COS 198-5 - Environmental drivers of seasonal shifts in abundance of wild pigs (Sus scrofa) in a tropical island environment

Background/Question/Methods

Wild pigs (Sus scrofa) threaten sensitive flora and fauna, cost billions of dollars in economic damage, and pose a significant human-wildlife conflict risk. Surprisingly, basic life history information is often lacking in their introduced range, making it difficult to develop management strategies tailored to their biological requirements. Similar to other large terrestrial mammals, pigs possess the ability to shift their range based on local climatic conditions or resource availability. However, seasonal shifts in resource selection may differ between temperate and tropical environments further complicating management decisions. The objectives of this study were to (i) model the distribution and abundance of wild pigs throughout a single calendar year; (ii) determine the most important environmental variables driving changes in pig distribution and abundance; and (iii) highlight key differences between seasonal models and their potential implications for the management of the species. These study objectives were achieved using zero-inflated models constructed from abundance data obtained from extensive field surveys and remotely sensed environmental variables. These data were collected across an elevational gradient ranging from sea level to 9,000 ft covering both tropical and temperate climates on the island of Maui, Hawaiʻi.

Results/Conclusions

Our models demonstrate a considerable change in the distribution and abundance of wild pigs throughout a single calendar year and identify the most important variables driving those changes. We show that rainfall and vegetation height were among the most influential variables for pig distribution during the spring and distance to adjacent forest and vegetation density were among the most significant for the fall. Further, our seasonal models show that areas of high conservation value may be more vulnerable to threats from wild pigs at certain times throughout the year, an outcome which was not captured by more traditional modeling approaches. Our results suggest that (i) wild pigs can considerably shift their range throughout a calendar year, even in tropical environments, (ii) pigs prefer dense forested areas in the presence of either hunting pressure or an abundance of frugivorous plants, but may shift to adjacent areas in the absence of these conditions and (iii) seasonal models provide valuable biological information that would otherwise be missed by more common modeling approaches. These findings highlight the importance of considering biologically relevant time scales that provide key information to better inform management strategies, particularly for species whose ranges include both temperate and tropical environments.