Fear, human shields and the redistribution of prey and predators in protected areas

Abstract

Protected areas form crucial baselines to judge ecological change, yet areas of Africa, Asia and North America that retain large carnivores are under intense economic and political pressures to accommodate massive human visitation and attendant infrastructure. An unintended consequence is the strong modulation of the three-way interaction involving people, predators and prey, a dynamic that questions the extent to which animal distributions and interactions are independent of subtle human influences. Here, I capitalize on the remarkable 9-day synchronicity in which 90% of moose neonates in the Yellowstone Ecosystem are born, to demonstrate a substantive change in how prey avoid predators; birth sites shift away from traffic-averse brown bears and towards paved roads. The decade-long modification was associated with carnivore recolonization, but neither mothers in bear-free areas nor non-parous females altered patterns of landscape use. These findings offer rigorous support that mammals use humans to shield against carnivores and raise the possibility that redistribution has occurred in other mammalian taxa due to human presence in ways we have yet to anticipate. To interpret ecologically functioning systems within parks, we must now also account for indirect anthropogenic effects on species distributions and behaviour.

Figure 1

(a) Location of Grand Teton National Park (red outline) within (inset) Greater Yellowstone Ecosystem (GYE), paved roads (black lines) and relative concentrations of brown bears (high density, stippled overlay). (b) (i) Newborn and (ii) calf and mother with highway and drainage fence. (c) Eight-month-old calf remains with immobile mother during recollaring.

Figure 2

(a) Dates (±1 s.d.) of 90% most clumped moose births. (b) Relationships between birth sites (log median distance) and a paved road on the date of birth (r²=0.73; p<0001) in relationship to expanding brown bears (r²=0.814; p<0001). Circles, log distance to road; squares, bears per month. N is the number of females giving birth in high-density brown bear area.