Tuesday, 8 January 2013

It’s Here, The Conclusion you have all been waiting for…

It is now sadly time to come to a conclusion and unmask one of the biggest ‘whodunit’ mysteries. In this blog I will be stating the most important findings of this research, as well as delivering my own thoughts of what I believe to be the most likely cause of megafaunal extinction. The outcome of these blogs has revealed that climate and man are the two main culprits of extinction.

Man's Impact
The impact of man is one of the most popular reasons for the extinction of megafauna during the Late Pleistocene. Growing support for this theory is largely due to the arrival of Homo sapiens coinciding with the demise megafauna. This was found in many continents including Australia (Roberts’s et al 2001), North America and Eurasia. It is important to note that human overkill was not the same in each continent. Some regions may have experience blitzkrieg, whilst others might have shown evidence of protracted overkill. Increased number of Homo sapiens is a key factor which would have driven increased levels of hunting, and may have pushed megafauna to extinction. Numerous findings of sophisticated hunting technology such as spears, harpoons and nets (mostly used by Clovis hunters of North America) reinforce evidence to suggest that overkill was responsible for the decline of these great beasts. This is reinforced by Wong (2012) who states how changes in technology were responsible for the extinction of certain carnivores in East Africa. Bulte et al (2006) provides another theory, suggesting that hunting of mini-fauna would have increased chance encounters with megafauna leading to their eventual extinction. Looking at man’s influence in Australia, it was found that the extinction of 60 faunal species coincided with the arrival of humans 65,000 years ago (Jonson 2006). Evidence of butchered animals in Cuddie Springs (New South Wales) is an example which strengthens the overkill hypothesis. The extinction of animals resistant to glacial/interglacial cycles is another reason that portrays man as the culprit behind this controversial mystery. Hunting would have also selectively targeted larger animals, which provides an explanation of why only megafauna became extinct during the Late Pleistocene. The hunting of mega herbivores might have even caused the decline of carnivores that relied of these food sources (Wong 2012), illustrating the detrimental impact man can have on megafauna. The only continent that shows a co-existence between man and megafauna was Africa, and consequently this region experienced much fewer losses then other areas. The fire hypothesis has also shown to have a considerable effect of megafauna through extreme temperatures and landscape modification. The studies by Rick et al (2012) reveal that fire was of vital importance to humans as it was used for light, cooking, warmth, and allowed the creation of new technologies. Human induced fires were more common than lightning events, and therefore its effects can be linked to man’s impact on megafauna. Similarly studies in Tight Eastern Cave (South West Australia) found increasing charcoal concentrations coinciding with the arrival of Homo sapiens, suggesting that human induced fire was frequent. The impact of fire would have restructured plant communities causing vegetation to change. This might not have sustained megafauna and consequently led to their demise (Gill et al 2009). Overall, whilst it is clear that fire had some impact of megafaunal populations, it cannot be considered a key driver of extinction due to lack of evidence. We also looked at the likelihood of the occurrence of an extra-terrestrial event during the late Pleistocene (see Firestone et al 2007). Whilst the impact of a comet would have caused the extinction of megafauna, the lack of reproducible evidence (Haynes et al 2010) weakens this hypothesis. Man can be seen to be responsible for the death of megafauna through bringing hyper-disease (mostly carried by domesticated dogs). Megafauna had weak immune systems due to not being exposed to diseases. Their inability to withstand pathogens meant that hyper-disease is a mechanism of extinction. Rothschild and Laub (2006) reinforce this believe 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. Whilst it is plausible in part, this theory lack much needed supporting evidence.

Whilst there are many reasons to suggest that man played a huge role in the extinction of megafauna, there is evidence which contradicts this. The lack of kill sites is a large factor that weakens the overkill hypothesis. Other evidence which disagrees includes the relationship between technology and hunting. Many believe that the improvement of technology was coupled with a varying diet as Homo sapiens had the newly found ability to obtain alternative food sources such as fish. Agriculture during the late Pleistocene may also reveal that man had access to an alternative food source, which would suggest that other factors might be responsible for the extinction of megafauna. Overall, poor quality fossil data sets make it exceptionally hard to determine whether primitive man caused megafaunal collapse.

There are many reasons why climate can be seen to be responsible for the collapse of megafauna. During the late Pleistocene climate was subject to large scale rapid oscillations between glacial and interglacial conditions. Such transitions would cause landscape modifications which in turn would have reduced the amount of suitable areas in which megafauna could survive. Climate changes would have also altered ecosystems and resulted in large vegetation changes due to the reduced growing season of plants. This would result in species with small ranges to subsequently die out. This is corroborated by Wroe (2006) and Dodson (1998) who found that Australia experienced an expansion of arid areas. Evidence which agrees with this hypothesis is also stated by Prescott et al (2012) who stated that the most rapid episodes of population decline were associated with the highest periods of temperature decrease. Such changes would have caused species such as the Eurasian musk ox and the woolly rhinoceros to become extinct (see Lorenzen et al 2011).
However, there is much evidence which disagrees with this hypothesis. The overall strength of the ‘man being responsible for extinction’ (mentioned above) severely weakens the climate hypothesis.

In my opinion I believe that the combination of both anthropogenic and climate forcing’s caused the extinction of the majority of megafauna. This belief can be strengthened because of the following reasons:
·         I believe that climate had the potential to exacerbate human impact. Glacial periods could have caused increased levels of hunting for survival.
·         Climate oscillations could have also been a significant factor in the evolution of tools specifically designed to hunt prey more efficiently. This resulting in increased numbers of megafauna being hunted and consequently led to increased extinctions.
·         The best example which incorporates both human and climate is the extinction of the woolly mammoth. Research by Nogues-Bravo et al (2008) found that suitable climate conditions for the mammoth reduced drastically between the Late Pleistocene and the Holocene resulting in 90% of its geographical range disappearing. Therefore climate would have significantly decreased the mammoth’s population size, and consequently would make them more vulnerable to extinction when hunting occurred.

Studies by Prescott et al (2012) and Prideaux et al (2007) found that the timing of megafaunal extinction is related to both climate and human forcing factors. Overall I believe Climate change could have weakened megafaunal populations, and with the combined presence of humans (which would have hunted, caused fires, and brought diseases) megafaunal extinction would have been inevitable. Hopefully with improved fossil records and data records the actual reason behind megafaunal extinction will be revealed.

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