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| Could Disease have caused the extinction of megafauna? |
We are almost reaching an end of the various factors which might
have contributed to the decline of megafauna during the late Pleistocene. In this
blog I will discuss the hyper-disease hypothesis, looking at whether this factor can
be seen to be a plausible mechanism for the extinction of megafauna. So far, we
have seen that the most likely causes of widespread extinction are climate and
man. We have also uncovered other hypothesis such as the occurrence of an extra terrestrial event and the impact of fire. Without doubt, the impact of
disease would have caused some megafaunal decline, but whether this factor was
large enough to cause the complete extinction of certain large animals is still
unknown.
The hyper-disease is defined as:
"...the extinction of large mammals during the late Pleistocene to indirect effects of the newly arrived aboriginal humans (MacPhee & Marx, 1997). It Proposes that humans or their commensals introduced once or more highly virulent diseases into vulnerable populations of native mammals, eventually causing extinctions." (Lyons et al 2004: 859).
In historic
times, humans have wiped out vast populations of each other during ‘first
contact’ scenarios when diseases were accidentally transmitted (2). Consequently, this mechanism can be seen to
be a likely cause for the extinction of megafauna during the late Pleistocene,
when two previously isolated species all of a sudden came into close contact
(3).The disease hypothesis largely attains credit through lack of evidence
supporting the climate or the blitzkrieg theory (1). Some scientists support
the idea that megafauna had a weak immune system as they had never been exposed
to diseases before and consequently were not able to withstand pathogens. Therefore
it was not the influence of a changing climate or man’s overkill that caused
extinction, but the pathogens carried by dogs, rat’s, birds, parasites and
other living baggage that accompanied the continent’s first human arrival (1).
This is reinforced by Dr Ross MacPhee (a mamalogist at the American Natural
History Museum in New York) who stated that the overkill hypothesis is far too
simple. Furthermore, that lack of kill sites (remains of butchered animals),
strengthens the hyper-disease theory. Therefore, whilst there is evidence that
disagrees with the hunting hypothesis, man could have caused the extinction of
species through bringing disease. Reasons for the demise of megafauna have been
controversial, unlike other extinction events, it coincides with periods of
climate variability as well as the first appearance of human hunters. Extinction
was also rapid, targeting primarily megafauna. Consequently, the disease
hypothesis can be seen as a plausible mechanism for such extinction patterns as
it could have spread quickly across continents, reducing animal populations to
levels which they could not recover. Dr
Preston A. Marx (virologist at the Aaron Diamond AIDS Research Centre) believes
that the animals were infected by lethal pathogens unknown to their immune systems
(1).
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Alternative evidence that supports this hypothesis is that
disease would have persisted for many years after it was introduced, being
carried by people or organisms that arrived with people. Had any megafauna been
able to withstand the disease it would have ultimately infected new
generations-leading to eventual extinction. Rothschild & Laub (2006)
support the hyper-disease theory by showing the extinction of a particular type
of mammoth through human carried tuberculosis. Evidence of this was found in the
disease being present in 52% of the 118 skeletons that were surveyed.
Overall, the hyper-disease theory is new and still being
developed. Whilst it is plausible in part, it lacks much needed supporting
evidence. Furthermore there is lack evidence uncovering a pathogen that has the
capability to cause such widespread extinctions. Whilst Rothschild &Laub(2006) were successful in discovering Tuberculosis that killed a type of
mammoth, there is no evidence to suggest that this disease was broad enough to
kill all the extinct megafaunal species. In spite of this, the hyper-disease
hypothesis should not be discredited. Whilst there is lack of evidence, there
are many believable aspects of this hypothesis. Perhaps, combining multiple
causes of extinction e.g. over-kill, climate, disease etc., we find the most probable
cause of megafaunal extinction.
A basic insight into the 4 main causes of mass extinction:
Mammoth remains in Serbia:
Could domesticated dogs be seen as significant factors causing mega-faunal extinction?
ReplyDelete
ReplyDeleteYes!!! There are many ways in which dogs could have contributed to the extinction of megafauna. Firstly, dogs transmit Eurasian diseases to new world carnivores, which would have caused a trans-specific epidemic. Domesticated dogs can also act as disease carriers, which would have affected a huge diversity of megafauna. Dogs would also assist in the tracking of large animals, making them easier to be killed by humans. They may have also aided in the immobilizing of human prey, and can be seen as an important factor supporting the overkill hypothesis. Dogs would also require meat to survive. Therefore hunting might have increased significantly to not only meet human consumption needs, buts also the requirements of domesticated animals.
Hope this helps
Hi Josh,
ReplyDeleteI don't really agree with you here! I just did a blog post on the same topic and you may want to have a look:
http://vanishedgiants.blogspot.co.uk/2012/12/dissecting-hyperdisease-hypothesis.html
I think the main 2 factors which are particularly damaging to this hypothesis are:
1) It is difficult to find evidence of a disease so powerful it wiped out that many species of megafauna. Even the only known modern disease which fulfills the criteria set out by Lyons et al (2004),of such a hyperdisease, the West Nile Virus, could not have caused the unique size-biased extinction pattern of the late Pleistocene megafauna (See the Lyons et al paper and their studies of the West Nile virus)
2) The Rothschild and Laub (2006) paper finds evidence of only one type of pandemic-scale disease in one particular species - the American Mastodon. It is difficult to find equivalent disease explanations for the extinction of such a large number and range of megafauna species.
Hey Li
ReplyDeleteNice Blog! Together we might crack the likely reason behind this controversial debate!
Yep, the two reasons you have mentioned are also included in my post. In my blog I didn’t say that I believed that the hyper-disease theory was the fundamental cause of widespread megafaunal extinctions. I only said that it has some credible aspects. With such little scientific evidence supporting or opposing with this theory, I find it hard to believe that you completely disagree with it. Yes, whilst other factors such as climate and human overkill are without doubt more important factors explaining extinction patterns, surely in some situations such as the Rothschilld & Laub case, hyper-disease was responsible. Instead of looking at single factors on their own, wouldnt it be reasonable to suggest that combining multiple factors such as climate, man, hyper-disease etc be the most accurate conclusion to areas lacking firm evidence?