Leveraging multiple data sources to assess competition between introduced wild pigs and native deer

Introduced species have diverse impacts on native wildlife and ecosystems.
Negative effects of introduced species on native species through
competition or amensalism are frequently hypothesized, but challenging to
test in the field, particularly for large vertebrates. Wild pigs (Sus
scrofa) are a widely distributed introduced species that are hypothesized
to compete with native wildlife. We used multiple data sources to evaluate
the strength of negative effects of wild pigs on native black-tailed deer
(Odocoileus hemionus columbianus) by looking at multiple niche dimensions
and fitness consequences for deer. We combined isotopic niche data with
camera surveys that provided density, spatial overlap, and temporal
overlap of deer and wild pigs. We also used cameras to gather data on deer
body condition and reproduction to use as fitness metrics. We evaluated
niche overlap between deer and wild pigs and evaluated if deer fitness was
related to the density of wild pigs. Our results illustrate overlap in
space, time, and isotopic niche between wild pigs and deer. Despite this
overlap, we observed no relationship between wild pig density and deer
body condition or reproduction, suggesting minimal effects of competition
or amensalism on deer. Our results confirm the resource overlap that has
been observed between deer and wild pigs in other systems, but contradict
the perception that wild pigs are negatively affecting deer through
resource competition. We demonstrate that the effects of wild pigs on deer
may be weaker than has previously been thought, depending on the resource
availability. Our approach also provides a framework for going beyond
measuring niche overlap to provide a more thorough understanding of
competition between large vertebrates in a field setting.