Variation in predator species abundance can cause variable selection pressure on warning signaling prey

Abstract

Predation pressure is expected to drive visual warning signals to evolve toward conspicuousness. However, coloration of defended species varies tremendously and can at certain instances be considered as more camouflaged rather than conspicuous. Recent theoretical studies suggest that the variation in signal conspicuousness can be caused by variation (within or between species) in predators' willingness to attack defended prey or by the broadness of the predators' signal generalization. If some of the predator species are capable of coping with the secondary defenses of their prey, selection can favor reduced prey signal conspicuousness via reduced detectability or recognition. In this study, we combine data collected during three large-scale field experiments to assess whether variation in avian predator species (red kite, black kite, common buzzard, short-toed eagle, and booted eagle) affects the predation pressure on warningly and non-warningly colored artificial snakes. Predation pressure varied among locations and interestingly, if common buzzards were abundant, there were disadvantages to snakes possessing warning signaling. Our results indicate that predator community can have important consequences on the evolution of warning signals. Predators that ignore the warning signal and defense can be the key for the maintenance of variation in warning signal architecture and maintenance of inconspicuous signaling.

Influences of geographic differentiation in the forewing warning signal of the wood tiger moth in Alaska

“…At least two studies have found some possible taxon-specific influences. The presence of common buzzards is also shown to be associated with increased attacks on aposematic patterns of European vipers (Valkonen et al 2012). Another study by Nokelainen (2013) found that male wood tiger moths with yellow hindwings were attacked less than those with white hindwings when the predator community was dominated by avian predators in the Paridae family.…”

Evaluating the potential for evolutionary mismatch in Batesian mimics: A case study in the endangered smooth snake (Coronella austriaca)

“…However, a previous field experiment tested the advantage of bearing a viper‐like phenotype against birds of prey and found that it reduced overall predation risk by a factor of 3 (CI 95%  = 2.44–3.88) (Valkonen et al., 2012). This benefit of viper mimicry is of similar magnitude to the 2.3‐fold (CI 95%  = 1.65–3.78) increase in human‐induced mortality.…”

“…It can therefore be expected that better copies of venomous model species were better protected from natural predation and selected for by natural selection. However, this may not hold against specialist predators that are not paying a cost for attacking the venomous model species and possibly favouring them in their diet (Endler & Mappes, 2004; Valkonen et al., 2012). In the same way, as long as it is not costly for humans to attack vipers, they will likely continue to do so.…”

Does spatial variation in predation pressure modulate selection for aposematism?

“…The current study revealed a tremendous variation in predation pressure (30%–80% attacked) across a large geographic area in South and East Asia, which is also supported by global patterns of predation gradients (Roslin et al., 2017). Local variations in predator community composition and differences in predation pressure have also been shown to be an important driver of diversity in aposematic signals (Mochida, 2011; Nokelainen et al., 2014; Valkonen et al., 2012). Theoretical modeling (Endler & Mappes, 2004) and field experiments with artificial prey (Willink, 2014) have shown that a predator's willingness to attack different colors or conspicuousness may vary leading to variations in warning signal.…”

“…Seasonal variation in predator communities has been shown to impose seasonally dependent selection pressure on aposematic signals of varying conspicuousness (Mappes, Kokko, Ojala, & Lindström, 2014). As aposematic and mimetic signals occur over large geographic areas (Davis Rabosky et al., 2016), spatial variation in the abundance and identity of predators could result in corresponding changes in predation pressure (Nokelainen, Valkonen, Lindstedt, & Mappes, 2014; Valkonen et al., 2012). Hence, we proposed the hypothesis that spatial variation in predation pressure drives conspicuousness‐dependent spatial variation in aposematic and mimetic signal fitness (Figure S1a, b).…”