Acoustic niche partitioning in an anuran community inhabiting an Afromontane wetland (Butare, Rwanda)

Abstract

The species richness and calling activity of an anuran community inhabiting an agricultural wetland area at 1645 m a.s.l. near Butare, Rwanda, was assessed using visual and acoustic transects. The community included 15 species which were readily distinguishable using morphological, bioacoustic and molecular features. Eight species (Xenopus victorianus, Amietophrynus regularis, Ptychadena anchietae, P. porosissima, Kassina senegalensis, Afrixalus quadrivittatus, Hyperolius kivuensis, H. lateralis) were taxonomically identified. The remaining seven species (three species of Hyperolius, two Phrynobatrachus, one Amietia, one Ptychadena) represent undescribed or currently unrecognized taxa, suggesting a significant magnitude of overlooked amphibian diversity in Afromontane communities. Acoustic niche analysis of the 14 species producing airborne advertisement calls integrated the spatial dimension, i.e. the microhabitat used for calling, the temporal dimension, i.e. the time of day when calling takes place, and the call structure dimension, i.e. the physical features of the advertisement call. Average standardized acoustic niche breadth was narrow (measured: 0.08, predicted: 0.07) and showed low variability (0.04–0.16) among species, which means that empirical data are in full agreement with the predictions of stochastic niche theory for species-saturated communities. Niche segregation was mainly based on advertisement call features, whereas spatial and temporal niche dimension contributed less. Measured average niche overlap (0.30) was intermediate between random overlap (0.51) and minimum possible overlap (0.11), indicating significant acoustic resource partitioning. The only taxon group with widely overlapping acoustic niches were Ptychadena spp., which might indicate a recent invasion of the community by one or two of the three species.

Key words: advertisement call, stochastic niche theory, species saturation, cryptic diversity.