Spatial and temporal variation in prey color patterns for background matching across a continuous heterogeneous environment

Varying benefits of generalist and specialist camouflage in two versus four background environments

Background-matching camouflage is a well-established strategy to reduce detection, but implementing this on heterogeneous backgrounds is challenging. For prey with fixed color patterns, solutions include specializing on a particular visual microhabitat, or adopting a compromise or generalist appearance, matching multiple backgrounds less well. Existing studies suggest both approaches can succeed, but most consider relatively simple scenarios, where artificial prey appear against two backgrounds differing in a single visual characteristic. Here, we used computer-based search tasks with human participants to test the relative benefits of specializing and generalizing for complex targets, displayed on either two or four types of naturalistic backgrounds. Across two background types, specialization was beneficial on average. However, the success of this strategy varied with search duration, such that generalist targets could outperform specialists over short search durations due to the presence of poorly matched specialists. Over longer searches, the remaining well-matched specialists had greater success than generalists, leading to an overall benefit of specialization at longer search durations. Against four different backgrounds, the initial cost to specialization was greater, so specialists and generalists ultimately experienced similar survival. Generalists performed better when their patterning was a compromise between backgrounds that were more similar to each other than when backgrounds were more different, with similarity in luminance more relevant than pattern differences. Time dependence in the relative success of these strategies suggests that predator search behavior may affect optimal camouflage in real-world situations.

Lichens and animal camouflage: some observations from central Asian ecoregions

Camouflage is a fitness-relevant trait that supports survival and fosters evolutionary adaptation by which animals match their body pattern to a background setting. Lichens are among the most common of these backgrounds that several animal species use for camouflage. Lichens are omnipresent and grow in wide arrays of colorations and compositions. Their composition and phenotypic diversity might facilitate cryptic coloration and habitat matching by various animal species. Here, we describe the role of lichens in providing camouflage to various animal species in central Asian and Caucasus mountain ecoregions, which are categorized as global biodiversity hotspots. Despite multiple ecological studies, no information is available on the role of this regions‘ lichen diversity in providing animal camouflage. Casual field observations of lichen camouflage are reported for four (one mammal and three reptile) species: the Persian Leopard’s Panthera pardus saxicolor body coat seems to closely match the colors and patterns of saxicolous lichens (Acarospora sp. and Circinaria sp.) in their habitat.  A similar background matching pattern was observed in both morphs of the Caucasian Rock Agama Paralaudakia caucasia upon crustose lichens: Caloplaca spp., Circinaria spp., and the Radde’s Rock Lizard Darevskia raddei to the crustose lichens Acarospora sp. and Caloplaca sp. Likewise, the Horny-scaled Agama’s Trapelus ruderatus grey matches with the color of multiple lichens (Lecanora spp., Circinaria spp., Protoparmeliopsis spp., Rinodina spp., and Anaptychia spp.). Our observations preliminarily suggest that lichens play an important role for species of different trophic levels, ensuring adaptation and survival through camouflage. We call for more field-based empirical and experimental studies in various terrestrial ecosystems in other parts of the world to test the role of lichens in local adaption and evolutionary plasticity of regional species.

Generalist camouflage can be more successful than microhabitat specialisation in natural environments

BACKGROUND

Crypsis by background-matching is a critical form of anti-predator defence for animals exposed to visual predators, but achieving effective camouflage in patchy and variable natural environments is not straightforward. To cope with heterogeneous backgrounds, animals could either specialise on particular microhabitat patches, appearing cryptic in some areas but mismatching others, or adopt a compromise strategy, providing partial matching across different patch types. Existing studies have tested the effectiveness of compromise strategies in only a limited set of circumstances, primarily with small targets varying in pattern, and usually in screen-based tasks. Here, we measured the detection risk associated with different background-matching strategies for relatively large targets, with human observers searching for them in natural scenes, and focusing on colour. Model prey were designed to either 'specialise' on the colour of common microhabitat patches, or 'generalise' by matching the average colour of the whole visual scenes.

RESULTS

In both the field and an equivalent online computer-based search task, targets adopting the generalist strategy were more successful in evading detection than those matching microhabitat patches. This advantage occurred because, across all possible locations in these experiments, targets were typically viewed against a patchwork of different microhabitat areas; the putatively generalist targets were thus more similar on average to their various immediate surroundings than were the specialists.

CONCLUSIONS

Demonstrating close agreement between the results of field and online search experiments provides useful validation of online citizen science methods commonly used to test principles of camouflage, at least for human observers. In finding a survival benefit to matching the average colour of the visual scenes in our chosen environment, our results highlight the importance of relative scales in determining optimal camouflage strategies, and suggest how compromise coloration can succeed in nature.