Responses of Soil Invertebrate and Bacterial Communities to the Removal of Nonnative Feral Pigs from a Hawaiian Tropical Montane Wet Forest

Abstract

Feral pigs (Sus scrofa) are perhaps the most abundant, widespread, and economically significant large, introduced vertebrate across the Pacific Island region. This species has played a role in the degradation of native ecosystems and the extinction of multiple species of plants and animals on Pacific islands and has negative effects on both the ecotourism and agricultural industries. Despite numerous published studies on feral pigs in the Pacific Island region, some fundamental aspects of feral pig ecology remain poorly characterized, particularly belowground. To address these knowledge gaps, this thesis analyzed relationships between soil macroinvertebrates and microbes and feral pigs using nine sites located inside and outside of feral pig removal units representing a ~25-year environmentally-constrained chronosequence of removal in tropical montane wet forests in Hawai‘i. The results of these studies indicate that areas with active trampling by feral pigs correlate with lower abundance, biomass, and species richness of all soil macroinvertebrates. Comparatively, active rooting correlated with higher abundance and biomass of nonnative earthworms (Lumbricidae and Megascolicidae) and ground beetles (Carabidae). Further, my results indicate an overall increase in the net biodiversity of soil bacterial communities following feral pig removal, with biodiversity positively correlating to time since removal. Comparatively, environmental characteristics, including mean annual temperature and elevation, are better predictors of differences in functional and phylogenetic biodiversity among soil bacterial communities than feral pig removal. Collectively, these results indicate that the removal of feral pigs largely does not affect soil macroinvertebrates but does increase the diversity of bacterial communities, which could increase ecosystem stability.