Abstract
Artificial nighttime lights have important behavioral and ecological effects on wildlife. Combining laboratory and field techniques, we identified behaviorally relevant levels of nighttime light and mapped the extent of these light levels across the city of Chicago. We began by applying a Gaussian finite mixture model to 998 sampled illumination levels around Chicago to identify clusters of light levels. A simplified sample of these levels was replicated in the laboratory to identify light levels at which C57BL/6J mice exhibited altered circadian activity patterns. We then used camera trap and high-altitude photographic data to compare our field and laboratory observations, finding activity pattern changes in the field consistent with laboratory observations. Using these results, we mapped areas across Chicago exposed to estimated illumination levels above the value associated with statistically significant behavioral changes. Based on this measure, we found that as much as 36% of the greenspace in the city is in areas illuminated at levels greater than or equal to those at which we observe behavioral differences in the field and in the laboratory. Our findings provide evidence that artificial lighting patterns may influence wildlife behavior at a broad scale throughout urban areas, and should be considered in urban habitat planning.
Highlights
Population growth, economic development, and urbanization have increased the density and extent of artificial lights in natural, seminatural, and urban settings[1,2,3], leading to concerns about “ecological light pollution4.” Though ecologists, astronomers, and other interested parties demonstrate that increases in artificial nighttime light represent a significant component of global change[5,6], a general lack of public concern[7,8] has resulted in limited research to inform antiphotopollution policies[9]
To identify commonly occurring light levels, we used finite mixture models to cluster illumination values across our control points. We used these clusters as reference points to select illumination levels to test in our laboratory experiments
Because our estimated illumination levels reflect only horizontal illumination, and to better approximate an animal roaming through the urban environment, we identified estimated illumination levels for 1,000 randomly sampled points outside building footprints within 300 meters, 500 meters, and 1 kilometer of each camera, computing the mean estimated illumination for each buffer distance and illumination level dividing points using our best-fitting regression tree model
Summary
Population growth, economic development, and urbanization have increased the density and extent of artificial lights in natural, seminatural, and urban settings[1,2,3], leading to concerns about “ecological light pollution4.” Though ecologists, astronomers, and other interested parties demonstrate that increases in artificial nighttime light represent a significant component of global change[5,6], a general lack of public concern[7,8] has resulted in limited research to inform antiphotopollution policies[9]. Light is a powerful and consistent environmental signal that communicates important daily and seasonal changes in an organism’s environment[12,13]. It is associated with numerous biological and ecological impacts, potentially acting as a novel evolutionary selection pressure[14]. While there has been considerable work on artificial nighttime lighting using satellite data to assess habitat erosion at the landscape scale[2,32,33], few studies use remotely sensed data to directly study artificial light’s impacts on wildlife behaviors[34,35]. There are no studies that use such techniques to connect behaviorally relevant artificial light levels observed in laboratory settings to observational data. We use estimates of these levels to assess the degree to which artificial light degrades greenspace within the city
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