Assessing the Causes of Late Pleistocene Extinctions on the Continents (Barnosky 2004)
Barnosky’s review paper focused on evidence that supports the idea that humans were responsible for the extinction of megafauna on some, but not all continents during the late Pleistocene extinction event. Abiotic (climatic and ecological) changes in combination with biotic (human) impact contributed to the extinction of megafauna within the Northern Hemisphere, but the Southern Hemisphere remains to be studied further. In summary, evidence from paleoclimatology, chronology, ecology, archaeology, and simulations strongly supports human impact on megafauna due to Clovis hunter introduction and the hunting of extinct species.
The chronology of the Northern High-latitude areas of Alaska, Northern Europe, and Siberia showed a coincidence of climatic change with extinction pulses of warm adapted animals from 45 to 20 RCBP (Radio Carbon Years Before Present) and cold adapted animals 12 to 9 ky RCBP. The pulse in Eurasia also coincided with increases in human populations in areas where pre-sapiens humans had hunted for 400,000 years without causing extinction. In central North America, there was strong clustering of extinctions with the arrival of clovis style hunters. In Australia, the extinction of megafauna was chronologically placed soon after the arrival of humans, but before any identified major climate changes. South America and Africa lack sufficient data and analysis to identify causes of extinction or why Africa experienced comparatively less megafauna extinction than Australia or North America.
Why do you think megafauna extinctions rates were lower in Africa (8 genera) and Eurasia (9 genera) than Australia (50 genera) or North America (33 genera)?
Two unresolved points of debate arise when determining the extent of human hunting of megafauna: What can be considered evidence of human hunting megafauna? Are there too little kill sites to support overkill models (especially with taxa that are more uncommon in the fossil record)? What are your thoughts?
Do you think their evidence is enough to support this idea? If not, in what ways can the idea be supported?
Climatic changes during the late Pleistocene triggered vegetation changes and drove megafauna into different areas where they were most likely vulnerable. In some areas, this was not the case to say that change in vegetation compared with extinctions. However, the recent deglaciation of the late Pleistocene was neither less nor more greater than how it was during the past 700,000 years.
Why do you think the late Pleistocene extinction climatic change was unique if it wasn’t different than over the past 700,000 years?
Barnosky's article referring to the late Pleistocene extinction of much of the mega fauna suggesting that it was anthropogenic causation as the climatic changes with reglaciation and deglaciation were not greater or less than those seen in the last 700,000 years.The late Pleistocene extinction was unique as it wasn't just abiotic factors only but a combination of both abiotic and biotic factors that led to such a drastic extinction rate. On the continents where there is sufficient evidence,Australia & North America,the radical shift in the extinction rate correlate to human arrival and activity. In Europe & Africa the extinction rate of the mega fauna correlates more to ecological factors; destruction of habitat or changes in the organisms range,may contribute for the lack of an exorbitant extinction rate.
ReplyDeleteThere isn't a consensus about what constitutes evidence of human hunting of megafauna. Generally, cut marks or breakages of fossil bone is considered to be acceptable evidence in Africa and Eurasia but this isn't considered acceptable in North America. There's not even a mention in the article about what is considered acceptable evidence of human hunting of megafauna in North America and Australia. Could this be one reason why these two continents are showing larger rates of megafauna extinction? If there is confusion about what may or may not be evidential human hunting it could cause an increase of reports.
ReplyDeleteThis Pleistocene climate change could seem different from all the others because of the appearance of humans, like the authors stated. It seems likely that these megafaunal extinctions (especially the larger extinction events) were tied to both climate change and humans' hunting. Climate change was also probably a big factor in manipulating movement of humans. Could including extinction information for smaller fauna in the same areas shed some light on human- vs. climate change-driven extinctions?
ReplyDeleteMaybe Eurasia and Africa show lower numbers of large critter extinction because diversity in these areas weren't high to begin with? I'm not sure about the fossil records in these areas though, so I could be wrong. It could also be the "monograph effect" that Dr. Smith explained in class: more scientists want to study the fossil records in Australia and North America, so there's more information from these parts. Again, not too sure about this. Another possible explanation, like the authors suggested, could be that the hunting strategies of humans and pre-humans in Africa and Eurasia may not have been fully developed yet, giving the large critters a better chance of survival. Also, really like Sarah's above comment! A lack of uniformity when documenting evidence could be messing up some of the data and skewing the conclusions.
In the paper, Barnosky et al. address that pre homo sapiens did not cause extinctions, because their populations were too low. Could another reason be that pre homo sapiens were not hunting yet and that the reason for the cause of mega fauna extinctions is due to the cause of learning to hunt? Also, in Africa is there any evidence for previous extinctions to megafauna when humans were beginning to evolve and learning how to hunt successfully?
ReplyDeleteWhat I found interesting about this paper, which appears to be a recurring theme in discussion papers as well as in the overall course, is the use of a multidisciplinary approach to assess the causes of Late Pleistocene extinctions. Through utilizing evidence from paleontology, climatology, archeology, and ecology Barknosky, et al. (2004), were able to gather more clues on the contribution of humans in the creation of special conditions where megafauna extinction could take place. I also think the fact that there is not a widely supported consensus on what constitutes a kill site would make making clearer assumptions on the role of humans in the Late Pleistocene extinction more difficult so this needs to be addressed. Lastly, I also had a lot of difficulty understanding the kind of simulation models the authors used to look at predation with life history parameters, I’m not sure if this was just me but I thought more background information on these models would have been useful to understand the data presented in this paper.
ReplyDeleteThe paper mentions that it has been theorized that lower number of extinct genera in Africa and Eurasia may be due to the fact that humans had coexisted with these species for thousands of years, while in Australia and North America they were an "invasive species". It was also mentions that homo sapiens sapiens typically had a more diverse diet than pre sapiens, and therefore may have populated beyond what the megafauna populations could support. I agree that is hard to come to a consensus about what can be classified as evidence of human hunting given the variance between continents, which makes finding a universal standard difficult. It is also difficult to establish overkill models with taxa that are typically more rare in the fossil record. The late Pleistocene extinction was unique in that both humans and climate change contributed to extinctions in varying degrees across the globe, not unlike today's extinction crisis.
ReplyDeleteIn terms of what can be considered evidence of human hunting megafauna, I think difference is how evidence for human hunting is defined (per continent) is one of the factors that should be defined. As mentioned by Sarah, the article does not really note what is considered evidence of hunting in any of the continents, nor the differing ideas about what constitutes evidence of human hunting evidence. In North America, only five mammalian genera have secure contexts where they are believed to have been hunted by humans during the pleistocene: Camelops (one site), Equus (one site), Cuvieronius (one site), mammut (two sites), and mammuthus (11 sites). Based on this, I am not against the over hunting hypothesis, but I do not believe that there is enough evidence to support overkill for all extinct pleistocene species, especially when the majority of the recovered kill sites are mammoth/mastodon. Thus, I think environmental change must have played a role.
ReplyDeleteI would think that the larger rate of extinctions in Eurasia and parts of South America as opposed to Africa are due to the fact that environmental change isn't the same everywhere on the planet. Currently, the Arctic is experiencing the largest amount of warming while the tropics are experiencing relatively little. This gradient of change could potentially affect species in more temperate regions than in hot ones, especially coming out of a climate that was colder than it is today.
ReplyDeleteThis paper shows that there was evidence of over hunting but not strong enough evidence for the overkill hypothesis. However, I do not believe that this paper was very clear about what can be considered evidence of human hunting between continents. I believe that the majority of extinction was (and still is) due to humans. However, evidence has also shown that climate change is playing a significant roll in it as well.
ReplyDeleteIn response to the question about why there is a difference between extinction rates on different continents I would have to say that since there were humans adding to population decline due to climate changes we would have seen such higher numbers of loss of those megafauna. Where in Africa and Eurasia we don't see such dramatic climate changes although we still have the introduction of humans adding to the population declines.
ReplyDeleteAs I was reading the abstract of this particular paper, I was struck by the idea that the authors seemed to implicate the importance of "pronounced climate change" in the scope of late Pleistocene extinctions (Barnosky, et al. 2004). However, the "Climate Change and Ecological Effects" section of the paper indicates that paleoclimate records reflect that the climate changes associated with the late Pleistocene transition did not differ significantly in terms of speed or magnitude from other climate shifts. Further, such climatic shifts, according to this section of the article, were not unusual in comparison to other climatic events. Given that these climatic changes were generally unremarkable when compared to other climate shifts, I found myself wondering why the authors continued to assert that climate change during this period was "pronounced", and played such a large role in the extinction of Pleistocene megafauna.
ReplyDeleteI would like to agree with what Kayleigh said about the changes in the climate zones contributing to the difference between extinction rates of the continents. I would like to add that like the paper stated homo sapians could have been an evasive species hunting to extinction while building their own population in the new continents. That was the opposite compared to Africa and mid Eurasia where it is believed that the homosapians co-evolved with the megafauna leading to non over hunting techniques. The addition of climate change more in continents outside of Africa and Eurasia could have also lead the megafauna to drive out of their niches looking for food causing easy predation for homosapians leading to the extinction of those species and possible rise to homosapiens
ReplyDeleteThe paper shows that while increase in human populations across the continents was definitely a variable, it seemed inconclusive as far as being the primary reason for mega fauna exinction across continents. Theres seems to be a disparity between what constitutes as evidence of hunting between continents, and the fact that Africa lacks as much evidence as other continents, or the fact that Eurasia which has a much different climate had less loss of mega fauna due to "hunting" calls into question whether the primary causes were more abiotic rather than human caused. Sure humans played a large role, but Im not convinced by the article it was only due to humans.
ReplyDeleteWhile evidence to support both climatic changes (ie. fauna)and increased hunting were discussed as reasons for extinction rates. The question you posed as to why extinction rates vary across continents may be due to availability of resources, A possible argument for this may be that mega fauna may have been the most nutritious resource in colder temperature in the Americas when human migration to the Americas first began resulting in higher extinction rates. Although evidence may be biased to showing more extinction rates in the Americas and Australia due to climatic changes, suitable environment for preservation, and also settlement of land not only further burying sites but altogether destroying them when settling new towns or cities. As to what constitutes evidence of mega fauna hunting cut marks were cited within the paper although many classes in anthropology/ archeology do talk about the fact that animals may produce similar marks as human hunting, I'm curious myself as to how this is differentiated so bones may be sorted for usefulness to this study.
ReplyDeleteI find it fascinating that humans were thought to have this much impact on the ecology of earth so early into our history. It only reinforces the fact that humans can and will have a great impact on the organisms around them. I think that further evidence will support the hypothesis of a major human influence on mega fauna.
ReplyDeleteI find it fascinating that humans were thought to have this much impact on the ecology of earth so early into our history. It only reinforces the fact that humans can and will have a great impact on the organisms around them. I think that further evidence will support the hypothesis of a major human influence on mega fauna.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteit makes sense that these species would go extinct due to climate change. as the temperature increased they would have to move more north which would move them away from their food source. the combination of warming on species adapted to cold and predation caused extinction. what the paper does not cover was possible competition for resources with humans. as the humans would be using trees, hunting and clearing land.
ReplyDelete