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| Lesmeister, D.B.; Nielsen, C.K.; Schauber, E.M.; Hellgren, E. | |
| Spatial and temporal structure of a mesocarnivore guild in Midwestern North America | |
| 2015 Wildlife Monographs (191): 1-235 | |
Ecological communities are most commonly structured by a mixture of bottom-up processes such as habitat or prey, competition within the same trophic level, and top-down forces from higher trophic levels. Carnivore guilds play a vital role in the broader ecological community by stabilizing or destabilizing food webs. Consequently, factors influencing the structure of carnivore guilds can be critical to ecosystem patterns. Coyotes (_Canis latrans_), bobcats (_Lynx rufus_), gray foxes (_Urocyon cinereoargenteus_), raccoons (_Procyon lotor_), red foxes (_Vulpes vulpes_), and striped skunks (_Mephitis mephitis_) occur sympatrically throughout much of their geographic ranges in North America and overlap in resource use, indicating potential for interspecific interactions. Although much is known about space use, habitat relationships, and activity patterns of the individual species separately, little is known about factors that facilitate coexistence and how interactions within this guild influence distribution, activity, and survival of the smaller carnivores. For example, gray fox populations appear to have declined in Illinois since the early 1990s and it is unknown if the increase in bobcat and coyote populations during the same time period is the cause. We conducted a large-scale noninvasive carnivore survey using an occupancy modeling framework to quantify factors affecting the structure of this widely-occurring carnivore guild. We used baited remote cameras during 3- week surveys to detect carnivores at 1,118 camera-points in 357 2.6-km2 sections (clusters of 3- 4 cameras/section) in the 16 southernmost counties of Illinois (16,058 km2) during January- April, 2008-2010. We collected microhabitat data at each camera-point and landscape-level habitat data for each camera-cluster. In a multi-stage approach, we used information-theoretic methods to develop and evaluate models for detection, species-specific habitat occupancy, multispecies co-occupancy, and multi-season (colonization and extinction) occupancy dynamics. We developed hypotheses for each species regarding the occupancy of areas based on anthropogenic features, prey availability, landscape complexity, and vegetative landcover. We used photographic data, Poisson regression, and mixed-model logistic regression to quantify temporal activity of carnivores in the study area and how interspecific factors influence temporal patterns of activity. Of the 102,711 photographs of endothermic animals we recorded photographs of bobcats (n = 412 photographs), coyotes (n = 1,397), gray foxes (n = 546), raccoons (n = 40,029), red foxes (n = 149) and striped skunks (n = 2,467). Bobcats were active primarily during crepuscular periods, and their activity was reduced with precipitation and higher temperatures. The probability of detecting bobcats at a camera point decreased after a bobcat photograph was recorded, suggesting avoidance of remote cameras. Across southern Illinois, bobcat occupancy at the camera-point and camera-cluster scale (Ÿå. point = 0.24 ñ 0.04, camera-cluster Ÿå. cluster = 0.75 ñ 0.06) was negatively influenced by anthropogenic features and infrastructure. Bobcats had highrates of colonization (Ÿµ. = 0.86) and low rates of extinction (ŸÇ. = 0.07) during the study, suggesting an expanding population, but agricultural land was less likely to be colonized. Nearly all camera clusters were occupied by coyotes (Ÿå. cluster = 0.95 ñ 0.03) during the entire study. At the camerapoint scale, coyote occupancy (overall Ÿå. point = 0.58 ñ 0.03) was higher in hardwood forest stands with open understories than in other habitats. Compared to coyotes, gray foxed occupied a lower portion of the study area (Ÿå. point = 0.13 ñ 0.01, Ÿå. cluster = 0.29 ñ 0.03) at all scales. At the camera-cluster scale, gray fox occupancy was highest in spatially-complex areas with high proportions of forest, and positively related to anthropogenic features within 100% estimated home-range buffers. Red foxes occupied a similar proportion of the study area as gray foxes (Ÿå. point = 0.12 ñ 0.02, Ÿå. cluster = 0.26 ñ 0.04), but were more closely associated with anthropogenic features. Indeed, at all three scales of red fox occupancy analysis, only anthropogenic feature models occurred in the 90% confidence set. Camera-cluster extinction probabilities were higher for both gray foxes (ŸÇ. = 0.57) and red foxes (ŸÇ. = 0.35) than their colonization rates (gray fox Ÿµ. = 0.16, red fox Ÿµ. = 0.06), suggesting both species may be declining in southern Illinois. Striped skunks occupied a large portion of the study area (Ÿå. point = 0.47 ñ 0.01, Ÿå. cluster = 0.79 ñ 0.03) and were associated primarily with anthropogenic features, especially if the features were surrounded by agricultural land and not forest. Raccoons were essentially ubiquitous within the study area, being photographed in 99% of camera clusters. In some instances, the presence of other carnivores appeared to be an important factor in the occupancy of the 4 smaller species, but in general, habitat models were more supported than co-occurrence models. Habitat had a stronger influence on the occupancy of gray foxes and red foxes than did the presence of bobcats. However, the level of red fox activity was negatively correlated with bobcat activity. Gray fox occupancy and level of activity were reduced in camera-clusters occupied by coyotes, but were not related to bobcat occupancy. When not considering the presence of coyotes, gray foxes appeared to use camera points with fewer hardwood and more conifer trees, which was counter to previous findings. However, when adding the effect of coyote presence, gray fox Ÿåpoint models indicated a positive relationship with hardwood stands. Therefore, gray foxes were more likely to occupy camera points in hardwood stands than conifer stands if coyotes were also present; suggesting that hardwood stands may enhance gray fox-coyote coexistence. The 2 fox species appeared to co-occur with each other at the camera-point scale more frequently than expected on the basis of their individual selection of habitat. Similarly, camerapoint occupancy of red foxes was higher when coyotes were present. These apparent canid associations may be a response to locally-high prey abundance or an unmeasured habitat variable. Activity levels of raccoons, bobcats, and coyotes were all positively correlated. Collectively, our results suggest that although gray foxes and red foxes currently coexist with bobcats and coyotes, the foxes have reduced activity in the areas occupied by larger carnivores, especially when bobcats and coyotes are highly active. Further, hardwood stands may contain trees with structure that enhances tree-climbing by gray foxes, a behavior that probably facilitates coexistence with coyotes. Therefore, efforts to manage gray foxes should focus on maintaining and increasing the amount of mature oak-hickory forest. Additionally, the varying results from different scales of analyses underscore the importance of considering multiple spatial scales in carnivore community studies. |
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