Predation - Practice Questions & MCQ

• It is an interspecific interaction, where an animal called predator kills and consumes the other weaker animal called prey. This is a biological control method.
• Predation as nature’s way of transferring the energy fixed by the plants to higher trophic levels.
• Although animals eating plants are categorised separately as herbivores, they are, in a broad ecological context, not very different from predators.

Role of Predators in an ecosystem:

• Predators keep prey populations under control. But for predators, prey species could achieve very high population densities and cause ecosystem instability. 
• Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population. 
• Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. 
• In the rocky intertidal communities of the American Pacific Coast the starfish Pisaster is an important predator. 
• In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of interspecific competition.

Strategies adapted by prey to avoid predation:

• If a predator is too efficient and over exploits its prey, then the prey might become extinct and following it, the predator will also become extinct for lack of food. 
• This is the reason why predators in nature are ‘prudent’. 
• Prey species have evolved various defenses to lessen the impact of predation. 
• Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator. 
• Some are poisonous and therefore avoided by the predators. 
• The Monarch butterfly is highly distasteful to its predator (bird) because of a special chemical present in its body.
• Interestingly, the butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed.

Adaptations in plants to deter herbivores:

• For plants, herbivores are the predators. 
• Nearly 25 percent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants). 
• The problem is particularly severe for plants because, unlike animals, they cannot run away from their predators.
• Plants therefore have evolved an astonishing variety of morphological and chemical defences against herbivores. 
• Thorns (Acacia, Cactus) are the most common morphological means of defence. 
• Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it. 
• The weed Calotropis grows in abandoned fields. The plant produces highly poisonous cardiac glycosides and that is why you never see any cattle or goats browsing on this plant. 
• A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced by them actually as defences against grazers and browsers.