Modeling the spatial effects of disturbance: a constructive critique to provide evidence of ecological thresholds

Journal Article

Title: Modeling the spatial effects of disturbance: a constructive critique to provide evidence of ecological thresholds
Publication Date:
June 05, 2017
Journal: Wildlife Biology
Volume: 2017
Publisher: Nordic Board for Wildlife Research
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Citation

Powell, L.; Brown, M.; Smith, A.; Harrison, J.; Whalen, C. (2017). Modeling the spatial effects of disturbance: a constructive critique to provide evidence of ecological thresholds. Wildlife Biology, 2017.
Abstract: 

Biologists and conservation planners are frequently asked to evaluate the spatial effects of anthropogenic disturbance on species of conservation concern. The linear response of a demographic parameter, such as survival or abundance, to the distance-from-disturbance is often used to inform spatial restrictions on development. The linear response, we argue, does not model the most common biological mechanisms that cause changes to demographic parameters, nor does it provide an estimate of a threshold that planners could use to protect species of concern. In the Great Plains of North America, biologists are increasingly concerned about the impact of energy development on populations of four species of grouse. To address this gap in our ability to properly assess distance thresholds, we developed a framework of four response patterns (null, linear, stair step, ramped) to describe the potential effects of a disturbance on biological processes relevant to nesting grouse located along a gradient from the disturbance. We simulated position and survival of grouse nests along a 25-km disturbance gradient to mimic the response to disturbances. We evaluated the relative support for a set of linear and nonlinear models in a known fate analysis of nest survival. Each of the underlying response patterns was detected with an appropriate model in a model selection framework (ωAIC = 0.61–0.75) when the sample size of nests was high (n = 500), and thresholds were identified when present. In a low sample size scenario (n = 50 nests) that may be typical of shortterm empirical sampling schemes, the stair step threshold was detected, but the more complex, ramped threshold was not detected. We provide recommendations regarding study design and inference for ecological and policy thresholds, and we encourage researchers to be cautious about the manner in which threshold responses are assessed and described.

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