Artificial night lighting and anthropogenic noise alter animal activity, body condition, species richness, and community structure
Available at: https://digitalcommons.calpoly.edu/theses/2187
Date of Award
MS in Biological Sciences
College of Science and Mathematics
College of Science and Mathematics
Sensory pollution from artificial night-lighting and anthropogenic noise have increased at a dramatic rate over the last several decades. Alterations to the sensory environment have been found to affect wildlife in a wide variety of ways including behavioral changes, physiological responses, changes in species interactions, and altered community structure. Increased levels of light and noise pollution can originate from many sources including roads, energy development and infrastructure, and urbanization. Even remote or protected areas are not immune to the effects of increased sensory disturbances with 63 percent of protected areas within the United States found to have been exposed to a doubling of background noise levels due to anthropogenic activity and skyglow, the scattering of artificial light by the atmosphere, extending hundreds of kilometers from the source. Despite a large body of work investigating the effects of light or noise pollution acting alone, relatively few studies have examined the effects of both stimuli acting together even though they frequently co-occur. Better understanding how these stressors, especially when present simultaneously, are affecting ecosystems is critical to ongoing mitigation and conservation efforts.
In Chapter 1, we investigated the effects of increased levels of light and noise pollution, both singularly and in tandem, on pinyon mouse (Peromyscus truei) activity and body condition. Using a full factorial study design allowed us to isolate the effects of both stimuli when acting alone as well as any potential interactions between the two when both were present. We used standard trapping methods across a gradient of light, noise, and both combined while also accounting for variations in moonlight, vegetative structure, and weather. We found that an increased level of artificial night-lighting resulted in lower trap success of pinyon mice while there was no effect of noise on trap success. There was no effect of elevated light levels on body condition but there was a negative effect of noise on body condition early in the season. Later in the season, neither light nor noise influenced body condition. No interactive effects between light and noise were found.
In Chapter 2, we studied the effects of anthropogenic light and noise, singularly and in tandem, on species richness and community structure using camera traps in a manipulative field experiment. We investigated these effects at both the species level and the taxonomic level (nocturnal mammals, diurnal mammals, lagomorphs, birds, mesocarnivores, and ungulates). We showed that both light and noise pollution did alter species richness and that these effects can differ depending on the scale of observation. Increased levels of night-lighting had a scale-dependent effect on species richness such that increases in light levels had a negative effect on richness at the camera level, but light-treated sites had the highest estimated cumulative richness. In contrast, noise was found to have a negative effect on richness for birds. When both stimuli were present, the addition of night-lighting mitigated the effects of noise for birds. For community structure, noise-treated sites were the most dissimilar from other treatments, indicating that increased levels of anthropogenic noise likely have the largest effect on community structure in this study. We also found evidence of a possible rescue effect of light that counteracts the negative effect of noise. That is, combined treatment sites were significantly dissimilar from both light and noise sites but not from the control sites.
Together, our results provide evidence that alterations to the sensory environment from anthropogenic activity can affect wild animal populations in multiple ways. As human development increases to meet the demands of growing human populations, more ecosystems will be exposed to increased levels of sensory disturbance, making the understanding of how these changes affect wildlife critical to ongoing conservation efforts.