Possibilities for error during communication by neotropical frogs in a complex acoustic environment
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Differences in vocalizations promote accurate identification of species during mate choice. The properties of vocalizations vary, however, and overlap in the properties of different species' calls raises the possibility of errors in species identification. A general model of these possibilities is provided by discriminant function analysis (DFA). To illustrate this use of DFA, we consider possibilities for error in the classification of advertisement calls by Hyla ebraccata in a diverse community of neotropical hylid frogs. The analysis used three features of their calls: duration, dominant frequency, and pulse repetition rate, separately and in combination. These properties are known to be used for mate choice by female H. ebraccata and many other species of frogs. With only one feature, DFA misidentified 12–32% of individuals, either by assigning H. ebraccata calls to other species (missed detections) or by assigning calls of other species to H. ebraccata (false alarms). With two call parameters, DFA committed few or no errors. If the analysis included the relative abundances of the different species, there were even fewer errors. Thus DFA can use as few as two features to identify calls of H. ebraccata almost without error. The dispersion of the different species in discriminant-function space was random, not overdispersed as expected, regardless of the call features included in the analysis. The lack of overdispersion might be explained by differences in selection on calls of common and rare species. This application of DFA indicates several ways in which understanding the possibilities for errors can advance our understanding of the evolution of communication in general.
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