Optimal-Foraging Predator Favors Commensalistic Batesian Mimicry

Atsushi Honma,Takayoshi Nishida,Koh-Ichi Takakura,Andy Gardner

doi:10.1371/journal.pone.0003411

Atsushi Honma, Takayoshi Nishida + Show 2 more

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https://doi.org/10.1371/journal.pone.0003411

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Abstract

BackgroundMimicry, in which one prey species (the Mimic) imitates the aposematic signals of another prey (the Model) to deceive their predators, has attracted the general interest of evolutionary biologists. Predator psychology, especially how the predator learns and forgets, has recently been recognized as an important factor in a predator–prey system. This idea is supported by both theoretical and experimental evidence, but is also the source of a good deal of controversy because of its novel prediction that in a Model/Mimic relationship even a moderately unpalatable Mimic increases the risk of the Model (quasi-Batesian mimicry).Methodology/Principal FindingsWe developed a psychology-based Monte Carlo model simulation of mimicry that incorporates a “Pavlovian” predator that practices an optimal foraging strategy, and examined how various ecological and psychological factors affect the relationships between a Model prey species and its Mimic. The behavior of the predator in our model is consistent with that reported by experimental studies, but our simulation's predictions differed markedly from those of previous models of mimicry because a more abundant Mimic did not increase the predation risk of the Model when alternative prey were abundant. Moreover, a quasi-Batesian relationship emerges only when no or very few alternative prey items were available. Therefore, the availability of alternative prey rather than the precise method of predator learning critically determines the relationship between Model and Mimic. Moreover, the predation risk to the Model and Mimic is determined by the absolute density of the Model rather than by its density relative to that of the Mimic.Conclusions/SignificanceAlthough these predictions are counterintuitive, they can explain various kinds of data that have been offered in support of competitive theories. Our model results suggest that to understand mimicry in nature it is important to consider the likely presence of alternative prey and the possibility that predation pressure is not constant.

Highlights

Ever since the phenomenon of mimicry was first described [1,2], it has drawn a great deal of attention, and it has been intensively studied as an example of Darwinianevolution [3,4,5,6,7,8]
We propose here a mimicry model in which the Pavlovian predator system [18,20] is expanded by including alternative prey and a predator that follows optimal foraging strategy ( = a Darwinian predator), because the existence of alternative prey to the aposematic prey species has a significant effect on mimicry [33,34,35]
We developed a simulation model in which a psychologically based Monte Carlo predator [18,20] behaves according to optimal foraging theory [38,39], and examined how the introduction of alternative prey affected Model–Mimic relationships, and whether these relationships depended on the relative or absolute density of the Model species

Summary

Introduction

Ever since the phenomenon of mimicry was first described [1,2], it has drawn a great deal of attention, and it has been intensively studied as an example of Darwinian (co)evolution [3,4,5,6,7,8]. Because predator psychology is expected to affect the relationship between Model and Mimic, we assumed two different manners of learning by the predator: a fixed learning rate, where the learning rate a was held constant over each feeding trial and palatability was influenced by only the asymptote of the estimated value En; and a variable learning rate a, in which the learning rate depended on prey palatability as well as on the asymptotic level of avoidance.

Results

Conclusion