Elucidating the ecological consequences of defaunation has important implications for managing ecosystems and for our understanding of community and ecosystem ecology. Defaunation results in the loss of large terrestrial herbivores whose ecological functions include suppressing understory vegetation through herbivory and non-trophic, physical plant destruction. A largely uninvestigated and potentially significant consequence of defaunation is the indirect effects on invertebrates that defaunation may have by changing the forest floor environment. Because invertebrates are important for multiple ecosystem processes, it is critical we understand the effects defaunation may have on invertebrate communities. We investigated how defaunation influences: 1) understory vegetation density, 2) terrestrial macroinvertebrate communities, and 3) the rates of three important ecosystem processes (litter decomposition, seed predation, insectivory) and the contribution of macroinvertebrates to these processes conducted a study between faunally-intact and defaunated forests using a nested design of 5 faunally-intact and 6 defaunated sites, each comprised of 3 plots. In each plot we recorded understory leaf cover and, with exclosure experiments, compared seed and insectivory rates and assessed the relative contribution of macroinvertebrates versus vertebrates to these processes. Using exclosure treatments with litterbags, we compared decomposition rates and the relative contribution of fungi and macroinvertebrates to decomposition.
Results/Conclusions:
We found that defaunated sites had drastically fewer termites and denser understory vegetation than intact sites. We also found a positive correlation between web-dwelling spider abundances and understory density. Despite these differences, the ecosystem processes we examined appeared robust to defaunation. Although invertebrates are the dominant drivers of seed predation, insectivory, and decomposition in this system, invertebrates were less functionally important in driving both decomposition and insectivory in defaunated forest relative to faunally-intact forest. Taxa such as fungi, microbial decomposers, and small mammals and birds remaining in defaunated forests may compensate for the functional decline of invertebrates in this system. Our results illustrate the potentially important consequences of large vertebrate loss for understory communities but suggest that functional redundancy between species may reduce negative impacts on some ecosystem processes. We report here a necessary early step in understanding how defaunation impacts life in understory invertebrate communities, and what this implies for ecosystem processes.