Factors influencing occupancy dynamics of a carnivore guild

Background/Question/Methods

Bobcats (Lynx rufus), coyotes (Canis latrans), gray foxes (Urocyon cinereoargenteus), and red foxes (Vulpes vulpes) are mesocarnivores that occur sympatrically throughout much of their ranges and are ecologically important.  Although much is known about the habitat associations for these species individually, few studies have assessed covariates influencing occupancy (ψ), detection (ρ), co-occurrence (φ), colonization (γ), and extinction (ε) probabilities of mesocarnivores at large scales.  During January–April 2008–2010, we used remote cameras to conduct 3-week surveys at 1,178 sites in 357 2.6-km² sections (60 sections were surveyed in 2008 and 2010 to assess multi-season dynamics) stratified by the proportion of forest cover throughout the 16 southernmost counties of Illinois, USA (16,096 km²).  We characterized sites by both microhabitat and landscape factors, and analyzed encounter histories in program PRESENCE 3.0 to identify covariates influencing ψ, ρ, φ, γ, and ε. 

Results/Conclusions

Coyotes had the highest overall occupancy estimates (0.79); followed by bobcat (0.64), gray fox (0.25), and red fox (0.21).  In resurveyed sites, bobcat and coyote site occupancy increased from 0.81 to 0.92 (γ = 0.94, ε = 0.10) and 0.71 to 0.90 (γ = 0.81, ε = 0.06), respectively. Conversely, we observed a decrease in sites occupied by gray fox (0.37 to 0.25, γ = 0.15, ε = 0.57) and red fox (0.19 to 0.13, γ = 0.06, ε = 0.54).  Coyote ρ decreased at higher temperatures, but ρ of other species was not affected by measured survey covariates.  Gray fox ψ was positively related to percentage of forest cover, but negatively influenced by basal area and amount of coarse woody debris.  Red fox ψ was lower in sections with more forest cover, and was most strongly associated with human dwellings.  Habitat model selection was complicated for coyotes; however, most competing ψ models had coarse woody debris as a positive covariate.  Occupancy model uncertainty also existed for bobcats, with forest cover (positive) and proximity to human dwellings (negative) being the most influential covariates.  We suggest that presence of larger carnivores influence fox space use, where fox φ is less than expected with coyotes present, and declining fox ψ is correlated with expanding ψ of bobcats and coyotes.  Our study provides insights into the habitat characteristics and interspecific relationships that influence carnivore guild structure at a large spatial scale.