The dual benefits of aposematism: Predator avoidance and enhanced resource collection

School of Biological Sciences, Biosciences, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.
Evolution (Impact Factor: 4.61). 06/2010; 64(6):1622-33. DOI: 10.1111/j.1558-5646.2009.00931.x
Source: PubMed

ABSTRACT Theories of aposematism often focus on the idea that warning displays evolve because they work as effective signals to predators. Here, we argue that aposematism may instead evolve because, by enhancing protection, it enables animals to become more exposed and thereby gain resource-gathering benefits, for example, through a wider foraging niche. Frequency-dependent barriers (caused by enhanced conspicuousness relative to other prey and low levels of predator education) are generally assumed to make the evolution of aposematism particularly challenging. Using a deterministic, evolutionary model we show that aposematic display could evolve relatively easily if it enabled prey to move more freely around their environments, or become exposed in some other manner that provides fitness benefits unrelated to predation risk. Furthermore, the model shows that the traits of aposematic conspicuousness and behavior which lead to raised exposure positively affect each other, so that the optimal level of both tends to increase when the traits exist together, compared to when they exist in isolation. We discuss the ecological and evolutionary consequences of aposematism. One conclusion is that aposematism could be a key evolutionary innovation, because by widening habitat use it may promote adaptive radiation as a byproduct of enhanced ecological opportunity.

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    • "It has been suggested recently that aposematic species may have advantages over cryptic ones during the exploitation of newly available resources (Speed et al., 2010). That is because aposematic colouration grants individuals the protection to freely move around and explore, for example, new habitats as local predators would quickly learn that they are unpalatable (Speed et al., 2010). If prey can survive from the attack (Skelhorn and Rowe, 2006), or predators are neophobic (i.e., refuse to attack novel prey (Marples and Kelly, 1999)), or they have inherited tendencies to avoid such prey (Lindström et al., 1999a), these can indeed enhance the invasion success. "
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    ABSTRACT: The striking colour-pattern variation of some aposematic species is paradoxical because selection by predators is expected to favour signal uniformity. Although the mechanisms allowing for the maintenance of such variation are not well understood, possible explanations include both non-adaptive processes like drift and gene flow; and adaptive processes, such as an interaction between natural and sexual selection, spatial and temporal variation in selection, a link between behaviour or other fitness-related traits and phenotype, and predators’ ability to generalise among different signals. Here we test whether warning-signal polymorphisms, such as that of dyeing poison frogs (Dendrobates tinctorius), could be maintained by differences in detectability among morphs. We did experiments in the wild using wax models with different aposematic colour patterns vs. cryptic ones, and examined the attack rates by wild predators over time. We also tested the detectability of different aposematic morphs by ‘human predators’ under different light environments. We found that cryptic frog models were attacked more than aposematic models, but there were no differences in bird attack rates towards the different aposematic morphs. However, we found that detectability of different morphs depends both on predator experience and light environment. We suggest that the interaction between differential detectability and signal efficiency among morphs in different light conditions could be a mechanism aiding to the maintenance of warning-signal polymorphisms. Our results highlight the importance of considering the light environment at which predators have their first encounters with aposematic prey for future studies on predation in the wild.
    Behavioural Processes 08/2014; 109(B):164-172. DOI:10.1016/j.beproc.2014.08.014 · 1.57 Impact Factor
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    • "The rate of various behavioral elements, such as movement, foraging, and sexual displays influence conspicuousness of prey, as well as conspicuousness influences the escape behavior of prey (e.g., Galatowitsch and Mumme 2004; Pröhl and Ostrowski 2011; Ozel and Stynoski 2011). Therefore, behavioral traits that increase exposure should be favored in aposematic animals (Speed et al. 2009). However, only a few studies have addressed the correlation between behavioral and coloration conspicuousness, and most of them are based on comparisons across species. "
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    ABSTRACT: Aposematism and crypsis are often viewed as two extremes of a continuum of visual conspicuousness to predators. Theory predicts that behavioral and coloration conspicuousness should vary in tandem along the conspicuousness spectrum for antipredator strategies to be effective. Here we used visual modeling of contrast and behavioral observations to examine the conspicuousness of four populations of the granular poison frog, Oophaga granulifera, which exhibits almost continuous variation in dorsal color. The patterns of geographic variation in color, visual contrast, and behavior support a gradient of overall conspicuousness along the distribution of O. granulifera. Red and green populations, at the extremes of the color distribution, differ in all elements of color, contrast, and behavior, strongly reflecting aposematic and cryptic strategies. However, there is no smooth cline in any elements of behavior or coloration between the two extremes. Instead populations of intermediate colors attain intermediate conspicuousness by displaying different combinations of aposematic and cryptic traits. We argue that coloration divergence among populations may be linked to the evolution of a gradient of strategies to balance the costs of detection by predators and the benefits of learned aversion.
    Evolution 10/2013; 67(10):2783-2794. DOI:10.1111/evo.12153 · 4.61 Impact Factor
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    • "Our study is complementary to (and in part inspired by) that of Stankowich et al (2011) which examined ecological correlates of colour patterns in carnivores. But ours is different in its approach in four major ways: (1) Our focus is on how chemical defence influences the niche space that a species can occupy (Stamp and Wilkens 1993; Merilaita and Tullberg 2005; Speed et al 2010), not on which broad aspects of the habitat (e.g. density of vegetation) are related to aposematism. "
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    ABSTRACT: Avoidance of predation can impose opportunity costs on prey species that use behavioural avoidance strategies to evade detection. An animal that spends much time hiding or remaining immobile, for example, may have less time for other important activities such as foraging or finding mates. Here we examine the idea that the evolution of chemical defence may act to release prey from these constraints, freeing defended prey to exploit their habitats more effectively, and increasing their niche space. We tested this hypothesis using comparative methods on a mammal group containing both chemically defended and non-defended species: Musteloidea. We found that defended species had a more omnivorous diet and were more likely to be active during both day and night than non-defended species. We also found that chemically defended species were less likely to be strictly diurnal or to show sexual size dimorphism, and had earlier maturing females and a shorter lifespan than non-defended species. Taken together, our results support the hypothesis that chemical defence increases the niche space available to a species. More generally, this also supports recent suggestions that strategies taken to avoid natural enemies can have important effects on diverse components of life history.
    Evolutionary Ecology 09/2013; 27(5). DOI:10.1007/s10682-013-9629-z · 2.52 Impact Factor
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