Changes in “soundscapes” from human noise disturbance alter avian community assemblages, foraging behavior, and reproductive success. Such changes in avian communities could result in alterations in plant herbivory, morphology and physiology, via changes in consumption of herbivorous insects by insectivorous birds. We continuously broadcasted (24-hrs/day) recordings of natural-gas-wells from April-October 2015 in sagebrush-steppe habitat in Idaho, USA. This approach isolates the direst effects of noise from associated indirect effects of human activities. Sagebrush steppe is one of the most endangered ecosystems in North America, and we focused on natural-gas-well extraction noise because this noise has been shown to affect avian predators in previous studies. Increases in energy-development infrastructure dramatically alter the background sound levels for much of the vast ‘Sagebrush Sea’, and has the potential to interfere with important ecosystem services. We hypothesized that an altered soundscape would change insect abundances (via changes in avian predators; assessed in a separate study), insect herbivory, and physiology and productivity in sagebrush shrubs (Artemisia tridentata ssp. wyomingensis). We predicted that we would observe increases in shrub herbivory at Noise-On sites, because of reductions in avian predation on herbivorous insects. We further predicted that we would observe decreased physiology and productivity in shrubs at Noise-On sites because of physiological costs associated with increased herbivory damage.
Results/Conclusions
Total arthropod abundance was not different between sites; however, more insects (13.5%, n.s.) from sap-feeding families occurred on shrubs in Noise-On sites. There were no observable differences in herbivory damage, and stem growth/cm was 19.5% greater (n.s.) at Noise-On sites; noise significantly increased both shrub respiration and photosynthesis, and a significant day×noise interaction occurred for light-reaction photochemistry and photosynthesis–contrary to our initial hypotheses. These differences in physiology were observed only at the beginning of the growing season, and then decreased to levels at or below our control sites. We hypothesize that the increases in photosynthesis and respiration that we observed were compensatory responses from increased sap-feeding damage in sagebrush at Noise-On sites, because of reduced bird predation on sap-feeders. Boosts in photosynthesis and growth because of modest increases in herbivory have been reported in previous studies, whereas more intense herbivory can lead to declines in photosynthesis. To our knowledge, this collaborative study is the first to quantify how changes in a soundscape can directly, or indirectly, affect ecosystem dynamics across multiple trophic levels.