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, Bastille‐Rousseau 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.