All species on this planet not only co-exist but also depend on each other for their survival. Just as plants depend on animals for their existence, animals too depend on plants directly or indirectly for their survival. As a result, in any habitat, plants, animals and microbes interact in various ways to form a community. When populations of two different species interact, it leads to interspecific interactions. Such interactions may benefit, harm or have a neutral effect on one or both species.
When members of one species called the predator feeds on another species called the prey, the interaction is known as predation. For plants, herbivores are the predators, which in turn are predated by carnivores. In fact, predation helps in the transfer of energy from one trophic level to another.
Apart from functioning as ‘conduits’ for energy transfer, predators also help to keep prey populations under control.
In some cases, the prey species grows so large that it may cause instability in the ecosystem if predators are absent. Another function of predators is to help maintain species diversity, thereby minimising the intensity of competition among competing prey species.
If a predator is highly efficient, it can overexploit its prey, thereby resulting in the extinction of its prey and eventually itself. However, such a situation rarely occurs in nature as predators are prudent. They do not kill too many prey and leave some for later. Several prey species too have evolved various defences to lessen the impact of predation. Some species of insects and frogs use camouflage to protect themselves from predators. Moreover, some prey contain poisonous chemicals, which keep predators away. These are some ways in which animals escape predation.
In fact, nearly 25 per cent of insects are phytophagous, which means they feed on plant sap and other plant parts. Therefore, plants have developed a variety of morphological and chemical defence mechanisms against herbivores. The presence of thorns and spines is the most common morphological means of defence in some plants like Acacia and cactus. Also a few plants like Calotropis and some fungi have chemical defence mechanisms which include the production of harmful and distasteful chemicals. A wide variety of chemicals such as nicotine, caffeine, quinine and opium extracted for commercial purposes are actually produced by plants as defences against grazers. Therefore, in nature, species not only co-exist but also show various interspecific interactions, predation being the most common.