The Bengal tiger has to be one of the most beautiful members of the cat family.
Their orange and black striped coats, broad heads and impressive teeth captivate the attention of thousands zoo visitors all over the world. However, the same sight in the wild can get the heart racing, adrenalin flowing and possibly cause the onset of sheer terror.
To researchers from the University of Minnesota, the sight of wild Bengal tigers in the Sundarbans mangrove forests of Bangladesh are rewarding and baffling. Conducting a study for the U.S. Fish and Wildlife Service, they were surprised to discover that the tigers in this region were almost half the size of Bengal tigers elsewhere in South Asia. The female Sundarbans tigers’ average weight was 76.7 kg (170lb), compared to other Bengal tigers that averaged 138.2 kg (304 lb).
Astonishingly, the research team’s conclusion for the drastically smaller size of the Sundarbans tigers was smaller prey. That’s right, smaller prey. In one of the researcher’s own words, “This could be related to the small size of deer available to tigers in the Sundarbans, compared to the larger deer and other prey available to tigers in other parts.”
Following this logic, then any captive bred tigers should also be much smaller because of the smaller pieces of meat they are fed at the zoos. Or what about other large carnivores that eat smaller prey, shouldn’t they also be smaller? Wouldn’t you think that if the deer in the Sundarbans region are smaller, that the tigers would just eat more deer?
However, the real reason for the smaller size of the Sundarbans tigers was revealed in the same article and I am surprised that the authors seemed to have missed it completely. The Sundarbans tiger population is geographically separated from any other tiger population by at least 300 km (190 miles).
Geographic isolation is a well known mechanism for isolating genetic traits in populations. These isolations can result in the rapid formation of a new species or subspecies.
In my master’s thesis, I discovered the same thing in the Mediterranean gecko, Hemidactylus turcicus, introduced into the United States around 1900. They colonize via the Founder’s Principle establishing new populations that are geographically isolated from each other. Through my research I discovered that geckos in Arizona were nearly 13% to 20% smaller than the ones collected from Texas. There was also a marked difference in behavior between the two general populations.
When one population is isolated from the main or parent population, it can be a contributing cause for differences such as size of the individuals in the smaller isolated population. I strongly suspect that the same is true for the Sundarbans tigers. The isolation of nearly 200 miles from the nearest population of Bengal tigers could quite possibly have resulted in a genetic change that resulted in smaller bodies in this region.
The Founder’s Principle is a great example of how natural selection works in favor of the biblical creation model and not evolution. It is based on the loss of genetic variability due to geographic isolation. For molecules-to-man evolution to work you need an ever increasing amount of genetic information and variability, rather than a reduction. This is a very simplified explanation of a much more complex mechanism that I hope to write more about at a later time.