1 | INTRODUCTION
Cities are a rapidly growing, emergent habitat type with projected increases to 120 million ha globally by 2030 (McDonald et al. 2018). These human pressures increasingly drive the decline of apex predators at a global scale (Ripple et al. 2014; Young et al. 2016). Similar to apex predators, humans can induce non-consumptive consequences on subordinate species through changes in space and time use (Ciuti et al. 2012; Clinchy et al. 2016). However, humans are unique in their top-down pressures in that they can exert fear effects across trophic levels, superseding hierarchies in natural systems (Smith et al. 2017; Suraci et al. 2019). The resultant heterogeneity of apex predator distribution from human pressures can induce differences in community structure as well as coexistence mechanisms within the carnivore guild (Berger 2007; Muhly et al. 2011; Moll et al. 2018). In urban areas, where spatial overlap among species are inevitable due to the limited amount of habitat available, temporal partitioning may be particularly important for species’ persistence (Adams and Thibault 2006; Santos et al. 2019; Stark et al. 2020).
Urban-rural gradients provide natural experiments for comparisons of ecosystem function between natural and anthropogenic forces (McDonnell and Pickett 1990; Ellington and Gehrt 2019). Thus far, urban-rural gradients have predominantly highlighted changes in physical characteristics (e.g., body size) that can affect ecological interactions, or changes in biodiversity and species composition across taxa (Marzluff 2001; Urban et al. 2006). Although not specifically casted in an urban-rural framework, there are further evidence that humans and built structures can alter animal behavior (Van Donselaar et al. 2018; Avilés-Rodríguez and Kolbe 2019). For example, a global meta-analysis found that intensity of human pressure can drive increased nocturnality and reduce movement (Gaynor et al. 2018; Tucker et al. 2018). Altered time use due to humans can further translate into altered interspecific interactions (Lewis et al. 2015; Gallo et al. 2019). Recasting the implications of urban expansion from the primary focus of degradation to evolutionary potential occurs by considering them as novel ecosystems that have conservation value (Kowarik 2011; Seto et al. 2011; Alberti 2015). We leverage and expand upon the urban-rural gradient formed by human pressure to examine spatiotemporal dynamics between a widely distributed carnivore and a smaller sympatric competitor.
As a highly adaptive mesocarnivore, coyotes exploit a wide range of habitats and exhibit tolerance to disturbance with their diets and microbial community relating such variation across populations (Flores-Morales et al. 2019; Bekoff and Gese 2003; Colborn et al. 2020). Coyotes exemplify mesopredator release through range expansion that aligns with human caused extirpation of wolves. Though coyotes are subordinate to gray wolves where they are sympatric, they are an aggressor species for several smaller carnivores and account for high rates of mortality for some species (e.g., Vulpes velox ,Vulpes macrotis ) (Berger 2007; Bekoff and Gese 2003). As a result, coyotes are commonly cited as a species that can act as both a mesopredator or an apex predator in their community, depending on the presence of the gray wolf (Prugh et al. 2009; Roemer et al. 2009; Colborn et al. 2020). Similarly, raccoons (Procyon lotor) exhibit tolerance to human pressures and spatially overlap through much of the coyotes North American range (Timm et al. 2017; Kays 2018). Coyote-raccoon interactions are interesting because of how widespread both species are, the size difference that should typify intraguild aggression or predation, and yet lack evidence for any sort of spatial or temporal partitioning (Gehrt and Clark 2003; Donadio and Buskirk 2006; Shedden et al. 2020). There has yet to be a study that examines the temporal dynamics of these two species across the urban-rural gradient.
Raccoons exhibit spatiotemporal variation in behavioral attributes, leading us to expect that the response of raccoons to coyotes may vary by differences in habitat and other characteristics across sites (Beasley et al. 2011). Gehrt and Prange (2007) put forth a convincing argument that raccoons and coyotes do not fit into the mesopredator release hypothesis, and there little evidence that coyotes act as a control on the abundance or spatial use of raccoons (Lesmeister et al. 2015). Telemetry studies of raccoons have found some evidence of mortality due to coyotes, but only as a rare occurrence (Gehrt and Clark 2003; Prange et al. 2003). In North Carolina, the temporal use of coyotes and raccoons largely overlapped and that raccoons overall exhibited low levels of vigilance, indicating low levels of fear from coyotes (Chitwood et al. 2020).
Given that coyotes pose some risk to raccoons based on size and sympatry, but that overall risk is low, we tested whether raccoons showed any finer scale shifts in time based on heterogeneity in coyote risk within a site. Employing a camera survey across an urban-rural gradient, we tested whether raccoon time differed between intensities of coyote spatial use. For context, we tested the variation in raccoon time use across two scales: between sites (across the urban-rural gradient) and within site, between years (interannual variation) (Figure 1), with hypotheses that: a) there raccoon time use at the most urban site would be significantly different than at the other three sites, and b) interannual variation would be more least pronounced at the urban site. Based on the strong fear effects that humans can exert on wildlife, we hypothesized that raccoon time use would not shift on the urban end of the gradient, due to activity patterns of both species avoiding peak hours of human activity. Conversely, we hypothesized that raccoons would shift in areas of intense coyote use on the rural end of the spectrum. As anthropogenic pressures increase, our knowledge of contemporary baseline ecological interactions becomes dated. Thus, it becomes essential to understand how these competitive interactions compare across landscapes with varying human pressures.