Long-term data reveal equivocal evidence for intraguild suppression among sympatric canids

Interspecific interactions among predators can shape ecological communities across trophic levels, including among predator guilds. The strength and directions of these interactions, however, may vary spatially and temporally in regions undergoing widespread landscape changes (e.g., urbanization, agricultural production). We investigated intraguild effects of coyotes (Canis latrans), a de facto apex predator, and land-cover changes on abundance indices of red foxes (Vulpes vulpes) and gray foxes (Urocyon cinereoargenteus) using two long-term and independent time series: direct observations of canids by archery deer hunters (26 years) and harvest data from canid trappers (41 years) from across Illinois, USA. Abundance indices from both time series for red and gray foxes declined whereas coyote abundance indices increased, suggesting increasing coyote abundance may have led to decreases in fox population abundances. Empirical support among candidate models explaining fox declines was generally equivocal yet differed between fox species. Models including effects of coyote abundance were generally competitive for red foxes and estimated negative coyote effects even after controlling for declining farm size. The empirical support among our landscape hypotheses also varied by species despite increasing forest cover and farm size during our study. The estimated effects of coyote in our study were weaker than reported at more northerly latitudes suggesting that increasing coyote populations may not be fully responsible for observed declines in fox populations in the midwestern USA.