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

[peter]

GUATE

Many thanks for two very interesting posts (1009 and 1010). I especially liked the part on tiger evolution, as it is based on the most recent peer-reviewed documents. It must have taken a lot of time to get to sound conclusions. Be sure it is much appreciated! 

In this post, I'll respond to both posts from the top down.


1 - POST 1009

a - Panthera tigris amoyensis and Panthera tigris corbetti 

Last year (2015), I decided to go over everything I have in order to get to a few conclusions. I started with length, body dimensions and weight. Later, skull measurements were added. The next step was tables, corrected for age and status (captive and wild). As I have quite a lot on Javan and Sumatran tigers, I decided to do them first.

Just before I started the project which would have lasted for quite some time (about a year, I thought), those I know intervened. They said the house was close to a collapse. If I was to prevent total desintegration, something had to be done right away. They would do most of the work, but the condition was I had to forget about tigers for the moment. The next day, I got a hammer and started a journey into the unknown. 

Just after we had started, those who own the houses in the neighbourhood decided the time had arrived to upgrade just about everything. This means the residents were bombed out of their beds five days a week for many months. What I'm saying is I was overtaken by reality. Apart from a few sound decisions, reality is about maintenance and upgrading things just about all the time. In order to pay for it, one has to take care of the money as well. 

Forumwise, this year was a slow one. At least, for me. The forum did well, but I didn't have the time to invest. In some time, however, I'll be up and running again. One of the things I'll change first, is Photobucket. The reason is it's unreliable, if not a total mess. This means I'll have to transfer over 3100 scans to a new provider. If any of you has a proposition, I'll listen.

Returning to measurements. I have quite a bit on Panthera tigris amoyensis and Panthera tigris corbetti. The problem is I just don't have the time needed to get to work. From memory, I can say the range in size is impressive. One reason is both China and Indochina are very large. The result is a lot of variation (landscape and conditions).

Tigers in the southern part of Malaysia, including Terengganu, are smallish to intermediate in size with males averaging about 8.7 in total length 'between pegs'. Those in the northern part (like Perak), however, are larger and, especially, more robust. From Perak to the east, all the way to Vietnam, tigers seem to be quite large. Those in southern parts of Vietnam, however, were decidedly smaller. Tigers living in the region between Perak and the northern part of Burma also are smaller, but not by much. Those in the Naga Hills, with males averaging about 8.7 in total length 'between pegs', are similar in size to those in the southern part of Malaysia and Vietnam. Annam tigers, at the extreme eastern edge of the Perak-Annam axis, were as large as many Indian tigers. To the north and northwest of that region, they declined in size, but tigers in the northeastern part seemed to have been a bit larger. Male Amoy tigers most probably averaged just below 9 feet 'between pegs' in total length, but they were less robust than the slightly shorter tigers shot in central parts of China.

The average of Mazak (good to read you finally got the book) for Panthera tigris corbetti, if anything, was a bit too careful. Also remember individual variation was much more pronounced a century ago, when tigers could still travel. Some of the tigers shot in the southern tip of Malaysia by the Sultan of Johore, for example, were as large as an average Indian tiger (well over 9 feet straight). One of the tigers shot by the Sultan had a skull with a greatest total length of about 365 mm.

b - Sunda tigers

Those who saw or hunted tigers in Indonesia over a century ago agreed Bali tigers were definitely smaller than those in Java or Sumatra. They also agreed it was more than likely that Java tigers, and males in particular, swam to Bali every now and then. This would explain the size of some males shot in Bali. 

There is another way to get to an estimate on Bali tigers by using information from Sumatra and Java. Assuming sexual demorphism was about similar on all islands, one could conclude male Bali tigers averaged 100-110 kg. (meaby a bit more). The average, however, would have been below the average for Sumatra. The reason is skull measurements and verified weights and measurements of reliable reporters strongly suggest Sumatran male tigers were larger animals. If Sumatran males ranged between 115-130 kg. (my estimate would be closer to 120), male Bali tigers would have been below that mark.

If we add individual variation, which was and is quite pronounced in tigers, a large male Bali tiger could have reached 105 + 25-35% = 130-140 kg., whereas a large male Sumatran tiger could have reached 120 + 30-35% (large mammals show more pronounced extremes) = 155-165 kg. Experienced Dutch hunters who thought exceptional males reached 170 kg. or even a bit more could have been close, as large and healthy populations tend to produce more pronounced exceptions. Javan tigers, although a bit larger, would have struggled to get to that mark. One reason is they were a bit less robust. Furthermore, they, numberswise, walked the edge between 1900-1930. If we use 105, 120 and 130 kg. as averages for Bali, Sumatra and Java (males), we could be close to the mark. Exceptional males might have added 30-35, 45-50 and 35-40 kg. respectively. My estimate for all Sunda tigers would be 70-80 kg. for females (range 55-105) and 115-125 for males (range 85-155). A century ago, some males might have (well) exceeded 155 kg.

c - Evolution

The new documents, again, offer a new view on the past. The idea that the Toba eruption had more impact than assumed before has profound consequences in that it's very unlikely tigers survived anywhere but in some parts of southern China and northern Indochina. This means the southeastern part of Asia (now Indonesia) was recolonised by tigers after the Toba eruption. If we include the assumption that the bridge between mainland Asia and what's now Malaysia and Indonesia only closed about 12 000 years ago and distinct local types, therefore, developed in a relatively short period of time, we should be able to find some evidence pointing in that direction.

In skulls, to a degree, it seems to be there, in that skulls of Indian tigers and Javan tigers are quite close in many respects. Apart from size, the main difference is in the occiput (narrower in Javan tigers) and, perhaps, the mandibula (more often concave in Javan tiger skulls). This points to a specific adaption. As it is also seen in skulls of tigers that lived in the same region many thousands of years earlier, it's likely the adaption had to be related to what's now Java. My guess is it was an adaption to large prey animals. As this adaption also would have resulted in a large tiger, one would expect to find a few traces. My guess is Javan tigers could have been quite large animals until a few thousand years ago, when conditions changed and they had to adapt. The adaption resulted in less size, but the occiput didn't change. This means Javan tigers didn't change the way they used their jaws. The question is why. Maybe Gir lions can help in this respect, as some male skulls also have a narrow occiput.  

Although there is some evidence for genetic exchange (referring to overlap in skull structure), skulls of Sumatran tigers are very different from Javan tiger skulls. They also are different from skulls of other tiger subspecies. One reason could be Sumatra, which is very different from all other regions that have tigers. It's quite remarkable that this island, although densely forested, has different large animals. It almost seems as they were trapped when conditions changed. Maybe Sumatran tigers adapted, which could have resulted in two distinct types; one a typical jungle cat going for typical (smallish) jungle animals and another one developing into a larger animal going for larger prey animals. I can hear you say males and females, but this isn't likely as it's the only local type where skulls of males and females overlap. This is the reason I concluded Sumatra (could have) had two distinct types. Most tigers would have been small to medium-sized, but some are larger. As deforestation continues, chances are more tigers will develop into larger animals going for larger prey animals.               


2 - Post 1010

a - Table

As you used a method used by others in similar conditions, there's no reason for criticism. The only thing I can think of is the method originally was developed to estimate the weight of large animals, but the results nevertheless seem quite decent. That leaves a reliable (large) data base. In this respect, I might be able to help a bit. 

In some months, I will post tables about Javan and Sumatran tigers. Every table will have individual entries only, meaning you will be able to find the skulls you didn't use for your tables. After posting the tables, I will try to find the old Dutch hunter magazins. I know they are there. Might take a lot of time, but I assume there will be a lot of information. I also assume those unable to read Dutch didn't read them. Reply