Noisy neighbours at the frog pond: effects of invasive cane toads on the calling behaviour of native Australian frogs
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Invasive species can disrupt the communication systems that native biota use for reproductive interactions. In tropical Australia, invasive cane toads (Rhinella marina) breed in many of the same waterbodies that are used by native frogs, and males of both the invader and the native taxa rely on vocal signals to attract mates. We conducted playback experiments to test the hypothesis that calls of toads may influence the calling behaviour of frogs (Limnodynastes convexiusculus and Litoria rothii). Male L. convexiusculus adjusted their calling rate and the variance in inter-call interval in response to a variety of sounds, including the calls of cane toads as well as those of other native frog species, and other anthropogenic noise, whereas L. rothii did not. Within the stimulus periods of playbacks, male L. convexiusculus called more intensely during long silent gaps than during calling blocks. Thus, males of one frog species reduced their calling rate, possibly to minimise energy expenditure during periods of acoustic interference generated by cane toads. In spite of such modifications, the number of overlapping calls (within stimulus periods) did not differ significantly from that expected by chance. In natural conditions, the calls of cane toads are continuous rather than episodic, leaving fewer gaps of silence that male frogs could exploit. Future work could usefully quantify the magnitude of temporal (e.g. diel and seasonal) and spatial overlap between calling by toads and by frogs and the impact of call-structure shifts on the ability of male frogs to attract receptive females.
KeywordsInvasive species Acoustic communication Anuran Playback experiments Bufo marinus
The Northern Territory Land Corporation provided facilities for the study. Dave Armstrong, Lucy Hurlstone, Jerry Hemphill and the staff of Beatrice Hill Farm allowed us access to their properties for the study. We thank Melanie Elphick for her assistance with manuscript preparation, and two anonymous reviewers for their helpful comments. This work was supported by the Australian Research Council.
The research was in compliance with ethical guidelines and the current laws of Australia. Anurans were studied under protocols approved by the USYD Animal Ethics Committee and Parks and Wildlife Commission of the Northern Territory.
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