Landscape composition drives the impacts of artificial light at night on insectivorous bats

Abstract of the related publication : Among the most prevalent sources of biodiversity declines, Artificial Light At Night (ALAN) is an emerging threat<br> to global biodiversity. Much knowledge has already been gained to reduce impacts. However, the spatial variation<br> of ALAN effects on biodiversity in interaction with landscape composition remains little studied, though it is<br> of the utmost importance to identify lightscapes most in need of action. Several studies have shown that, at local<br> scale, tree cover can intensify positive or negative effects of ALAN on biodiversity, but none have – at landscape<br> scale – studied a wider range of landscape compositions around lit sites. We hypothesized that the magnitude of<br> ALAN effects will depend on landscape composition and species’ tolerance to light. Taking the case of insectivorous<br> bats because of their varying sensitivity to ALAN, we investigated the species-specific activity response to<br> ALAN. Bat activity was recorded along a gradient of light radiance. We ensured a large variability in landscape<br> composition around 253 sampling sites. Among the 13 bat taxa studied, radiance decreased the activity of two<br> groups of the slow-flying gleaner guild (Myotis and Plecotus spp.) and one species of the aerial-hawking guild<br> (Pipistrellus pipistrellus), and increased the activity of two species of the aerial-hawking guild (Pipistrellus kuhlii<br> and Pipistrellus pygmaeus). Among these five effects, the magnitude of four of them was driven by landscape composition.<br> For five other species, ALAN effects were only detectable in particular landscape compositions, making<br> the main effect of radiance undetectable without account for interactions with landscape. Specifically, effects<br> were strongest in non-urban habitats, for both guilds. Results highlight the importance to prioritize ALAN reduction<br> efforts in non-urban habitats, and how important is to account for landscape composition when studying<br> ALAN effects on bats to avoid missing effects.