Visual Deception Defenses
Overview
This OER was created to inform individuals about the visual mechanisms which allow animals, primarily prey, to defend themselves in nature. These different mechanisms are incredibly complex, and could provide a reader with more insight into how these mechanisms function in nature. The types of defense mechanisms that this OER explores include camouflage, mimicry, and deimatic modifications.
Visual Deception & Confusion: A Look at Defensive Mechanisms in Animals
Animals rely on several different means of defense to ensure their ability to survive in nature, and one such method is visual deception. Defense by visual deception, in a broad definition, is when animals use visual signaling to deceive or dissuade potential predators. Visual signaling is a complex behavior. Numerous factors. such as color, pattern, viewing angle, size, and shadowing all influencing what is perceived by the observing animal or predator. This arms animals who use visual deception with a means to defend themselves with a multitude of tools and methods to survive in the presence of a predator. Most of the methods and applications of visual deception fall into three main categories of defense mechanisms: mimicry, camouflage, and deimatic modifications. Mimicry is when an animal resembles another species of animal, plant, or even an inanimate object with sometimes a near identical appearance. Camouflage is the mechanism where animals blend in with their surroundings to prevent predators from identifying them, knowing their location, or seeing their movements. Camouflage is also called cryptic coloration and relies heavily on the animal's physical characteristics to match the features of the environment (Boudreau et al 2011). Finally, deimatic displays are when animal species spontaneously produce an appearance that scares, confuses, or distracts potential predators during encounters. As further explained below, all of these visual deception defenses are elaborate and have a wide range of applications from species all across the animal kingdom.
A variety of species protect themselves from predators by utilizing mimicry to confuse and evade. For these species, ocular deception works by mimicking other species or singular natural objects around them. One example of a species using mimicry as a defensive mechanism can be seen deep in the oceans of the Caribbean. The bottom feeding octopus, Macrotritopus defilippi, was recorded on multiple separate occasions, from multiple different subjects, exhibiting the movement patterns and body shape of the sand-dwelling flounder, Bothus lunatus (Hanlon et al. 2010). As seen in Figure 1 below, the octopi were photographed on multiple occasions modifying their physical shape and movement behaviors to copy that of the flat and slow-moving flounder.
Figure 1: Macrotritopus defilippi performing flounder mimicry. (A) Normal backward swimming; October 2000. (B) Apparent flounder mimicry; October 2000. Figure 1. The Biological Bulletin. Open Access. Four examples of the bottom-dwelling octopus mimicking the sand-dwelling flounder.
Normally these octopi suffer from attacks from local predators such as sharks, but when mimicking the flounders, the octopi suffer from far fewer attacks (Hanlon et al. 2010). This is just one example of a species actively using mimicry to protect themselves, however, some species have evolved over hundreds of thousands of years to benefit from passive mimicry. Species like the False Coral Snake, Oxyrhopus petolarius, benefit from mimicry as a defense mechanism by confusing predators into believing they are poisonous and not worth attacking (Buasso et al. 2006). In this case the false coral snake has evolved over time to develop the same ring coloration and similar color pattern as the poisonous species of coral snake, Micrurus fulvius. Instead of actively changing their physical shape or movement patterns like the bottom-dwelling octopi, these coral snakes inherit the mimicry traits of their ancestors to protect themselves from predators. One last example of mimicry can be seen not in an animal mimicking another, but an animal using mimicry to match an object in the environment around them. The common stick-bug, Phasmatodea, seen all over the world, also uses mimicry as a defensive mechanism. The stick-bug does this exactly as its name states, it mimics a stick (Purser 2003). As seen below in Figure 2, two stick-bugs use mimicry to match the branch they are hanging on to hide from predators.
Figure 2: A pair of mating phasmids suspended below a branch in secondary forest near Rotorua, New Zealand. Photo 3. Jungle Bugs: Masters of Camouflage and Mimicry. Special Permission. Two Stick-bugs using environmental mimicry as a defensive mechanism
As one can see, a multitude of species utilize mimicry as a defensive mechanism to protect themselves from predators around them. This comes in the form of active mimicry, changing their physical makeup and behavior to confuse and evade attackers. Passive mimicry is another form of mimicry that can be seen in animals evolving over time to mimic poisonous species. Lastly, it can be seen in species using mimicry to match singular environmental objects and hide from the eyes of their predators. Unlike camouflage where species match the whole environment, not just one object.
Camouflage, also defined as crypsis, allows an animal to conceal itself from predators by blending into its environment using a specific color, pattern, and shape. The overall defense mechanism works by exploiting a predator’s cognitive ability (Cuthill 2019). The colors and patterns displayed by animals, combined with optical factors can reduce the salience of primitive features, surfaces, edges, body parts, and even the whole body of an animal (Merlaita et al. 2017). Camouflage can take on a number of different visual forms including background matching, disruptive coloration, distraction marks, and self shadowing. These colors and patterns can remain the same throughout an animal’s entire life, or can change rapidly depending on a specific species’ type of camouflage. This means of defense is incredibly diverse and exists across a broad range of species within the animal kingdom.
Perhaps the most broad form of camouflage, background matching relies on a species’ ability to resemble their environment using a variety of colors and patterns (Cuthill et al. 2017) When an animal’s environment is homogeneous, with no variation in texture, luminance, and hue, a single optimal camouflage pattern exists. This form of camouflage can be seen in Figure 3, which demonstrates a nightjar’s ability to conceal itself within the leafy ground environment. The efficacy of background matching can be limited by the outline of an animal as it creates discontinuities between the concealed species and its background. In a heterogeneous environment, species prioritize matching one background well, at the expense of appearing more visible in a different background (Michalis et al. 2017).
Figure 3: "A Long-tailed Nightjar in Gambia. It is on the ground camouflaged amongst leaves." by Gisela Gershon Lohman Braun is licensed under CC BY-SA 2.0 Nightjar relying on background matching to disguise itself on the forest floor
Different from background matching, certain species employ disruptive coloration, which relies on breaking up an animal’s outline by using a variety of high contrast patterns. These patterns occur near the edges of an animal’s outline to interrupt cognitive recognition of normal objects (Price et al. 2019). This type of camouflage works best when the luminance of the animal matches that of its background, but is not as dependent on the background mirroring animal patterns. One example of disruptive coloration occurs in precocial plover chicks. These chicks are able to use their neoptile feathers to effectively diffuse their outline, thus increasing their survivability (Rohr et al. 2021). In Figure 4 below, a tiger can be seen employing disruptive coloration patterns to camouflage itself. This form of camouflage is found to be more effective in environments with multiple backgrounds, rather than a homogeneous one.
Figure 4: "Tiger in high grass" by Akshit Deshlande is licensed under CC BY-SA 4.0 Tiger relying on disruptive coloration to camouflage itself among grasslands
Countershading, or self shadow concealment is a form of camouflage that relies on an animal having a darker appearance on the top of their body, and lighter on the bottom. When light falls above a species, a luminance gradient is produced across the body’s surface. An organism’s combination of countershading with this luminance effect allows this organism to have uniform darkness, and a lack of depth relief. This form of camouflage can be found in a large range of animal groups such as deer and sharks.
Figure 5: "Great white shark at Guadalupe Island" by Horizon Charters is licensed under CC BY-SA 4.0 Great white shark exhibiting countershading camouflage
One of the most effective means of crypsis is active camouflage, also known as adaptive camouflage. This type of camouflage relies on a species ability to dynamically change different colors, often in a short period of time. Active camouflage allows a species to blend in with a variety of backgrounds, often through background matching. This type of camouflage provides a greater advantage compared to a species’ that has a fixed pattern, providing greater adaptability in heterogeneous background patterns. Active camouflage has a number of impressive biological and mechanical systems that allow certain species to rapidly adapt to a number of environmental factors. Due to specific neuro-musculo organs species such as the cuttlefish and a variety of octopi are able to control bumps on their skin that can disrupt their body shape and change texture (Gonzales-Bellido et al. 2018). These bumps, also known as papillae, allow for rapid changes in color and texture in these animals, with a fast expression and retraction system, as well as long term expression abilities. This rapid color change can be found in types of reptiles on land, such as chameleons, while pelagic species use this method of camouflage in water. One such species is the rockpool goby, shown in Figure 6, which is able to change its color in less than one minute (Stevens et al. 2014).
Figure 6: "Figure 3. Examples of changes in brightness of fish." by Stevens et al. is licensed under CC BY 4.0 Rock gobies demonstrating ability to rapidly change color
Certain factors place constraints on the effectiveness of camouflage. One such factor is the size of an animal, which affects the distance at which a target can be detected, depending on habitat size and spatial acuity of a viewer. An animal’s shape also influences the effectiveness of camouflage, as an unnatural shape not found in an environment can alert viewers to the presence of an animal, as well as unusual posture or orientation. Motion is perhaps the largest of these constraints, as most animals have to move at some point in their life. When an animal moves, it breaks the uniformity of the animal’s appearance with its environment, however some factors, such as background motion mitigate this factor (Cuthill et al. 2017). Despite its proven effectiveness in nature, camouflage is not a foolproof defense mechanism, and relies on a vast amount of factors to conceal prey from predators.
Another major consideration of the research about camouflage was the way changes in the environment can affect this visual defense mechanism. Unfortunately, with the growing climate change issue, certain animal species that use passive seasonal camouflage such as snowshoe hares are negatively impacted. Using data gathered by a research team in North America, the team explains how “phenological mismatches, when life-events become mistimed with optimal environmental conditions, have become increasingly common under climate change” (Zimova et al. 2019). In North America, the snow season is becoming increasingly shorter which results in an increased chance of a mistimed molting of the snowshoe hare’s winter coat. This ties human connection with visual deception research and conveys the potential impacts humans have on defense mechanisms that animal species rely on to survive.
In many animal species, altering the physical shape or form of an individual’s body is a form of physical deimatic behavior that intimidates or scares away predators. This is another form of defensive behavior similar to other tactics previously discussed. However, physical deimatic behavior is the way in which an animal modifies its appearance so that it seems obscure or odd which makes a predator hesitant to attack (Olofsson et al 2012). Sending dishonest or false signals is the basis of deimatic behavior.
Figure 7: A frilled-neck lizard enlarging its neck frill as a display of intimidation towards a predator. Chlamydosaurus kingii by Miklos Schiberna, Public Domain
The use of misinformation is weaponized to preserve fitness and the life of the individual (Mokkonen 2015). This form of deception relies on recognition errors in those that are perceiving the subject to make them think that they are seeing something foreign or completely new (Mokkonen 2015). Naturally, animals will be nervous to engage with a new animal or object. Examples of this behavior as a defense, can include quick and rhythmic motion such as moths that will flap their wings aggressively and in abnormal patterns which, in experimental and observed cases, deters predatory birds from eating them (Olofsson et al 2012). Normally, these moths flap their wings when flying but this is in a very predictable pattern that others will observe as normal. This change in behavior is a way to bluff and show other animals that something is wrong, it can communicate that no one should come near them. Other ways that animals utilize physical deimatic behavior to defend themselves is enlargement and shapeshifting.
In Opisthobranchs, specifically the Glossodoris cincta, enlargement of the mantle through muscle flexing can make the mollusk appear different compared to its normal form (Ghazali 2006). In an experimental test of this phenomenon, the presence of crabs and fish prompted the mollusk species to flex itself 100% of the time (Ghazali 2006). It is deduced that this behavior is used when the creature feels threatened and is a defense mechanism to prevent premature death.
Similar techniques can be observed in snakes. Many snakes, under predation of larger animals, will create poses that indicate an imminent defensive attack towards the animal that is intimidating the snake (Cox 2021). This stimulus induced behavior expresses a bluffing tactic or deimatic technique that sends signals to the predator that something is wrong in order to deter them (Cox 2021). This is a deceptive signal that is only applied in situations that make the animal feel as though they are in danger. The same method is observed in crustaceans when they move their chelipeds in abnormal movements (Arnott 2010). This is another way that animals bluff and send false messages to predators. Moving the cheliped in a different manner can imply that the crab is ill or erratic which is not advantageous to eat for predators (Arnott 2010). All of these behaviors described are physical modifications that are deimatic or bluffing in nature. This behavior has been observed as being very effective in defending oneself and prolonging an individual’s lifespan. Over long periods of evolution, countless species have adopted these behaviors because of their usefulness.
Figure 8: A snake coiling its tail in a physical display of aggression to defend itself and a crab flashing its chelipeds. "Wild snake encounter" and "Rabid crab" by Unsplash, Public Domain
In the animal kingdom, species use countless defense mechanisms to survive harsh environments riddled with predators and other threats. As explained, visual deception is a popular defense mechanism used across the animal kingdom to increase the survivability of species that are more susceptible to harm in an engagement with a predator. Visual deception, like most other categories of defense mechanisms, comes in many different forms as well as methods of using each form. Whether it is resembling other animals or plants, blending into the environment, or spontaneously enabling a startling or confusing display, visual deception allows animals to avoid predator encounters. Thanks to the advancements and new approaches in animal behavior studies, so much is known about visual deception defenses used by species all over the world. However, as animal behavior becomes more inclusive to people from all walks of life, new perspectives and ways of thinking will help to discover more about visual deception as well as all aspects of animal behavior. This is why it is so important, especially as individuals in STEM, to be open-minded and pursue a future of science that boasts inclusiveness and diversity.
The accumulation of information regarding the aforementioned defense mechanisms was done so by acknowledging the impact of research in this field. In the near future more underrepresented and marginalized groups will have better access to the content provided not only here but also in the area of study relating to animal behavior. With this comes the responsibility to allow for multiple perspectives to be used when researching subjects and make open education resources digestible for any and all groups (Bass et al. 2016). Higher education has ushered in a new era in diversity and inclusion which means that members of the science community need to uphold this trend and foster growth for marginalized groups such that their participation is continued for the betterment of the subject and higher education (Bass et al. 2016). It is important to keep this in mind as oftentimes disabled individuals and minorities can be victim of stigmatization in science and their opinions and voices can be left unheard (Marks 2017). A small percentage of the science community is part of these demographics yet their share outside of STEM is larger. This disparity needs to be abolished and the inclusion of these groups should be prioritized and acknowledged (Marks 2017). In this paper, this is done by acquiring sources from a plethora of backgrounds that provide the most diversity that the team was able to achieve. The team made sure to consider the author’s background for every source that was included. It is important to keep in mind that where the article originated and who originated it are two factors that can shape how inclusive the information is. An article that comes from an indiginous source may capture information that isn’t prevalent in mainstream science. On top of this, the narrative used in this OER does not assert absolute dominion over facts and interpretations, but provides the more raw and widespread undisputed phenomena that are observed in nature. This includes the behaviors of the mollusk, octopus, tiger, fish, sea slug, and more that were exemplified in this document. In an effort to overcome implicit bias, the authors did not assert new trends that are not previously acknowledged in the science community. This nurtures an environment of openness and inclusion that scientific papers should incorporate.
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