The truth about cats and dogs: Landscape composition and human occupation mediate the distribution and potential impact of non-native carnivores

Humans alter landscapes and native species distributions in many ways, including alterations mediated via domestic pets. While the negative impacts of domestic cats are well documented worldwide, the ecological effects of domestic dogs have received less scientific attention, particularly in the United States. Prevalence of free-ranging dogs may be especially problematic in areas with low density, but relatively ubiquitous human populations. We used camera-trap data collected during a 2008-2010 landscape-scale study consisting of 1181 camera stations (357 camera clusters) stratified over 16 counties in southern Illinois, USA, to estimate occupancy for domestic cats and dogs. We compared models of occupancy for three land cover types (forest, grassland, and wetland) in relation to anthropogenic features and estimated and compared the proportion of the region occupied by each species. Cats occurred across a moderate proportion of the landscape (ψ¯  = 0.44 ± 0.13 SE) and were associated with anthropogenic features. Moreover, we found domestic dog occupancy was greater across the landscape (ψ¯  = 0.59 ± 0.09), influenced more generally by land cover type, and was highest on grasslands and privately owned land. Domestic cat occupancy was more localized than that of dogs and less influenced by land cover type compared to anthropogenic features. Model averaged probability of dog occupancy was >0.50 across 19,049.39 km2 of the region (>99%), but only 2270.53 km2 (11.8%) for cats. Thus, while domestic cats may pose a more intensive threat to wildlife within the area they occupy, the impact of domestic dogs is likely to be more geographically extensive. Predicting the potential effects of these non-native species is complicated by a nuanced interaction between landscape composition, human density, and human behavior, and upends simplistic perceptions of the relative threats posed by the two species.