Risk assessment based on indirect predation cues: revisiting fine‐grained variation

Abstract

To adaptively express inducible defenses, prey must gauge risk based on indirect cues of predation. However, the information contained in indirect cues that enable prey to fine‐tune their phenotypes to variation in risk is still unclear. In aquatic systems, research has focused on cue concentration as the key variable driving threat‐sensitive responses to risk. However, while risk is measured as individuals killed per time, cue concentration may vary with either the number or biomass killed. Alternatively, fine‐grained variation in cue, that is, frequency of cue pulses irrespective of concentration, may provide a more reliable signal of risk. Here, we present results from laboratory experiments that examine the relationship between red‐eyed treefrog tadpole growth and total cue, cue per pulse, and cue pulse frequency. We also reanalyze an earlier study that examined the effect of fine‐grained variation in predator cues on wood frog tadpole growth. Both studies show growth declines with increasing cue pulse frequency, even though individual pulses in high‐frequency treatments contained very little cue. This result suggests that counter to earlier conclusions, tadpoles are using fine‐grained variation in cue arising from the number of predation events to assess and respond to predation risk, as predicted by consumer–resource theory.

Top-down pulses reduce prey population sizes and persistence

“…While the effects and interactions of top-down and bottom-up factors have been frequently explored in the ecological literature, the effects of temporal variability have only been well explored from the bottom-up 2 , 17 . Just as resource pulses affect community dynamics and trophic interactions via changes to growth and reproduction rates 18 , prey switches 19 , and coexistence among competitors 20 , it is likely that variation in prey abundance that results from pulses of predation (via removals of prey) could also have important effects on food web interactions 21 , 22 . Here, we demonstrated how pulsed removals of individuals from a population undergoing logistic growth results in lower equilibrium population sizes than continuous removals (Fig.…”

Habituation in anuran tadpoles and the role of risk uncertainty

“…In this regard, anuran tadpoles show a variety of behavioral responses, such as a decrement in activity and an increase in refuge use (e.g., Skelly 1994;Mirza et al 2006;Fraker 2008;. Several studies have shown that tadpoles are able to identify different traits associated with predation risk cues such as concentration, frequency, phylogenetic relatedness, among others (Schoeppner and Relyea 2005;Ferrari et al 2009;McCoy et al 2015). It has also been shown the ability of tadpoles to modify the antipredator response and recognize predation risk cues through learning (Ferrari et al 2009;Gonzalo et al 2010;Polo-Cavia and Gomez-Mestre 2014;Chivers et al 2016;.…”