18 February, 2016

Are predators really needed in nature?

There is an argument about why predators like the tiger and the leopard are really needed in the jungle. If not for the predators, apparently, the meek (non-predators) would multiply so much and consume so much of the vegetation that the ecological balance of the jungle would be upset.

The above argument is often syncretically extended to human societies and applied to human relationships, business, governance and so on. Predatory strategies abound in all these places, where the "meek" are destroyed or consumed by the "strong" (euphemism for predators) not just to feed the predator's sense of entitlement, but also purportedly, to keep some kind of social balance.

It is easy to see the flaw in this argument. There are several forests that are home to deers and other "meek" creatures, with no predators to feed on them (for instance, the Jayamangali deer sanctuary near Tumkur). These forests have not exactly dwindled due to the deers. Deer population has not exactly grown in an unfettered fashion because of the vegetation and absence of predators.

Evolutionary forces are at work that regulates the deer population despite having no predators to feed on them.

The above justification for the existence of predators gives too little credit for the sophistication of evolutionary survival strategies. Evolution often plays out in very nuanced ways and has its own mechanisms to estimate the survivability of offspring in the given context.

Populations usually grow in an unfettered fashion when they are suddenly released from a stressful situation (for example, the baby boom following the second world war). But in a steady state with no external threat, the population also tends to stabilize to an optimal reproduction rate.

The justification for predators assumes that the meek (non-predators) are also stupid. As long as there are resources, the meek will keep growing until they choke to death. It goes without saying that it is a preposterous assumption. The meek do not feed on others -- but this does not mean that they are stupid enough to not be able to regulate themselves. They may well be intelligent enough to estimate the demand for resources by the population and live accordingly.

In fact, I would like to argue that predators are just a local optima in the evolutionary game over the ages. They are going to be overshadowed as the evolutionary system jiggles its way out of the local optima. Predators get instant payoffs by feeding on others. However, predators also easily become the object of distrust and non-cooperation by others. The predators need to be strong all the time. The moment they lose their strength, they stand to be overpowered by the ample number of enemies they would have created. Predators are usually lonely and territorial, thus reducing their robustness towards facing unanticipated changes in the environment.

Predatory strategies are hence unlikely to be evolutionarily stable strategies (ESS). The great predators from the dinosaurs like the T-Rex or Velociraptor were the first to be extinct. None of the predatory dinosaurs seem to have evolved into the birds of today and retained the same level of predatory abilities. The predatory abilities of birds today are vastly diminished compared to their ancestors -- the dinosaurs.

Similarly, the most ferocious of the wild animals are also usually the most endangered ones. Lions and tigers are endangered, while pigeons, deers and rabbits are not.

Finally, to argue that predators have a "purpose" for existence, is to accept that life on earth is a result of "intelligent design" rather than evolution. Predators just evolved from the dynamics of the past. There is no reason to believe that this evolutionary quirk is stable or sustainable.

So, it is quite likely that the (sophisticated) meek shall indeed inherit the earth.

2 comments:

Abhijith N said...

I have great trouble in attributing a "purpose" for existence.Evolution is probably totally random.Hence there is really no "need" for either the meek or the dominant animal.It just happens to be the case that we have a bunch of animals.Some tend to eat other animals while others tend to eat plants (living things). Also , you cannot decide a species to meek or dominant based on interspecies behaviour.It is like saying all the non-vegetarian people in Bangalore are more dominant in comparison to the meek vegetarians. But, I believe that predators have a lower chance of survival in an evolutionary sense because they are dependent on prey. A deer can live in a forest with no tiger. But a tiger can't live in a forest with no prey.

Srinath Srinivasa said...

Agree.. one way to look at the argument in this post is that, what we call as the "meek" is the default way in which life runs. Predators have mostly been evolutionary quirks -- second-order creatures if you will, which evolved to capitalize on the existence of the meek. It does not necessarily mean that predators are "necessary" -- to answer that question, we will need to ask, "necessary for what purpose?" thus admitting an intelligent design, dimension to life.