A recent study has revealed something alarming: artificial light pollution may be more damaging to the environment than previously thought, affecting all trophic levels within a community. Published in Journal of Applied Ecology from the Environment and Sustainability Institute at the University of Exeter (Cornwall, UK), the study’s findings indicate global implications for ecosystems that exist near to human development. By looking at the effects of artificial nighttime light on producer growth and herbivore populations in a simple ecosystem, Bennie et al. measured the light’s bottom-up, top-down, and indeterminate effects, or those operating independent of food chain dynamics. The study’s results have ramifications for conservation in natural and semi-natural ecosystems, namely that efforts made should attempt to minimize disruption by reducing the light pollution that is currently ubiquitous.
The authors argue that natural and semi-natural ecosystems exposed to human-made light, like roadside berms and hedgerows, have value that is threatened by this pollution. These small, man-made ecosystems are often neglected in conservation efforts. Bennie et al. state that that “continuous artificial light at night equivalent to that recorded in roadside vegetation under street lighting, can cause population-level effects on plants and invertebrates, that these effects can be mediated by both top-down and bottom-up processes, and that the nature of these effects depends on the lighting technology employed” (Bennie et al., 2018). Essentially, while some nighttime lighting is less damaging than others, all forms affect producer and invertebrate populations that are critical to ecosystem function and can impact predator-prey dynamics, resource availability, and animal behavior. To combat these effects, the authors suggest that cities utilize LED lights to better control the emitted wavelength and produce less ecosystem disruption.
To arrive at these conclusions, the researchers studied the influence of different types of light pollution on a grassland ecosystem’s producers, herbivores, and predation dynamics. They found that both artificial nighttime light and herbivore presence significantly affected the number of flower heads generated by L. pedunculatus, the system’s key producer; as the base of the grassland ‘food web’ L. pedunculatus provides other species energy, shelter, or sustenance for their prey. Amber light resulted in about 50% fewer flower heads, white light about 30% fewer, and herbivore presence about 45% fewer than the plant grown alone in natural conditions (Bennie et al., 2018). When both herbivores and predators were present, the interactions of these dynamics with artificial light produced a more serious effect.
These interactions between light and interspecies relationships were also evident in D. reticulatum, the gray field slug, a herbivore acting on L. pedunculatus. Slug abundance decreased 55% under a combination of white nighttime light and predation, while predation or white nighttime light alone had no significant effects. This illustrates the complex ways in which light pollution can interact with dynamics and relationships within an ecosystem: assumptions can never be made automatically about how species are affected by the light we produce.
Artificial light also impacted populations of the pea aphid, A. pisum, another herbivore consuming L. pedunculatus. These aphids are an important food source for larger predators, other insects that are in turn consumed by birds, mammals, and reptiles. Aphids were 17% less abundant under amber nighttime light but unaffected by white light, predator presence, or interactions between the factors (Bennie et al., 2018). As such, swapping out the amber lights pervasive in street lamps for white would eliminate light pollution’s effect on this species.
To be sure, the authors are not suggesting that light pollution can or should be completely eliminated. Nighttime lighting is critical for the function of cities and safe driving conditions across the world. The authors simply suggest that when lighting is needed for safety or public amenity, its timing, location, and brightness should be limited to what is absolutely necessary. Secondly, while light pollution is often ignored by conservation efforts, the importance of other types of pollution these efforts combat can not be negated or reduced. Chemical, plastic, and air pollution all unmistakably affect ecosystem health, and conservationists should attempt to reduce light pollution in conjunction with these other man-made effects.
Overall, to decrease ecological damage, the authors suggest planning outdoor lighting according to a few basic principles of lighting design. If possible, avoid illumination around natural and semi-natural environments, taking care around species more susceptible to artificial light and assuming that ecosystem effects are much wider than simply known impacts on specific species. As mentioned above, limit light where possible, and control the wavelengths emitted in different situations. This could mean switching the amber lights along roads for white LEDs, limiting lights’ ‘on’ time with motion sensors or timers, or even just households making an effort to turn off their lights at night. Buildings could be designed with reduction of light emittance as a priority, providing the added benefit of reduced energy usage, another important method of conservation. Through these few adjustments, we can minimize the ecological impact of our light pollution and reduce systemic damage to ecosystems.