Quantifying the impact of wild pigs on global biodiversity and the spatiotemporal ecology of feral pigs on Maui, Hawai‘i

Abstract

Wild pigs (Sus scrofa) are one of the most-wide spread terrestrial mammals on the planet and have costly impacts to both natural and managed environments. They were listed as one of the top 100 world’s worst invasive species and have caused precipitous population declines and extinctions of some of the most critically endangered species on the planet. Their ability to function as both a top predator and destructive herbivore has made them a particularly serious threat throughout island ecosystems where species are not evolutionarily adapted to defend against such behaviors. In continental ecosystems, they have been shown to fundamentally alter predator-prey dynamics, compete with native fauna, and cause billions of dollars of environmental damage. Given the extensive body of literature documenting these various threats there remain large gaps in our basic understanding of pig ecology and the extent at which they threaten biodiversity. To address these knowledge gaps, this thesis quantified the extent of wild pig threats to 59,590 terrestrial taxa using the largest species data base available: The International Union for the Conservation of Nature’s Red List. This thesis also analyzed the spatial ecology of feral pigs on Maui over the spring and fall of 2018 using species distribution models. Results from this thesis indicate that wild pigs threaten 672 taxa world-wide, with plant taxa and herpetofauna (amphibians and reptiles) particularly at risk. Wild pigs threaten nearly as many taxa as domestic dogs and feral cats, who are often regarded by the conservation community as the most problematic invasive species to biodiversity. On Maui, the spatial ecology of feral pigs appeared heavily driven by both temporally variable environmental conditions and differences in hunting pressure. Between the spring and fall of 2018 feral pigs significantly shifted from mixed alien forests into sensitive native mesic shrublands. Management efforts to reduce the significant shift of pig abundance into these sensitive native ecosystems are of the utmost concern.