Mismatch between risk and response may amplify lethal and non-lethal effects of humans on wild animal populations

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Justine A. Smith, Wildlife, Fish, and Conservation Biology, University of California - Davis, Davis, CA, Kaitlyn M. Gaynor, National Center for Ecological Analysis and Synthesis, University of California - Santa Barbara, Santa Barbara, CA and Justin P. Suraci, Conservation Science Partners, Inc., Truckee, CA

Background/Question/Methods
Human activity has rapidly transformed the planet, leading to declines of animal populations around the world through a range of direct and indirect pathways. Humans have strong numerical effects on wild animal populations, as highly efficient hunters and through unintentional impacts of human activity and development. Human disturbance also induces costly non-lethal effects by changing the behavior of risk-averse animals. Here, we examine how the unique strength of these lethal and non-lethal effects is amplified by mismatches between the nature of risk associated with anthropogenic stimuli and the corresponding response by wild animals. Specifically, we propose a novel framework through which to categorize and test the mechanisms that lead to inappropriate or inadequate risk responses by animals to human stimuli. We also evaluate the fitness and demographic costs of risk-response mismatch and identify avenues for applying this framework to confront modern conservation challenges.
Results/Conclusions
The unique characteristics of cues associated with anthropogenic stimuli include novelty, unreliability, spatiotemporal disconnect, pervasiveness, and diversity. These characteristics explain why and when animals fail to appropriately (a) detect, (b) assess, and (c) respond to both benign and lethal anthropogenic stimuli. The individual costs of over-response to a benign stimulus (Type I error) include reduced reproductive success or effective habitat loss, whereby the cost of under-response to a lethal stimulus (Type II error) is often increased mortality probability. These individual costs can manifest at the population level for endangered species; we report that for many IUCN-listed species, sources of decline reflect significant effects of risk-response mismatch. Conservation measures that can better align animal perception and response with risk and mitigate unintended consequences of human disturbance include intentional habituation to recreation, introduction of more reliable risk cues associated with lethal stimuli, and regulations on noise and light disturbances at the wildland-urban interface.