The influence of predators, competitors, and habitat on the use of water sources by a small desert carnivore

Abstract

Free water can influence the ecology of desert species. While the use of free water is influenced by physiological factors (e.g., species-specific water requirements, moisture in forage, temperature), nonphysiological factors, such as habitat characteristics and interspecific interactions, are also important. In fact, for species of concern, interspecific interactions and habitat can be important factors influencing their spatial and temporal use of the landscape and its resources. The kit fox (Vulpes macrotis) is a small carnivore considered to be a species of concern over much of its range, and two of the most important conservation challenges it faces are related to (1) habitat and (2) predation/competition by intraguild species. Our objective was to determine the influence of habitat characteristics, predators (bobcats [Lynx rufus], coyotes [Canis latrans]), and potential competitors (badgers [Taxidea taxus], gray foxes [Urocyon cinereoargenteus]) on the use of water by kit foxes. From June to September 2010-2012, we used remote cameras to monitor carnivores at 63 water sources in the Mojave Desert. We used zero-inflated mixed-effects models and a twostage model selection analysis to evaluate the influence of habitat, predators, and competitors on spatial visits to water by kit foxes. We also assessed temporal avoidance of intraguild predators and competitors by kit foxes at water sources using a coefficient of overlap. We found that visual obscurity, overhead canopy cover, badgers, and coyotes influenced spatial visits of kit foxes. In addition, kit foxes exhibited strong temporal overlap with badgers and bobcats, moderate temporal overlap with gray foxes, and weak temporal overlap with coyotes. Taken together, our study demonstrates that the spatial and temporal use of water sources by kit foxes is dynamic, depending on habitat characteristics and the activity of intraguild predators and competitors.

Can a mesocarnivore fill the functional role of an apex predator?

“…Three out of four mesocarnivores in Fort Hood had significantly lower relative abundance than in Santa Cruz (Figure 4), which may indicate suppression in Fort Hood where coyotes have been released and/or released in Santa Cruz where coyotes are suppressed by pumas, although other factors may affect this as well. This pattern of suppression is commonly observed with large canids in before-and-after studies when apex predators are lost (Brook et al, 2012;Kamler et al, 2003;Newsome & Ripple, 2015) and could be due to direct killing or reduced access to resources (Hall et al, 2021;Palomares & Caro, 1999). It is also possible that the higher number of mesocarnivore species in Fort Hood led to higher competition than in Santa Cruz, which could also affect species' relative abundance.…”

“…Gray foxes spatially avoided coyotes in Santa Cruz and were the only mesocarnivore to have offset temporal activity from coyotes in Fort Hood. Many studies have found such avoidance between canids (Hall et al, 2021; Kamler et al, 2003; Levi & Wilmers, 2012), and it is possible these effects are stronger within closely related species (i.e., taxonomic families; Prugh & Sivy, 2020) rather than being purely body size based. Taken together, these results partially support our hypotheses of what we would observe if coyotes acted as apex predators in Fort Hood, but they strongly support the mesopredator release hypothesis.…”

“…Specifically, we expected coyotes to have higher relative abundance in Fort Hood than in Santa Cruz (Newsome & Ripple, 2015), bobcats to have lower relative abundance, and the other mesocarnivores to have increased or stable relative abundance between Fort Hood and Santa Cruz if coyotes fill the full functional role, and all of the smaller mesocarnivores to have lower relative abundance if coyotes only partially fill it (Newsome & Ripple, 2015). Additionally, smaller mesocarnivores should show spatial and temporal avoidance of coyotes in Fort Hood (Hall et al, 2021), as coyotes are a potential predator and less likely to provide carrion than pumas (Table 1). However, if coyotes do not fill any part of the functional role of an apex predator, we would not expect to see suppression of the smaller mesocarnivores.…”

“…Apex predators also shape the behavior and populations of mesocarnivores through competition due to shared prey (Prugh & Sivy, 2020; Wang et al, 2015). This competition includes direct killing of mesocarnivores (Palomares & Caro, 1999), mediating behavior through fear (e.g., avoidance; Brook et al, 2012; Hayward & Slotow, 2009), and a combination of provisioning food as carrion while also reducing access to other resources (Hall et al, 2021; Prugh & Sivy, 2020; Wilmers et al, 2003). As a result of this competition, mesocarnivores may have reduced abundance (Brook et al, 2012), avoid apex predators spatially and/or temporally (de Satgé et al, 2017; Hall et al, 2021; Hayward & Slotow, 2009), and can be pushed into less desirable habitat, such as high human‐use areas (Di Bitetti et al, 2010; Thinley et al, 2018).…”

“…This competition includes direct killing of mesocarnivores (Palomares & Caro, 1999), mediating behavior through fear (e.g., avoidance; Brook et al, 2012; Hayward & Slotow, 2009), and a combination of provisioning food as carrion while also reducing access to other resources (Hall et al, 2021; Prugh & Sivy, 2020; Wilmers et al, 2003). As a result of this competition, mesocarnivores may have reduced abundance (Brook et al, 2012), avoid apex predators spatially and/or temporally (de Satgé et al, 2017; Hall et al, 2021; Hayward & Slotow, 2009), and can be pushed into less desirable habitat, such as high human‐use areas (Di Bitetti et al, 2010; Thinley et al, 2018). Smaller carnivores may also benefit from apex predator suppression of larger mesocarnivores (Allen et al, 2015; Levi & Wilmers, 2012; Newsome & Ripple, 2015; Wang et al, 2015), as this releases them from similar suppression by the mesocarnivore (a form of mesopredator release; Crooks & Soule, 1999; Levi & Wilmers, 2012; Prugh et al, 2009).…”