Defaunation of large mammals alters understory vegetation and functional importance of invertebrates in an Afrotropical forest

Abstract

Hunting has reduced or eliminated large-bodied vertebrates in many areas across the tropics, contributing to the global process of defaunation. Elucidating the ecological consequences of hunting has important implications for managing ecosystems and for our understanding of community and ecosystem ecology. We present data collected through a combination of comparative and experimental approaches to assess how faunally-intact and heavily-hunted forests in Gabon differ in understory vegetation structure, macroinvertebrate fauna, ecological processes, and the relative importance of different taxa driving those processes. Our results show that hunted sites had denser understory vegetation and hosted approximately 170 times fewer termites compared to faunally-intact sites. While web-building spiders were positively associated with understory vegetation density, this effect did not translate to significantly higher abundances in heavily-hunted forests. Additionally, the overall rates of decomposition, insectivory, and seed predation/removal on the forest floor appeared robust to both defaunation and the associated increases in understory vegetation density. However, our exclosure experiments revealed that the contribution of invertebrates to decomposition was approximately 25% lower in hunted sites compared to faunally-intact sites. Results suggest potential resilience in this complex ecosystem such that microbial or other taxa not measured in this study may compensate for the reduced functional contribution of invertebrates to decomposition. However, while our results illustrate potential resilience, they also indicate that indirect effects following defaunation, such as increases in the density of understory vegetation, may alter invertebrate communities on the forest floor, with potential consequences for the mechanisms, and therefore the dynamics, driving critical ecosystem processes.