Self-organising cicada choruses respond to the local sound and light environment

1. Periodical cicadas exhibit an extraordinary capacity for
self-organising spatially synchronous breeding behavior. The regular
emergence of periodical cicada broods across the US is a phenomenon of
longstanding public and scientific interest, as the cicadas of each brood
emerge in huge numbers and briefly dominate their ecosystem. During the
emergence, the 17-year periodical cicada species Magicicada cassini is
found to form synchronised choruses, and we investigated their chorusing
behavior from the standpoint of spatial synchrony. 2. Cicada choruses were
observed to form in trees, calling regularly every five seconds. In order
to determine the limits of this self-organising behaviour, we set out to
quantify the spatial synchronisation between cicada call choruses in
different trees, and how and why this varies in space and time. 3. We
performed 20 simultaneous recordings in Clinton State Park, Kansas, in
June 2015 (Brood IV) with a team of citizen-science volunteers using
consumer equipment (smartphones). We use a wavelet approach to show in
detail how spatially synchronous, self-organised chorusing varies across
the forest. 4. We show how conditions that increase the strength of audio
interactions between cicadas also increase the spatial synchrony of their
chorusing. Higher forest canopy light levels increase cicada activity,
corresponding to faster and higher-amplitude chorus cycling and to greater
synchrony of cycles across space. We implemented a
relaxation-oscillator-ensemble model of interacting cicadas, finding that
a tendency to call more often, driven by light levels, results in all
these effects. 5. Results demonstrate how the capacity to self-organise in
ecology depends sensitively on environmental conditions. Spatially
correlated modulation of cycling rate by an external driver can also
promote self-organisation of phase synchrony.

1. 周期蝉展现出非凡的空间同步繁殖行为自组织能力。美国各地周期蝉群体的定期涌现是长期以来公众与科学界共同关注的现象——每个群体的蝉都会大量涌现，并在短期内主导其生态系统。涌现期间，17年周期蝉物种Magicicada cassini被发现形成同步合唱，我们从空间同步性的角度对其合唱行为展开了研究。2. 观察发现蝉群在树上形成合唱，每五秒规律鸣叫一次。为明确这种自组织行为的边界，我们着手量化不同树木中蝉鸣合唱的空间同步性，以及其在时空维度上的变化方式与原因。3. 2015年6月，我们与公民科学志愿者团队合作，在堪萨斯州克林顿州立公园（第四代群体）使用消费级设备（智能手机）完成了20次同步录音。我们通过小波分析方法详细展示了森林中空间同步的自组织合唱行为如何变化。4. 我们揭示了增强蝉之间音频交互强度的条件如何提升其合唱的空间同步性：较高的林冠层光照水平会增加蝉的活动，对应更快、振幅更大的合唱周期，以及空间上更显著的周期同步性。我们构建了蝉交互的弛豫振荡器集合模型，发现由光照水平驱动的更频繁鸣叫倾向会引发上述所有效应。5. 研究结果表明，生态学中的自组织能力对环境条件具有高度敏感性；外部驱动因素对周期率的空间相关调制也能促进相位同步的自组织。