Wait...There's ghosts in Yellowstone?
Joshua Miller's paper 2011: Ghosts of Yellowstone: Multi-Decadal Histories of Wildlife Populations Captured by Bones on a Modern Landscape
In the second reading from this week, Joshua Miller takes on
a blast to the past with his study on death assemblages in Yellowstone National
Park. The purpose of his study was to evaluate whether or not the death
assemblages in the temperate setting of Yellowstone are able to embody the
richness and overall structure of the community that is currently in
Yellowstone. What Miller did was take population data on local ungulate species
(elk, bison, pronghorn, bighorn sheep, mountain goats and moose) in Yellowstone
and sought out to dig out death assemblages in the park to see if those groups
would correlate with current population data. What they found was that the
death assemblage data represents historic population changes more than it does
the more recent population changes. This is because the death assemblages and
current living populations have species that are significantly different from
the historical data and have experienced population expansions or contractions
within recent time. What expansions and contractions in population do you think
they are talking about?
Miller discussed weather Stages (WS) on bones. At each stage
there were physical traits that helped identify each weathering stage
postmortem exposure. There are 6 stages WS0-WS5 and they all describe the
amount of weathering that has been imposed on the bones. This way of
determining bone weathering was done by Miller and his colleagues in
Yellowstone National Park and a previous study of large-mammal death
assemblages in Amboseli, Africa. The weathering stages allowed a non-invasive
way for biologists and paleontologists to find out more about a species
especially in areas where there was little record kept or no record at all. The
bones were found in 4 generalized habitats using transects with 1-kilometer
minimum to avoid looking at bones of the same animal in different areas. The
bine assemblages were then compared to the living ungulate community where 95%
bootstrapped confidence intervals were calculated for each species. Do you
think the data they got is reliable? Do you think that analyzing death
assemblages is a good way to predict population trends in the future?
Alycia Snell and Kayleigh Glandon....stay turned for the summary on the Terry paper
In Response to Mill's summary, I believe that the expansion and contractions they were talking about is more migration and drift of populations, since they are largely different from past populations maybe more evolutionary changes occurred in the current populations to separate them further from the past. For the weathering did they preform these techniques in different temperate regions throughout Yellowstone?
ReplyDeleteMiller states that most terrestrial large mammal studies are conducted in tropical African localities and the bones decay at a faster rate than arctic and temperate latitudes (pg 2). I am wondering what are some factors that create better climates to preserve bones? Could there be a latitude bias in the fossil record? Would there be more bones preserved in the arctic and temperate latitudes compared to equatorial latitudes in the fossil record?
ReplyDeleteWhen they talk about population expansion and contraction, I think they are looking at migration and known causes of death such as epidemics and fires. This would allow them to better date remains and thus more accurate trends. As for the accuracy: they state that this is not commonly done in temperate regions. As such, I would suggest multiple runs be performed in similar locations, possibly with better population records, to validate it. What variables in weathering differ between biomes?
ReplyDeleteI also believe that they were referring to migration when they were talking about expansion and contraction. I am curious if these techniques would work in other climates? Can this study be done in similar climates and would these results confirm or support their findings in this study?
ReplyDeleteTerry 2010 paper
ReplyDeleteIn this article, Terry’s primary goal is to determine whether utilizing fossilized remains (in this case specifically small-mammal prey caught by owls) provide a valid and accurate representation of living communities and ecosystems over time. Focusing mainly on the predation of owls on small rodents in the Two Ledges Chamber cave system in Nevada, Terry compares the long term concentrated small-mammal death assemblages (post-mortem rodents eaten and regurgitated into pellets, thus preserved) with data from modern trapping surveys to determine the correlation in the live-dead agreement. Terry’s primary goals are: 1) to evaluate the ecological fidelity of the modern small-mammal community of Two Ledges Chamber. 2) determine the effectiveness and accuracy of the technique over time (from months to centuries). 3) Finally, to assess how spatial averaging affects the landscape-picture as reconstructed from the skeletal/fossilized remains, and determine to what degree have modern communities/ecosystems been altered.
For her study Terry found a cave that consistently had owl pellets which contain local small mammal skeleton remains in them. Using this and the fact that the remains weren’t very obstructed by humans she was able to pull a source of fossils, surficial skeletal assembles and modern skeletons from today to compare to a poll from traps that were set to capture modern small mammals that were statistically consistent in the owls diet. Using the mammal data she then spread out the range to 5 locations to observe where the population comes from as well as abundance (Figure 6). To analyze her data she compared the percentage of living species to the dead assemblage and compared the dead species found in the live community to determine the live-dead agreement of the species. To analyze her statistical data she used Spearman rho and Bray-Curtis similarity index to determine that the agreement between all samples were high. This means that the fidelity of the small mammal community has remained similar throughout time, thus giving paleontologists and neonatologists new tools and a valid model to quantify “live-dead agreements” of terrestrial communities/ecosystems.
The greatest draw back of the study stemmed from the spatial arrangement; while it was found that the small mammals that were pulled from the 5 different locations were consistently similar over time, location did play a role as the pellets were mainly focused around the cliffs and cheatgrass showing the highest live-dead agreement. The cliff showed the highest agreement meaning it was hunted the most, and thus accuracy of the study might decrease in areas not suitable for hunting. How could Terry’s techniques/approach be changed to accurately assess an environment with low predation or one where the pellets are not deposited? Also the environment created by the Two Ledges Caves is very ideal for preservation of fossil/skeletal remains. How would Terry’s proposed model fare in different environments and would it still be valid for understanding the taphonomy of terrestrial systems?
Following up with what Hailey G said - I too wondered if the same techniques used in the Miller paper could work on different and maybe more extreme environments. For example, would the methods of preservation in more extreme environments allow for different weathering stages, or would there be no difference? Would one of these environments allow for other preservation biases than the ones listed in this paper?
ReplyDeleteIn reference to the question concerning population expansions and contractions, I believe that Miller specifically implicated factors such as disease, as well as the re-introduction of certain predators into an area of interest (e.g. wolves). The reduction in rate of disease infection has the potential to increase the population of a species whose abundance was previously negatively affected by a particular disease. Relatedly, the increase in a predator population in a given area would reduce (in theory) the abundance of a prey species (such as elk). Personally, I find that the data collected by the researchers can be considered fairly reliable in the scope of the conclusions drawn by Miller. However, due to the novelty of conducting such a research project in a temperate climate, I do think that more work is necessary in order to ensure the legitimacy of the results in varying climates.
ReplyDeleteIn response to Miller’s study, I particularly found the data highly fascinating and reliable. The reader is given sufficient background information to understand the historical context of ungulates living in Yellowstone and the changes that this ecological environment has experienced due to the re-introduction of wolves, which have acted as predators to the elk population, as well as the re-appearance of mountain goats to this particular ecosystem. I, too, agree with Andrew that these two factors could have contributed to the expansion and contraction events that Miller discusses in his study. Furthermore, I agree with the author that looking at death assemblages for specific species can provide great insight into the overall ecological change for species living within certain ecosystems. Using the data and tools that Miller has used, what are some predictions that can be made about the population of mountain goats within this ecosystem? This study states that the death assemblages of mountain goats are likely experiencing a temporal lag because of their recent reappearance to Yellowstone, but can any inferences about what their temporal changes be made based on the information presented in this article? Are their death assemblages likely to follow preservation bias or contradict them? Lastly, what can be some of the conservation and remediation goals/strategies that can be made for Yellowstone as a consequence of the data gathered through this study?
ReplyDeleteIn relation to the reliability of the data, my main concern is one brought up by Nathan-- if they are using surface site remains, it is difficult to know whether the assemblage is a palimpsest of dates or not. By dating more remains, they may be clearer as to the age range of their assemblage. The environment of the area is going to impact the age of their assemblage based on the amount of erosion or deposition in the different areas where they surveyed-- this will determine the rate at which bones are either buried or exposed. I am not knowledgeable about the environment in the Yellowstone area and thus can not make my own conjectures as to the age of their assemblage age. The age, in part, can be determined by the weathering stages of Behrensmeyer (1978) and based on these categories it seems like the assemblage falls within the recent historic period; however, relying on the weathering index may become an issue when in different environments, to reference the comments by Hailey Griego and Agathe C, such as in more tropical climates where the weathering stages are not as well defined or apparent. In this case, dating more bones would be one way to improve their reliability. Once assemblage context is understood, I agree that analyzing death assemblages is a good way to predict population trends in the future because it allows us to see how animals in that area have reacted to events in the past in order to extrapolate how they may act in the future.
ReplyDeleteThe data obtained by Miller exceed what was previously known about the death assemblages of Yellowstone.This adds to the historic record helping with the understanding of the past.The analyzing of death assemblages is a good way to predict population trends in the future as it connects the past and the present, with such evidence it will beneficial in the future. This is not without concerns, will Miller or others be able to replicate the techniques so that it can used in different climates and locations? Can this be developed into a more conclusive procedure since this is not customary climate the work conducted. Will it be compared to other methods to test its reliability and efficiency? Also, Does Miller have the intention of looking for old better preserved assemblage to solidify his evidence?
ReplyDeleteFollowing up on what was said by Italia, I would also agree that the data Miller collected was reliable as well as insightful because we can see the fluctuations of ungulate species in this particular ecosystem. I found this research to be important because it could shed some light on what type of population dynamics we can expect in the future as well as to see what sort of trends this particular ecosystem has followed since the conditions are constantly changing. This sort of research is very important in allowing us to get a better understanding of history in places without a well preserved record. It seems that this study can be repeated in other areas around the world with a poor historical record in order to understand trends in Earth's history and we can use it as a possible barometer for our current conditions. Assemblage context seem to be in the introductory stages and that much more research must be done in order to make death assemblages an accurate predictor for the future but this is an excellent place to start in order to further this type of research.
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ReplyDeleteIt is interesting that the death assemblage method can be used for such different climates. I would like to see a study of death assemblages done in arctic climates, since on page six Miller said that cooler climates cause extended bone survival. Would this mean that the results for an arctic study would be more accurate because of better bone preservation? If so how would these results compare to the temperate and tropical studies?
ReplyDeleteI believe that the population changes over time could be from two distinct causes: immigration/emigration into an area, and dynamics of predator/prey relationships. The migration to/from the area could explain the apparent expansions/contractions that are seen in the area. Those changes over time could also be explained in part by the relative amounts of predators and prey that exist in the area at that time. http://www.isleroyalewolf.org/data/data/home.html (Example is of the moose and wolf populations on Isle Royale in Lake Superior where there are temporal changes in both populations that are not derived from migration.) It would be interesting to see what are the changes in the predators in the Yellowstone area over the time scales studied to see if their relationship with the local ungulates has changed as well.
ReplyDeleteFor the analysis of death bed assemblages, it would be interesting to see whether or not the progression of WS1 to WS5 was altered by different climates. In addition to test and see if there is a latitude bias re: CHD, it would also be interesting to see if alternate factors such as water accumulation might have an effect on those rates. Precipitation volumes and net water flux through an area could have the potential to alter bone-weathering rates, even between the generalized habitats (rolling grassland, river margin, etc.) mentioned in the paper.
As with other student who've read this paper, I was also wondering what the results would look like in environments/climates other than that of Yellowstone's. I feel that if more research was done, this would be an excellent predictor of global climate change. I'd also like to know how/if this model could fit the different ecosystems that are rapidly changing.
ReplyDeleteI actually posted this last night but not sure why it didn't stay posted:
ReplyDeleteFor the expansion and contraction, I think they mean any type of migration, sudden spike in reproduction of species in the area, predator/prey interactions, climate, abundance of resources, and many other factors that can influence a species in an area.
I'm not sure the weathering they are doing is very helpful because the areas aren't all the same climate wise because of the area they are in as well as the distance from the equator and the parts of the land. I'm wondering how these different areas compare to others within the same latitude.
It is strange to me that Miller's method worked as well as it did. I would have expect there to be a strong "pull of the recent" as older bones are more likely to be swept away or smashed into indiscernible pieces. I do agree with Miller's acknowledgement that larger bodied ungulates are more likely to be over exaggerated in their abundance. It also seems that this method seems to have a somewhat narrow window of efficiency in studying population changes. Too far back and you have very little bones to work with (unless they were deposited in a cave or some other low disturbance area), too close to the present and not enough animals have died to give an adequate representation to the death assemblage. So if you want to document changes within the last month or the last thousand years, this probably isn't the method for you. I also wonder how this method might be effected by the presence of "bone-eating" scavengers like hyenas. I could imagine this approach to work well in caverns or other areas where large amounts of bones are deposited and left relatively undisturbed. On a side note I would love to see future research to determine if the Mountain Goat naturally occurred in Yellowstone before the the first ungulate surveys were conducted and if so why did they disappear.
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