Anthropogenic changes to the nighttime environment

Abstract

How the relative impacts of anthropogenic pressures on the natural environment vary between different taxonomic groups, habitats, and geographic regions is increasingly well established. By contrast, the times of day at which those pressures are most forcefully exerted or have greatest influence are not well understood. The impact on the nighttime environment bears particular scrutiny, given that for practical reasons (e.g., researchers themselves belong to a diurnal species), most studies on the impacts of anthropogenic pressures are conducted during the daytime on organisms that are predominantly day active or in ways that do not differentiate between daytime and nighttime. In the present article, we synthesize the current state of knowledge of impacts of anthropogenic pressures on the nighttime environment, highlighting key findings and examples. The evidence available suggests that the nighttime environment is under intense stress across increasing areas of the world, especially from nighttime pollution, climate change, and overexploitation of resources.

Keywords: ecology; light; night; nocturnal; pressures.

Figure 1.

Nighttime and pollution: (a) Artificial light at night affects life history traits. We show effect sizes with postmean and 95% credible interval for each trait from a meta-analysis of biological impacts of artificial light at night. The numbers in parentheses indicate the sample size and the asterisks the significance level, with *p < .05, **p < .01, and ***p < .001. Image: Redrawn from Sanders and colleagues (2021) with permission. (b) Seasonal variation in diurnal patterns of PM_2.5 (particulate matter with diameter less than 2.5 micrometers) in Beijing, China. There were increased nocturnal concentrations in the autumn (the long dashes), winter (the dashes), and spring (the solid lines) and increased diurnal concentrations in summer (the dotted lines). Image: Redrawn from Yao and colleagues (2015) under CC BY 4.0 license. (c) Mean shell size of the planktonic early life (D-veliger) stage of the Mediterranean mussel (Mytilus galloprovincialis) decreases with exposure to a mean lower pH (ocean acidification) since the start of calcification (sampling time was 68 to 72 hours after fertilization). Image: Redrawn from Kapsenberg and colleagues (2018) under CC BY 4.0 license. (d) Fine particulate matter slows down cooling rates in urban areas at night. During a heavy pollution event in Beijing in November 2015 the rate of increase in urban PM_2.5 (the lower dark circles) was greater than rural PM_2.5 (the lower light circles). The increased concentration of fine particulate matter resulted in relatively slower decline in minimum temperature (T_min) in urban areas (the upper dark circles) than rural areas (the upper light circles). Data: Zheng and colleagues (2018). The gray shading and moon silhouettes illustrate periods during which the sun is below the horizon (nighttime).

Figure 2.

Nighttime and climate change: (a) Influence of the seasonal mean maximum and mean minimum temperatures on grain yield of rice in the Philippines. Image: Redrawn from Peng and colleagues (2004); original Copyright 2004 US National Academy of Sciences. Temperature increase (x-axis) is from a nighttime minimum of 22 degrees Celsious (°C) and a daytime maximum of 29°C. (b) Responses of 72 mammal species to climate change. Species with a flexible activity pattern show different responses than expected, whereas diurnal species all decreased their elevational range and flexible and nocturnal species increased their elevational range. Image: Redrawn from McCain and King (2014) with permission. (c) Interacting pressures—interactions between nighttime warming and artificial light at night on the predation of aphids by Coccinella septempunctata. Image: Redrawn from Miller and colleagues (2017) with permission. (d) There was a marked increase in the proportion of hunts (the light circles with a dashed line) and kills (the dark circles with a solid line) made at night relative to day in the Brazilian Amazon at around the time that LED lights became widely available (the vertical gray dashed lines represent the mean and standard deviation of date of uptake of LED flashlights. Image: Redrawn from Bowler and colleagues (2020) under CC BY 4.0 license.

Figure 3.

Nighttime havens: (a) The percentage of flying insects in the gut contents of the invasive cane toad (Rhinella marina) increased under artificial light at night. Image: Redrawn from Komine and colleagues (2020) under CC BY 4.0 license. (b) Human induced increases in nocturnality in five case study species. The boxplots show the median, 25% and 75% quartiles, and minimum and maximum across red-brocket deer (Mazama americana) and subsistence hunting, coyote (Canis latrans) and hiking, sable antelope (Hippotragus niger) and sport hunting, tiger (Panthera tigris) and forest product collection and farming, and wild boar (Sus scrofa) and urban development. Data: Reanalyzed from Gaynor and colleagues (2018) under the Science journals default license. (c) As maximum daytime temperatures increase the African wild dog Lycaon pictus decreases its activity in the day (the light circles) and increases its activity at night (the dark circles). Image: Redrawn from Rabaiotti and Woodroffe (2019) under CC BY 4.0 license. We averaged the mean model estimates and mean standard errors across denning and nondenning periods for daytime (the light dashed lines) and nighttime (the dark dotted lines); the original authors calculated the model estimates using mean values for rainfall and moonlight. (d) Diel patterns in the percentage of time that Bryde's whales (Balaenoptera edeni) spent above 15 meters depth (the maximum ship draught), leaving them at greater risk of ship strikes at night. Image: Redrawn from Soldevilla and colleagues (2017) under CC BY license. The silhouettes were freely downloaded from PhyloPic (www.phylopic.org) under CC0 1.0 Public Domain Dedication.