An Email to a Friend - Even More on Food Chains

Old C.,

I quite agree with the elaboration you have just made.
Factually the what eats what chain is so intricate that some natural scientists would rather switch to the term "food web".

The body size factor is normally true in most predations, where size means brute force. And brute force works in many cases.
In some cases such as the lion preying on the buffalo, individuals of the lion pride cooperate with each other tacitly and strategically to bring down a buffalo much larger in body size.

In the case of scavenging, just like the vulture cleaning up the carcass of a large mammal, the larger the carcass, the better the feast for the scavenger bird.

When it comes to the ecosystem, besides its extreme complicatedness, it runs on an always changing delicate equilibrium. The equilibrium shifts from time to time favouring different life forms in different times, owing to the evolutionary reality and climate changes, etc.
In an equilibrium every living species adapts to the overall environment or merely its confined micro-environment, thus has its own place.

Some species dominate in different ecosystems, propagate well despite the eco-differences, and appear just everywhere, like us humans and the cockroach which eats just anything; some barely survive to hang on with their slim reproduction in confined habitats, like the giant panda and the orang-utang. Now we know that we humans have been evolving really fast, and the giant panda has been so sluggish that it is more or less a living fossil in the evolutionary perspectives.

We humans have been able to dominate on almost all inhabitable lands on earth, not because we possess the ultimate adaptability. We simply don't need to be adaptive in the original sense of the adjective. In most cases we alter the environments by irreversibly damaging the ecosystems to create the living conditions we want culturally, but not necessarily we need biologically.

In nature, adaptability of a species to an existing or a changing environment means capability of surviving and reproducing in a way that sustains. The adaptive species then has its place. Adaptability is an evolutionary outcome. The mechanism of evolution is based simply on genetic mutations. Genetic mutation is a simple trial and error process. Every now and then a species would produce offspring not adaptive to the existing and slowly changing environment. Such offspring would become a dead-end of diversification. In the same time a species would also produce offspring adaptive to an abrupt environmental change taking place or having just taken place, like an ice age. In such case the original species would die out, leaving the diversified offspring to live on. This is the story of evolution. And this is the history of most existing live forms. Keep producing adaptive offspring according to the change of food sources is one key of evolving.
Sometimes there would be mega natural disasters, like the eruption of a super volcano which took place some 73,500 years ago in Sumatra. The eruption of Mt. Toba wiped out many species directly, and still more species indirectly by bringing about huge global climate change scientists would call "volcanic winter" for years on end, thus breaking many food chains.
Some scientists believe that this eruption also helped select about only 2,000 ancestral individuals of Homo sapiens, to propagate to dominate every corner of the earth some 70 millennia later.
This hominid, like the chimpanzee, ate just anything, he could be more infamous than any other species for eating his own kind. Could this be one of the keys for him to survive that volcanic winter that lasted several years?

The panda eats almost nothing but bamboo. Yet it doesn't "know" bamboo would secure its survival for generations to come, it simply instinctively sits there and chews bamboo leaves and shoots all day, just like the wildebeest does the grass in the Serengeti. Now we know that animals feeding on a narrow food source are more likely to go hungry. The ancestral panda just didn't know its way. Mother Nature showed it the path. The panda used to be carnivorous long, long ago. Later it adapted to an omnivorous life. Now it feeds 99% on bamboo. Its intestines show that it should still be a carnivore. Yet only its diversified descendant that ate only bamboo survived.
Mother Nature has always been pointing to the wrong directions. A species which goes into a dead-end will have no way out.
The living species on earth, even to re-include those which have been wiped out of the earth surface by us humans, are just of only a tiny little number compared to all those once roamed the earth.

You said "in nature every species has to choose its best way to survive".
I reckon that no species can "choose its best way to survive", not even us humans with a big thinking brain.
Mother Nature has written down the Way as AGTC codes in our genes that would translate into instincts. We listen to the calls of our instincts. We don't choose which way to go, we instinctively obey the orders given by Mother Nature.
Our instincts tell us to take in food, so we do, and eat ourselves to get sick.
Our instincts tell us to accumulate, so we do, and get obsessed in possession.
Our instincts tell us to reproduce, so we do, and have propagated to crowd the earth.
Our instincts tell us to make shelter, so we do, and build large cities that damage the lands and pollute the waters.
Our instincts tell us to avoid wasting energy, so we do, and avoid doing physical exercise, which is a key to maintaining good health.
Our instincts tell us to stay comfortable, so we do, and don't start a family which could make the prime of our life miserable.

If we are really to choose our best way to survive, the first step we should take is to contemplate how far we should go along with our instincts