plant species. While some vertebrate species are more sensitive to hunting than others, the cumulative impact of hunting across the Amazon basin remains poorly quantified. This study seeks to understand how subsistence hunting affects vertebrate populations and, by extension, the ecological services they provide, especially seed dispersal. 

Goals and Methods

The goal of the study was to quantify the effects of subsistence hunting on the population densities of 30 mid-sized to large-bodied vertebrate species in the Amazon and to assess the implications for seed dispersal services. The authors conducted a large-scale meta-analysis using data from 101 Neotropical forest sites, comparing vertebrate population densities between non-hunted and hunted areas. They utilized both “unnested” (broad comparisons without accounting for habitat variation) and “nested” (paired comparisons within similar habitats) analyses to determine changes in species abundance relative to hunting pressure. Species were categorized as seed dispersers or seed predators, and the study examined how body size and dietary habits influenced susceptibility to hunting.

Conclusion

The study found that 22 out of 30 species experienced significant population declines under heavy hunting pressure, with large-bodied frugivores such as woolly monkeys, spider monkeys, and forest tortoises showing declines of 90–96% in intensively hunted areas. Body size was the strongest predictor of population decline; larger species were disproportionately impacted. As a result, seed dispersal services in heavily hunted forests are severely diminished, particularly for large-seeded plant species. The findings highlight the pervasive, basin-wide impact of hunting, showing that many Amazonian forests, although structurally intact, are functionally degraded due to defaunation.