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in a commune with ants produce stridulations to exploit the acoustic sensitivities of their tenders and gain access to more care and protection (DeVries, 1990).
Finally, but no less important, is the reliance of inver- tebrates on sound for its ability to carry general information about the environment. Environmental processes like wind, rain, fire, and moving water (e.g., streams, rivers) all produce sound with specific acous- tic characteristics. In a recent study, forest patches with broadcasted sounds of a white water river were found to be home to more web-building spiders than similar forest patches without these sounds (Gomes et al., 2020). It is likely that each ecosystem, with its unique makeup of soils, plants, animals, and environmental processes, has an acoustic signature that invertebrates pick up on to make decisions or determine habitat quality. Just as the broadcasted crackle of a healthy coral reef was found to attract a diversity of fishes to a depopulated reef (Gordon et al., 2019), so too might sounds emanating from eco- systems inform invertebrates of their quality.
In these collected reports of invertebrate behavior, researched by hundreds of investigators, published over decades, and randomly assembled, are the beginning brush- strokes to a complete picture of invertebrate bioacoustics that is in every way as vibrant as the one that’s been painted for vertebrates. Invertebrate bioacoustics suggests, with emphasis, the first step to understanding sound in the natural world: human perceptions are limiting. Acoustics are penetrating, diverse, time warping, alien, and complex. The ubiquity of a sound makes it a reliable and ever-present source of information accessible to even the smallest organ- isms. It is no wonder that many invertebrates rely on sound to perform important daily activities and thus are vulnerable to the impact of anthropogenic sound.
Invertebrates and Anthropogenic Sound
When the idea and threat of anthropogenic sound took hold in the first decade of the twenty-first century (Shannon et al., 2016), it brought to attention the acoustic vulnerabilities of vertebrate animals that had previously eluded ecologists. Excited scientists established acoustic monitoring programs, created sound libraries, and began documenting the acous- tics of ecosystems. Ostensibly, this was and continues to be an effort to create an acoustic record of nature before it dis- appears. Like any attempt to describe the nature of things, though, it omitted the inconvenient aspects of doing so.
Baseline values for ecosystem acoustics in the form of par- ticle motion or substrate-borne vibrations were ignored and remain nonexistent.
One such example, a 2015 attempt to create awareness of noise pollution in Grand Teton National Park, WY (GTNP; see nps.gov/grte/index.htm), involved noise meters installed along Park roadsides (National Park Service, 2015). The meters penetrated the quiet of each vehicle’s interior with a green-yellow-red visualization of the airborne pressure wave drivers introduced into the ecosystem. Missing from these meters was an indication of the particle motion and substrate-borne vibrations emanating from vehicles as they progressed through the Park: the granite pebbles, aspen leaves, sagebrush stems, and pine boughs rattling long after they passed and the millions of disrupted invertebrate individuals who depend on sound for survival and reproduction.
Noise from human activities is dominated by frequencies below 2,000 Hz, which happens to correspond with those frequency sensitivities of the majority of terrestrial and marine invertebrates (Popper and Hawkins, 2018; Raboin and Elias, 2019). As sound radiates out from a source, it encounters invertebrates of all kinds and intrudes into their acoustic worlds as a novel stimulus, abundant in time, space, and modality. For example, noise from vehicles passing an aspen stand in the GTNP may encounter a tree, a branch, a leaf and with them, a single female planthopper sitting atop its matte surface (Figure 3). Vibrations from the vehicles
Figure 3. Planthoppers (order Hemiptera, family Tropiduchidae) send and receive substrate-borne vibrations along plant stems and leaves to identify, locate, and assess potential mates. Photograph courtesy of Marshal Hedin.
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