Anthropogenic noise has received considerable recent attention, but we know little about the role that sources of natural noise have on wildlife abundance and distributions. Rivers and streams represent an ancient source of natural noise that is widespread and covers much of Earth. We sought to understand the role that whitewater river noise plays on arthropod abundance in riparian habitats across a desert landscape. For two summers, we continuously broadcasted whitewater river noise and spectrally-altered river noise (shifted upwards in frequency, but maintaining the same temporal profile) to experimentally tease apart the effects of two characteristics of noise – sound levels and background spectral frequency – on arthropod abundances. We used five types of trapping methods, placed across 20 sites within the Pioneer Mountains of Idaho, USA, to collect and identify 151 992 specimens to the order level. We built Bayesian generalized linear mixed-effects models with noise characteristics and other habitat variables such as riparian vegetation, elevation, temperature, and moonlight. Of the 42 models we built (one for each order-trap type combination), 26 (62%) indicated a substantial response to at least one noise variable – sound pressure level, background spectral frequency, or an interaction between the two. Fourteen of 17 (82%) arthropod orders responded to noise in some capacity: Araneae, Coleoptera, Collembola, Dermaptera, Hemiptera, Hymenoptera, Lepidoptera, Neuroptera, Opiliones, Orthoptera, Plecoptera, Raphidioptera, Thysanoptera and Trichoptera. Only three groups appeared to be unaffected, Acari, Archaeognatha and Diptera. Results from this study suggest that the natural acoustic environment can shape arthropod abundances both directly and indirectly (via predator–prey relationships). Future work should further examine the role that the indirect effects of noise play in food webs. Natural noise should be considered an important ecological niche axis, especially as we continue to alter natural acoustic environments and replace them with anthropogenic ones.
Available at: http://works.bepress.com/jesse_barber/52/