Diferentes padrões de atividade vocal de espécies de anuros amazônicos formam assembleias acústicas em escala diária

Abstract

Anuran vocal activity throughout the day is primarily modulated by photoperiod, and secondly, social context and environmental setting. Therefore, divergent species responses to these factors can result in the formation of temporal acoustic assemblages — i.e. sets of species that are vocally co-active at predictable times throughout the nycthemeral period (24-h cycles). Photoperiods are largely invariant in tropical regions over annual cycles, thereby ensuring that sampling of the diurnal distribution of vocalizations is largely unaffected by time of year. Here, we (1) describe the temporal distribution of vocal activity of several species of Amazonian anurans in an archipelagic landscape fragmented by river damming and determine the most effective time to survey anurans; (2) investigate the formation and composition of temporal acoustic assemblages throughout the day; and (3) assess how island size — as a proxy of intra- and interspecific social contexts — affects anuran vocal activity times. We used acoustic sensors to sample 78 sites (74 islands and four mainland forest sites) for five consecutive days between July and December 2015. We used an automatic detection algorithm to identify anuran species in a total of 216,217 1-minute recordings (> 3,600 hours). Recordings for each species were classified into four time periods: dawn (05:00 - 06:55), day (07:00 - 16:55), dusk (17:00 - 18:55) and night (19:00 – 04:55). Most anuran species were recorded throughout the daily period, although we also observed concentrated vocal activity during the Dusk and Night periods. Four daily periods corresponded to markedly distinct temporal assemblages, whereas the Night period whas the most distinct and cohesive in terms of acoustic composition. Island size, a proxy of population sizes and species richness, positively affected the vocal activity time of anuran assemblages, supporting that there are factors beyond photoperiod that modulate the daily vocal activity of these species. We have broken new ground in classifying the vocal activity of mega-diverse anuran assemblages in Amazonia by detecting the partition of temporally structured assemblages throughout the daily period.