ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)

[peter]

TIGERS IN NORTHERN INDIA AND NEPAL - PART XVIII


Nepal (ecosystem and maps)


a - The effect of ecosystems on the size of tigers 

The first posts of this series, as you will remember, mainly consisted of lengthy descriptions on the geography of Nepal in general and southern Nepal in particular. Smythies said the southern part consisted of 3 different regions. These perhaps can be considered as mini-ecosystems. Tigers were seen in all 3 in his day, but today things are somewhat different.

I intended to post a number of Nepal maps in some time to conclude the series, but decided to change the schedule today. The reason is the information posted on a thread recently started by Shardul. The title of the thread is 'The Terai Tiger'. I would advice to have a look, as the information posted is interesting.  

Shardul's view is that Terai tigers are different from those in other parts of India. I agree. One reason is their appearance is somewhat different. Tigers in most parts of southeast Asia (including Sumatra, but not southeastern Russia) often are a bit darker and more marked than those in northern India and Nepal. They also have more and darker stripes. Many tigers in southeastern Asia are jungle dwellers; they are moderately long and have shorter skuills than most lions. Tigers in northwestern India and Nepal, on the other hand, are not as dark, relatively tall and very long. The body proportions also seem to be different.  

Another reason I agree with Shardul is size. Terai tigers, and those in the extreme west of northern India and those in central Nepal (Chitawan) in particular, are longer and heavier than anywhere else (averages). The difference with tigers living in northeastern and southwestern India is limited (about 4 inches), but the constrast with tigers living in other parts of India is more pronounced. For confirmation, have another look at the tables I recently posted.

Those interested in the reasons have to consider different factors. Evolution is one. Tigers spread from southeastern China to other parts of Asia in different waves. The first waves ended in what is now Indonesia (remains of tigers have also been found in Japan, Palawan and Borneo), the Caspian region and Manchuria. Tigers in these regions, so it seems, were not severely affected by the Toba outburst about 75 000 years ago. Tigers in other parts of Asia, however, were. Another wave, many thousands of years later, could have ended in southwest Asia and central India (India had tigers about 12 000 years ago). The Terai was populated a few thousand years later. This wave could have consisted of larger animals. Remember most remarks on evolution have a speculative character.  

Another factor to consider is habitat. Tigers living in dense forests seldom exceed 9 feet in total length 'over curves' and 350 lbs. (males). Those in Sumatra are even shorter and only seldom get to 330. Tigers living in elevated and barren regions could have been a bit larger, but males well exceeding 9 feet 'over curves' and 400 pounds were few even a few centuries ago. Tigers inhabiting elevated regions with forests were a bit larger, but animals exceeding 9.6 'over curves' and 400 pounds on a regular basis were most often seen in forested regions interrupted by savannah-like plains. The reason is these regions had large ungulates. Examples are Annam (Vietnam); parts of Thailand and Cambodja; southern and eastern parts of the Caspian region; Manchuria and southeastern Russia, and central and northern parts of India.

The region just south of the Himalayas, according to Smythies, was ideal tiger country. He wasn't the only one who got to that conclusion. The result was large animals. Male tigers exceeding 10 feet 'over curves' and, say, 450 pounds empty have been recorded in quite many regions, but northern India and, in particular, Nepal always were known for the size of tigers. 

          
b - Map of different landscapes in northern India, Nepal, Sikkim and Bhutan
         
The map below was posted by PC today on the thread mentioned above ('The Terai Tiger'). It shows 6 different landscapes just south and east of the Himalayas. The Terai Arc, in the extreme west (dark green), is clearly separated from the other 5. This is the region that produced the largest tigers. Male tigers in northwestern India are about 2 inches longer in total length 'over curves' than those in northeastern India (the region in purple), whereas those in Nepal are 2-3 inches longer than those in northwestern India. Tigers in the heart of the Terai Arc landscape (Chitawan) are about 5 inches longer than those in northeastern India.

Remember that tigers in northeastern India are far from small. Kaziranga tigers (just south of the region in purple) could be a bit different from those in the northeast, but I would be surprised if they outsized those in the northeast. There are no data about Bhutan (and Sikkim) tigers (red on the map), but they seem to be large animals. Remember Bhutan tigers, in contrast to those just south of them, inhabit very elevated regions. They are the only true mountain tigers of today.

Let the map sink in. Than read the tables I posted in this series (tigers in northern India and Nepal) again. The conclusion is that the different landscapes produced slightly different tigers. All tigers just south of the Himalayas are large animals, but those in the extreme northwest in particular stand out. This means it is very likely that there is a connection between landscape (ecosystem) and size.

Here's the map of the Himalaya ecoregion first posted by PC:  

*This image is copyright of its original author

c - Map of the Terai Arc Landscape

The map below was also first posted by PC in the thread 'The Terai Tiger'. It has details on the Terai Arc (Indian side). The region not only is large. More important is that there are no large cities. This means that the exchange of genes still is possible (to a degree). This region, with Russia, most probably has the best future.  

I could be wrong, but I think that most large individuals were seen in the extreme northwest.

*This image is copyright of its original author

d - A few Nepal maps


d1 - British India

This map is interesting for more than one reason. Remember the part directly west of Nepal (including Kumaon) used to belong to Nepal. Also remember that Nepal was never part of British India:  

*This image is copyright of its original author

d2 - Old psysical map of Nepal: 

*This image is copyright of its original author

d3 - The former Ghurka Empire:

*This image is copyright of its original author

d4 - Nepal districts:

*This image is copyright of its original author

d5 - Nepal hydro map:

*This image is copyright of its original author

d6 - Nepal ecological map:

*This image is copyright of its original author

d7 - Nepal geology (south of the Himalayas):

*This image is copyright of its original author

e - Conclusion

If you're interested, you could read the first posts in this series again. I think Smythies really did a good job. Add the maps in this post and the tables posted before. This should enable you to get to an answer to the question if there is a connection between landscapes and the size of tigers. My guess is there is (at the level of averages), but there's a bit more to size than ecosystems only. A wild big cat can get to his potential if the conditions are right, but the drive and the limits of size, most unfortunately, are all but unknown. It would be an interesting topic for a debate.  

My take is evolution could be more important than many assume, but the problem is a lack of good information. Will get back to that one in the near future. Reply