Mechanism At Negative Retroaction                                      or Genetic Feedback 3°

Hawk hunting

Genetic inferiority,in the mechanism at negative retroaction, may be specific towards a particular limiting factor (predation, competition, virus) or generic. Many predators, for example, attack, above all, those who would anyway starve as they are unable to get food, or die for disease. Among 15 sparrows, a sparrow-hawk can recognize the one blind in one eye and 15 out of 17 homing pigeons, preys of the peregrine falcon, were somehow ill[1].

sparrowhawk

At this point we can enunciate a law: the final result of the factors limiting population is a product that doesn’t change with the changing of the single factors. If one of the limiting factors is reduced or eliminated the product doesn’t change because the other factors increase automatically.

When man intervenes by altering natural balances and eliminating, artificially, one of the above-mentioned regulating factors, inevitably the active factors left replace the others, and since their absolute value increases, the final product doesn’t change: a given number of individuals, of a certain species, present in a certain territory.

In parks or artificial reserves, predation, famine and competition don’t act any longer as factors limiting the number of mammals, but in these cases disease is often the fourth factor which acts with the same final efficacy we would get if the other three were acting.

Recently in the Tanzanian park of Serengeti 30% of a population of 3,000 lions was killed by a virus similar to distemper. The same happened owing to an unknown virus in a reserve of bears in North Italy.

Lion reproducing

The epidemic of FELV, the feline Leukaemia which affected 17% of street cats in Rome is even more interesting.

Thanks to the intervention of the nice cat ladies[2] felines don’t depend any longer on the factor famine for their survival, while predation, like for other domestic animals, stopped acting long time ago. This doesn’t prevent the factor disease, in this case the virus of Feline Leukaemia, from intervening to regulate the population.

Cat lady

Then it’s important to notice that, always in Rome, AIDS is present in the street cat colonies.

Cats’ H.I.V. or F.I.V. (Feline Immunodeficiency Virus) is passed through sexual contacts, saliva and the blood cats exchange through scratches and bites.

Where there are a high feline concentration, fights for the territory are, in fact, very frequent.

One of the mechanisms F.I.V. favour their transmission to new hosts with, is the one that produces organic alterations in cats’ brain so increasing their aggressiveness.

Let’s conclude this study about animal world by pointing out, once again, how human action can interfere on the mechanisms regulating the population of a certain species and how this can damage man himself.

The rat number of a determinate community was said to increase up to threshold values, beyond which an epizootic which brings their number back to values even inferior than the ones of the beginning, breaks out.

Rattus Norvegicus

Obviously many species of rats exist, among them Rattus Norvegicus (brown), Rattus Rattus (the notorious black rat) and Mus Musculus are the most organized of their family.

Rattus rattus (black mouse

What man has done over the centuries has altered natural balance in favour of these three species. This has happened because human beings have indirectly protected the latter from their enemies, have offered them plenty of food with the refuses, have taken them around the world (another synonym for Rattus Rattus, besides black rat, is Boat Rat). So Norvegicus spreads anywhere there are leftovers.

Rattus Rattus can climb very well and occupies the top floors and the roofs of the houses the basements and the sewers of which are occupied by Norvegicus.

Always for its ability as a climber Rattus Rattus gets on the boats along the ropes[3] and spreads all over the world[4].

Finally Mus Musculus is the smallest of all and can enter where the others cannot.

House mouse (Mus musculus)

Fleas are rat habitual parasites and, as such they are responsible for plague spreading, one of the commonest epizootics of these rodents.

The innatural increase of rats causes an increase, which is as much extraordinary, of fleas, their parasites. When rats die, fleas greatly increased can’t find any other solution but passing to man, so taking Pasteurella Pestis[5] with them.

So epizootic ( an infectious disease of animal world) is turned into an epidemic[6] (an infectious disease of man)

A mechanism of numerical regulation of animal world passes the bacterium and fleas, its vectors, to man because the latter doesn’t recognize or disregards the importance of nature laws.

[1] Lack D. Predation on birds. In The natural regulation of animal numbers, pag.157. Oxford at Clarendon Press.1954.

[2] Those ladies who take care of street cats are called like that in Rome.

[3] Inthe movie Nosferatu, starring Klaus Kinski, an actor who died some time ago.

Nosferatu -Kinski

There is a very beautiful scene where just the black rat is the protagonist: the ship, with the coffin containing the Vampire’s body(Non Spirato/Nosferatu), docks slowly and mysteriously, since it is without a crew, in the port of a city in the North. Along the ropes a multitude of black rats swarm into the city and spread the plague.

The vampire’s boat dcks in Wismar

 [4] Pollitzer R, Meyer K F, The Ecology of Plague. In Studies in Disease Ecology. Pag.445-8 Edited by May J M Hafner Publishing Company Inc. New York 1961.

[5] Ibidem Pag.463-4

[6] Ibidem Pag.477

See also:

1) Mechanism at negative retroaction or genetic feedback 1

2) Mechanism at negative retroaction or genetic feedback 2