Insects, bats and artificial light at night: Measures to reduce the negative effects of light pollution

Abstract

Light largely influences the biological world. It is used by organisms for several purposes. However, the influence of artificial light on species interaction, populations and ecosystems is not well documented. Also, technical and political measures are not used consistently. This study will examine how and to what extend artificial light affects Lepidoptera, Diptera, Coleoptera and insectivorous bat species and also provide for measures to reduce potential negative effects. There are some limitations to the study, since only specific insect and bats species of the European Union are taken into consideration. Also, only measures for the EU are given and long-term effects are not examined. Insects and bats can see different wavelengths of light. Both bats and insect species use light for partitioning of activity between day and night, dark repair and recovery, circadian clocks and photoperiodism, visual perception and spatial orientation. Artificial light is mainly produced by lamps. The outdoor artificial light is mostly used in urban and western areas in the world. High pressure sodium, low-pressure sodium, high-pressure mercury, metal halide, compact fluorescent, LED, incandescent/Halogen and fluorescent tube lamps are most commonly used outdoor, as street lamps. The effect of those types of lamps varies. For insects and bats, street lamps can have an effect on their daily rhythm and several physiological processes. Artificial light affects individuals, but it also has an effect on populations and ecosystems. Literature to provide for examples of this phenomenon is very scarce. Artificial light can affect the population itself, by increasing the mortality or reproduction rate, but it can also change the interaction between species of the same family or even predator-prey relationships. For some species with small and fragmented populations, artificial light could cause local extinction. Also, some species that are favoured by artificial light could outcompete another species. Four different scenarios for the effect of artificial light on the predator-prey relationship between bats and insects are considered. However, the possible differences in effect between insect species or bat species is not taken into consideration. Light pollution can be defined as being the degradation of the photic habitat by artificial light. Even though there are still huge gaps in the knowledge about the effect of artificial light at night on these specific species, the knowledge that already has been retrieved is worrying. Light pollution has the potential to disrupt the stability of species and some literature shows that light pollution is already an important factor in the decline of some vulnerable species. There are some studies that have determined limit values for light pollution and some formulas are conducted in the past years. However, these findings have not yet been integrated in EU laws and legislations. When countries individually develop these regulations, this could create economical unequal environments for companies and individuals, thereby undermining the open economy principle of the EU. Since artificial light is a potential problem for the biological world, it is important that further steps are taken concerning guidelines for the use of artificial light in the EU. There are several technological and political measures that are suitable for EU regulations. These measures can be integrated in a plan specifically set up for the species examined in this study. However, other organisms should also be included in these guidelines. Therefore, further research on the effect on other species is needed.