Relationships between soil macroinvertebrates and nonnative feral pigs (Sus scrofa) in Hawaiian tropical montane wet forests

Abstract

Nonnative feral pigs (Sus scrofa) are recognized throughout the New World as a highly significant introduced species in terms of ecosystem alteration. Similarly, nonnative soil macroinvertebrates (e.g. earthworms, ground beetles) invade and alter the structure and function of native habitats globally. However, the relationship between feral pigs and soil macroinvertebrates remains largely unknown. This study analyzed relationships between these taxa using nine sites located inside and outside of feral pig management units representing a * 25 year chronosequence of removal in tropical montane wet forests in Hawai'i. Soil macroinvertebrates were sampled from plots categorized as: actively trampled by feral pigs, actively rooted by feral pigs, feral pigs present with no signs of recent activity, or feral pigs removed over time. In total, we found 13 families of primarily nonnative soil macroinvertebrates. Plots with active trampling correlated with lower total macroinvertebrate abundance, biomass, and family richness. Plots with active rooting were correlated with higher abundance of nonnative earthworms (Lumbricidae and Megascolicidae) and ground beetles (Carabidae). The abundance, biomass, and biodiversity of macroinvertebrates did not vary with time since feral pig removal. Collectively, these results indicate: (1) trampling by feral pigs negatively influences soil macroinvertebrates; (2) feral pigs either modify habitats while rooting thereby facilitating earthworm and ground beetle habitat use or selectively seek out target prey species of soil macroinvertebrates; and (3) removal of feral pigs has minimal impacts on soil macroinvertebrates over time. These results are important globally due to the broadly overlapping ranges of S. scrofa and nonnative macroinvertebrates.

Invasive Wild Pigs: A Significant Disturbance in Coastal Forests

“…Although studies are scarce, results from predation studies in the Coastal Plain support further study into the soil impacts of invertebrate consumption by wild pigs [29,30,32]. Significant alterations to soil dynamics resulting from the impacts of wild pigs can have cascading effects on soil chemistry and composition, as has been shown in both their native [50,53,54] and non-native range [29,30,36,42,55].…”

“…Urbanization is associated with: increases in soil temperature, soil moisture dynamics, macroinvertebrates such as earthworms, decomposition rates, nitrogen-mineralization, and nitrification rates, and decreases in microinvertebrate populations, fungal communities, stem density, and leaf litter depths are just a few of the impacts of urbanization [10,12,17,21,23,95]. As explored earlier, wild pigs are associated with increases in soil temperature, decomposition rates, macroinvertebrate populations, nitrogen mineralization, and nitrification rates; they also decrease microinvertebrate populations, leaf litter depth, stem density, and alter fungal communities [31][32][33][34][35][36][37][38]40,[45][46][47][48][49][50][51][53][54][55]. As each of these alterations has cascading impacts on soil dynamics and nutrient cycling, these alterations can result in significant alterations to the function of soil as well as to the composition and distribution of vegetation.…”

A comparison of abundance and distribution model outputs using camera traps and sign surveys for feral pigs

“…Feral pigs occupy six continents, having been intentionally introduced by humans for food provisioning and game recreation (Barrios-Garcia and Ballari 2012). They are often referred to as ecosystem engineers, fundamentally altering ecosystems through a suite of impacts on soil properties, plant and animal communities, and hydrological processes (Hone 2002;Nogueira-Filho et al 2009;Cole and Litton 2014;Hess 2016;Wehr 2018). Additionally, feral pigs negatively impact agriculture and livestock production through predation, competition, habitat disturbance and disease transmission (Gentle et al 2015).…”