Explain predation in detail.

Besides acting as 'conduits' for energy transfer across trophic levels, predators play other important roles. They keep prey populations under control.

But for predators, prey species could achieve very high population densities and cause ecosystem instability.

When certain exotic species are introduced into a geographical area, they become invasive and start spreading fast because the invaded land does not have its natural predators.

The prickly pear cactus introduced into Australia in the early $1920$ 's caused havoc by spreading rapidly into millions of hectares of rangeland.

Finally, the invasive cactus was brought under control only after a cactus-feeding predator (a moth) from its natural habitat was introduced into the country.

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 inter- specific competition. If a predator is too efficient and overexploits 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.

For plants, herbivores are the predators. Nearly $25$ per cent of all insects are known to be phytophagous. The problem is particularly severe for plants because, unlike animals, they cannot run away from their predators.