Artificial light at night causes top‐down and bottom‐up trophic effects on invertebrate populations

Abstract

Globally, many ecosystems are exposed to artificial light at night. Nighttime lighting has direct biological impacts on species at all trophic levels. However, the effects of artificial light on biotic interactions remain, for the most part, to be determined. We exposed experimental mesocosms containing combinations of grassland plants and invertebrate herbivores and predators to illumination at night over a 3‐year period to simulate conditions under different common forms of street lighting. We demonstrate both top‐down (predation‐controlled) and bottom‐up (resource‐controlled) impacts of artificial light at night in grassland communities. The impacts on invertebrate herbivore abundance were wavelength‐dependent and mediated via other trophic levels. White LED lighting decreased the abundance of a generalist herbivore mollusc by 55% in the presence of a visual predator, but not in its absence, while monochromatic amber light (with a peak wavelength similar to low‐pressure sodium lighting) decreased abundance of a specialist herbivore aphid (by 17%) by reducing the cover and flower abundance of its main food plant in the system. Artificial white light also significantly increased the food plant's foliar carbon to nitrogen ratio. We conclude that exposure to artificial light at night can trigger ecological effects spanning trophic levels, and that the nature of such impacts depends on the wavelengths emitted by the lighting technology employed. Policy implications. Our results confirm that artificial light at night, at illuminance levels similar to roadside vegetation, can have population effects mediated by both top‐down and bottom‐up effects on ecosystems. Given the increasing ubiquity of light pollution at night, these impacts may be widespread in the environment. These results underline the importance of minimizing ecosystem disruption by reducing light pollution in natural and seminatural ecosystems.

Artificial light at night at the terrestrial-aquatic interface: Effects on predators and fluxes of insect prey

“…Most have documented increases in predator abundance or body mass in response to ALAN [31,36,37], but others observed reduced abundance or fitness traits. Several studies have shown ALAN confers benefits to invertebrate predators such as terrestrial beetles and spiders [31,34,54]. A decline was observed, however, in the fitness of non-tetragnathid orb-weaver species in the presence of ALAN [55,56].…”

Pollination and fruit infestation under artificial light at night:light colour matters

“…For example, it has been suggested that artificial light at night can have important consequences for plants that have adjusted to natural light–dark cycles 3 . Effects of light at night may as well cascade between trophic levels, for example by changes in herbivory 4 , 5 , which can be both resource and predation controlled 6 . Also, light at night can interfere with the activity and behaviour of nocturnal moths 7 and disrupt plant-pollinator interactions with negative consequences for pollination 8 .…”

Artificial light at night erases positive interactions across trophic levels

“…In particular, results of these studies have emphasized how the suppression of natural light/dark cycles might cause, among others, circadian disruption in birds and invertebrates, loss of orientation in sea turtles, bees and moth, as well as changes in reproductive timing of birds and fish, in plant phenology and in the trophic pressure among terrestrial or aquatic organisms (see Davies & Smyth, , and references therein). Future scenarios are predicted to worsen, with more impacts on individual species, due to a larger sensitivity to blue emissions caused by LEDs (Davies & Smyth, ), and on assemblage dynamics, due to the exacerbation of cascading effects through trophic interactions (Bennie, Davies, Cruse, Inger, & Gaston, ; Manfrin, ; Sanders, Kehoe, Cruse, Veen, & Gaston, ).…”

“…In fact, in contrast to other sources of abiotic stress, ALAN is expected to disrupt natural circadian regulations of organisms, with consequent alteration of the composition and diversity of assemblages, due to differences in light optima and sensitivity among species. In addition, effects can cascade from one organism to another and influence entire habitats, along paths generated by top-down and bottom-up relationships shaping communities (Bennie, Davies, Cruse, Bell, & Gaston, 2018b;Bennie, Davies, Cruse, Inger, & Gaston, 2015;Bennie, Davies, Cruse, Inger, et al, 2018a;Sanders et al, 2018). At this height on the shore, microscopic organisms forming surface biofilms represent the main food resource for grazers on sandy, muddy and rocky shores (Al-Zaidan, 2006;Jenkins et al, 2001;Nagarkar, Williams, Subramanian, & Saha, 2004).…”