Dietary niche variation in an invasive omnivore: the effects of habitat on feral pig (Sus scrofa) resource use in Hawaiʻi

Invasive omnivores may have profound impacts on ecological communities
through diet selection, particularly when their functional roles differ
from those in their native range. While the threat of feral pigs (Sus
scrofa) to native plant communities in Hawai‘i is well known, their
trophic dynamics and the drivers of variation in their diet remain
understudied. We investigated the feral pig trophic niche on Hawai‘i
Island using stable isotopes (13C and 15N) and Bayesian mixing
models to identify drivers of variation in resource use. We also
reconstructed intra-individual variability for six subsampled individuals
to understand temporal variation in resource use and individual diet
specialization. Our results revealed feral pigs on Hawai‘i Island exhibit
a broad trophic niche characterized by diverse diets, with substantial
overlap in resource use across districts and habitats. Differences in
dietary composition in the transition from forest to open habitat were
driven primarily by a decline in invertebrates and an increasing reliance
on resources enriched in 15N, which may reflect a shift in protein sources
with habitat. Pigs in forested areas exhibited a smaller trophic niche
than those in open habitats, largely driven by differences in feeding
strategies and resource availability. Diets for subsampled individuals
varied little, suggesting feral pig resource-use strategies in Hawai‘i
tend to be relatively stable through time. Individual niche-width was
relatively narrow compared to that of feral pigs in Hawai‘i at large,
indicating the relatively wide feral pig dietary niche is characterized by
substantial intraspecific diet specialization, likely as a result of
strong intraspecific competition. Understanding the drivers of feral pig
resource use offers key information for management strategies aimed at
mitigating their ecological impacts in imperiled systems like Hawai‘i.