Nightly patterns of calling activity in anuran assemblages of the Cerrado, Brazil

Species Assembly of Highland Anuran Communities in Equatorial Africa (Virunga Massif): Soundscape, Acoustic Niches, and Partitioning

The soundscape is a complex arrangement of sounds originating from animals and the environment. It is considered a reliable proxy for ecosystem niche structure at the community level. Acoustic communities of anuran species include advertising males, which compete in acoustic space for conspecific females. Stochastic niche theory predicts that all local niches are occupied, and the acoustic community is species-saturated. Acoustic niches, which include the spectral and temporal call structure and diel and seasonal patterns of call activity, are of similar breadth with small overlap. We tested these predictions in four communities inhabiting pristine wetlands at 2546-3188 m a.s.l. in the Volcanoes National Park, Rwanda. We sampled 74 days of hourly 5 min recordings of the local soundscape (September 2019-March 2020) using passive automated monitoring devices (Songmeter SM4). We identified species based on the advertisement call features and measured call activity as calls per minute. The communities included 4-6, species depending on wetland structure, with a shared stock of three species (Hyperolius castaneus, H. glandicolor, Leptopelis kivuensis). Independent of elevation, niche breadth for call features was similar among species and overlap reduced by partitioning the frequency range used. The diel and seasonal niche breadth of specific call activity varied according to the local temperature regime at different altitudes representing the variable part of the acoustic niche. We conclude that communities are indeed species-saturated and acoustic niches differ primarily by the fixed call features remaining locally adaptable by the modulation of the call activity pattern, corroborating the predictions of the stochastic niche theory.

Drivers of assemblage-wide calling activity in tropical anurans and the role of temporal resolution

Temporal scale in animal communities is often associated with seasonality, despite the large variation in species activity during a diel cycle. A gap thus remains in understanding the dynamics of short-term activity in animal communities. Here we assessed calling activity of tropical anurans and addressed how species composition varied during night activity in assemblages along gradients of local and landscape environmental heterogeneity. We investigated 39 anuran assemblages in the Pantanal wetlands (Brazil) with passive acoustic monitoring during the peak of one breeding season, and first determined changes in species composition between night periods (early, mid and late) using two temporal resolutions (1- and 3-hr intervals). Then, we addressed the role of habitat structure (local and landscape heterogeneity variables from field-based and remote sensing metrics) and ecological context (species richness and phylogenetic relatedness) in determining changes in species composition (a) between night periods and (b) across days. Nocturnal calling activity of anuran assemblages varied more within the 1-hr resolution than the 3-hr resolution. Differences in species composition between early- and late-night periods were related to local habitat structure and phylogenetic relatedness, while a low variation in compositional changes across days was associated with low-heterogeneous landscapes. None of these relationships were observed using the coarser temporal resolution (3 hr). Our findings on the variation of calling activity in tropical anuran assemblages suggest potential trade-offs mediated by fine-temporal partitioning. Local and landscape heterogeneity may provide conditions for spatial partitioning, while the relatedness among co-signalling species provides cues on the ecological overlap of species with similar requirements. These relationships suggest a role of niche dimensional complementarity on the structuring of these anuran assemblages over fine-temporal scales. We argue that fine-temporal differences between species in breeding activity can influence the outcome of species interaction and thus, addressing temporal scaling issues can improve our understanding of the dynamics of animal communities.

Annual and daily patterns of calling activity in male Scinax fuscomarginatus (Anura: Hylidae) from Central Brazil

Bioacoustics is an effective way of recording detailed data during population surveys and monitoring. In the present study, we used an automated digital recorder (ADR) to describe the temporal variation in the calling activity of Scinax fuscomarginatus (Lutz, 1925) in central Brazil. We also evaluated the role of climatic variables (air temperature and precipitation) on calling activity by using a Generalized Additive Model (GAM). We conducted the recordings at five ponds in the Cerrado savanna of Rio Verde Municipality, in Goiás state between November 2013 and October 2014. The analysis of the 43.2 hours of acoustic recording showed that S. fuscomarginatus has a prolonged breeding pattern. The ADR provides a fine-scale description of the nocturnal calling pattern, as well as the oscillations between the rainy and dry seasons. The results of the analytical model also indicate that calling patterns were related to minimum (but not maximum) air temperatures and precipitation, which may be related to their reproductive and thermoregulatory requirements. Based on these findings, we conclude that the ADR method has potentially valuable applications for the collection of data on the natural history of anuran species, as well as supplying important insights for conservation initiatives.