A practical approach to measuring the acoustic diversity by community ecology methods

The study of the diversity of animal signals on within- and among-species
levels is the key to uncover mechanisms that shape the evolution of
communication systems. However, the methods used to quantify acoustic
diversity (like repertoire size) lack to grasp several aspects of acoustic
diversity. Here, we propose a new framework for the study of animal
communication, in which we decompose the acoustic diversity with the
methodological toolbox from community ecology. We explore how different
diversity estimates reflecting different aspects of acoustic diversity can
be applied to characterise the complexity of acoustic signals. We propose
that this approach can be used in a wide range of animal taxa to derive
further insights about the function and evolution of communication systems
besides the traditional methods. To illustrate the use of our approach in
a case study, we used the song of collared flycatcher (Ficedula
albicollis) as a model system. Based on three frequency and time
variables, we calculated three diversity indies (FRic, FEve, and FDiv) to
characterise the distribution of song elements (syllables) in the acoustic
parameter space. We aimed to uncover the interrelations of diversity
indices, reveal the degree of among-individual consistency, and
investigate their relationships with certain aspects of individual
quality. We found that the chosen diversity indices were largely
independent from each other and showed different consistency patterns that
were timescale dependent indicating different signalling potential of
individual-specific attributes. We also found that FEve strongly related
to the age of males. Our case study showed that decomposing the diversity
into different components can reveal additional biologically meaningful
aspects of birdsong.