Abstract

Camouflage through background matching is a widespread antipredator strategy in which animals blend in with their background to avoid detection. To maximise survival in a variable natural environment, animals can have colourations that either match one of the backgrounds maximally (i.e. specialist strategy) or match multiple backgrounds partially (i.e. generalist strategy). Theoretical work indicates that the optimal strategy depends on the extent of visual difference between the backgrounds (i.e. heterogeneity) or how commonly the animal will encounter the background types. However, the role of another critical determinant of detection, the visual complexity of the background, on optimal camouflage strategy (specialist versus generalist) in the face of background heterogeneity, remains unknown. Here, we performed a virtual predation experiment employing humans as surrogate ‘predators’ and explored how background complexity influences camouflage in heterogeneous backgrounds. Under low heterogeneity, we found the latency to attack generalists was higher than that for specialists on a complex background, but there was no difference between specialists and generalists on a simple background. At intermediate heterogeneity, both specialist and generalist targets took a similar time to be attacked irrespective of complexity, suggesting that both the strategies may co-exist. In contrast, at high levels of heterogeneity, we found generalists were attacked sooner when compared to specialists irrespective of whether the background was simple or complex. Our results thus suggest that complex backgrounds favour the evolution of a generalist background matching strategy that maximises fitness in multiple backgrounds but only when the visual difference between the backgrounds is low. Overall, our study provides key insights highlighting the underappreciated role of background complexity on the optimization and evolution of camouflage colouration in a heterogeneous environment.

Significance statement

Many animals often face the challenge of encountering multiple visually distinct backgrounds due to variation in their environment, i.e. background heterogeneity. How should animals optimise camouflage when there is background heterogeneity? Theoretical studies have proposed that animals may match one of the many backgrounds (specialise) or match multiple backgrounds partially (generalise) as an optimal solution. However, cognitive constraints from the predator’s perspective may also have a role to play in this optimization problem, but this has not been examined. Our experiments involving humans as ‘predators’ show that when background complexity renders the search task more difficult, generalist targets took a longer time to be attacked than specialist targets, but only in less heterogeneous backgrounds. However, irrespective of complexity, specialist targets are better than generalists at avoiding attack in highly heterogeneous backgrounds. Cognitive constraints of predators may, therefore, play a significant role in the optimization of camouflage colouration in heterogeneous environments.

中文翻译：

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背景复杂度和最佳背景匹配伪装

摘要

通过背景匹配进行伪装是一种广泛的反掠食者策略，在这种策略中，动物会与其背景融为一体以避免被发现。为了在可变的自然环境中最大化生存，动物可以具有与最大背景之一匹配的颜色（即专家策略）或部分与多个背景匹配的颜色（即通才策略）。理论工作表明，最佳策略取决于背景之间视觉差异的程度（即异质性）或动物遇到背景类型的频率。但是，面对背景异质性，检测的另一个关键决定因素，即背景的视觉复杂性，在最佳伪装策略（专家对通才）上的作用仍然未知。这里，我们进行了以人为替代“掠食者”的虚拟捕食实验，并探索了背景复杂性如何影响异构背景中的伪装。在低异质性下，我们发现攻击通才的潜伏期比复杂背景下的专家要高，但是在简单背景下通才和专家之间没有什么区别。在中等程度的异质性下，无论复杂程度如何，专家目标和通才目标都需要花费相似的时间来受到攻击，这表明这两种策略可以共存。相反，在高度异质性下，我们发现通才比专家更容易受到攻击，而不论背景是简单还是复杂。因此，我们的结果表明，复杂的背景有利于通才背景匹配策略的发展，该策略可最大化在多个背景中的适应性，但前提是背景之间的视觉差异很小。总的来说，我们的研究提供了重要的见解，突出了背景复杂性在异构环境中优化和演变伪装色的作用不足。

重要性声明

由于环境的变化，即背景异质性，许多动物经常面临遇到多个视觉上不同的背景的挑战。存在背景异质性时，动物应如何优化伪装？理论研究已经提出，作为最佳解决方案，动物可以匹配许多背景之一（专业）或部分匹配多个背景（一般）。但是，从捕食者的角度来看，认知约束也可能在此优化问题中发挥作用，但是尚未对此进行检查。我们的以人类为“掠食者”的实验表明，当背景复杂性使搜索任务更加困难时，与专业目标相比，通才目标受到的攻击时间更长，但背景的异质性较低。但是，不管复杂程度如何，在避免高度异构的背景下进行攻击时，专家目标比通才要好。因此，捕食者的认知限制可能会在异构环境中优化伪装色方面发挥重要作用。