Carnivore coexistence in Chicago: niche partitioning of coyotes and red foxes

Abstract

Mesopredators including coyotes (Canis latrans) and red foxes (Vulpes vulpes) often co-occur in urban environments, but how niche partitioning facilitates their coexistence remains unclear. Highly urbanized areas can be spatial refuges for smaller mesopredators (i.e., spatial human shield effect), however these species also may coexist through temporal niche partitioning. We used camera traps (n = 110 sites) across an urbanization gradient in Chicago to examine coyote-fox interactions from 2011 to 2018. We analyzed spatial partitioning through multi-season occupancy models and structural equation modeling (SEM), and quantified temporal overlap between canids and with humans. Coyotes most often occurred in natural areas, and urbanization reduced their colonization rates and increased their extinction rates. Initial occupancy for red foxes was negatively impacted by urbanization, but their extinction rates depended on a surprising interaction between coyotes and humans. When coyotes were rare, fox extinction was related positively to human activity; but when coyotes were more common, fox extinction was related negatively to human activity. This outcome may reflect a human shield effect at a within-site scale. The SEM further supported the negative impact of urbanization on both canids, and lack of an effect of coyotes on the distribution of foxes. Diel activity of coyotes and red foxes indicated temporal niche partitioning intensified at more urbanized sites. Our results suggest the spatial human shield effect is not operating across sites in Chicago. Instead, coyotes and red foxes may share green spaces, especially in highly urbanized areas, where species coexistence is promoted by temporal niche partitioning.

Generalized nonlinearity in animal ecology: Research, review, and recommendations

“…Specifically, a “human shield” effect might reduce the interference competition experienced by foxes from coyotes, which are more human averse and therefore less abundant in more developed locations that foxes readily inhabit (Moll et al., 2018 ). However, this relationship does not always cleanly manifest (Cervantes et al., 2023 ; Mueller et al., 2018 ), suggesting that a nonlinear relationship among these variables could be present. Thus, these species act as a useful case study to explore nonlinearity in a GLM framework by extending a traditional GLM to a GAM.…”

“…Specifically, a "human shield" effect might reduce the interference competition experienced by foxes from coyotes, which are more human averse and therefore less abundant in more developed locations that foxes readily inhabit (Moll et al, 2018). However, this relationship does not always cleanly manifest (Cervantes et al, 2023;Mueller et al, 2018), suggesting that a nonlinear relationship among F I G U R E 2 Results of a literature review of studies published between 2018 and 2022 in five leading ecological journals. The pie chart shows the proportion of studies (out of a total of 162) that included transformations of independent variables, multicoefficient models (abbreviated "multi-coef," in figure; these included models with more than one coefficient for an independent variable), both, or neither.…”