Potential trade-offs of our contact-RSF model and limitations in
wild pig systems
Similar to habitat selection, which often varies across different
populations, landscapes, and years because of spatial heterogeneity and
inter-annual changes in environmental suitability (Boyce 1979), a
particular landscape feature may also affect contact in different ways
across different ecosystems. In the FL site, we found selection was
strong for wetlands, but contact was depressed relative to use. However,
in the TX site, female wild pigs tended to avoid wetlands, and wetlands
were neither selected for nor avoided by males. Also, wetlands did not
have a significant impact on female-male and male-male contacts. This is
likely due to the spatial representation of wetlands in this ecosystem
of limited small, seasonal, or ephemeral wetlands (Bailey 1998). Similar
differences in findings of population, landscape, and seasonal-specific
resource selection have been suggested in other species (McCorquodale
2003, BastilleāRousseau and Wittemyer 2019). Thus, scaling up local
contact-RSFs to other landscapes or larger populations requires careful
consideration of landscape-specific factors that may affect both
resource selection and contact patterns.
Challenges to modeling habitat selection with use-available frameworks
are well known, particularly around the definition of availability
(Keating and Cherry 2004, Johnson et al. 2006). Such issues also impact
interpretation of outputs from our application of RSFs to contacts.
Here, availability was defined as the areas where theoretical contacts
between two individuals could occur (i.e., the home range overlap during
the overlapped tracking period), which is different from the
availability sample used in the individual-RSFs (i.e., the home range
during the overlapped tracking period). There are alternative ways to
define the availability in the contact-RSF, such as defining it as the
union of home ranges. This would enable a scale-wise comparison between
contact-RSF and individual-RSF, but logistically, contact could only
occur in the home range overlap areas. Investigating how different
used-available designs impact contact-RSF interpretation will require
further research.
In empirical systems, one limitation is that some between-group contact
events might have resulted from mating behaviors rather than resource
acquisition. The primary mating season in the FL site seemed to be in
August, which is not covered in our study period (Buckley 2021). In TX,
some female wild pigs appeared to be farrowing during the period of this
study (N. P. Snow, Personal observation), and subsequently may have
isolated themselves from conspecifics during that time. Given that there
is a lack of information on timing of reproduction, it was not feasible
for us to filter out interactions driven by mating behaviors in the case
studies.