Ecosystem Collapse in Pleistocene
Australia and a Human Role
in Megafaunal Extinction
This article is about how human colonization affected the ecology of Australia during the Pleistocene, between 50,000 to 45,000 years ago. The researchers in this study set out to show that climate was not a deciding factor in the decline of large mammals. Rather, human colonization had a much greater effect on which organisms persisted and which went extinct. The finding was less about how humans directly affected the megafauna but instead changed the availability of food resources for the organisms.
Since no ecological records exist during this time for this area they used carbon isotopes to determine the diet of relevant animals for this time frame. The researchers used the results they obtained from the isotope data on bird eggshells and marsupial teeth to determine that there was a collapse in the ecosystem between 50,000-45,000 years ago. They collected eggshells from Dromaius novaehollandiae and Genyornis newtoni from dunes around Lake Eyre, Port Augusta, and the lakes of Darling-Murray. In order to avoid any possible overlap in the eggshell analyses they ensured the collection sites were separated by at least 100 meters or more. The researchers compared the isotopic data of C3 and C4 plants in the diet of the two avian species to determine if there was an associated shift with human colonization.
The results show that human interference was responsible for the extinction of one animal and the change in diet of the other. Genyornis newtoni were not able to adapt to a diet consisting of mostly C3 plants after humans destroyed their dominant food source of C4 plants. However, the Dromaius novaehollandiae, as a whole, consistently supplemented their diet with both C3 and C4 plants before the arrival of humans and so, when humans destroyed the C4 plants they were able to adapt and survive by switching their diet to mainly C3 plants. Wombat teeth were used to determine if these results showed a similar trend of dietary change after human colonization across less similar species. The results from this analysis was similar to that which they obtained from the extant Dromaius novaehollandiae and the extinct Genyornis newtoni.
Questions
1. Were there any other things that the researchers could have done to avoid biases in this study?
2. What could researchers do to determine if this ecological shift was localized or widespread?
Australia and a Human Role
in Megafaunal Extinction
This article is about how human colonization affected the ecology of Australia during the Pleistocene, between 50,000 to 45,000 years ago. The researchers in this study set out to show that climate was not a deciding factor in the decline of large mammals. Rather, human colonization had a much greater effect on which organisms persisted and which went extinct. The finding was less about how humans directly affected the megafauna but instead changed the availability of food resources for the organisms.
Since no ecological records exist during this time for this area they used carbon isotopes to determine the diet of relevant animals for this time frame. The researchers used the results they obtained from the isotope data on bird eggshells and marsupial teeth to determine that there was a collapse in the ecosystem between 50,000-45,000 years ago. They collected eggshells from Dromaius novaehollandiae and Genyornis newtoni from dunes around Lake Eyre, Port Augusta, and the lakes of Darling-Murray. In order to avoid any possible overlap in the eggshell analyses they ensured the collection sites were separated by at least 100 meters or more. The researchers compared the isotopic data of C3 and C4 plants in the diet of the two avian species to determine if there was an associated shift with human colonization.
The results show that human interference was responsible for the extinction of one animal and the change in diet of the other. Genyornis newtoni were not able to adapt to a diet consisting of mostly C3 plants after humans destroyed their dominant food source of C4 plants. However, the Dromaius novaehollandiae, as a whole, consistently supplemented their diet with both C3 and C4 plants before the arrival of humans and so, when humans destroyed the C4 plants they were able to adapt and survive by switching their diet to mainly C3 plants. Wombat teeth were used to determine if these results showed a similar trend of dietary change after human colonization across less similar species. The results from this analysis was similar to that which they obtained from the extant Dromaius novaehollandiae and the extinct Genyornis newtoni.
Questions
1. Were there any other things that the researchers could have done to avoid biases in this study?
2. What could researchers do to determine if this ecological shift was localized or widespread?
In Miller et al.'s paper, they claim that humans changed the climate from 60Ka to 45Ka by burning the landscape and this caused the change an environment from C4 plants to C3 plants. Is there any direct evidence in the geological record of burning plants like a charcoal bed in Australia?
ReplyDeleteThis could make their case even stronger if humans altered the landscape through slash and burn techniques if scientists could find a charcoal bed and date the charcoal bed using radiocarbon dating.
Researchers could determine if this ecological shift was localized or widespread by surveying more sample sites. This study backs up its evidence twice with the isotopic analysis of the egg shell and also the isotopic data from the wombats teeth. To give their hypotheses substantial backing the authors could have provide data on what causes the transition of C4 to C3 plants if as stated could not be from the climate.I do agree with the aforementioned concerned noted by CHD, the authors were consistent in providing evidences for their claims but none for the change in landscape, only stating so.
ReplyDeleteIt seems as thought the transition from C4 to C3 plants was the biological event that caused the genyornis species to go extinct but it seems like in figure 2B that its diet consumed of C3 plants as well as C4 so it shouldn't seem as a direct reason to go extinct. I just wonder what other causes could lead to the extinction besides that and humans. As for the researchers they could have surveyed more sites like Lizon stated or possibly another source of evidence to get a proxy of the C3 and C4 plant life around the time of the extinction.
ReplyDeleteAs I was reading this paper, I found myself wondering how, exactly, one would go about directly testing the hypothesis that human-induced biomass burning (as an agent for a loss in C3 and C4 plant diversity) led to the extinction of megafauna. Additionally, the title of the paper suggests a "Human Role in Megafaunal Extinction". However, I can't seem to find anything in this paper that directly supports this assertion. Rather, a hypothesis regarding the potential role of humans in the megafaunal extinction was presented. Given the data reported by the researchers, I find the implication of a "human role" to be something of a stretch. This is because they did not provide any direct data to support the assertion that humans were responsible for the ecosystem reorganization, that eventually lead to the extinction of megafauna.
ReplyDeleteAfter reading through the article and the comments I couldn't help but agree with Andrew more. Although it is easiest to see from the geological record that humans do have a huge impact on the extinction of megafauna through hunting, as we saw in previous papers we have read. But the evidence that was presented in this paper didn't really get to the answer to the question which was did humans cause the extinctions by burning through all the megafaunas resources causing an increase in temperature?
ReplyDeleteI agree with Andrew. I read this paper and took from it that humans were the cause of extinction of C4 plants but where was the data to support this?
ReplyDeleteThis paper's weight is largely dependent on whether or not one agrees with their implied assumptions that a human-altered fire regime was the determining factor in changing the ecology of these birds. However, they don't really offer concrete evidence that supports this. I would like the authors to present solid evidence of fires such as charcoal beds that CHD mentioned.
ReplyDeletethere are plenty of examples of humans effecting the ecosystem due to farming or logging and perhaps the author assumes the their assumption is fine but as others have said they should provide a source for their assumptions. in general the author needed to back up their claim with more evidence. i believe the author could make a much stronger case with more reaserch.
ReplyDeleteHuman caused habit loss and or resource loss for animals and resources is prevalent till this day and in these cause we know the cause of loss but in this paper it seems that we need more evidence for what caused the loss of c4 plants plus animals with a more diverse diet will always have more probability of survival in situations such as this.
ReplyDeleteI find it very interesting that time and time again we see evidence for human caused extinction in large animals yet there is no call to action to do anything about it. Seeing this shift from c4 to c3 plants could give us some insight into what animals may do now that forests are declining and grasslands are disappearing.
ReplyDeleteusing the eggshells of australian emu the delta 13 C value were caluated for three different sites, showing variation in diet of Dromaius before and after 45 ka, this suggested that climates was not the control on their dietary variation. Genyornis was observed to target a more specializzed diet from their delta 13 C values between 140 and 50 ka. I honestly felt like they could have bridged the relationship between the ecological shift due to human colonization better by expanding on background information that was given.
ReplyDeleteI thought prior comments were interesting regarding this type of shift from C4 to C3 plants and how they relate to human activity is interesting. In our current political climate I think it is unfortunate that we see so much legislation never go anywhere solely based on party lines, I can't help but to wonder if politicians came from a more scientific background they could possibly deal with climate change better. I would've liked to see more data with real world applications to this sort of research.
ReplyDeleteWhat I really appreciated in this article is that it didn't address how humans have directly impacted species' abundance but rather how we have indirectly impacted them by our usage of resources, which were also the same resources these flightless birds utilized. I think that we need more studies like this because we often times focus on how humans DIRECTLY impact the abundance and extinction rates of animal species but i think it is interesting to investigate how we indirectly impact them. How does our usage of resources such as water, plants, and soil keep affecting species nowadays and how will it keep doing so in the future?
ReplyDeleteWith everyone mentioning C3 and C4 plants, I also agree that this could've been a big change due to humans. Considering the isotopic ratios in C3 and C4 plants, we may see a change in the ratios if we could.
ReplyDeleteAs with the bias and ecological shift, they can use more sample sites to study so that there won't be much bias.
The researchers could have studied smaller animals with similar diets to Genyornis newtoni to confirm if the cause of its extinction was less human hunting and more plant community changes.The researchers could sample fossils and pollen data from more sites across Australia, perhaps even pollen from sediment cores along the shores of the continent and around current lakes and rivers and in areas where lakes and rivers once persisted but no longer persist.Also I'm also wondering if these vegetation changes might have been influenced by climate swings (warmer and drier climate patterns might favor fire hazards which humans could more easily proliferate).
ReplyDeleteThe shift from C4 to C3 plants seems to be the prevalent cause. However, they should test more variables and data points than simply the egg shells and wombat teeth. Alterations in climate and other abiotic and biotic factors would have been interesting to note. Despite this the most probable cause is most likely human influenced
ReplyDelete