Ecological impacts of selective logging in the Amazon: lessons from dung beetles

Abstract

Selective logging is one of the main drivers of forest degradation in tropical forests, which makes the understanding of its biological consequences essential to inform conservation strategies associated to timber production in those forests. It is also important to examine whether the most frequently used study designs are likely to reveal the true impacts of human activities, thus provide reliable information to develop effective conservation strategies. This thesis aims to fill these knowledge gaps by using an experimental design known as before-after-control-impact (BACI) to quantify the impacts of selective logging on tropical dung beetles and their ecological functions. The first chapter (Chapter 2) compares to what extent space-for-time (SFT) and before-and-after approaches draw different conclusions regarding the relationship between selective logging intensity and dung beetle species richness and biomass. This chapter shows that SFT studies, the most frequently used approach, may underestimate the impacts of forest degradation on biodiversity. The Chapter 3 investigates the presence of thresholds in dung beetle responses to logging intensity, and whether those would be influenced by the spatial scale at which logging intensity is measured. The results from this chapter show that biological responses to selective logging can be non-linear and scale-dependent. The chapter 4 addresses the role of forest structure in mediating the responses of dung beetles and mediated faecal processes to selective logging occurrence. The results show that changes in the forest structure due to selective logging (here measured as canopy openness) not necessarily explain the negative and disproportionally stronger effects of this disturbance on dung beetle biomass and species richness. Therefore, while highlighting that selective logging did not influence two environmental variables (leaf litter and soil sand content) or dung beetle-mediated faecal consumption and soil bioturbation; this chapter shows that the linkages among these four components were modified after the selective logging. Finally, the last experimental chapter (Chapter 5) examines the amount of body fat of three dung beetle species to investigate for the first time in the literature whether selective logging could induce sublethal effects on tropical invertebrates. The results show that dung beetles sampled within selectively logged forests have a higher proportion of body fat than those from undisturbed forests, which matches with the negative impacts of selective logging on the relative abundance of each examined species. Overall, this thesis discuss about the challenges to conserve the biodiversity and ecosystem functioning in a world where forest degradation rates are increasing every day.