Extreme environment habitability
This week one of our readings was written by our professor Dr. Smith. This article researched the effects of temperature on woodrats after Lake Manly drained during the mid-Holocene which resulted in a dramatic increase in temperature, this location is where Death Valley is presently. This article studies the effects that these climate changes had on two species of woodrats (N.lepida and N. cinera). The study showed how wood rats were able to adapt and adjust on a phenotypic scale based on what climate they were dealing with. Paleohistory of events over the last 20,000 years has been made possible by studying tree rings, ice cores and pollen cross dating to name a few methods.
Death Valley is a unique location to research past events because of the separation of rock layers in correspondence to geological times which makes it an ideal place to conduct this sort of study. Along with the layers, this region has a unique elevation differentiation of -84 meters to higher than 3400 meters which allows for studying the organisms that inhabited this area at a multitude of different elevations.
In the rats that were studied, we bear in mind that there is an inverse relationship between body mass of the rats and the temperatures in which they can withstand. In the methods it is mentioned that body mass is a heritable trait and one that is chosen for or against depending on the temperature of the climate since it is variable during this stage in time. In the methods section it is studied how fossilized middens could be used in order to understand what species of rat lived in the region at the time.
Through studying this multitude of effects on rats as a result of climatic change, we get a better understanding of how the body mass really depends on the temperature of the climate being inhabited as well as the species of plants that grow at differing elevations. From this research we are able to have a better understanding of how organisms like woodrats will adapt to environmental changes, such as a warmer environment. This work studies the ability of organisms to experience adaptations in order to deal with the Earth since it is not a static ecosystem. However that being said, it is worth noting that there is a maximum limit to the amount of adaptations a Neotoma can undergo in order to maintain life. By studying the climatic limits on these woodrats, we have a better understanding of how global warming may effect organisms as well as to understand how sensitive a lot of vegetation is to climatic change. From this we will be able to understand how serious this issue and invest more into researching how to combat it as well as how to make sure we can adjust.
Death Valley is a unique location to research past events because of the separation of rock layers in correspondence to geological times which makes it an ideal place to conduct this sort of study. Along with the layers, this region has a unique elevation differentiation of -84 meters to higher than 3400 meters which allows for studying the organisms that inhabited this area at a multitude of different elevations.
In the rats that were studied, we bear in mind that there is an inverse relationship between body mass of the rats and the temperatures in which they can withstand. In the methods it is mentioned that body mass is a heritable trait and one that is chosen for or against depending on the temperature of the climate since it is variable during this stage in time. In the methods section it is studied how fossilized middens could be used in order to understand what species of rat lived in the region at the time.
Through studying this multitude of effects on rats as a result of climatic change, we get a better understanding of how the body mass really depends on the temperature of the climate being inhabited as well as the species of plants that grow at differing elevations. From this research we are able to have a better understanding of how organisms like woodrats will adapt to environmental changes, such as a warmer environment. This work studies the ability of organisms to experience adaptations in order to deal with the Earth since it is not a static ecosystem. However that being said, it is worth noting that there is a maximum limit to the amount of adaptations a Neotoma can undergo in order to maintain life. By studying the climatic limits on these woodrats, we have a better understanding of how global warming may effect organisms as well as to understand how sensitive a lot of vegetation is to climatic change. From this we will be able to understand how serious this issue and invest more into researching how to combat it as well as how to make sure we can adjust.
" Liberty, equality, fraternity, or death - the last, much the easiest to bestow, O Guillotine!"
ReplyDelete-The paper written by Dr. Smith, Dolly L. Crawford, Larisa E. Harding, Hilary M. Lease, Ian W. Murray, Adrienne Raniszewski, and Kristin M. Youberg, "A tale of two species: Extirpation and range expansion during the late Quaternary in an extreme environment" is more or less an analysis of how the changing distributions and body sizes of two species of woodrat, Neotoma lepida (the desert woodrat) and Neotoma cinerea (the busy-tailed woodrat), can be related to past temperatures in Death Valley, although perhaps some of the conclusions have farther-reaching implications.
-The first data collection portion of the study involved an extensive review of museum specimens and Dr. Smith's own unpublished notes coupled with data from the Historical Clamatic Record. They used a 50-100 year average and adjusted the temperatures based on elevation and other relevant variables.
-Using these data, they generated a body mass/temperature index for the two woodrat species (Figure 3).
-The second data collection portion centered around determining the body size and age of rats living in ancient middens. The body size of woodrats has been heavily studied and is well shown to correlate inversely with the ambient temperature (higher temperature = smaller rats, lower temperature = larger rats). Specifically, the size of woodrat pellets (dung) preserved in middens was used to determine the body size of the rats living in the middens (previous studies by Dr. Smith show a connection between woodrat pellet width and body mass).
-They collected 74 woodrat middens, which were then divided into 66 discrete time periods (radiocarbon dating and pellet sizes were used together to determine the quantitative ages of the middens) (Figure 4). The average width of the twenty largest pellets (¿from each time period?) were used to calculate body mass. The smaller pellets were excluded since, presumably, they came from younger animals.
-Using these data, they generated a body mass/time index for the two woodrat species (Figure 5).
(Continued)
ReplyDelete-The body size of modern woodrats in the lab has been shown to correlate with temperature. It seems that this tendency is also attributable to woodrats of the past, going back a considerable time period (~24,000 years ago). The shifts in estimated body size correlate with ancient temperature reconstructions from other studies.
-This is an excellent example of concordance. By itself, a method dependant on determining ancient temperatures from…
1) radiocarbon dates adjusted for estimates of previous atmospheric conditions
2) the estimation of body size from pellet width averages
3) the correlation of actually body size measurements with temperatures estimates derived from historical temperature measurements mathematically manipulated to adjust for elevation, and finally,
4) the association of the body size approximations of long-dead organisms whose physiological relationship with ambient temperature may have evolved through time
… might be too error-ridden to be trustworthy. Multiply the human error that could (potentially) contribute to all of these four steps and you might expect that any results derived from this method would be tenebrous.
This study, HOWEVER, is not meant to stand by itself. Far from it, it is meant to be a highly detailed addition to the current data we have. Unlike some studies which seem to try to prove great and dubious propositions all on their own, this work is clearly a restrained (but important) continuation of a grander endeavor. When we compare the results of the study to other past-climate models, we find that there is a fairly close parallel. The fact that the data came out as nicely as it did is awe-inspiring, considering the potential for miscalculation. This means that Dr. Smith (and her colleagues) must have done a fine job adjusting for error. And since their data appears to 'make sense' it means we can say something about woodrat evolution. It seems that the temperature-based constraints on woodrat body size have stayed fairly constant throughout time. That's the sort of thing that might allow for less extensive studies based on woodrat body size in the future - since a 'standard' has been established by this work.
-In a more abstruse realm, this study also provides some possible answers to questions about the future of mammal adaptation in a rapidly changing world. The extirpation of the larger species of woodrat (Neotoma cinerea) from the east side of death valley may suggest that the rate of temperature change observed in the late Holocene represents the minimum rate at which mammals like woodrats can adapt to changes in ambient temperature.
--Toll
I think that Toll touched on most of what was in the paper. It was interesting how the two species of wood rats did not co-habit the same space. This makes it easy to determine who lived where and at what time. It is also interesting that more of these middens have not been removed and analyzed.
ReplyDeleteWas there other vegetation that these creatures ate? This study focuses on juniper as their primary food source, but there must have been other things they ate, so that when the juniper disappeared they did not starve.
It was very interesting that the body size of the animal could be determined by the fecal pellet size. Also that these pellets were so well preserved. I also thought that it was interesting that in looking at the differing body sizes one could tell the difference in climate. When the body sizes were smaller, they could tolerate higher ambient temperatures. This is a great climate temperature indicator. This body size temperature gauge corresponded to the temperatures computed from the Historical Climatic Record, which were revised to reflect the different elevations.
I agree with Consuela that the concept of looking at differing body sizes in order to tell the difference in climate is a very interesting fact especially considering the difference was only of approximately 1500m. Smith et al. (2009) note that approximately 71% of mammalian species exhibit a "significant relationship between environmental temperature and body mass" (131). To what degree does the temperature different (in this case determined by elevation) result in a change in mass size? Or maybe in other words, what does the elevational/temperature difference need to be in order to begin to see changes in mass size? Smith et al. (2009) mention that the lack of packrat middens between the elevations of 1000-600m may have something to do with a "limited abundance of woodrats at specific elevations" (129).
ReplyDeleteSmith et al. (2013) note that the apparent body mass differences could be merely a result of a "restricted range of samples" (120); however, I find the possibility intriguing. Perhaps additional radiocarbon dates and an expanded sample size to other areas with middens created by both of these species of packrats could help elucidate the cause.
This paper focuses on the diversity of body size in wood rats in relation to temperature shifts in Death Valley, and if the rodents occupied certain regions of the desert. It was stated that as the temperature of the environment increased, the body size of the rats were more likely to be smaller than when the temperature was cooler. This study really epitomizes mammalian adaptation to climate change (specifically temperature change) which is important since we all know the implications that this has.
ReplyDeleteI am curious on how we could use this study to help determine body size (and possibly the successfulness) of mammals like the wood rat in context of future climate conditions.
Personally, I was very interested to learn that the fecal pellets of rodents (specifically Woodrats) can be used to estimate the body size of an individual. As I was reading the section of the paper that discussed this, I was initially concerned as to the potential error associated with the selection of only the largest samples of fecal pellets. However, this concern was remedied given that other methods, including the selection of a greater number of pellets, as well as the single largest pellet, yielded the same estimates of body mass. I agree with Asia in that it would be interesting to determine the requisite temperature change in order to see a change in the body mass of these organisms. Relatedly, about how long (in generations) does it take for a temperature change to influence rodent (Woodrat) body mass?
ReplyDeleteIt seems like everything was perfectly aligned for this study. The authors point out that a majority of mammals exhibit a relationship between body mass and temperature (as Asia pointed out above), so perhaps this kind of study is repeatable. I'm sure there are other ecosystems out there that have (1) two different critter species with no crossover in their body mass and (2) who conveniently save their leftover poop and plant matter for our inspection. But do these ecosystems have the right climate to save the middens thousands of years later? Can we only recreate this study in an arid environment or one with lots of caves?
ReplyDeleteWhen describing how they separated the two different woodrat species by body mass, the authors briefly explained that choosing a threshold of 300g should "underestimate the actual prevalence" of the bushy-tailed woodrat. Would this skew the results of the study in any way? Would it have any effect at all? Am I just not looking hard enough in the paper?
This paper shows an animals change in body size in response to a changing climate really well. Figures 5 & 9 showed the inverse correlation between estimated body size and temperature really well. I thought that the decreases in estimated body mass caused by a warming climate tangentially touched on the application of Bergman's Rule. However, I still wonder how larger, extant taxa might have responded to this change as these rodents did.
ReplyDeletewhat i find most fascinating is that the successful adaptive response was to become smaller. this would decrease the surface area to volume ratio of the rats and therefore cause them to lose heat more rapidly, increase their metabolism requiring them to eat a greater percentage of their body mass per day, all of which would lead to a more active lifestyle. all of which seems counter intuitive given that water and food have become limited resources. it seems to me that adaptations like those of the African elephant to become large and efficient herbivores would offer a greater competitive advantage. the most likely explanation for why becoming smaller would be better would be that they did not have the genetic capacity to become large enough to be of use. rather their maximum size was likely not large enough to be of use, which left them the singular option of becoming small for the greatest competitive advantage.
ReplyDeleteIt is interesting that temperature changes had such an effect of the body size of the woodrats. The temperature changes put selective pressure on them to have a smaller body mass in order to better deal with the heat. I wonder if global warming continues if other types of animals will be able to adapt in this same way in the future? Will many types of animals be smaller in the future because of the rising heat or will they not be able to adapt quickly enough and die off?
ReplyDeleteWhile I do find the relationship between body size and temperature interesting,I also thought how they were able to track the geographic ranges of these animals from the Pleistocene to now quite interesting also. Besides the question of how they will survive with future temperature changes as Jessica asked, I am curious to know predictions for changes to their geographic range and whether or not small changes to their geographic ranges are already being noticed to alleviate stress from the increasingly changing temperatures to keep an optimal body size.
ReplyDeleteI thought this paper was pretty interesting because there was a 71% significant relationship body mass and environmental temperature. As Jessica mentioned, I am also curious if they would be able to survive with future changes in temperatures? Would they simply continue to get smaller or will the consequences of a smaller body lead to their extinction?
ReplyDeleteThis paper presents some perplexing questions as well as answers to important questions. I wonder how many of the smaller pellets that were excluded for fear of being contributed by juveniles were actually pellets made by adult N. Lepida. I am also reluctant to agree with Smith's conclusion that pellet-mass estimates in the 200's were attributed to N. lepida rather than smaller N. cenerea (smaller pellets could be made by sub-adult N. cenerea, since cooler temperatures were shown to cause them to grow larger and thus could result in larger juveniles). I am curious events could have transpired to extirpate N. cenerea from the Amargosa Ridge. If I had to propose a theory, I would say that perhaps temperatures on the peak of Amargosa Ridge briefly reached highs unbearable to the N. cenerea population, but survivable to the Junipers (due to their longer lifespans).
ReplyDeleteHi all,
ReplyDeleteA few responses to your comments, which were fairly spot on.
First, we have now done ancient DNA analysis on these middens, which largely (but not completely) agree with our assignment of paleomiddens to species based on body mass. A few of the questionable middens in the ~300g range did turn out to actually be large N. lepida. But, none of this actually changed the patterns in any quantitative way.
Second, we have conducted studies on modern animals that shows these body size changes in populations can occur in as short as a single generation. This occurs because intense heat during the summer selects against larger animals (and/or warming winter temperatures allow smaller animals to survive), thus leading to detectable shifts in the population over the course of a year. In general, a shift of about 1 degree C results in a shift of about 10g in the mean population body mass, although this varies by woodcut species.
Third, we do think there are implications in terms of what this means for global climate change. In another study that looks at middens across the entire range of N. cinerea, we ask how often animals were able to cope with environmental change over the past 25 ka. In general, animals moved a bit in elevation and shifted body size in accordance with selective pressures. We were able to quantify some locations in the far north where temperature shifts exceeded their adaptive capability, which was quite interesting (this mss in currently in review).
Finally, with the exception of Akodon in south America (which are not well studied) there is no other comparable record for the late Pleistocene. Yet, we expect this sort of adaptive response might be more common then previously appreciated.
Felisa
The relationship between body size and temperature posed in this paper is indeed very interesting along with other findings associated with that. With that said I wonder if such results of an experiment can be applied to such rapid climate change as we are seeing now?
ReplyDeleteI believe that the results of this experiment could be applied to the rapid climate changes that are happening now. I think that as we see an increase in global temperature we can find both, changes in body size and movement to higher elevations. Possibly not together but one or the other. As Felisa mentioned above, studies have shown that populations can change their body size in as little as a single generation, which I thought was quite impressive. With that evidence I'm sure that as the global climate increases we would ultimately see that over generations we would see a rapid increase in body size just as we would climate.
ReplyDeleteAs stated above by my colleagues this paper shows the correlation between temperature to that of body size. It is engaging how the research was utilized find the past ecology of the neotoma and how these practices can be employed in the future to understand the change going on in the environment and geology and how organisms can be indicative of such changes. The question I have about this study is the link mentioned with N cinerea and juniper distribution, it seems like both co-exist as they fall into the same habitat? Is it then that they are part of the same niche, as they play specific roles in their ecosystem and thus the correlation.
ReplyDelete