Brief note on the importance of predation in nature

This is an interaction in which one organism; predator kills another, prey for food. This is a process of paramount importance not only in natural ecosystems but to man also, because he is either directly a predator himself (as when he captures fish from the sea, hunts game animals in a forest), or has to deal with natural predators which are directly harmful to him or kill prey that are beneficial to him.

First, let us consider the importance of predation in nature. Following are its important roles:

1) Predation helps to channelize through different trophic levels the energy fixed by photosynthetic plants. But for predation, the ‘grass-deer-tiger’ food chain would not obviously exist! Remember, the grass ‘considers’ deer as its predator; in this sense, to a plant the sparrow that eats its seeds is also a predator.

2) Predators can bring down the intensity of intraspecific competition in a community by selectively preying on the competitively superior species and keep their densities low. This permits the weaker species to persist in the habitat.

3) Predators also appear to be responsible for maintaining high species diversity in many biological communities. Experimental removal of all predators from a community has been known to lead to the elimination of some species and a general decline in species diversity.

4) Predators in some cases can regulate the population densities of their prey. Predation is obviously not beneficial to the individual organism that is killed and eaten as food, but to the prey population as a whole, the predator could be very beneficial.

In an ideal situation, the prey and predator populations show what are called ‘coupled oscillations’ over a period of time.

Let us see how these oscillations come about: in a habitat with plentiful resources, prey numbers start increasing, consequently predators get more food and produce more offspring. With increasing predator population in the habitat, more and more prey is killed bringing their population size down eventually.

Now, because of low prey densities in the habitat, the predators cannot obtain enough food and therefore, their numbers start falling. These events lead to oscillation in the densities of both prey and predator. It is important to mention here that the situation could turn out to be entirely different if the predator is not ‘prudent’ or he is ‘too efficient’ at killing the prey. Under these conditions, the predator will seek out and kill every prey individual, drive the prey species to extinction, and subsequently will eliminate himself, through starvation!

If a predator is choosy and so specialized that it depends almost exclusively on a particular prey species, then we can expect the evolution of these prey and predator to be linked to each other. In this ‘co-evolution’, the prey tends to evolve defenses specifically to escape from that predator while the predator tends to evolve adaptations to counter those defenses and become more efficient in capturing that prey.

As we stated earlier, predators could help keep the prey population under check. Although such is not always the case with large-sized prey, for example, moose, wildebeest, etc. There is strong evidence that populations of many small prey species like insects, zooplankton, etc., in nature are kept under control by their predators, if the natural predators are eliminated, the prey population is released from predation pressure and increase in an exponential fashion. This is the explanation for the sudden and unpredicted increase in the densities of pests when chemical pesticides are sprayed non-selectively by man with the intention of actually killing them!