Defence Against Predation, Practice Problems and FAQs

Winston Churchill was the prime minister of Britain during the second world war. He was also a writer and a soldier. He once said “we sleep soundly in our beds because rough men stand ready in the night to visit violence on those who would do us harm”. He said this about the soldiers who protect the country from attacks of enemies. Have you ever seen them fighting? Yes, you have seen them on television. They have a particular uniform while fighting. The colour of the uniform of the Indian army is olive green. Right? Why is the colour olive green? Why did they choose such a colour? 

During the Burma campaign in world war II, there was a dense rain forest encounter. So to blend with the terrain the British Indian army changed the Khaki uniform to olive green. This helped them to hide from the enemies inside the forest. This mechanism is known as camouflage. The use of any material, colour, or lighting combination for hiding so that it will make animals or things difficult to notice or disguise them as something else, is known as camouflage. 

                    Fig: Soldiers with their camouflage uniform inside forest

Have you ever seen camouflages in animals or plants? You might have noticed the change in colour of chameleons while moving from one place to another. Why are they doing so? It is because of the same reason we mentioned above. They do so to protect themselves from predators. It is actually a defensive mechanism adapted by them. The spines in some plants are also developed for the defence against their predators. Just like this most of the animals and plants have their own defensive mechanism to protect themselves from the predators and it will be sometimes specific for each of their predators. Now we will discuss more about these defensive mechanisms in this article. 

Table of contents

• Predation
• Defence against predation
• Practice Problems
• FAQs

Predation 

The biological interaction between two organisms where one organism which is the predator that captures, kills and feeds on another living organism which is known as the prey is called as predation. It is a +/- type of interaction, because one organism is harmed by another one in this population interaction. 

                                            Fig: Predation

Flow of energy in predation

Predators can kill their prey before eating or they kill while they eat. Predation can be considered as a natural way of transferring energy. Some energy is gained by the prey while having food and this energy is transferred to the predator when the predator eats the prey. 

                                                      Fig: Flow of energy

Just like the predator-prey interaction between the tiger and deer, the bird eating a seed is also a predator and prey interaction. Every prey will try to avoid their interaction with predators. Ability to run away from predators is a kind of adaptation by animals, but for plants they have to develop some kind of chemical defences or physiological defences. We will now the wide range of antipredator strategies that prey exhibit, from chemical defences to warning colouration, camouflage, and mimicry. 

                                                       Fig: Predators

Defence against predation

What would happen if the predator develops extraordinary skills and efficiency? Yes, the prey population will decrease quickly and could perhaps go to extinction very soon. It will make a great impact on the predator population and the ecosystem too. Ultimately the predator would run out of food and go extinct. 

Thus, nature has a way to maintain a balance by giving the prey ways to avoid predators and also makes the predators prudent enough to not exploit the prey population. So these ways are called the defence against predation. The mechanisms adapted by the animals and plants are different. So first we will check out the defence against predation in animals. 

Defence against predation in animals

There are many defence mechanisms present in animals to escape from the predator. Some of them are listed below:

• Camouflage 
• Chemical defence
• Mimicry
• Physical defence
• Refuge

Camouflage 

The ability of preys to merge with their surroundings to avoid predators is known as camouflage. It is also known as cryptic colouration, because most of the time the colour of the prey will blend with their background. 

Examples of camouflage

There are many animals which show camouflage as an antipredator mechanism. Let us discuss some of them.

Camouflage in grasshopper

Grasshoppers such as Cicadella viridis which are green can blend with the leaves they feed, so that they will not get eaten by their predators. 

                             Fig: Camouflage in grasshopper

Camouflage in leaf wing butterfly

There is a butterfly called leaf wing butterfly or Charaxinae which can mimic dry leaves. Here the wings of the butterfly can mimic even the veins of the leaves, so that they will not get eaten by their predators. 

                              Fig: Camouflage in leaf wing butterfly 

Camouflage in owl butterfly

An owl butterfly or Caligo eurilochus resembles the eye of an owl. In this way they send their predator away. 

                    Fig: Camouflage in owl butterfly

Camouflage in stick insect

Stick insects or Phasmatodea are those which have long and slender bodies. So that they can mimic branches and twigs which are their usual habitats. In this way they escape from their predators.

                                     Fig: Camouflage in stick insect

Camouflage in leaf insect

The family Phylliidae of the Kingdom Animalia possess leaf insects or walking leaves. They mimic leaves. Here the wings of the insects can mimic even the veins of the leaves. In this way they hide from their predators.

               Fig: Camouflage in leaf insect

 Camouflage in frogs 

Some species of frogs are cryptically-coloured or camouflaged to avoid being detected easily by predators like snakes. 

                                  Fig: Camouflage in frogs

Chemical defence

Aposematic colouration or warning colouration is associated with the chemical defence. This is a kind of defence mechanism by which the prey will advertise an unpalatable taste. 

Examples of chemical defence

The major example in the chemical defence mechanism is the toxic chemical present in the monarch butterflies (Danaus plexippus). 

The caterpillars of monarch butterflies have the ability to accumulate cardiac glycosides from milkweed plants. Cardiac glycosides are emetic chemicals which can cause vomiting to the predators. So these caterpillars have a bold colour which shows the presence of the toxic chemicals in them. The chemicals can be also present in the adult butterflies which also shows bold colouration. This makes the monarch butterflies distasteful to the predator like blue jay bird (Cyanocitta cristata) which avoids eating them.

                                   Fig: Chemical defence by monarch butterfly

Mimicry

Many species have some resemblance to some other species. The species showing resemblance is called the mimic and the other species is called the model. So the resemblance of two species can protect the mimic from their predators. There are two major types of mimicry seen in the animals. They are listed below:

• Batesian mimicry
• Mullerian mimicry

Now we will discuss more about different types of mimicry.

Batesian mimicry

It is named after the English naturalist Henry Bates. In Batesian mimicry, the model is an unpalatable species (not pleasant to taste) and the mimic is a palatable species. Through mimicking the colour of the model, the predators will not come for the mimic, expecting the same taste of the model.

There is a non venomous scarlet king snake which can mimic the venomous coral snake. Since both the snakes show the same pattern on their body, the scarlet king snake gets protection from their predators. 

                                Fig: Scarlet snake mimicking the coral snake in pattern

Mullerian mimicry

The name Mullerian came from the name of a German biologist, Fritz Müller. In this type of mimicry, many poisonous species converge to look the same, advertising their distasteful design.

So that the predators will not eat the species with particular colour, thinking that they are toxic.

The black and yellow striped bands found on many different species of bees and wasps are one of the examples of mullerian mimicry. 

                                         Fig: Bee and wasp

Physical defences 

Physical defence of prey against predators is common. It is the development of some body parts on organisms for their protection from predators. The shells present in the turtles and tortoises are one of the best examples of physical defence. 

                                           Fig: Tortoise 

The tough exoskeleton in the beetles and venomous stingers of scorpions are other examples. The jumping ability of grasshoppers is also a kind of physical defence from the clutches of predators.

                                    GIF: Dung beetle

Refuge

Refuge is a protective mechanism in animals. Here the organism obtains protection from the predator by hiding in an area where it is inaccessible or cannot easily be found. For example, to maintain a higher population density rats will find refuges like tall grass, which allow them to hide from predators like owls and cats.

Defence Against Predation in Plants 

Phytophagous insects are those which feed on plant sap and other plant parts. It has found that nearly 25 percent of all insects are phytophagous. But the plants cannot run away from their predators just like animals do. So they have to develop morphological and chemical adaptations of defence. Most of the defence mechanisms in plants are coevolved with the predators. The defence against predation in plants can be classified as follows:

• Morphological defence
• Chemical defence
• Indirect defence
• Reduced apparency

Morphological defence

Morphological defences or structural defences can help the plants from herbivores. The common structures which help the plants for defence are as follows:

• Spines and thorns
• Trichomes 
• Thick leaves 
• Microscopic needle like and sand like particles

Spines and thorns

Spines and thorns are the sharp epidermal extensions of leaves and stems respectively. It is more effective against large herbivores rather than the smaller ones. 

                                                        Fig: Spines in plants

Trichomes 

Trichomes are also the epidermal extensions which are the hair-like structures. They are not sharp, but because of the unpleasant texture they prevent the herbivores from consuming the plants and also prevents the insects from laying eggs on the plants.

                                                        Fig: Trichomes

Thick leaves 

Sclerophylly is the term used to describe the thick leaves. The thick or rigid leaves and stems are difficult for the herbivores to chew. Hence it acts as a defensive mechanism in plants. Cellulose and lignin are the compounds which give the toughness to the plant parts. 

                                    Fig: Thick leathery leaves of Banksia serrata

Microscopic needle like and sand like particles

Silica or calcium are the non toxic minerals that are stored in the plants. These are used as a physical defence. When silica is released into the extracellular spaces, it will form stone-like structures called phytoliths. Phytoliths can increase wear on the mouth parts of the insects or teeth of vertebrates. 

                           Fig: Phytoliths in plant tissue

Calcium ions will bind to oxalate which is an organic anion and it will form crystals in cell walls, vacuoles and trichomes. These crystals can pierce the mouth tissues of herbivores. 

Chemical defence

Some plants can produce chemicals which may affect the health of the herbivores. Such chemical compounds which can deter the herbivores from feeding the plants are considered as the chemical defence. Such compounds can inhibit the feeding and digestion of the predator or herbivore. Sometimes it can disrupt the reproduction of the herbivore and even be fatal. 

The chemical compounds produced as defence can be secondary metabolites or it can be produced through the mutualistic interaction between endophytes (fungi).

Examples of chemical defence

There is a weed grown in fields called Calotropis or giant milkweed, which contains highly poisonous cardiac glycosides and because of this, no herbivores feed on it.

                                             Fig: Calotropis plant

Some commercial plant products are actually produced by the plants as a defence mechanism. Some of them are opium, caffeine, nicotine, quinine, strychnine etc.

                    Fig: Commercial plant products that are used as defence against herbivores

Trichomes in stinging nettle

Trichomes are considered as a morphological defence. But when combined with chemical defences, it can also act as glands which secrete sticky resins that are responsible for irritation in the grazing herbivores. Stinging nettle (Urtica dioica) is an example of this. They can produce trichomes which can break easily and inject painful chemicals when large mammals graze on it. 

                                  Fig: Stinging nettle plant

Indirect defence 

Plants can attract animals which are the predators of the herbivores that eat a particular plant and it is known as indirect defence. Plants attract the predators with food rewards, shelters or by chemicals signalling the prey availability. 

For example bullhorn acacia (Vachellia cornigera) uses indirect defences to encourage the ants to live inside the hollow thorns on their leaves. This will help the acacia from their predators. 

                              Fig: Ants living in bullhorn acacia

Reduced apparency 

Through decreasing the apparency the plants can hide from the herbivores. To make it effective, plants can be in spatial refuges or in biotic refuges. 

Spatial refuges 

These are the areas that are physically inaccessible to or hidden from the herbivores. 

Biotic refuges 

These are the areas where the herbivores find neighbouring plants of a different species to consume. 

Practice Problems

Q 1. Which of the following options is correct about the assertion and reason given below?

Assertion: The non venomous scarlet king snake mimics the venomous coral snake.

Reason: Scarlet king snakes get protection from their predators. 

a. Both the assertion and the reason are true and the reason is the correct explanation of the assertion
b. Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion
c. Assertion is true, but the reason is false
d. Both the assertion and the reason are false

Answer: In Batesian mimicry, the model is an unpalatable species (not pleasant to taste) and the mimic is a palatable species. Through mimicking the colour of the model, the predators will not come for the mimic, expecting the same taste of the model. There is a non venomous scarlet king snake which can mimic the venomous coral snake. Since both the snakes show the same pattern on their body, the scarlet king snake gets protection from their predators. Here the assertion and the reason are true and the reason is the correct explanation of the assertion. Hence the correct option is a. 

Q 2. Match column I (Defence mechanism) with column II (Examples) and find the correct option from below:

a. A - I, B - II, C - III, D - IV, E - V
b. A - IV, B - III, C - II, D - V, E - I
c.  A - I, B - II, C - IV, D - V, E - III
d. A - I, B - II, C - III, D - V, E - IV

Answer: The ability of preys to merge with their surroundings to avoid predators is known as camouflage. Grasshoppers which are green can blend with the leaves which they feed. Mullerian mimicry is the type of mimicry, by which many poisonous species converge to look the same, advertising their distasteful design. The black and yellow striped bands found on many different species of bees and wasps are one of the examples of Mullerian mimicry. 

Physical defence is the development of some body parts of organisms for their protection from predators. The shells present in the turtles and tortoises are one of the best examples of physical defence. Plants can attract animals which are the predators of the herbivores which eat a particular plant and it is known as indirect defence. Bullhorn acacia use indirect defences to encourage the ants to live inside the hollow thorns on their leaves.

The chemical compounds which can deter the herbivores from feeding the plants are considered as the chemical defence. There is a weed grown in fields called Calotropis, which contains highly poisonous cardiac glycosides and because of this, no herbivores feed on it. Hence the correct option is b.

Q 3. How can mineral ions protect plants from their herbivores?

Answer: Presence of microscopic needle like and sand like particles is a type of morphological defence adapted by the plants. Silica or calcium are the non toxic minerals that are stored in the plants. These are used as a physical defence. When silica is released into the extracellular spaces, it will form stone-like structures called phytoliths. Phytoliths can increase wear on the mouth parts of the insects or teeth of vertebrates. Calcium ions will bind to oxalate which is an organic anion and it will form crystals in cell walls, vacuoles and trichomes. These crystals can pierce the mouth tissues of herbivores. 

Q 4. Explain the defensive mechanism present in monarch butterflies?

Answer: Aposematic colouration or warning colouration is associated with the chemical defence. This is a kind of defence mechanism by which the prey will advertise an unpalatable taste. The major example of the chemical defence mechanism is the toxic chemical present in the monarch butterflies. The caterpillars of monarch butterflies have the ability to accumulate cardiac glycosides from milkweed plants. Cardiac glycosides are emetic chemicals which can cause vomiting in the predators. So these caterpillars have a bold colour which shows the presence of the toxic chemicals in them. The chemicals can be also present in the adult butterflies which also shows bold colouration. This will make the Monarch butterflies distasteful to the predator. As a result, predators like the blue jay bird (Cyanocitta cristata) will avoid eating the butterflies.

FAQs

Q 1. What is predator satiation?
Answer: The production of many progeny at a time by all individuals in a population to satiate or fully satisfy the predator is known as predator satiation. This is also a method of defence mechanism by the animals. Through this technique, some of the progenies in the population could survive and can retain stability of the population in the ecosystem. For example, the production of more tadpole larvae occurs in frogs, but half of the tadpoles will be eaten by predators like fishes.

Q 2. Defence mechanism of porcupine fish?
Answer: Porcupine fish adapts intimidation as a defence mechanism. This will discourage predators from eating the prey. So while having a predator attack, the porcupine fish inflates or puffs themselves to large proportions.


                                          Fig: Porcupine fish

Q 3. What is considered as aggressive mimicry?
Answer: Just like the adaptations of prey against their predators, predators also have adaptations to help them catch prey. Aggressive mimicry is one such adaptation. In aggressive mimicry the predators will mimic a harmless model, so that the prey will come close to the predators. Crab spiders mimicking the flower is an example of aggressive mimicry. Crab spiders will take up the colour of the flower and will wait on the centre of the flower. This will help the spiders to catch their prey which will be the pollinator of that flower.

                                                  Fig: Crab spider

Q 4. What is domatia?
Answer: A tiny chamber produced by plants which helps to house the arthropods is called domatia. These structures provide shelter for predators which helps them from the harsh environmental conditions or other predators. The domatia can be shallow crevasses covered with trichomes and they are seen in avocados or with multiple chambers as seen in Acacia. 

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