Abstract
Human activities in protected areas can affect wildlife populations in a similar manner to predation risk, causing increases in movement and vigilance, shifts in habitat use and changes in group size. Nevertheless, recent evidence indicates that in certain situations ungulate species may actually utilize areas associated with higher levels of human presence as a potential refuge from disturbance-sensitive predators. We now use four-years of behavioral activity budget data collected from pronghorn (Antilocapra americana) and elk (Cervus elephus) in Grand Teton National Park, USA to test whether predictable patterns of human presence can provide a shelter from predatory risk. Daily behavioral scans were conducted along two parallel sections of road that differed in traffic volume - with the main Teton Park Road experiencing vehicle use that was approximately thirty-fold greater than the River Road. At the busier Teton Park Road, both species of ungulate engaged in higher levels of feeding (27% increase in the proportion of pronghorn feeding and 21% increase for elk), lower levels of alert behavior (18% decrease for pronghorn and 9% decrease for elk) and formed smaller groups. These responses are commonly associated with reduced predatory threat. Pronghorn also exhibited a 30% increase in the proportion of individuals moving at the River Road as would be expected under greater exposure to predation risk. Our findings concur with the ‘predator shelter hypothesis’, suggesting that ungulates in GTNP use human presence as a potential refuge from predation risk, adjusting their behavior accordingly. Human activity has the potential to alter predator-prey interactions and drive trophic-mediated effects that could ultimately impact ecosystem function and biodiversity.
Highlights
Predators impact prey through two key processes, firstly by directly killing and removing individuals from the population and secondly through the indirect effects of predation risk that result in prey species modifying their behavior [1,2]
Our research focused on two parallel sections of road running north to south along the eastern base of the Teton Range: the Teton Park Road, a 22 km section of paved two lane road, and the 27 km unpaved River Road, accessible only by four-wheel-drive vehicles and running along the Snake River approximately 2–5 km east of the Teton Park Road
Traffic levels differed significantly between the two sites with an average of 2.6 (60.11 SE) vehicles per observation at the Teton Park Road and 0.1 (60.02 SE) vehicles per observation at the River Road
Summary
Predators impact prey through two key processes, firstly by directly killing and removing individuals from the population and secondly through the indirect effects of predation risk that result in prey species modifying their behavior [1,2]. Human disturbance in natural and protected areas has been shown to affect wildlife populations in a similar manner to predation risk, including greater rates of movement and vigilance, reduced foraging, shifting habitat use and increases in group size [15,16,17,18,19]. These behavioral responses result in potential fitness costs as a result of increased energy expenditure, loss of foraging opportunities and the direct impact of physiological stress on reproductive success and survival [15,20]. Anthropogenic disturbance in protected areas exhibits greater spatial and temporal predictability, being largely a function of visitors using defined park infrastructure (e.g. roads and trail networks) during daylight hours
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