Survival Instincts

 🔐 Charles Darwin's Origin of species explains how survival instincts are acquired through adaptations and conveyed to generations by learning or by genetic transmission.

Everyday life in the wild is a continual struggle to survive and remain in existence. Plants and animals have through time evolved to defend themselves against herbivory or predation. The predator-prey relationship is a perpetually dynamic one. Both kinds endlessly develop tactics and schemes by which they must survive. For example, if a predator discovers a strategy demonstrated by the prey, the predator modifies its tactics to overcome the challenge. In this article, we shall review mechanisms developed by preys that enable them to survive through time. 

In the constant struggle for survival between predators and prey, prey has evolved traits and mechanisms to avoid being devoured. These behaviours include visual information-transmission techniques (such as camouflaging, cryptic and colour display, self decorations, e.t.c.), physical adaptations (playing dead, flight, or fighting off the predator) and chemical modes of defence.

A perfect case of cryptic colouration by Moths. Photo courtesy: istockphoto

 🔐 Predators learn to avoid certain organisms based on the capabilities they present especially when they have no trick to outmanoeuvre them.

Let's see some instances of anti-predatory mechanisms developed by preys.

• Resemblance benefit

Mimicry is a phenomenon whereby an organism evolves to resemble another organism to the benefit of one or both. Visibility is usually of central importance. There are various kinds of mimicry but two are of supreme significance

• Batesian mimicry: this form of defence occurs when a species (S1) that is factually innocuous protectively impersonates another species (S2) that are potentially dangerous to the predator. This is beneficial when the signal requires the vision of the predator. For instance, S2 might be a poisonous, bitter-tasting or unpalatable insect or reptile. S1 takes advantage of this by appearing physically identical to it. The predator which could be incapable of discriminating between the two species would avoid them altogether as a consequence. This mechanism is used by insects (e.g butterflies and ants) and reptiles.

Due to the similarities between wasps and hornets (both are stinging insects), they are equally avoided by their potential predators. Photo courtesy: istockphoto

• Mullerian mimicry: This form of mimicry involves two species that are unrelated to each other but possess similar characteristics of being nasty, dreadful or harmful to predators. For example, they might both be toxic to the threat. The predator, therefore, avoids both. Examples of this mimicry are hornets, yellowjackets and wasps. These stinging insects are unrelated but possess synonymous black and yellow stripes. Insectivores therefore must avoid any insect with these colour patterns. 

Mimicry is usually observed in evolutionarily unrelated species

• Cryptic colouration

This pertains to any method which is employed by any organism to conceal its presence in a given space. This is used by predators and prey alike. They make themselves discreet to the observer and uses it to prepare a surprise attack or to escape sight. Below are a few examples of cryptic techniques of prey.

• Figure of confusion

A multicoloured organism might evade an attack by disrupting its figure against a background. The organism might be perceived but will not be recognized as the familiar prey. In some cases, the motion of the animal might contort the perception of the image and mesmerize the observer's visual processing. The actual magnitude of size and speed of the animals may be inaccurately computed all to be the advantage of the prey. The leafy seadragon is a popular aquatic organism whose jagged contours resembles seaweeds. This creature usually goes unapparent and its movements are also similar to that of seaweeds. The outline of moths usually blends with tree barks diminishing their visibility.

The leafy seadragon remains inconspicuous among the seaweeds. Photo courtesy: istockphoto

 • Emerging in new skins

Cephalopods, octopuses and reptiles (e.g chameleon and lizards) are champions of the game. These animals actively reorganize chromophores in their skins generating new colours, allowing them to blend with the external environment. They could also contract muscles to change shapes.

Octopuses rapidly change colour and shape, blending indiscriminately with their surroundings either to initiate an attack or to avoid being victims. Photo courtesy: istockphoto

 • Strange Masquerades

Some animals mimic boring inanimate objects like twigs, leaves, sticks and stones. Some look like walking leaves (katydids). additional examples are the stick insects and stone bugs.

Stick insects may be easily mistaken for sticks that are uninteresting to their predators. Photo courtesy: istockphoto

 • Optical apparatus

To avoid being noticed from above and below, glass frogs possess optically see-through bodies. This mechanism is usually unusual to the predator and may not recognize it as a usual diet. In some cases due to reflection and background effects, the animal may not be beheld at all. This works best if the ratio of the refractive indices of the water and the muscles is a small value. 

The so-called glass frogs under appropriate environments appear disguised as their transparency conceals their shape, making them difficult to notice. Photo courtesy: istockphoto

Some fishes such as sardines are extensively reflective due to microscopic structures in their scales which strongly reflect light. To viewers above, the presence of the fish is missed at it shines just as the clear and reflective waters.

 • Armoury and weapons of war

Some animals like armadillos, bivalves, turtles, molluscs, nautilus e.t.c.  possess hard shells into which they retreat when posed with danger. Spiders spin webs that can not be accessed by other organisms, offering some protection. Some animals possess sharp claws, horns beaks or teeth that they use to defend themselves. Instead of being submissive casualties of the attack, they might actively fight off the predators either independently or in groups.

The shells of armadillos effectively safeguard their delicate bodies during an attack. Photo courtesy: istockphoto

 • Chemical ammunitions

Many animals are equipped with chemical weapons which they use whenever danger comes up. They concentrate these toxins in their skins, spines or glands and unleash them when a threat arises. Brightly coloured Poison arrow frogs (dendrobates and phyllobates) secrete one of the most dangerous toxins known to man. The toxins are found in their skins and contact with them could prove fatal. The frogs 'move freely without fear' but most predators dare not encounter these species. This phenomenon where a brightly coloured organism honestly warns predators is known as Aposematism. Blue-ringed octopuses and colourful caterpillars are often dangerous (just a single larva can kill a grown-up animal). Some snakes particularly those in the sea are brightly coloured. These types of snakes are usually among the most dangerous, and many predators might be aware of that. In aquatic systems, the 'crown of thorns starfish is one of the most dangerous animals on the seabed. Stinging rays, stonefishes, sea anemones, e.t.c are all poisonous aquatics. The electric eel and the stargazer are notorious for delivering high electrical voltages to their enemies. In these cases, the predator usually becomes the sufferer of the attack.

Pufferfishes have dual protective devices. Externally they project spines that injure their enemies. They also incorporate potent poisons in their bodies. Unfortunately, they would have to be consumed in the endeavour to prove that their species are harmful. Over time, predators learn to avoid them. Photo courtesy: istockphoto

In some instances, animals like the poisonous butterflies and fishes (e.g pufferfish), the prey with chemical defence actually would have to lose its life in the endeavour to prove that such species should be avoided exclusively. Predators, therefore, learn to avoid these organisms.

Poisonous arrow frogs produce highly poisonous alkaloids which paralyse and kill any danger that confronts them. Photo courtesy: istockphoto

 • Autotomy

After all efforts of defence have failed, some animals give themselves a last chance to escape by shedding a portion of their body. For example, lizards or geckos who are unfortunate in escaping might decide to shed their tails or limbs. These body parts wriggle and automatically grab the predator's attention. This gives enough time for the animal to flee from the distracted predator. But guess what, they are capable of regrowing the lost limb or tail!!!

 In a fight or defence, crustaceans might lose a leg or claw. They would later acquire the lost limb in their next moulting period. 

 • Athletic display

Jumping gazelles. Predators become intimidated acknowledging that they might never capture them. Photo courtesy: istockphoto

Some animals with no harmful attributes such as deers and butterflies might intimidate their potential predators by exhibiting athleticism or skills. This is to signal to the predator that it should never bother chasing it as it's very much healthy and would certainly escape from a chase. The observer is discouraged and gives up as it concludes that an attack would not be worthwhile.

 • Flight for life

Gazelle, Impalas and springboks simply run away when they sight danger. The prey's anatomy is usually well suited for escaping and could outrun its threat. The gazelle has a slender body and powerful legs which supports its lightweight. Biomechanics also reveals that skeletal dynamics are extensively developed making flight very effective. Birds fly away when they sense danger. Some insects like the butterflies fly erratically while others possess powerful wings and fly with great speed. Animals such as rabbits and rodents living in burrows seek protection by sprinting into their homes. Arboreals escape by climbing trees to avoid being attacked.

 • Out of sight, out of mind

Bats are nocturnal reducing their chances of being preyed upon. Photo courtesy: istockphoto

Some animals keep out of predators' eyes by arising at night. They live in caves, trees or underground and are only functional at night. It is expected that most animals especially predators would be inactive during the darkness. This lessens their chances of being preyed upon animals such as bats sleep during the day and emerge at night to feed. Such animals are usually adapted to nocturnal life by having enhanced eyesight or sonar-like systems.

Plants also evolved strategies to avoid being attacked by herbivores and to ensure their continued existence. Find out how in my forthcoming episode.