Collateral damage or a shadow of safety? The effects of signalling heterospecific neighbours on the risks of parasitism and predation

Abstract

Although males often display from mixed-species aggregations, the influence of nearby heterospecifics on risks associated with sexual signalling has not been previously examined. We tested whether predation and parasitism risks depend on proximity to heterospecific signallers. Using field playback experiments with calls of two species that often display from the same ponds, tú ngara frogs and hourglass treefrogs, we tested two hypotheses: (1) calling near heterospecific signallers attractive to eavesdroppers results in increased attention from predatory bats and parasitic midges (collateral damage hypothesis) or (2) calling near heterospecific signallers reduces an individual's predation and parasitism risks, as eavesdroppers are drawn to the heterospecifics (shadow of safety hypothesis). Bat visitation was not affected by calling neighbours. The number of frog-biting midges attracted to hourglass treefrog calls, however, rose threefold when played near tú ngara calls, supporting the collateral damage hypothesis. We thus show that proximity to heterospecific signallers can drastically alter both the absolute risks of signalling and the relative strengths of pressures from predation and parasitism. Through these mechanisms, interactions between heterospecific guild members are likely to influence the evolution of signalling strategies and the distribution of species at both local and larger scales.

Evaluation of Conspecific Attraction as a Management Tool across Several Species of Anurans

“…Importantly, potential playback areas should be carefully vetted for quality so that individuals are not attracted to ecological traps [39]. Playbacks may also attract non-target species, including undesirable competitors, predators, or parasites [40,41]. While we did not see any noticeable response by heterospecific anurans to playbacks in any of our experiments, heterospecific information use is generally common between species that share some ecologically similar parameter [42].…”

Adaptive changes in sexual signalling in response to urbanization

“…One camera was positioned close (~0.5 m) to the setup to observe approaching females and one camera was farther away (~2 m) to observe bat attacks. Bat attacks were defined as an individual approaching the speaker and changing the course of its flight path within the video frame; a more detailed description of the criteria for approaching bats and female frogs has been published previously 60 . The speaker setup was placed away from any calling male or chorus.…”

Predator recognition and anti-predatory behaviour in a recent aquatic invader, the killer shrimp (Dikerogammarus villosus)

“…However, native predators may also be reluctant to feed on novel prey due to neophobia (Champneys et al 2018), and this could result on lower predation pressure on invasive species (Crawley 1987; MacNeil et al 2000; Trowbridge 1995; Wells & Henderson 1993). Killer shrimp could also benefit from a ‘shadow of safety’ effect if their relative low abundance during the earlier stages of invasion deflects predation pressure to the more abundant native prey (Trillo et al 2016). Killer shrimp can rapidly become the dominant species in invaded benthonic communities (Dick & Platvoet 2000) and can become the most abundant food resource for fish feeding on macroinvertebrates.…”