insects Review Enlightening Butterfly Conservation Efforts: The Importance of Natural Lighting for Butterfly Behavioral Ecology and Conservation Brett M Seymoure ID Department of Biology and Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 80523, USA; [email protected]; Tel.: +1-970-495-2004 Received: 11 January 2018; Accepted: 6 February 2018; Published: 12 February 2018 Abstract: Light is arguably the most important abiotic factor for living organisms. Organisms evolved under specific lighting conditions and their behavior, physiology, and ecology are inexorably linked to light. Understanding light effects on biology could not be more important as present anthropogenic effects are greatly changing the light environments in which animals exist. The two biggest anthropogenic contributors changing light environments are: (1) anthropogenic lighting at night (i.e., light pollution); and (2) deforestation and the built environment. I highlight light importance for butterfly behavior, physiology, and ecology and stress the importance of including light as a conservation factor for conserving butterfly biodiversity. This review focuses on four parts: (1) Introducing the nature and extent of light. (2) Visual and non-visual light reception in butterflies. (3) Implications of unnatural lighting for butterflies across several different behavioral and ecological contexts. (4). Future directions for quantifying the threat of unnatural lighting on butterflies and simple approaches to mitigate unnatural light impacts on butterflies. I urge future research to include light as a factor and end with the hopeful thought that controlling many unnatural light conditions is simply done by flipping a switch. Keywords: anthropogenic factors; light pollution; polarized light; sensory pollution 1. Introduction Over the last two hundred years, humans have dramatically changed the lighting conditions on Earth [1,2]. This change in lighting includes anthropogenic lights during the night, anthropogenic fires and gas flares, as well as the destruction of habitats that produced distinct light environments [3–5]. In fact, nearly all protected areas across the world have had an increase in night time lighting since 1992 [6,7], and it is estimated that over eighty percent of humans live under light polluted skies [2]. Furthermore, 65% of tropical Asian and Sub-Saharan African forests have been lost, whereas only 10% of Mediterranean forests remain, and 36% of tropical rainforests have been destroyed [8]. Of the remaining forests on our planet, 70% are one kilometer from an edge [9]. Thus, the natural light conditions that forest canopy provide have been greatly reduced by human activities [9]. This alarming change in natural lighting conditions has direct ecological consequences including loss of biodiversity and risk of species extirpation and extinction [10–13]. Previous research has documented the effects of changes to natural light conditions on wildlife ranging from changes in predation, reproduction, phenology, migration and orientation, community level interactions, behavior, communication, and physiology [10,13–17]. However, our understanding of how changes in natural light conditions affect butterfly behavior and conservation status remains largely unknown. Here, I introduce the problem of unnatural lighting, both diurnal (habitat destruction and change) and nocturnal (anthropogenic lighting), in the context of butterfly ecology and conservation. I then review what is known about the importance of light for butterflies across myriad Insects 2018, 9, 22; doi:10.3390/insects9010022 www.mdpi.com/journal/insects Insects 2018, 9, 22 2 of 25 biologicalInsects functions2018, 9, x FOR ranging PEER REVIEW from, but not limited to, phenology, orientation, foraging, predator-prey2 of 25 interactions, and reproduction. Lastly, I introduce a framework for furthering our understanding of the effectsecology of unnatural and conservation. lighting on I then butterflies review what and theis kn stepsown about to mitigate the importance unnatural of lightinglight for butterflies on butterflies. As butterfliesacross myriad are a biological “charismatic” functions fauna, ranging focusing from, on but conserving not limited naturalto, phenology, light conditionsorientation, inforaging, the context predator-prey interactions, and reproduction. Lastly, I introduce a framework for furthering our of preserving butterfly biodiversity may be an excellent way to conserve natural light conditions for all understanding of the effects of unnatural lighting on butterflies and the steps to mitigate unnatural species including the less “charismatic” species like bats and moths, which may be more vulnerable. lighting on butterflies. As butterflies are a “charismatic” fauna, focusing on conserving natural light conditions in the context of preserving butterfly biodiversity may be an excellent way to conserve 2. Nature and Extent of Light natural light conditions for all species including the less “charismatic” species like bats and moths, Naturalwhich may light be more conditions vulnerable. are dependent upon time, space, and environmental factors [5,18]. Light conditions change throughout the day, night and year. Lighting is also dependent upon the 2. Nature and Extent of Light landscape (e.g., forest vs. savannah), weather, lunar cycle and celestial bodies. Furthermore, lighting is complicatedNatural by its light own conditions physical are properties dependent which upon time, include space, wavelength, and environmental frequency, factors polarization, [5,18]. Light hue, chroma,conditions and intensity change throughout [19]. It is vital the day, that night lighting and ye isar. studied Lighting with is also all dependent of these parameters upon the landscape in mind as biological(e.g., functionsforest vs. havesavannah), evolved weather, under lunar specific cycle lighting and celestial conditions bodies. that Furt dependhermore, upon lighting time, is space, complicated by its own physical properties which include wavelength, frequency, polarization, hue, weather, and the spectral properties of light. chroma, and intensity [19]. It is vital that lighting is studied with all of these parameters in mind as 2.1. Physicalbiological Parameters functions ofhave Light evolved under specific lighting conditions that depend upon time, space, weather, and the spectral properties of light. What is light? Light is part of the electromagnetic spectrum and can be understood as a stream of photons2.1. Physical and aParameters collection of ofLight electromagnetic waves, see [19]. 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