The word habitat refers to the natural environment or home of a group of organisms. Habitats are places where a species or community of organisms live and obtain the food, water, shelter, and other resources necessary for survival and reproduction. A habitat can be as small as a single leaf or as large as an entire ecosystem.
When you think of the word habitat, it’s natural to picture a large area of land with specific environmental features and conditions. Perhaps the image that comes to your mind is a lush tropical rainforest, a vibrant coral reef system, or acres of sparse, dry savannah. These are all examples of habitats, the natural environments of a group of organisms where they live and work to survive and reproduce, seeking shelter, food, and water. Habitats can vary immensely in appearance and environmental conditions, but the thing they all have in common is to support and give a place to the various forms of life that are adapted to living in their specific conditions.
If you pay attention to the image you thought of, you might notice a subtle but notable bias: you are most likely picturing a habitat during the day. This is a diurnal or daytime bias, a tendency to view the natural world through a human-centric lens, where daytime is seen as the default time window for life and activity, and the night is ignored or overlooked. This bias can be attributed to the fact that humans are diurnal creatures who carry out most of our activity under natural or artificial light. Although this bias helps us to understand and study other diurnal creatures, it can lead us to overlook many fascinating and essential aspects of nighttime, where many species are adapted to thrive in the dark.
You might be wondering what the difference is – if the boundaries of a habitat remain the same, does it matter if you think of it during the day or at night? The answer is yes, it matters significantly. The key difference between day and night is the amount of visible light present, and while humans and diurnal animals have evolved to see well under sunlight, many creatures have adaptations that let them thrive in its absence, and in fact necessitate its absence. For example, many nocturnal animals, such as owls, bats, and some species of primates, have highly developed senses of hearing and vision that allow them to navigate and find prey in the dark. Some species of plants, such as night-blooming flowers, have evolved to attract pollinators that are active at night, such as bats and moths. The same spatial area is inhabited by a whole group of different creatures at night, and the landscape is transformed while diurnal creatures rest.
In this way, we can think of the night as a spatial habitat — a habitat that exists wherever it is dark at night without the interference of anthropogenic lighting. Spatial habitats give their inhabitants space to roam within to conduct the activities they need for survival, and natural darkness creates a nocturnal spatial habitat once the sun goes down. Once you reframe your view of habitats to include nighttime, it’s easy to see why nighttime lighting is so disruptive. It actually transforms the habitat from a nocturnal one into a diurnal one, and many nocturnal animals like cougars[1], bats[2], and tawny owls[3], will avoid illuminated areas, making turning on a street light as damaging to their habitat as more explicit physical habitat degradation through actions like deforestation. Lighting areas within a habitat at night is a subtle but powerful form of habitat erosion.
Although light pollution is pernicious to nocturnal habitats, it is arguably the easiest and most instantaneous form of habitat loss to reverse. All you have to do to restore nocturnal habitats is to turn off the lights and keep as many areas as possible naturally dark.