Sensory Stressors Impact Species Responses Across Local and Continental Scales

Author

Ashley A. WilsonFollow

DOI: https://doi.org/10.15368/theses.2020.139
Available at: https://digitalcommons.calpoly.edu/theses/2224

Date of Award

9-2020

Degree Name

MS in Biological Sciences

Department/Program

Biological Sciences

College

College of Science and Mathematics

Advisor

Clinton Francis

Advisor Department

Biological Sciences

Advisor College

College of Science and Mathematics

Abstract

Pervasive growth in industrialization and advances in technology now exposes much of the world to anthropogenic night light and noise (ANLN), which pose a global environmental challenge in terrestrial environments. An estimated one-tenth of the planet’s land area experiences artificial light at night — and that rises to 23% if skyglow is included. Moreover, anthropogenic noise is associated with urban development and transportation networks, as the ecological impact of roads alone is estimated to affect one-fifth of the total land cover of the United States and is increasing in space and intensity. Existing research involving impacts of light or noise has primarily focused on a single sensory stressor and single species; yet, little information is known about how different sources of sensory stressors impact the relationships within tightly-knit and complex systems, such as within plant-pollinator communities. Furthermore, ANLN often co-occur, yet little is known about how co-exposure to these stressors influences wildlife, nor the extent and scale of how these stressors impact ecological processes and patterns.

In Chapter 1, we had two aims: to investigate species-specific responses to artificial night light, anthropogenic noise, and the interaction between the two by using spatially-explicit models to model changes in abundance of 140 of the most prevalent overwintering bird species across North America, and to identify functional traits and contexts that explain variation in species-specific responses to ANLN stressors with phylogenetically-informed models. We found species that responded to noise exposure generally decreased in abundance, and the interaction with light resulted in negative synergistic responses that exacerbated the negative influence of noise among many species. Moreover, the interaction revealed negative emergent responses of species that only reacted when both ANLN were presented in combination. The functional trait that was the most indicative of avian response to ANLN was habitat preference. Specifically, species that occupy closed habitat were less tolerant of both sensory stressors compared to those that occupy open habitat. Species-specific responses to ANLN are context-dependent; thus, knowing the information that regulates when, where, how, and why sensory pollutants influence species will help management efforts effectively mitigate these anthropogenic stressors on the natural environment.

In Chapter 2, using field-placed light manipulations at sites exposed to a gradient of skyglow, we investigated the influence of direct and indirect light on the yucca-yucca moth mutualism by quantifying chaparral yucca (Hesperoyucca whipplei) fruit set and the obligate moth (Tegeticula maculata maculata) larval density per fruit. Although many diurnal insects are thought to exhibit minimal phototaxis, we show that direct light attracted adult moths and incited higher pollination activity, resulting in an increase in fruit set. However, larval recruitment decreased with elevated light exposure and the effect was strongest for plants exposed to light levels exceeding natural moonlit conditions (> 0.5 lux). Contrarily, increases in ambient skyglow resulted in an increase in both fruit set and larva counts. Our results suggest that plant-pollinator communities may respond in complicated ways to different sources of light, such that novel selection pressures of direct and indirect light have the potential to benefit or disrupt networks within complex diurnal plant-pollinator communities, and ultimately alter the biodiversity reliant on these systems.

By analyzing pervasive stressors across a continental-wide scale, we revealed considerable heterogeneity in avian responses to light and noise alone, as well as the interaction between them. Based on overall responses to the interaction between light v and noise, we suggest management efforts should focus on ameliorating excessive noise for overwintering bird species, which should decrease the impact from synergistic responses, as well as the negative impact from noise alone. There is still much to learn about responses to these stressors and smaller-scale studies should take our approach of systematically assessing interaction responses to ANLN. Moreover, our small-scale study revealed both local sources of direct light and skyglow impact the recruitment for both yucca moths and their reciprocal plant hosts. However, it is still unknown if or why other diurnal pollinators experience positive phototaxis, and whether direct lighting influences the physiology, behavior, or multiple factors relating to reproduction and fitness. Correspondingly, it is unknown if the novel selection pressures of direct and indirect light are disrupting complex diurnal plant-pollinator communities. Future research on artificial night light will need to investigate the intricate responses of diurnal pollinators to both direct and indirect light that will identify concrete mechanisms relating to physiological or behavioral susceptibility and inform predictions on how wide-spread communities will shift with this global driver of emerging change.