tag:blogger.com,1999:blog-41834185289408230302024-02-07T21:42:03.884-08:00Vanished Giants - Nature's Scythe or Man's Spear? Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.comBlogger14125tag:blogger.com,1999:blog-4183418528940823030.post-5767794800076871632013-01-08T17:16:00.005-08:002013-01-08T17:19:21.650-08:00Concluding Comments <br />
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<span style="font-family: Trebuchet MS, sans-serif;">The mystery of the vanished giants is no easy one to solve.
This is still very much a dynamic field where new research reveals more
dimensions of the puzzle and throws up more questions than answers. After
gaining a better understanding of the topic through keeping this blog, I am
ever more aware that the answer is not a simplistic, uni-dimensional one.</span></div>
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<span style="font-family: Trebuchet MS, sans-serif;"><o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">I found the arguments where human impacts are the ‘last
straw’ for already stressed populations struggling to adapt to climate change
the most convincing. Critics have argued that megafauna survived the previous glacial-interglacial
transitions, citing anatomically advanced humans with sophisticated hunting
technologies as the only differentiating factor. This is a simplistic view of
past climates which assumes that all transitions are the same. There is evidence
that the late Pleistocene was unusually, warmer rather than cooler than the
Holocene and supported a rich mosaic of vegetation types which was in turn able
to support a huge variety of megafauna. This disappeared during the Holocene. Besides, ‘megafauna’ is not a static concept;
Graham and Lundelius (1985) concept of ‘co-evolutionary disequilibrium’
suggests that species often co-evolve in unique and individualistic ways,
meaning that the species composition of ecosystems change all the time. The
late Pleistocene was a biotically unique period, limiting comparability with
other glacial-interglacial transitions. <o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Besides, extinctions did not happen in the rapid
‘Blitzkrieg’ manner that some researchers have argued. Especially in Eurasia,
where humans were not necessarily present in all areas, extinctions occurred
gradually and even happened in areas where there were no humans, e.g. the Irish
Elk. The African Anomaly also adds another piece to the puzzle – African
hunters were also sophisticated but it is the continent which experienced the
fewest extinctions, and there is evidence that climate change was less
pronounced in Africa. <o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Whispers from Ghosts
Past: Lessons for the Future<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">So where does this all leave us? I do not think it is
possible to provide a conclusive answer to the mystery of the vanished giants,
but I hope I have left room for more thought. I also hope that a better
understanding of past climates and extinct species would lead us to be more
aware of the importance of modern conservation – once species are lost, they
are irrevocably gone. <o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">I can see 3 major takeaways from this blog:<o:p></o:p></span></div>
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<span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;"><b>Our current level of biodiversity is already a depauperate version</b> of what it once was, yet human impacts are resulting in ever more extinctions than before.</span><span style="text-indent: -18pt;"><br /><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></span><span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;"><b>Today, our actions are themselves causing climate change. </b>In the late Pleistocene, climate change was essentially separable from human impacts such as hunting.<b> </b>Today, we have entered what Nobel Prize winner Paul Crutzen (2002) calls ‘The Anthropocene’ – human impacts have reached such unprecendented levels that they have become significant geological forces. </span><div>
<span style="text-indent: -18pt;"><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></span><span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;"><b>The late Pleistocene megafauna extinction event has shown that the adverse impacts of humans and climate change are a lethal combination for species biodiversity</b>, and the effects are further amplified today. </span><span style="text-indent: -18pt;"><br /></span><ul><span style="text-indent: -18pt;">
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<b><span style="font-family: Trebuchet MS, sans-serif;">References</span></b><br />
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<span style="font-family: Trebuchet MS, sans-serif;">Crutzen, P. J. (2002) The ‘anthropocene’, <i>Journal de Physique IV, </i>12, 10, pp. 1-5<i> <o:p></o:p></i></span></div>
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Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-43305990167786892112013-01-07T13:10:00.001-08:002013-01-07T13:10:27.931-08:00The Late Pleistocene Extinction Event and How It Stacks Up to Extinctions Today<br />
<span style="font-family: Trebuchet MS, sans-serif;"><b>The Big Five, and a Sixth?</b></span><br />
<span style="font-family: Trebuchet MS, sans-serif;">This is my last blog post before I conclude and I thought it would be useful to compare the late Pleistocene megafauna extinction to modern extinction rates. Indeed, the latter is so severe that there has been concern that we are causing the ‘6th mass extinction’ through habitat destruction, killing of species, changing global climate and introducing non-native species. </span><br />
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<span style="font-family: Trebuchet MS, sans-serif;">There have been 5 mass extinctions in the past: near the end of the Ordovician, Devonian, Permian, Triassic and Cretaceous Periods. A mass extinction is defined as ‘having extinction rates spikes higher than in any other geological interval of the last 540 million years and exhibiting a loss of over 75% of estimated species’ (Barnosky et al 2011: 51). </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">A discussion on the evidence surrounding the 6th mass extinction is beyond the scope of this blog; Xijia has an interesting blog here on this topic.</span><br />
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<span style="font-family: Trebuchet MS, sans-serif;"><b>Modern Extinction Rates </b></span><br />
<span style="font-family: Trebuchet MS, sans-serif;">This <a href="http://www.nature.com/nature/journal/v471/n7336/pdf/nature09678.pdf" target="_blank">paper by Barnosky et al (2011)</a> gives a bit more insight on how extinction rates are calculated. Although this paper is primarily about the 6th mass extinction, it does provide a comparison figure for the Pleistocene extinction event. A widely-used metric in this field is extinctions per million species-years (or E/MSY). The ‘natural’ background rate of extinction is 1 E/MSY, i.e. if there were 1 million species on Earth, one would go extinct per year. Rates are estimated using fossil extinctions that occurred in million-year time bins. Current rates are projected to a million years, as current extinctions have occurred within very short timespans (a few decades to hundreds of years). It is important to note that extrapolation may introduce inaccuracies, and the shorter the time intervals, maximum ESY and its variance increase. </span><br />
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<span style="font-family: Trebuchet MS, sans-serif;">Using a paleontology database combined with lists of recently extinct species, the most complete set of which are available for mammals, the results are as follows:</span><br />
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<span style="font-family: Trebuchet MS, sans-serif;"><b>The extinction rates observed for the past 1,000 years (24 E/MSY in 1,000 year time bins – 693 E/MSY in one-year intervals) is much higher than the maximum late Pleistocene extinction rate (9 E/MSY) and definitely higher than the background rate.</b></span><br />
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<span style="font-family: Trebuchet MS, sans-serif;">Clearly we are in the midst of a very severe biodiversity crisis and losing species much faster than they can be replaced. Given the already severe loss of biodiversity that was the late Pleistocene megafauna event (with the result that our planet is already a depauperate version of its former self in terms of biodiversity), this is a major cause for concern. While some have attempted to put an economic value on biodiversity (See <a href="http://enviro-nomics.blogspot.co.uk/2012/11/a-brief-introduction-to-economics-of.html" target="_blank">Ali's blog</a>), as we have seen biodiversity is intrinsically important in maintaining the balance of ecosystems, which are highly complex and interdependent systems. </span><br />
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<span style="font-family: Trebuchet MS, sans-serif;"><b>References</b></span><br />
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<span style="font-family: Trebuchet MS, sans-serif;">Barnosky, A. D. et al (2011) ‘Has the Earth’s sixth mass
extinction already arrived?’, <i>Nature, </i>571,
pp. 51-57</span><o:p></o:p></div>
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Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-92122639073027217722013-01-03T08:12:00.001-08:002013-01-03T08:16:58.793-08:00Is Pleistocene Re-Wilding Viable for Conservation Today?<br />
T<span style="font-family: Trebuchet MS, sans-serif;">he mammoths have vanished, so what do we do now? An obvious answer is to realize the ecological and intrinsic importance of today’s surviving megafauna and do our best to protect them, but a group of scientists have gone one (controversial) step further: they want to ‘broaden the underlying premise of conservation from managing extinctionto encompass restoring ecological and evolutionary processes’ (Donlan et al 2006: 660). They argue for the introduction of Pleistocene rewilding in North America, which involves:</span><br />
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<li><span style="font-family: Trebuchet MS, sans-serif;">Reintroducing modern species descended from Pleistocene species that once lived in North America OR</span></li>
<li><span style="font-family: Trebuchet MS, sans-serif;">Reintroducing ecological proxies for Pleistocene species if the above do not exist </span></li>
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<span style="font-family: Trebuchet MS, sans-serif;">This <a href="http://biology.unm.edu/fasmith/web_page_pdfs/donlan%20et%20al.%202006%20am%20nat.pdf" target="_blank">paper by Donlan et al (2006) </a>summarizes the key
arguments supporting Pleistocene rewilding in North America.<o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Ecological Arguments<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Megaherbivores and large carnivores play important roles in
ecosystems and have been dominant in ecosystems for the past 200 million years,
until their widespread extinction in the late Pleistocene. Given their
instrumental roles (See also my previous blog post on the role of megaherbivores
and extinction consequences), it must follow that restoring them would have
positive benefits.<o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Large predators’ roles include the following:<o:p></o:p></span></div>
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<li><span style="font-family: 'Trebuchet MS', sans-serif; font-size: 7pt; text-indent: -18pt;"> </span><b style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;"><i>Buffering against climate change: </i></b><span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;">To
cite a contemporary example, evidence from a Wilmers and Getz (2005) paper
shows that the reintroduction of gray wolves have helped maintain carrion availability
for the survival of other scavenger species, important since snow thaws earlier
in Yellowstone due to climate warming.</span></li>
<li><span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;"><br /></span></li>
<li><span style="font-family: 'Trebuchet MS', sans-serif; font-size: 7pt; text-indent: -18pt;"> </span><b style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;"><i>Controlling disease (some of which can
spread to humans): </i></b><span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -18pt;">Another
contemporary example concerns the lyme disease epidemic (spread to humans by
ticks) which occurred in North America in the early 2000s was probably caused
by peak populations of white-tailed deer, once kept under control by gray
wolves.</span></li>
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<span style="font-family: Trebuchet MS, sans-serif;">Grey Wolf</span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Evolutionary and
Conservation Benefits<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Pleistocene rewilding is a way to transform conservation
biology from mere preservation of existing species to reconstructing ecosystem
processes and species interactions. Donlan et al (2005) argues that what is ‘natural’
must be challenged; we often think of the 1492 Columbian landfall on America
and the state of the environment then as what is a ‘natural benchmark’ for
conservation, but this fails to recognize the rich biodiversity of the late
Pleistocene period. There are also additional positive benefits from
maintaining large viable populations of target species to facilitate adaptation
to climate change. North America could provide an additional refugia for
conserving the genetic proxies of Pleistocene megafauna (such as Asian
elephants, a proxy for mastodons), since these are endangered in Asia and
Africa, the only 2 continents which preserve a large diversity of megafauna. <o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Criticisms
<a href="http://www.hummingbirds.arizona.edu/Courses/Ecol406R_506R/Donlan_rebuttal_RubensteinEA_BiolConserv.pdf" target="_blank">(Rubenstein et al 2006)<o:p></o:p></a></span></b></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Effects on Ecosystems
are Unpredictable<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">We do not really understand how Pleistocene ecosystems
functioned and therefore should not attempt to reconstruct them. Rather,
Pleistocene rewilding may disrupt contemporary ecosystems, e.g. by introducing
new diseases, etc. Also, the effect of introducing ‘exotic’ species is unknown.
Even when reintroducing native species, their effects on the ecosystem are
unpredictable. For example, the introduction of one-humped camel in wreaked
havoc on Australia’s desert ecosystems as they selectively ate rare plant
species. <o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Reintroductions Do
Not Always Work<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Many modern-day examples show that even reintroducing native
species within their original geographic regions is not always successful. The
most successful examples (Przewalski’s horse and the Asian ass) are those where
only a short time between extinction in the wild and reintroduction, as the
ecosystem would not have changed much in that time frame. In other examples,
problems such as unexpected changes in environmental conditions, naivete
towards predators and diseases have rendered reintroductions unsuccessful. <o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Will Not Restore
Evolutionary Potential<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Most of the species which are supposedly to be introduced as
part of rewilding are genetically distinct from their ancestors, e.g. cheetahs
and lions. Thus, introducing them would not help restore the evolutionary
potential that once was during Pleistocene times. <o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">Anti-Conservation
Backlash<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Local and state governments in North America already face
much trouble from people about fears over native predator attacks, e.g. cougar
attacks on joggers. The introduction of exotic species such as elephants as
proxies for mastodons for example would generate even more human-wildlife
interactions and conflicts, such as those currently taking place in Africa. <o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">My Thoughts<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">After reading all of this, I feel that the Rubenstein paper
points out many pertinent problems that rewilding poses. Rewilding of native
species, on the other hand, is a more promising aim for modern conservation.
Pleistocene rewilding is much more difficult and prone to ecosystem-devastating
error. The difficulties in even establishing the causes of late Pleistocene
megafauna extinction reveals our lack of certainty about late Pleistocene
environments. Rather than trying to enforce ‘revolutionary’ ideas, I think
modern conservation should focus on preserving existing environments and
rewilding (where appropriate) of native species. <o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">I would like to end off with a link to an organization
supporting the contemporary re-wilding agenda. Its ideas centre mostly around
preserving ‘keystone’ species like large carnivores which play important roles
in regulating ecosystems. <o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;"><b><a href="http://rewilding.org/rewildit/" target="_blank">The Rewilding Institute:</a></b>
think-tank which supports rewilding programmes in America <o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Nevertheless, the controversy surrounding rewilding and the
question of whether this is right for the environment goes a long way to highlight
the fact that once these magnificent giants are lost, they have almost
certainly vanished for good.<o:p></o:p></span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">References<o:p></o:p></span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Donlan, J. et al (2005) Pleistocene rewilding: An optimistic
agenda for twenty‐first century conservation, <i>The American Naturalist, </i>168, 5, pp. 660-681<o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Rubenstein, D. R. et al (2006) Pleistocene park: Does
re-wilding North America represent sound conservation for the 21st century?, <i>Biological Conservation, </i>132, pp.
232-238<o:p></o:p></span></div>
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Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com4tag:blogger.com,1999:blog-4183418528940823030.post-38188590393133137032013-01-01T09:45:00.002-08:002013-01-01T09:45:21.152-08:00Dire Consequences<br />
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<span style="font-family: Trebuchet MS, sans-serif;">You may be wondering, what is the relevance of the Pleistocene megafauna extinction event to today’s world? Why does this topic remain so important to a whole plethora of researchers – paleo-climatologists, biologists and so on – when it happened in prehistoric times?</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">The answer is that it holds many important lessons for modern conservation and even the field of climate change. By studying the animals that once roamed the earth and their habitats, researchers can understand a great deal about past climates and in the process, gain a better understanding of both natural and human-facilitated climate change today. My last few posts will focus more on the implications which the Pleistocene megafauna extinction event holds for modern conservation. </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;"><b>Consequences</b></span><br />
<span style="font-family: Trebuchet MS, sans-serif;">Much attention has been focused on the causes of megafauna extinction, while the consequences have been much less studied. According to <a href="http://211.144.68.84:9998/91keshi/Public/File/41/335-6075/pdf/1483.full.pdf" target="_blank">Rule et al (2012)</a>, herbivorous megafauna have a large role in the ecosystem by:</span><br />
<br />
<ul>
<li><span style="font-family: 'Trebuchet MS', sans-serif;">maintaining vegetation openness and patchiness, removing material that would otherwise fuel landscape fire </span></li>
<li><span style="font-family: 'Trebuchet MS', sans-serif;">dispersing seeds </span></li>
<li><span style="font-family: 'Trebuchet MS', sans-serif;">physically disturbing soil </span></li>
<li><span style="font-family: 'Trebuchet MS', sans-serif;">recycling nutrients via excrement</span></li>
</ul>
<br />
<span style="font-family: Trebuchet MS, sans-serif;">A comprehensive paper by <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2684593/" target="_blank">Johnson (2009)</a> details the vegetational changes that have happened in various continents following the extinctions. A general pattern emerges:</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<b style="font-family: 'Trebuchet MS', sans-serif;">Changes in Vegetation Cover and Decreased Plant Biodiversity</b><br />
<span style="font-family: Trebuchet MS, sans-serif;">Vegetation becomes more uniform (zonal patterns) as there is less pressure from herbivore feeding. For example, a cave site with records of Middle Pleistocene fauna in Australia (400-230 kyr ago) gives evidence of extremely rich biodiversity, consisting of a giant wombat and 18 extinct large kangaroos. The large diversity of feeding habits supported a more diverse vegetation than today, probably a mosaic of woodland, shrubland and grassland. Today, vegetation is a uniform shrub steppe. </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><b><br /></b></span>
<span style="font-family: Trebuchet MS, sans-serif;"><b>Increased Fire</b></span><br />
<span style="font-family: Trebuchet MS, sans-serif;">Without herbivorous megafauna, plant material accumulates and fuels fire. Again, biodiversity decreases as only species with traits that allowed fire survival or post-fire regeneration would survive. For example, in Northeastern USA, burning increased several hundred years after the megafauna extinctions, as indicated by charcoal proxies. </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;"><b>A Disclaimer and a Conclusion</b></span><br />
<span style="font-family: Trebuchet MS, sans-serif;">The literature on the consequences of megafauna extinction on the ecosystem may be patch because of uncertainty over whether these vegetational changes were a cause or consequence of extinction. As mentioned in my earlier posts, climate change which led to vegetational changes has often been cited as a cause of extinction. Besides, there is also confusion as to whether humans played a major role in changing vegetation (e.g. increased burning) and hunting megafauna. Also, megafauna extinction was not associated with vegetational change in all places. </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">Although there is a decided lack of clarity on this issue, one thing is clear – the rich assemblage of Pleistocene herbivorous megafauna had helped to maintain biodiversity and their loss was a major loss to the ecosystem as well. One need only consider the large impact today’s surviving megafauna have on the environment to understand this. For example, African elephants are heavy browsers and help maintain savannah conditions by breaking branches of trees while feeding. White rhinos maintain short-grass lawns within thickets, impeding fire and protecting woody areas from conflagarations. Shifting grazing by bison maintains high species diversity in tallgrass prairie. They all help to maintain the savannah ecosystem on which hundreds of other species depend for survival. We need to understand the importance of conservation as preserving not just one species, but an entire ecosystem – imbalances upset the whole system. This is why in the face of human-induced climate and habitat change today, keeping the ecosystem in balance is ever more important. </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;"><b>References</b></span><br />
<span style="font-family: Trebuchet MS, sans-serif;">Johnson, C. N. (2009) ‘Ecological consequences of Late Quaternary extinctions of megafauna’,<i> Proceedings of the Royal Society of Biological Sciences</i>, 276(1667), pp. 2509–2519</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">Rule, S. et al (2012) ‘The aftermath of megafaunal extinction: Ecosystem transformation in Pleistocene Australia’, <i>Science</i>, 335, pp. 1483-1486 </span><br />
<div>
<br /></div>
Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-12645012277283612312012-12-20T07:22:00.001-08:002012-12-20T07:22:47.522-08:00A Word on Methodology: The Sporormiella Proxy<span style="font-family: Trebuchet MS, sans-serif;">In my <a href="http://vanishedgiants.blogspot.co.uk/2012/12/island-extinctions-and-case-of.html" target="_blank">previous post</a>, I mentioned the Sporormiella proxy used to determine abundance of Pleistocene megafauna in Madagascar. This is an analytical technique that has recently gained prominence in the study of the late Pleistocene megafauna extinction. There is an <a href="http://www.sciencedirect.com/science/article/pii/S1040618211003235" target="_blank">interesting paper by Feranec et al (2011)</a> about the Sporormiella proxy and the problems associated with using it.</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<br />
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">The Sporormiella
Proxy<o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Sporormiella is a fungus that is present on the dung of
herbivores. Sporormiella sporulating on dung release spores which adhere to nearby
objects (usually plant matter). Herbivores then eat this plant matter and the
spores, which pass through their digestive tracts, are released in their dung.
The spores of this fungus are preserved readily in lake sediments, and stratigraphic
changes in the abundance of this fungus in Pleistocene and Holocene sediment
sequences have been used as a proxy to define megafaunal presence, decline and
extinction globally. <o:p></o:p></span></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLEf8Jw2H4WsWhSVmiyro4ynkmb5YQnZOyGzlj9JH9sMjAJPJpAExUpKc06nQC0IXR4rjGBVGlXbwFER2gZ7CUCQPYNAefWrSMg0g3C2JUpeiyc3t6kDOGHM5aHiU_3067GJ0W43R5emA/s1600/Sporormiella+Spores.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><span style="font-family: Trebuchet MS, sans-serif;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLEf8Jw2H4WsWhSVmiyro4ynkmb5YQnZOyGzlj9JH9sMjAJPJpAExUpKc06nQC0IXR4rjGBVGlXbwFER2gZ7CUCQPYNAefWrSMg0g3C2JUpeiyc3t6kDOGHM5aHiU_3067GJ0W43R5emA/s1600/Sporormiella+Spores.jpg" /></span></a></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b></div>
<div class="MsoNormal" style="text-align: center;">
<b><span style="font-family: Trebuchet MS, sans-serif;">Sporormiella Spores </span></b></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">Problems <o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">The presence of Sporormiella is not exclusive to large
herbivore dung and has been found in the dung of small herbivores as well, such
as hares. Thus, it is difficult to use Sporormiella as a sole and direct proxy
for megafauna abundance unless specific species of Sporormiella associated only
with large herbivores can be identified. <o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">A stratigraphic decline in Sporormiella does not necessarily
indicate a decline in megafauna. For example, Sporormiella is more abundant
near lake shores than in the middle of lakes, so a decrease could simply mean a
rise in the lake level. Sporormiella may also be preserved to varying degrees
depending on type of lake sediment, lake levels, etc. A related point is that
the absence of Sporormiella does not indicate the absence of herbivores – some
modern day sites with abundant livestock have been shown not to contain
Sporormiella in <a href="http://ac.els-cdn.com/S0031018206001015/1-s2.0-S0031018206001015-main.pdf?_tid=c004fda6-4ab8-11e2-89e7-00000aacb35d&acdnat=1356016993_408663418989760c78c02d1bb9172ad9" target="_blank">Davis and Shafer’s (2006) study</a>. Thus, Sporormiella needs to be
calibrated to other indicators of large herbivore population and is
non-conclusive on its own. <o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Some academic papers must be viewed with some scepticism due
to methodological over-reliance on this particular proxy. For example, in a
<a href="http://www.geography.wisc.edu/faculty/williams/lab/pubs/Science%202009%20Gill.pdf" target="_blank">Gill et al (2009) paper</a>, a decline in Sporormiella in a Lake Appleman core in
Indiania which starts from 14,800 years ago and which pre-dates a major change
in the pollen assemblage is used to conclude that the late Pleistocene megafauna
extinction was not caused by (usually climate-linked) vegetation changes. They
also show that charcoal frequency increased at that site, indicating that human
factors (like vegetation burning) were probably behind the extinctions. However,
the tail end of the Sporormiella decline is also associated with a change in
lake sediment size, which may reflect changes in the sediment input and hence
catchment area of the Sporormiella source, rather than megafauna decline. <o:p></o:p></span></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">Conclusion <o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">While this analytical technique is certainly promising in
contributing to research on Pleistocene megafauna extinction, it still needs to
be refined. What is also important is to avoid complete reliance on just one
proxy; the conclusions drawn from using this proxy should be calibrated to
other indicators of megafauna abundance. <o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">References<o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Davis, O. K. and Shafer, D. S. (2006) ‘Sporormiella fungal
spores, a palynological means of detecting herbivore density’, <i>Palaeogeography,
Palaeoclimatology, Palaeoecology</i>, <i>237, 1, </i>pp. 40-50.<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Feranec, R. S. et al (2011) ‘The <i>Sporormiella</i> proxy and end-Pleistocene megafaunal
extinction: A perspective’, <i>Quarternary
International, </i>245, 2, pp. 333-338<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Gill, J. L. et al
(2009) ‘Pleistocene megafaunal collapse, novel plant communities, and enhanced
fire regimes in North America’, <i>Science</i>,
326, pp. 1100-1103<b><o:p></o:p></b></span></div>
<br />
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<br /></div>
Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-15050008443755653002012-12-16T08:33:00.000-08:002012-12-16T08:50:12.627-08:00Island Extinctions and the Case of Madagascar<b><span style="font-family: Trebuchet MS, sans-serif;">Island Extinctions</span></b><br />
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Islands which were only inhabited by humans after the late
Pleistocene megafauna extinction event offer interesting ‘control experiments’.
A compelling argument for human factors driving extinction is the time lag
between continent extinctions and those of nearby islands (Martin and Steadman 1999).
For example, New Zealand’s moas lasted 30,000 years longer than Australia’s
extinct giant bird, the mihirung, which went extinct during a Australia’s wave
of rapid megafauna extinction (before the late Pleistocene). <o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">The argument for prey naiveté on early contact with human
hunters finds support also in the remarkable tameness of wild birds in remote
islands which were undiscovered by prehistoric explorers. These include the
Galapagos, Christmas Islands, etc. Galapagos’ avifauna were unafraid of humans,
as depicted in historic accounts from 17<sup>th</sup> century sailors who
discovered the island (Martin and Steadman 1999). <o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">In this blog post I look closer at the island of Madagascar.
<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">Madagascar<o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><a href="http://cavereserve.org/resources/publications-burneys/Burney%20et%20al%202004%20chronology%20madagascar.pdf" target="_blank">This paper by Burney et al (2004)</a> discusses how islands can
be used to better understand megafauna extinction. Madagascar is interesting
because it is the last place on Earth where megafauna went extinct
prehistorically – extinctions in which humans had some part to play in most
other parts of the world occurred much earlier, during the late Pleistocene or
even earlier in Australia. Madagascar offers a relatively fresh record of
paleoecological change, since humans only arrived in the late Holocene, about 2,000
radiocarbon years ago. Very little is known about how or why this group of Iron
Age people came to Madagascar. Evidence of the first humans can be shown by
human-modified megafauna bones, such as cuts on the fossilized bones which show
removal of flesh from bone by a sharp object. <o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Very little is known about the late Pleistocene biota in
Madagascar. The amount of data increases greatly for megafauna in the
mid-Holocene, where conditions for fossil formation probably became more
favourable. For example, most lakes and swamps along the coastline formed only
after around 5,000 radiocarbon years ago. Nevertheless, there were major
climatic changes in in the late Pleistocene and pre-human Holocene, most of
which were survived by most of the megafauna. Although there have been range
shrinkages, there were no extinctions. Of the 9 genera of extinct lemurs dated,
only one is not securely dated to the human period. Some examples of major
climate change are as follows: <o:p></o:p></span></div>
<div class="MsoListParagraphCxSpFirst" style="mso-list: l0 level1 lfo1; text-indent: -18.0pt;">
<!--[if !supportLists]--><span style="font-family: Trebuchet MS, sans-serif; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-size: 7pt;"> </span></span></div>
<div class="MsoListParagraphCxSpFirst" style="mso-list: l0 level1 lfo1; text-indent: -18.0pt;">
<ul>
<li><span style="font-family: Trebuchet MS, sans-serif;"><span style="text-indent: -18pt;"> 20,000 radiocarbon years ago (LGM): widespread
dessication occurred. Lake Alaotra, a large lake in humid eastern Madagascar,
was dramatically reduced in area if not completely dry during that period.</span><span style="text-indent: -18pt;"><span style="font-size: 7pt;"> </span></span></span></li>
<li><span style="text-indent: -18pt;"><span style="font-family: Trebuchet MS, sans-serif;"> 10,000 calendar years BP: At another site called
Trtrivakely, pollen evidence shows the nearly complete replacement of heath vegetation
with wooded grassland.</span></span></li>
</ul>
</div>
<div class="MsoListParagraphCxSpLast" style="mso-list: l0 level1 lfo1; text-indent: -18.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">A drastic decline in megafauna, as shown by a huge decrease
in <i>Sporormiella</i> in sediments at 1700
radiocarbon years BP (within a few centuries of first human contact), was
observed. <i>Sporomiella</i> is a fungus
that grows in the dung of large plant-eating mammals, and it releases spores
which are preserved in sediments. The presence of these spores is used as a
proxy for the presence of megafauna. Humans could have hunted these megafauna
or altered their habitat. Before humans arrived, these herbivores had very few
predators other than large crocodiles. Although there is very scant evidence
for direct human hunting of megafauna, as in many other continents where
Pleistocene megafauna extinction has occurred, another way in which humans
could have contributed to the decline is through altering the existing fire
regime by further increasing fire incidence through burning for settlement and
agriculture and through hunting of plant-eating megafauna. The decline of large
herbivores such as giant hippos caused ground litter to accumulate, feeding
more fires. This can be shown by charcoal peaks above background values, first occurring
in the South West where humans first settled, and then spreading outward over
Madagascar. Nevertheless, the extinction pattern on Madagascar does not support
a Blitzkrieg hypothesis. There is an overlap of around 2,000 years from
earliest human evidence to the last occurrence of extinct megafauna. <o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">The chart (Burney et al 2004) shows a summary of events in Madagascar:</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9iTbrUh5CDGrTu39qDVhyphenhyphenREJYurcaHNekA_ebSvkYjt0xYFp73ZMK_3skurgmvkL91oIrcpDHr3zvhulqVTu39CrVY0IUW87C7h5AzLgpErbnpKz12hBvnIitTUmh_C66WcK_D6YP9vU/s1600/Chart.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg9iTbrUh5CDGrTu39qDVhyphenhyphenREJYurcaHNekA_ebSvkYjt0xYFp73ZMK_3skurgmvkL91oIrcpDHr3zvhulqVTu39CrVY0IUW87C7h5AzLgpErbnpKz12hBvnIitTUmh_C66WcK_D6YP9vU/s640/Chart.jpg" width="640" /></a></div>
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<br />
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">My Thoughts <o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">The evidence from Madagascar is indeed intriguing and I feel
it does make the argument for human factors in the extinction of megafauna more
compelling. Madagascar’s physical geography and vegetation is very similar to
Africa such that it is referred to as an ‘Africa in miniature’, and it is
probably safe to assume it went through similar climate changes and vegetation
responses as Africa. The megafauna on this island certainly survived all these
before the humans came, after which they experienced dramatic decline and
finally, extinction. The fact that it is an island is important; in a <a href="http://vanishedgiants.blogspot.co.uk/2012/12/africa-is-anomaly-in-pleistocene.html" target="_blank">previous post</a> I mentioned the reason for why Africa still has such a large diversity of
megafauna left is that it is larger and probably provided more refugia for megafauna. Madagascar probably provided more limited refugia for the stressed populations of megafauna. <o:p></o:p></span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">References<o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Burney, D. A. et al (2004) ‘A chronology for late
prehistoric Madagascar’, <i>Journal of Human
Evolution, </i>47, pp. 25-63.<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Martin, P. S. and Steadman, D. W. (1999) ‘Prehistoric
extinctions on islands and continents’ in MacPhee, R. D. E. (ed.) <i>Extinctions in Near Time: Causes, Contexts
and Consequences</i>, New York: Kluwer Academic/Plenum, pp. 17-50<o:p></o:p></span></div>
<div class="MsoNormal">
<br /></div>
<br />
<o:p></o:p></div>
Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-2801730169293173092012-12-07T15:32:00.000-08:002012-12-07T15:32:06.429-08:00Dissecting the Hyperdisease Hypothesis <br />
<span style="font-family: Trebuchet MS, sans-serif;">I decided to do a post on the disease hypothesis after Josh from<a href="http://no-mammoths.blogspot.co.uk/" target="_blank"> http://no-mammoths.blogspot.co.uk/ </a>suggested an interesting paper by <a href="http://link.springer.com/article/10.1007%2Fs00114-006-0144-8?LI=true" target="_blank">Rothschild and Laub (2006)</a>. Here is the <a href="http://no-mammoths.blogspot.co.uk/2012/11/pleistocene-megafauna-extinctions-hyper.html" target="_blank">link to his post</a> on this topic specifically. The hyperdisease hypothesis proposes that humans and their domesticates introduced novel hyperdisease to vulnerable populations of Pleistocene megafauna who had never encountered such diseases before and whose bodies were therefore unable to cope. Since migrations of animals from Europe to North America were not uncommon before the period we are studying, it is more likely that humans and their domesticates were the disease vectors (Lyons et al (2004).</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;"><b>Tuberculosis and the American Mastodon</b> </span><br />
<span style="font-family: Trebuchet MS, sans-serif;">Rothschild and Laub (2006) have suggested that new evidence for the hyperdisease theory has surfaced in the form of bone alterations from infectious tuberculosis found in just over half of 113 mastodon skeletons in the Western Hemisphere. Since not all animals infected with tuberculosis develop this bone alteration, it must follow that probably almost all of the mastodon population must have been infected with tuberculosis. The disease thus qualifies as a pandemic in the sense that it had an extremely high infection rate. Besides, it has a persistent presence in the fossil record from around 34,000 – 10,000 years BP, establishing that it must have been present in the late Pleistocene period. </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">However, there is a difference between infection and mortality – the disease was not necessarily fatal. Rothschild and Laub (2006) hypothesize that this disease may have weakened mastodons in the face of climate change and human impacts in the late Pleistocene, further stressing their populations. While the disease could have remained latent, the environmental stresses of that period could have resulted in a loss of latency, increasing mortality. However, it is unlikely that the hyperdisease could have been a major factor in the extinction event. </span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<b><span style="font-family: Trebuchet MS, sans-serif;">The Modern Day West Nile Virus: A Proxy for the Mystery Hyperdisease?</span></b><br />
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b>
<span style="font-family: Trebuchet MS, sans-serif;">I also found another paper by <a href="http://biology.unm.edu/fasmith/Web_Page_PDFs/Lyons_et_al_2004_WN.pdf" target="_blank">Lyons et al (2004)</a> which proposes some criteria for the hyperdisease theory to be plausible. </span><br />
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<ol>
<li><span style="font-family: Trebuchet MS, sans-serif;">It must be able to survive in a carrier state in a ‘reservoir’ species when there are no susceptible hosts to infect.</span></li>
<li><span style="font-family: Trebuchet MS, sans-serif;">It must have a very high infection rate.</span></li>
<li><span style="font-family: Trebuchet MS, sans-serif;">It must be extremely deadly with a 50-75% mortality rate</span></li>
<li><span style="font-family: Trebuchet MS, sans-serif;">It must be able to infect multiple host species without infecting humans</span></li>
</ol>
<br />
<span style="font-family: Trebuchet MS, sans-serif;">Lyons et al (2004) use the West Nile Virus in birds, a disease which has seen recent introduction and spread in North America’s bird population, as a proxy to test this hypothesis as it appears to fulfil all of the above criteria of a hyperdisease.</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">One of the unique features of the late Pleistocene megafauna extinction event was its size-selectivity – smaller and medium-sized animals were largely unaffected. Thus Lyons et al (2004) have tried to test if West Nile virus causes such size-selective infections in birds. It can be shown that it does not, as infection rate increases positively with body size (Fig. 1) and infection occurs across a range of body sizes. This contrasts with the pattern shown by late Pleistocene mammal extinctions. The x-axis of the graph shows the size category of the bird species infected by the West Nile virus and those of the mammals which went extinct during the late Pleistocene. It has been re-scaled for mammals since they contain a much larger range of body masses. Each filled square shows the percentage of species pool in each size category infected by the virus or that went extinct. </span><br />
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<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLz5LIUDntkv7wPogP_nBWgONoFQ8nLgGvcpy-zT8FDJfF-3LAHwygouBl7ZQvywmNfeAIHVH0j3GC-t_Bwe0ZagciifPid22Qy_RZC6N8-gkw1Oa39QtUU5gQUl8hnVsFwaFRxbpSU4Q/s1600/Figure+1.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="283" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLz5LIUDntkv7wPogP_nBWgONoFQ8nLgGvcpy-zT8FDJfF-3LAHwygouBl7ZQvywmNfeAIHVH0j3GC-t_Bwe0ZagciifPid22Qy_RZC6N8-gkw1Oa39QtUU5gQUl8hnVsFwaFRxbpSU4Q/s320/Figure+1.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Fig 1 (Lyons et al 2004)</td></tr>
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<span style="font-family: 'Trebuchet MS', sans-serif;">Some have argued that large body size makes species inherently vulnerable to extinction because of life history factors, e.g. low reproduction rates which make it harder for populations to recover from mortality caused by disease. However, Lyons et al (2004) counter-argue that if this is true, then larger species should have high extinction rates relative to smaller species over evolutionary time, which is not the case. </span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">The Verdict?</span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;">I find the hyperdisease hypothesis unconvincing so far and I think it is only considered seriously as a factor in the extinction event because of the general lack of evidence surrounding even the exhaustively-researched hypotheses of climate change and human hunting (e.g. lack of kill sites). However, the even more severe lack of evidence in the hyperdisease hypothesis is even more disturbing. The only known modern disease which fulfils the 4 criteria of a hyperdisease capable of wiping out megafauna during Pleistocene times, the West Nile virus, itself cannot be shown to cause the size-selective extinction pattern in modern day bird populations in North America. Besides, the paper by Rothschild and Laub (2006) only shows a pandemic-scale disease in one type of animal, the American mastodon. It is difficult to find equivalent disease explanations for all other megafauna species killed during the late Pleistocene (mammoth, for example, were not affected by this disease and were close cousins of the mastodon). Therefore, I conclude that hyperdisease is an unlikely explanation for the megafauna extinction event we are studying here.</span></div>
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<b><span style="font-family: Trebuchet MS, sans-serif;">References</span></b></div>
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<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div>
<span style="font-family: Trebuchet MS, sans-serif;">Lyons, S. K. et al (2004) ‘Was a hyperdisease responsible for the late Pleistocene megafaunal extinction?’, Ecology Letters, 7, pp. 859-868</span></div>
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<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Rothschild, B. M. and Laub, R. (2006) ‘Hyperdisease in the late Pleistocene: validation of an early 20th century hypothesis’, Naturwissenschaften, 93, 11, pp. 557-564</span></div>
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Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-11569141918662928962012-12-05T07:27:00.001-08:002012-12-05T07:36:52.820-08:00The African Anomaly<span style="font-family: 'Trebuchet MS', sans-serif; line-height: 18px;">Africa is the ‘anomaly’ in the Pleistocene megafauna extinction debate because it only lost 21% of its megafauna species, in contrast to the high levels of extinction in other continents. Today, it also contains a much higher level of megafauna diversity than other continents, including some species which have survived from Pleistocene times, such as the Cape Buffalo. </span><br />
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<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;"><b>Climate Change, Refugia and Disease</b></span></span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;"><br /></span></span>
<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;">Climate change in Africa has been associated with dramatic species extinctions in the whole Pleistocene, not only the late Pleistocene. 59% of the Pleistocene megafauna extinctions occurred in the early Pleistocene, 21% in the middle Pleistocene and 20% in the late Pleistocene. All of the late Pleistocene extinctions happened during the late Pleistocene/Holocene transition (Graham and Lundelius 1984). </span></span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;"><br /></span></span>
<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;">The present-day megafauna has been called a ‘living Pleistocene fauna’ (Graham and Lundelius 1984: 240) because of their diversity is almost similar to the diversity of the extinct Pleistocene megafauna. Graham and Lundelius (1984) argue that perhaps the rate and magnitude of climate change was slower in Africa than in other continents, thus explaining the lower rates of megafauna extinction. Savannah environments survived into the Holocene in Africa while they disappeared in other parts of the world. For example in South America, savannah environments were abundant during the late Pleistocene but is today restricted to only a few areas. Other explanations for the African Anomaly have been put forward, although many of these tend to be speculative as Africa is the least studied continent with regards to late Pleistocene megafauna extinction. One possibility is that Africa has a great variety of habitat types which may offer better refugia for megafauna pressured by human activities (Heller 2012). Another explanation could be the existence of diseases that prevented humans or livestock from living in certain areas. This is still true today, as exemplified by locally endemic livestock diseases making large tracts of attractive pasture in Africa unavailable for human settlement. This is a phenomenon unique to Africa (Heller 2012). </span></span><br />
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<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;"><b>Human Impacts?</b></span></span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;"><b><br /></b></span></span>
<span style="font-family: Trebuchet MS, sans-serif;"><span style="line-height: 18px;">Graham and Lundelius (1984) claim that it is unlikely that humans have had much ecological impact on Africa’s megafauna because they have been known to coexist with them for a much longer time than on other continents. Martin (1984) even attributes the lower extinction rates to lower prey naiveté as a result of adapting to the hunting styles of humans. However, the human impact cannot be underestimated. Klein (1984) points to archaeological evidence that the humans of the late Pleistocene/Holocene transition were much more competent hunters than earlier humans. For example, studies of archaeological sites of earlier humans have found that eland (a type of ungulate) remains occur more frequently. Within the archaeological sites of humans who lived in the late Pleistocene/Holocene period (but under similar environmental conditions), remains of wild pigs, which were more dangerous to hunt and therefore required more sophisticated hunting techniques such as traps for example, were more prevalent than those of eland. </span></span><br />
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<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-FTBXvxqkQ24yVo49oZYxlw292rdWsr6UymOmGP6n30LOzwFpYf7Xh8W_BVbFkW_pJF_nDH1ranprjbjaLi5-dX9KBt-ZwoK5w3hoJjMgxjr5mbrxYko0AcJn3Ry8jbpWhgktwlNiVMY/s1600/Eland.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-FTBXvxqkQ24yVo49oZYxlw292rdWsr6UymOmGP6n30LOzwFpYf7Xh8W_BVbFkW_pJF_nDH1ranprjbjaLi5-dX9KBt-ZwoK5w3hoJjMgxjr5mbrxYko0AcJn3Ry8jbpWhgktwlNiVMY/s320/Eland.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Eland</td></tr>
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYSqR1cFAK2UHRE1LQE7_pkH002EcY6YoJ6OYwn8_h_dgTHSWMlipCEHfufslHSdG-4C5Tis6IT4y-YKEAmLm_J8jyKLhkjWiLcPhNbgMLrZg49O8dJaCf2h4Xkm-jGzciCW1MXBPz_A8/s1600/African+Wild+Pig.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="215" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYSqR1cFAK2UHRE1LQE7_pkH002EcY6YoJ6OYwn8_h_dgTHSWMlipCEHfufslHSdG-4C5Tis6IT4y-YKEAmLm_J8jyKLhkjWiLcPhNbgMLrZg49O8dJaCf2h4Xkm-jGzciCW1MXBPz_A8/s320/African+Wild+Pig.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">African Wild Pig</td></tr>
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<span style="font-family: Trebuchet MS, sans-serif;"><b>The Cape Buffalo Study</b></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">A <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2012.05671.x/abstract?systemMessage=Wiley+Online+Library+will+be+disrupted+on+15+December+from+10%3A00-12%3A00+GMT+%2805%3A00-07%3A00+EST%29+for+essential+maintenance" target="_blank">recent paper by Heller et al (2012)</a> using genetic sequencing of African Cape buffalo, a species which has survived from the late Pleistocene period to the present-day, has found evidence of benign human – megafauna interaction during the late Pleistocene. Cape buffalo began a population expansion from 80,000 radiocarbon years ago and reached a peak at 8,000 radiocarbon years ago, which shows that humans and climate change had relatively little impact on the population. This study provides further evidence of benign human-megafauna co-existence during the late Pleistocene. To the extent that Cape buffalo is representative of the ecological dynamics facing other African megafauna, this new research also supports the Graham and Lundelius’ (1984) finding that most of African Pleistocene extinctions occurred in the early Pleistocene. If Klein is correct, this was at a time when human hunters were very poorly technologically developed. Thus, climate change would be the larger factor impacting megafauna populations in Africa. </span><br />
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<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiDeSwjy5ZOEmS9_S1LytsYPfCyvDwsjyo4sEQ-j4-qX77vrbVvSYOzz5I1Sn-CJcUwLoqNbcy6TAmYsZzDyTQd4YrU_glx6tUeWE-vwWIyPOQCCHsGeo596DnY99AR4XpGvZRDg1eqnjk/s1600/Cape+Buffalo.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="212" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiDeSwjy5ZOEmS9_S1LytsYPfCyvDwsjyo4sEQ-j4-qX77vrbVvSYOzz5I1Sn-CJcUwLoqNbcy6TAmYsZzDyTQd4YrU_glx6tUeWE-vwWIyPOQCCHsGeo596DnY99AR4XpGvZRDg1eqnjk/s320/Cape+Buffalo.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Cape Buffalo</td></tr>
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<span style="font-family: Trebuchet MS, sans-serif;"></span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><b>References</b></span><br />
<span style="font-family: Trebuchet MS, sans-serif;">Klein, R. G. (1984) ‘Mammalian extinctions and Stone Age people in Africa’ in Martin, P. S. and Klein, R.G. (eds.) Quaternary Extinctions, Arizona: Arizona University Press, pp. 553 – 573</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">Graham, R. W. and Lundelius, E. L. (1984) ‘Coevolutionary disequilibrium and Pleistocene extinctions’ in Martin, P. S. and Klein, R.G. (eds.) Quaternary Extinctions, Arizona: Arizona University Press pp. 223 – 249</span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span>
<span style="font-family: Trebuchet MS, sans-serif;">Heller, R. et al (2012) ‘Cape buffalo mitogenomics reveals a Holocene shift in the African human–megafauna dynamics’, Molecular Ecology, 21, pp. 3947–3959</span><br />
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Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-55037249027442696702012-11-19T12:06:00.003-08:002012-11-19T12:19:58.323-08:00Dwarfed Giants: Woolly Mammoths on Wrangel Island <br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhK0Ln3GQZ1esmBrug0vdNHXR0sreAVjLX0Mwsxibv8JRG6usl-bjld2jnP8ijrjhnaSQ1L-wYyB79u0iizYZwUd9134MnFwBMWG1smZ65jzihOUT3ETio9qxyjW_QwRT1zEgKiFUC9LqY/s1600/Map+of+Wrangel+Island.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="280" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhK0Ln3GQZ1esmBrug0vdNHXR0sreAVjLX0Mwsxibv8JRG6usl-bjld2jnP8ijrjhnaSQ1L-wYyB79u0iizYZwUd9134MnFwBMWG1smZ65jzihOUT3ETio9qxyjW_QwRT1zEgKiFUC9LqY/s400/Map+of+Wrangel+Island.jpg" width="400" /></a></div>
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<span style="font-family: Trebuchet MS, sans-serif;"><i><b>Fig 1: </b>Vartanyan et al (1993)<b> </b></i><i>Map of Wrangel Island<o:p></o:p></i></span></div>
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<span style="font-family: 'Trebuchet MS', sans-serif;">On the reading list for lecture 2 is an interesting (and
conveniently, very short!) article by </span><a href="http://www.nature.com/nature/journal/v362/n6418/pdf/362337a0.pdf" style="font-family: 'Trebuchet MS', sans-serif;" target="_blank">Vartanyan et al (1993)</a><span style="font-family: 'Trebuchet MS', sans-serif;"> on Holocene dwarf
mammoths on Wrangel Island, which survived long past the consensus extinction
date of around 12,000 radiocarbon years BP of the ‘normal’ mammoth. Numerous
sets of fossilized teeth 30% smaller than normal mammoth teeth have been found
on Wrangel Island, and were dated as young as 7,000 – 4,000 radiocarbon years
BP. Based on the relationship between tooth and body size, researchers have
concluded that the dwarf mammoth was 180-230cm in shoulder height, at least 30%
smaller than woolly mammoths on the mainland. </span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Wrangel Island provided an isolated refugia for the mammoth
in its dwarf form. In the late Pleistocene, Wrangel Island was part of the land
of Beringida, joined up with the lowlands of East Siberia, Alaska and the
present-day Arctic shelf. By 12,000 radiocarbon yeas BP, Wrangel Island was
separated from the mainland, separating the local population of mammoth from
the mainland population. This Arctic island had a much higher diversity of plant
types and open vegetation, which supported mammoth populations. Even in the
present day, the vegetation on this island is considered to be a poorer relic
of late Pleistocene grassland.
Nevertheless, the dwarfing of mammoth size is an adaptation which reflected
the severity of the stress that the original ‘normal’ mammoths faced in their
original habitat. <o:p></o:p></span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs6aQOk-WRQzFeC9J4oXIc58t9SEtJ_NYol6Jo3XMyqiTwy5JgVjzNUHpnVgds3IJtCGygbsrCdJHEcTzHp_7QMDylAe-Ag3UHwIIwFLv5Uk7jvKN9V-jvw5kolgdGs0xtBfQqWHkE62c/s1600/Timeline+of+Global+Woolly+Mammoth+Extinctions.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><span style="font-family: Trebuchet MS, sans-serif;"><img border="0" height="420" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs6aQOk-WRQzFeC9J4oXIc58t9SEtJ_NYol6Jo3XMyqiTwy5JgVjzNUHpnVgds3IJtCGygbsrCdJHEcTzHp_7QMDylAe-Ag3UHwIIwFLv5Uk7jvKN9V-jvw5kolgdGs0xtBfQqWHkE62c/s640/Timeline+of+Global+Woolly+Mammoth+Extinctions.jpg" width="640" /></span></a></div>
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<span style="font-family: Trebuchet MS, sans-serif;"><b><i>Fig 2:</i></b><i> Stuart (2005) Timeline of Mammoth
Extinctions in Different Regions<o:p></o:p></i></span></div>
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<span style="font-family: 'Trebuchet MS', sans-serif;">The significance of the Wrangel Island dwarf mammoths is
that they provide a better understanding of how megafauna extinction took place,
and the role of refugia. Extinction is not a one-off event in which animals are
quickly wiped out, but rather, a gradual shrinking of range as these they
increasingly found their environments unsuitable. Fig. 2 (above) illustrates
the staggered extinction of mammoths, with some populations making their ‘last
stands’ in certain places. A useful complementary article to read is </span><a href="http://ac.els-cdn.com/S0277379102000264/1-s2.0-S0277379102000264-main.pdf?_tid=8601a618-3109-11e2-a0cc-00000aab0f02&acdnat=1353192954_171f674dd936b157a4bb49b2e9942955" style="font-family: 'Trebuchet MS', sans-serif;" target="_blank">Stuart’s(2005) more recent paper</a><span style="font-family: 'Trebuchet MS', sans-serif;"> on new evidence of mammoths surviving much later than
previously thought in other places that provided similar refugia, such as the
new mammoth molars found in Estonia, which date to 10,000 radiocarbon years BP.
Another example is the continued existence of woolly mammoth in the far north
of Siberia, the Taymyr Peninsula, for another 2,000 radiocarbon years after
most of them became extinct around the world. As the Holocene period brought
warmer climates and forests rather than the open-steppe vegetation which
favoured mammoths, such colder refugia allowed mammoths to survive. However,
the Wrangel Island mammoths also add more mystery to the megafauna extinction
debate. If climates became unsuitable, surely the mammoths were more vulnerable
to change on an island, where migration was not possible, rather than on the
mainland? Could it be the lack of humans on the island? Could human activities
have inhibited the normal migrational responses of megafauna to climate change,
thus limiting their range?</span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">While the Wrangel Island mammoths raise even more questions
on the megafauna debate than can be answered, it provides important lessons for
modern conservation. Wrangel Island highlights the resilience and adaptability
of natural ecosystems to change, e.g. through migration and physical adaptation
(dwarfing). However, the combination of climate change and human impacts was
just too much for the megafauna to bear. Today, as our ability to alter the
environment is ever more profound, we need to be increasingly responsible for
the consequences of our actions.</span><o:p></o:p></div>
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<span style="font-family: Trebuchet MS, sans-serif;"><b>References</b></span><br />
<br />
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Vartanyan, S.
L. (1993) ‘Holocene dwarf mammoths from Wrangel Island in the Siberian Arctic’,
<i>Nature 362</i>, pp. 337-340.<o:p></o:p></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Stuart, A. J.
(2005) ‘The extinction of woolly mammoth (Mammuthus primigenius) and
straight-tusked elephant (Palaeoloxodon antiquus) in Europe’, <i>Quaternary International 126-128, </i>pp.
171-177.</span><i> <o:p></o:p></i></div>
Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com3tag:blogger.com,1999:blog-4183418528940823030.post-26290643368768591532012-11-07T07:19:00.002-08:002012-11-07T07:19:42.096-08:00The Uncertain Blitzkrieg Down Under<br />
<div class="MsoNormal">
<br />
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">By the late Quartenary, Australia had lost 23 out of 24
genera of its megafauna. The 2 main explanations for this are human mediation –
overkill and habitat destruction – and climate change. In this blog post I will
look at each in turn, and conclude that humans are not the primary cause of
megafauna extinction in Australia. While human ‘blitzkrieg’ was previously the
consensus, new research has shown increasing evidence that it is likely climate
change played a larger role in a majority of extinctions. </span><o:p></o:p></div>
<br />
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b>
<b><span style="font-family: Trebuchet MS, sans-serif;">Human Overkill and
Habitat Destruction</span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;">The main argument for proponents of the blitzkrieg
hypothesis is that most megafauna were present when humans arrived in
Australia, and they were subsequently wiped out by interaction with humans.
They point to the evidence that extinction of megafauna occurred around 45,000
calendar years ago, coinciding with human colonization of Australia and
predating climate change (Roberts et al 2001). Miller et al (2005) also show in
their research that records have shown a decline in food sources for the
Australian emu and marsupial wombat, attributed to human modification of the
drought- adapted environment of shrubs and grasses into the fire-adapted scrublands
of today.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;">However, <a href="http://www.pnas.org/content/102/23/8381.full.pdf+html" target="_blank">Trueman et al (2005)</a> argue that fossil evidence from
Cuddie Springs (Southeastern Australia) and other sites refute the consensus
that megafauna became extinct about 45,000 calendar years ago. Their research
has found that humans and megafauna co-existed for about 15,000 calendar years
after the arrival of humans. Besides, Wroe et al (2004) points to the complete
absence of any direct evidence implicating human mediation, e.g. kill sites, similar
to those that have been found in North America.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">Climate Change<o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;"><a href="http://ac.els-cdn.com/S0277379106001399/1-s2.0-S0277379106001399-main.pdf?_tid=858257aa-283a-11e2-ab6e-00000aab0f02&acdnat=1352224438_e9553af63cbbdc44ff24769cba370460" target="_blank">Wroe and Field (2006)</a> point to evidence from a variety of
climate proxies (pollen, charcoal, hydrology, etc.) that there was a broad
trend towards increasing aridification of the Australian climate in the Late
Quarternary, which overlaid glacial cycles. Thus, the Holocene interglacial was
drier than previous interglacials, disputing the idea that the
Pleistocene-Holocene transition was similar to previous transitions. The chart
below shows that lake levels and river flow in Northern and Southeastern
Australia started declining from around 50,000 calendar years ago, while dust
levels increased from around 200,000 calendar years ago. Other evidence from
pollen records show that around 200,000 years ago, grasses became more
prevalent relative to eucalyptus, indicating increased aridity. <o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghIw5rZvFhSugRdAM2e5a98fFhwtw0rcltwruL6NTDzYwpCLOj7I4sH7g8niMVptqtDtDielqyAwv7TkKgyABiI7vsLk1HzZpywWOQEUnjOGZzXyE8MAhhkR2-8Sw6Hcq8gY0o9bYTutU/s1600/Increasing+Aridification+of+Australian+Climate.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><span style="font-family: Trebuchet MS, sans-serif;"><img border="0" height="502" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghIw5rZvFhSugRdAM2e5a98fFhwtw0rcltwruL6NTDzYwpCLOj7I4sH7g8niMVptqtDtDielqyAwv7TkKgyABiI7vsLk1HzZpywWOQEUnjOGZzXyE8MAhhkR2-8Sw6Hcq8gY0o9bYTutU/s640/Increasing+Aridification+of+Australian+Climate.jpg" width="640" /></span></a></div>
<div class="MsoNormal" style="text-align: center;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="text-align: center;">
<i><span style="font-family: Trebuchet MS, sans-serif;"><b>Fig. 1:</b> Wroe and Field (2006)</span></i></div>
<div class="MsoNormal" style="text-align: center;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal">
<span style="font-family: 'Trebuchet MS', sans-serif;">Thus, non human-mediated climate change can be shown to have
caused the extinction, as these natural processes were in motion long before
humans arrived. However, it is certainly possible that humans played a role in
further stressing megafauna already stressed by these climatic changes,
although they cannot be seen to be a primary cause of the extinctions. </span><br />
<br />
<div class="MsoNormal">
<o:p></o:p></div>
</div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">An Alternative Model:
Staggered Extinctions of Australian Pleistocene Megafauna<o:p></o:p></span></b></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Wroe and Field (2006) suggest an alternative model of
staggered extinctions. Their more recent research shows that at least 65% of
the megafauna cannot be shown to have existed beyond 130,000 calendar years
ago. Only 13% of megafauna species during the Pleistocene co-existed with
humans, and at least half of these species survived 15,000 calendar years after
humans arrived. Thus, they argue for an alternative model of repeated range
contractions and limitation of refugia for megafauna as Australia’s climate
became increasingly arid, resulting in extinctions which predated human
contact.<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: Trebuchet MS, sans-serif;">Their model is supported by Cosgrove and Allen’s (2001)
study of Tasmanian rockshelters. Since early humans could only have reached
Tasmania by 37,000 calendar years ago through the development of a land bridge,
if humans caused extinction then megafauna should be shown to survive there
until the arrival of humans. However, no megafauna fossil remains younger than
46,000 calendar years ago could be found. <o:p></o:p></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
</div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-font-size: 8.0pt; mso-bidi-theme-font: minor-latin;"><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-font-size: 8.0pt; mso-bidi-theme-font: minor-latin;"><b><span style="font-family: Trebuchet MS, sans-serif;">References</span></b></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-font-size: 8.0pt; mso-bidi-theme-font: minor-latin;"><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="line-height: 115%; mso-bidi-font-family: Calibri; mso-bidi-font-size: 8.0pt; mso-bidi-theme-font: minor-latin;"><span style="font-family: Trebuchet MS, sans-serif;">Cosgrove, R. and Allen, J. (2001) ‘Prey choice
and hunting strategies in the Late Pleistocene: evidence from Southwest
Tasmania’ in Lilley, A. and O’Conner, S.
(Eds.), <i>Histories of Old Ages: Essays in Honour
of Rhys Jones.</i> Canberra: Research School of Pacific and Asian Studies, Australian
National University, Canberra, pp. 397–430.<o:p></o:p></span></span></div>
<br />
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Miller et al
(2005) ‘Ecosystem collapse in Pleistocene Australia and a human role in
megafaunal extinction’, <i>Science, </i>309,
5732, pp. 287-290<b><o:p></o:p></b></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Roberts, R.G. et al (2001) New ages for the last Australian megafauna continent-wide extinction about 46,000 years ago. <i>Science,</i> 292, 1888–1892.</span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Trueman et al
(2005) ‘Prolonged coexistence of humans
and megafauna in Pleistocene Australia’, <i>Proceedings
of the National Academy of Sciences of the United States of America, </i>102,
23, pp. 8381-8385<o:p></o:p></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
</div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Wroe, S. et
al (2004) ‘Megafaunal extinction in the Late Quaternary and the global overkill
hypothesis’, <i>Alcheringa</i>, 28, pp. 291–331.</span><br />
<span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -36pt;"><br /></span>
<span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -36pt;">Wroe, S.
and Field, J. (2006) ‘A review of the evidence for a human role in the
extinction of </span><span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -36pt;">Australian
megafauna and an alternative interpretation’, </span><i style="font-family: 'Trebuchet MS', sans-serif; text-indent: -36pt;">Quaternary Science Reviews, </i><span style="font-family: 'Trebuchet MS', sans-serif; text-indent: -36pt;">25,21-22, pp. 2692-2703.</span></div>
<div class="MsoNormal" style="margin: 0cm 0cm 0.0001pt 36pt; text-indent: -36pt;">
<br />
<div class="MsoNormal" style="margin: 0cm 0cm 0.0001pt 36pt; text-indent: -36pt;">
<o:p></o:p></div>
</div>
<br />
<br />
<br />Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com2tag:blogger.com,1999:blog-4183418528940823030.post-71612670224419834932012-11-03T11:55:00.000-07:002012-11-03T11:56:33.809-07:00Megafauna Extinction in Eurasia<br />
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;">Eurasia (Eurasia and Northern
Asia) lost 35% of its megafauna during the late Pleistocene, relatively fewer
than North America and Australia. Extinction patterns here differed from those
in North America; not all the extinctions occurred synchronously at the end of
the Pleistocene (Grayson 2007). For example, mammoths disappeared from many parts
of Eurasia at around 12,000 radiocarbon years ago, but lasted as late as 4,000
radiocarbon years ago on Wrangel Island. Similarly, giant deer disappeared from
Southwestern France between 12,000 and 11,000 radiocarbon years ago but not
from western Siberia until 7,000 years ago Stuart et al 2004). <o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;">The consensus is that Man was
unlikely to have caused megafauna extinction in Eurasia, as the first modern
humans (with sophisticated hunting tools) entered Eurasia around 50,000 radiocarbon
years ago, and there were no apparent extinctions then (Grayson 2007). However,
Stuart (1999) argues that the human role in Eurasia is not insignificant. For
example, according to radiocarbon-calibrated pollen profiles, vegetation able
to support mammoth was present more than 1,000 radiocarbon years after these
animals disappeared in the region, weakening the argument that environmental
change was the sole cause of extinction. Instead, he suggests that the
asynchronous nature of extinction in Eurasia could mean that extinctions only occurred
when animal populations were already undergoing significant stress from climate
change, and human hunting provided the last straw. This probably also explains
why there were 2 distinct waves of extinction in Eurasia which coincided with
periods of climate change (40,000 to 20,000 radiocarbon years before present
and 14,000 to 10,000 radiocarbon years before present), the latter of which is
the focus of this blog. <o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;">While Stuart’s argument is
convincing, I think an interesting counterargument can be found in Anthony Barnosky’s
1986 paper. He argues that Irish deer, which became extinct at around 10,000 to
12,000 radiocarbon years ago, before the arrival of humans in Ireland, were
wiped out not by Holocene warming but a brief cold spell just before warming.
This cold spell shortened feeding seasons for the Irish elk, which were also
unable to migrate to any refugia quickly enough as Ireland is an island. The
evidence is in lake sediment layers where pollen records suggest changes in
vegetation associated with colder weather and fewer elk bones, during a period
called the Nahanagan Stadial. He suggests that the accumulation of many local
causes of extinction could have led to the total extinction of megafauna. Nevertheless,
more work remains to be done on this fascinating hypothesis. <o:p></o:p></span><br />
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjgMxO4Io_Y64AVsm-73twYx267lmN-3iJB75heYp4HuLkNEsKTwD2JfkUnUznDX1B1qxpcS_QeMvcaalXsWlyYpuCnqKO_pHFym45REhyphenhyphenL1oB4b1UvMyj1Ex7ZC-V2KqucwJSB1BhKUj4/s1600/Irish+Elk.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjgMxO4Io_Y64AVsm-73twYx267lmN-3iJB75heYp4HuLkNEsKTwD2JfkUnUznDX1B1qxpcS_QeMvcaalXsWlyYpuCnqKO_pHFym45REhyphenhyphenL1oB4b1UvMyj1Ex7ZC-V2KqucwJSB1BhKUj4/s1600/Irish+Elk.jpg" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><i><span style="font-family: Trebuchet MS, sans-serif;"><br /><span style="font-size: small;">Figure 1: Irish Elk</span></span></i></td></tr>
</tbody></table>
<div class="MsoNormal" style="text-align: left;">
<span style="font-family: 'Trebuchet MS', sans-serif; text-align: justify;">Finally, I return to a discussion
of the climate change that occurred during the late Pleistocene. In my previous
blog post ‘Humans in the Wild West’, I discussed research showing that the late
Pleistocene-Holocene glacial transition was unique in the Northern Hemisphere
compared to other previous interglacials, both in climate and biological terms.
This caused megafauna extinction due to climate unsuitability. Nogues-Bravo et
al (2008) constructed a model which shows this for one species – the woolly
mammoth in Europe.</span></div>
<div class="MsoNormal" style="text-align: left;">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3ejZFgu4KTryoOhhRUyz2k-4eYuk8oOkSGwFbIL2yiMv6TfrBv0QXPaIhzvktazojD7jWPIcJHUHvNaQGXevYGsA2HoANZZ9L5_wg87fLwgdSE8oopLeznmXdMdQe1TEF3kQlOIVqSHo/s1600/Map+of+Mammoth+Habitat+Suitability.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="444" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3ejZFgu4KTryoOhhRUyz2k-4eYuk8oOkSGwFbIL2yiMv6TfrBv0QXPaIhzvktazojD7jWPIcJHUHvNaQGXevYGsA2HoANZZ9L5_wg87fLwgdSE8oopLeznmXdMdQe1TEF3kQlOIVqSHo/s640/Map+of+Mammoth+Habitat+Suitability.jpg" width="640" /></a></div>
<div align="center" class="MsoNormal" style="text-align: center;">
<i><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></i></div>
<div align="center" class="MsoNormal" style="text-align: center;">
<i><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></i></div>
<div align="center" class="MsoNormal" style="text-align: center;">
<i><span style="font-family: Trebuchet MS, sans-serif;">Figure 2: Maps of Projected
Climatic Suitability for the Woolly Mammoths in the Late Pleistocene and
Holocene (Nogues-Bravo et al 2008)</span></i></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;">The increasing intensities of red
show increasing suitability of mammoth habitat while increasing intensities of
green show decreasing suitability. Black dots show mammoth presence while black
lines show the northern limit of early humans. The figure shows that climate
and habitat suitability for mammoths decreased during the late Pleistocene.
Although humans did move Northwards, their presence did not seem to affect
mammoth presence as drastically as habitat suitability; even in areas untouched
by humans (north of black line), mammoth populations declined as habitat
suitability decreased. <o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: Trebuchet MS, sans-serif;">The causes of megafauna
extinction in Europe are certainly extremely complex. Climate change appears to
be the main culprit, since human populations coexisted with megafauna for over
50,000 radiocarbon years while accelerated extinctions only occurred in 2
distinct phases which were periods of distinct climate change. Extinctions in
at least some specific geographical locations, such as the Irish elk in
Ireland, were certainly distinct from the role of humans. <o:p></o:p></span></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></b></div>
<div class="MsoNormal">
<b><span style="font-family: Trebuchet MS, sans-serif;">References<o:p></o:p></span></b></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Barnosky, A.
(1986) “Big game” extinction caused by late Pleistocene climatic change: Irish
elk (Megaloceros giganteus) in Ireland’, <i>Quaternary
Research</i>, Vol. 25, 1, pp. 128-135<o:p></o:p></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Grayson, D.
K. (2007) ‘’Deciphering North American Pleistocene extinctions’’, <i>Journal of Anthropological Research, </i>Vol.
63, No. 2, pp. 185-213<o:p></o:p></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;"><br /></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="font-family: Trebuchet MS, sans-serif;">Nogues-Bravo,
D. et al (2008) ‘’Climate change, humans and the extinction of the woolly
mammoth’’, <i>PLOS Biology, 6(4), e79</i></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="background: white; color: #222222; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;"><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<span style="background: white; color: #222222; mso-bidi-font-family: Calibri; mso-bidi-theme-font: minor-latin;"><span style="font-family: Trebuchet MS, sans-serif;">Stuart, A. J. (1999). Late Pleistocene megafaunal extinctions
in MacPhee, R. D. E. (ed.) <i>Extinctions in Near Time: Causes, Contexts, and
Consequences</i>, New York: Plenum, pp. 257-269.<o:p></o:p></span></span></div>
<div class="MsoNormal" style="margin-left: 36.0pt; text-indent: -36.0pt;">
<br /></div>
Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-26959054182576131292012-10-28T11:37:00.000-07:002012-10-28T11:37:53.991-07:00All Creatures Great and Small (are important considerations in the megafauna extinction debate)<br />
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<span style="font-family: Trebuchet MS, sans-serif;">I came across an interesting journal article the other day
about introducing a behavioural economics perspective to megafauna extinction. This journal is interesting not only to me as
an Economics and Geography student, but also because it suggests the value of
an inter-disciplinary perspective to environmental geography. In the 2005 paper ‘Megafauna Extinction: A Paleo-economic Theory of Human Overkill in the
Pleistocene’, Bulte et al argue that previous scientific models of overkill
concentrated only on megafauna as prey for humans, while ignoring the entire
opportunity set facing the human hunters, which is the presence of substitute
foods and behaviours. One of these is hunting small animals or minifauna. <o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">Bulte et al have
designed a model which suggests that counter intuitively, hunting minifauna was
essential to the overkill hypothesis. Minifauna supported human populations and
allowed humans to reach critical densities which were large enough to wipe out
megafauna. Besides, hunting minifauna enabled more chance encounters with megafauna.
Complementing last week’s post, they suggest that the harsh environmental conditions
of the late Pleistocene may have triggered humans to engage in minifauna
hunting rather than more benign activities like agriculture. Minifauna did not go extinct because they
breed much more quickly than slow-breeding megafauna. <o:p></o:p></span></div>
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<span style="font-family: Trebuchet MS, sans-serif;">This echoes modern
day poaching behaviour in Africa. Poachers often hunt both rhinos and
elephants, and not only the more valuable rhino ivory alone, because the
probability of encountering rhinos is much smaller, making sole rhino hunting a
loss-making activity. Thus, poachers also hunt the relatively more abundant
elephants, taking rhinos as a bonus. Thus, elephant hunting is what economists
call a ‘complementary’ activity to rhino hunting, in the same way as hunting
minifauna was complementary to hunting megafauna for early humans. </span><o:p></o:p></div>
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<o:p><span style="font-family: Trebuchet MS, sans-serif;">Although the authors of this journal are economists rather than paleo or megafauna experts, they do make an important point about considering the behavioural incentives facing early human hunters and not simply portraying them to be the mechanistic 'superpredators' of most overkill models.</span></o:p></div>
Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com3tag:blogger.com,1999:blog-4183418528940823030.post-43400928911968113942012-10-20T13:11:00.000-07:002012-10-20T14:43:25.199-07:00The First Outlaws? Megafauna Murderers of the Wild West: Clovis Hunters <div class="separator" style="clear: both; text-align: left;">
<span style="font-family: Georgia, Times New Roman, serif; text-align: justify;">The late Pleistocene extinction of megafauna in North America was a unique event as previously, species that became extinct were small mammals. In the Pleistocene interglacial, extinction was almost entirely confined to large mammals (>1,000 kg) and medium-large ones (100 – 1,000kg) (Stuart 1991). North America lost 35 out of 45 megafauna genera during the Pleistocene (Grayson 2007: See Table). </span></div>
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<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjh0eikV8PRy-NAVaw-3ymuCTEokjovEFe6axbtxnucOk0fiR7RlNciUMpSwVHjCOU96d2-bhqO0a950ZL_mozaYXdn5V-bclFKnSOs544OnrhFajtL3X1fc8giJa1nnGzzzgg6AmjML40/s1600/table+of+extinct+megafauna+North+America.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><span style="font-family: Georgia, Times New Roman, serif;"><img border="0" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjh0eikV8PRy-NAVaw-3ymuCTEokjovEFe6axbtxnucOk0fiR7RlNciUMpSwVHjCOU96d2-bhqO0a950ZL_mozaYXdn5V-bclFKnSOs544OnrhFajtL3X1fc8giJa1nnGzzzgg6AmjML40/s640/table+of+extinct+megafauna+North+America.gif" width="414" /></span></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-family: Georgia, Times New Roman, serif;">Grayson (2007): Table of Extinct Megafauna of the Late Pleistocene</span></td></tr>
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<span style="font-family: Georgia, Times New Roman, serif;">Proponents of the ‘overkill’ or ‘blitzkrieg’ hypothesis emphasize that the megafauna extinctions of 11.5 - 10,000 radiocarbon years ago coincided with the arrival of humans with advanced hunting techniques in North America, called the Clovis hunters. This could explain why megafauna extinctions were concentrated in the late Pleistocene rather than previous inter-glacial transition periods, as the only differentiating element of the late Pleistocene was the presence of the first ‘anatomically modern’ humans. Since it was the animals’ first encounter with them, they did not yet have the behavioural skills to avoid predation. Paul Martin (1967) was one of the earliest and most enthusiastic proponents of this view. Haynes (1967) showed that the earliest known appearance of Clovis hunters was 11.5-11,000 years ago, although more recent evidence suggests that an earlier people before Clovis existed as early as 13,800 years ago and was already developing the tools that would later evolve into those of Clovis hunters (See photograph). Barnosky et al (2004) points out that most large-bodied survivors of the late Pleistocene extinction event were nocturnal, alpine or deep forest dwellers, making them more difficult targets for humans. Furthermore, Graham and Lundelius (1984) suggest that the killing of megaherbivores like mammoths and mastodons (the 2 mammals with the largest number of recorded kill sites) was especially damaging and upset the entire ecosystem, driving other animals which were not directly hunted by humans to extinction. Mammoths and mastodons, like modern day elephants, tore down trees and bushes while feeding, making them accessible to other herbivores who would not otherwise be able to reach them. The disappearance of herbivores would then result in the starvation of their predators. This could be a counter-argument to Grayson and Meltzer’s (2002) argument that only 2 megafauna genera – the woolly mammoth and mastodon – have been shown to be the prey of Clovis humans, and this is supported by just 14 kill sites. </span></div>
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<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjia9Am8HMBZXl0bRSmR99nO0VZbW3489U-i1h9puWUKkvb1-Nru_vO-Iz9fs-k1HLbe3NBbC1Fu8H6BEBpd9VfWdvU1zHAxMDcRysMlPvdkJXilmnaFA107iKbr5p0SnVZ33fkYyhSsx8/s1600/Speared+Mastodon+Bone+-+National+Geographic.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><span style="font-family: Georgia, Times New Roman, serif;"><img border="0" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjia9Am8HMBZXl0bRSmR99nO0VZbW3489U-i1h9puWUKkvb1-Nru_vO-Iz9fs-k1HLbe3NBbC1Fu8H6BEBpd9VfWdvU1zHAxMDcRysMlPvdkJXilmnaFA107iKbr5p0SnVZ33fkYyhSsx8/s320/Speared+Mastodon+Bone+-+National+Geographic.jpg" width="320" /></span></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-family: Georgia, Times New Roman, serif;">National Geographic (2011): CT scan showing cross-section of the broken tip of a spear embedded in a mastodon's rib (dated 13,800 years ago)</span></td></tr>
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<span style="font-family: Georgia, Times New Roman, serif;">Grayson and Meltzer (2002) argue against this generally accepted view of human predation driving megafauna extinction. They show that only 15 of the 35 genera that were supposedly killed by Clovis hunters actually survived to 11,000 radiocarbon years ago, which is when they would have encountered Clovis hunters. Besides, megafauna extinction in North America is by no means a unique phenomenon. The entire Northern Hemisphere experienced substantial species extinctions around 10,000 – 11,000 radiocarbon years ago. In Eurasia for example, many megafauna like reindeer, giant deer and mammoth also disappeared around the same time as those in North America did. Woodman et al (1997) support the view that humans cannot be blamed for giant deer extinction in Ireland as there were no people there during that time. </span></div>
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<span style="font-family: Georgia, Times New Roman, serif;">The reasons for why climate change has been rejected as a cause of megafauna extinction are encapsulated in Fiedel’s (2009:30) question: “if Holocene warming was so disastrous for megafauna, why wasn't there a wave of extinction around 125 ka in the last interglacial?” There are 2 arguments proponents of the climate change explanation use. The first is that the last interglacial was much warmer than previous interglacials and had fewer seasonal temperature variations, leading to mosaic vegetation types that supported a richer range of animal species (Graham and Lundelius 1984). When the open grasslands of the late Pleistocene gave way to thicker forests and vegetation which showed strong zoning according to climate during the Holocene, animal extinctions occurred as the less diverse vegetation could no longer support the previous level of biodiversity (Stuart 1991). Graham (1985) has also argued that the Pleistocene – Holocene transition was unique from previous transitions. Not only was Holocene climate and vegetation was very different from that of previous interglacial periods, but also unusually, the last interglacial was warmer, rather than cooler, than the Holocene in both North America and Europe. </span></div>
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<span style="font-family: Georgia, Times New Roman, serif;">The second is that the late Pleistocene was biotically unique. Scott (2010) argues that this assumes a static view of megafauna composition and hence, similar adaptations to climate change. He uses the example of bison becoming more widespread in North America. Guthrie (1980) proposed that since bison survived while other species perished during this period, this may suggest that competition from bison, along with failure to adapt to climate change, drove the megafaunal extinction event. Nevertheless, the key takeway from Scott’s paper is that ‘megafauna’ is not a static concept, and this has implications for evolutionary responses to climate change. This squares with Graham and Lundelius’ (1984) theory of ‘coevolutionary disequilibrium’ – species evolve individualistically and uniquely to climate change in ways that may become detrimental to other species. </span></div>
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<span style="font-family: Georgia, Times New Roman, serif;">Additionally, during 10,000 years of the Holocene very few land mammals became extinct, although human populations certainly increased dramatically (Stuart 1991). </span></div>
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<span style="font-family: Georgia, Times New Roman, serif;">Nevertheless, the extinctions in North America were definitely more sudden and severe than in Europe. The North American case supports the view of a greater, but not dominant, human role in extinction in relation to other regions. The arrival of Clovis hunters (not present in Europe) at a time of more profound climate change was probably the last straw for many species already suffering the stress from a changing environment.</span><br />
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<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMCw9to6vdZnUCHoC_anjE_AcIHQhrqfDke2c1cjPecUSQ-Svq2Avw6oetVn33Okmwna48GoBrp9VNek3NFNdpOfqsLVGYbAvQbeAui9y9xAlflgYx145nqYcriBhEsuleVMyr31QolLI/s1600/Mastodon+and+Woolly+Mammoth.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><span style="font-family: Georgia, Times New Roman, serif;"><img border="0" height="250" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMCw9to6vdZnUCHoC_anjE_AcIHQhrqfDke2c1cjPecUSQ-Svq2Avw6oetVn33Okmwna48GoBrp9VNek3NFNdpOfqsLVGYbAvQbeAui9y9xAlflgYx145nqYcriBhEsuleVMyr31QolLI/s640/Mastodon+and+Woolly+Mammoth.jpg" width="640" /></span></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-family: Georgia, Times New Roman, serif;">The Modern Elephant and its Prehistoric Cousins - A Similar Fate?</span></td></tr>
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Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com0tag:blogger.com,1999:blog-4183418528940823030.post-70075459766099781792012-10-11T10:04:00.000-07:002012-10-20T14:43:49.762-07:00In the Beginning...<br />
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<span style="font-family: Georgia, Times New Roman, serif;">Woolly mammoths, sabre-toothed tigers and other Pleistocene megafauna
roamed the Earth, forming a vital part of natural ecosystems. Today, they
occupy no more than a CGI-manipulated place in the popular imagination, with
appearances in natural history museums, animated movies and even in the hit TV
series Game of Thrones as the dire wolf. How these mighty beasts have fallen! <o:p></o:p></span></div>
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<span style="font-family: Georgia, Times New Roman, serif;">Natural climate change was long thought to be behind their
extinction, but recent studies have pointed to a new culprit: Man. Although Man
cannot be solely held responsible, evidence suggests that early humans played a
precipitating role in megafauna extinction which complemented the effects of
climate change, at least in a fair number of continents like North America,
Eurasia and Australia. Indeed, even in his less-than-glorious past, with his primitive
weapons and small numbers, Man has managed to sound the death knell for these
powerful creatures. With Man’s impact on biodiversity tremendously larger
today, the prospects for today’s megafauna - elephants for example – are dire.</span></div>
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<span style="font-family: Georgia, Times New Roman, serif;">That said, important lessons abound for modern conservation from
the unfortunate fate of these vanished giants. Human-induced climate change and
human impacts on the natural environment are ever greater today, and the past
has shown that these two factors have decimated two thirds of megafauna genera
between 50,000 and 10,000 years ago – 40,000 years is merely the blink of an
eye in geological time.</span></div>
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<span style="font-family: Georgia, Times New Roman, serif;">This blog explores the role of Man in Pleistocene megafauna
extinctions and bridges the lessons of the past with the implications for
contemporary conservation efforts. </span><o:p></o:p></div>
Anonymoushttp://www.blogger.com/profile/01382810622922230501noreply@blogger.com1