The shifting baseline of northern fur seal ecology in the northeast Pacific Ocean
This weeks reading included a paper by our own professor Dr. Newsome. This paper raises some great questions on historical data of ecological shifts in Northern Fur Seals. It uses some great methods to try and answer these questions to be used to guide conservation efforts for species decimated by pre-20th century hunting. NFS populations are declining because of unknown causes therefor it is important to interpret historical data in order to understand NFS populations in the past. Evidence has shown that biological communities were much different before Europeans arrived in America. In the paper it is discussed that post-columbian explorers encountered two NFS populations along the northeast pacific. A small mating population on the Farallon Islands off San Francisco and a much larger one on the Pribilof Islands in the Eastern Bering Sea. Using archaeometric, isotopic, genetic, and chronologic data to reveal prehistoric shifts in the ecology of NFS this paper generated a lot of useful information. The historical record shows us two stories about the NFS population in the pacific. In temperate-latitude breeding populations we see archeological evidence of NFS in the historical record until about 200 B.P. In central and northern California NFS populations in the historical record disappeared about 800 B.P. What does this tell us about our knowledge of the relative roles of human hunting versus climatic factors explaining this ecological shift? There were two possible explanations given by the paper for the common occurrence of NFS in archaeological sites. One was the remains of seals are from higher-latitude breeding populations that became stranded and were scavenged by Native Americans. What does this impose about the breeding habits of NFS if this were true? The other explanation was that the NFS came from near by breeding colonies located in temperate-latitudes. This would be a stark contrast from the breeding habits we see today in NFS. Using remains of NFS from archeological sites this paper was able to evaluate possible explanations like prehistoric NFS breeding populations being congregated near shore or possibly a change in the length of weening needed for offspring. Several pieces of evidence suggest that there were indeed populations of NFS in temperate-latitude areas in the Pacific. Natural variations in stable carbon isotope values provide information on foraging location because food web carbon 13 values are higher in nearshore versus open-ocean ecosystems. This stable isotope data can provide insights into foraging ecology and maternal strategies of historic NFS populations. It was found that carbon 13 levels in historic female NFS were lower then in Harbor Seals which are known to be nonmigratory and forage near shore. This indicates that that historic NFS populations were foraging in deep offshore areas and were not available for humans to hunt because of foraging close to shore like the HS. Based on that information why did isotopic distinctions among seals from different regions confirm that prehistoric NFS from California were not immigrants from higher latitudes but year-round residents of more temporal latitudes? Another trend seen by the archeological evidence of NFS in more temperate-latitudes was the abundance of pups equalling about 4 months of age. Using the isotope Nitrogen 15 we can estimate the feeding duration for pups and age of weening. Its takes about 8 months for Nitrogen 15 associated with nursing to be diluted by bone collagen turnover. The paper shows that remains of 9 to 12 and even 12 to 15 month old pups had high nitrogen 15 values that persisted much longer than in modern NFS populations. What was the best explanation the paper gave to why we were seeing this in the historical data? To make sure that these divergencies in NFS maternal strategies were not the result of interspecific differences ancient mitochondrial DNA sequences were compared to published sequences from Northeast Pacific Otariids including modern NFS. The results suggest like most otariids without the extreme selection forces of high-latitude winter conditions NFS populations weened their offspring much later in development. What reasons does the paper suggest why otariids developed this long term strategy?
The big picture to take from this paper is that Northern Fur Seals can provide one of the clearest examples of historic ecological change leading up to modern times. This paper has shown through a variety of methods that NFS indeed had populations of breeding seals in more temperate-latitudes then we see today. There is also evidence that NFS historically had very different breeding habits and behaviors then the modern seals we see today. All this information can be used in conservation efforts today because knowing the habits and limits of NFS historically can have a major impact on where and how we can restore NFS populations to what they once were pre-20th century. Knowing the plasticity of NFS to environmental change can tell us that they can adapt to environments previously thought to be uninhabitable by the species. Were there any flaws or areas of improvement that you thought of when reading this paper or answering some of the questions?
The big picture to take from this paper is that Northern Fur Seals can provide one of the clearest examples of historic ecological change leading up to modern times. This paper has shown through a variety of methods that NFS indeed had populations of breeding seals in more temperate-latitudes then we see today. There is also evidence that NFS historically had very different breeding habits and behaviors then the modern seals we see today. All this information can be used in conservation efforts today because knowing the habits and limits of NFS historically can have a major impact on where and how we can restore NFS populations to what they once were pre-20th century. Knowing the plasticity of NFS to environmental change can tell us that they can adapt to environments previously thought to be uninhabitable by the species. Were there any flaws or areas of improvement that you thought of when reading this paper or answering some of the questions?
For the question about why the otariids developed a long-term lactation strategy. The paper says they did this to protect the population from resource fluctuations. This makes sense because if the mother weened her pups off suddenly and there was a negative resource fluctuation, the pups would not be able to find enough food and they would die. If the mother weens her pups off gradually and a lack of food occurs, the pups could go back to nursing until there is enough food for them to be weened off completely.
ReplyDeleteDr. Newsome et al. write that prehistoric adult female NFS have lower ∂13C values than harbor seals because hunt in many deep ocean waters. I understand the correlation that low ∂13C values equal deep ocean waters and that high ∂13C values equal shallow marine environments, but why is there this correlation? Also, why are ∂13C and ∂15C values higher in temperate latitudes than high latitude ecosystems?
ReplyDeleteAlso, for ancient DNA methods what are you looking for when you extract DNA from the teeth? Are looking for skin, enamel, or something else? How would you know that a tooth would have DNA?
The lactation strategy they have is a means to prevent young deaths under bad conditions. I didn't notice any issues with the paper that I thought could be improved; I do however believe that this type of analysis should be used on other marine mammal species. If this is done, then we can better understand the "plasticity" marine mammals have to environmental changes.
ReplyDeleteIf possible, I would suggest mapping the distribution of prey species over time. Doing so would clarify whether the otariids were directly or indirectly influenced to change their ranges.
I am vexed. Despite being signed up for the blog, I am still unable to post any independently. I'll just post my analysis on this when its all finished. Bother.
ReplyDeleteIn terms of the question "what does the asynchronous decline in NFS breeding range tell us about our knowledge of the relative roles of human hunting versus climatic factors in explaining this ecological shift," I find the findings of the asynchronous collapse very interesting for that very reason. The results make clear that while humans were most likely involved in the ~200 yr BP population collapse around southern CA, the pacific NW and the eastern Aleutian Islands, environmental factors may have been involved in the ~8,400-800 yr BP decline in central and northern California. Newsome et al. (2007) cite the potential of the Medieval Climatic Anomaly to have impacted these NFS populations.
ReplyDeleteI think there are a couple of important ideas here: (1) often in archaeological literature, human populations are cited as the main factor in the decline of a species within a specific region (such as in the Pleistocene overkill hypothesis or the decline of animal populations by the Maya during the Terminal Classic period); however, as evidenced here, while human impact may be the cause of a change in an animal's population, there may also be other factors contributing to a decline of a species, such as environmental changes. (2) It is important to recognize that there are multiple potential causes for any one outcome that is seen in the historical record. Newsome et al. (2007) explored potential hypotheses within the article, arguing for the most rationale one based on the current evidence, not just for the difference in population decline of NFS, but also for the explanation of high d15N values in young-of-the-year. While Newsome et al. (2007) note that there is currently not enough data to pinpoint the exact cause of the decline in NFS populations in central and northern CA, they present potential hypotheses that can be explored and allow for future research to be done in that area rather than making an assumption about a cause for that population's decline.
Thus, to answer the question, it is important to have an understanding of both potential human and ecological factors when trying to understand an ecological change within an animal population; neither hypothesis of human impact nor environmental impact should be assumed without evidence.
Studying the lactation strategies of these seals was quite interesting, in that to keep the number of young seals from dying unexpectedly due to changes in the food sources was to wean the pups off gradually instead of all at once. This prevented the pups from starving due to lack of resources the mother would have thus reducing the amount of milk the mother is able to produce. From the data presented in the paper it showed that weaning pups at an early age would be most favorable today. This would possibly be because of the environmental changes that have impacted populations negatively due to the longer weaning periods and mothers would be lost to storms and other possible dangers the changes bring which would negatively effect the young because they wouldn't be ready to hunt or digest solid foods.
ReplyDeleteWhy can't I post here? I've tried a number of times!
ReplyDeleteOk that seemed to work.
ReplyDeleteThe earlier time that the population declined could have been due to a decline in available food for the weaned and weaning pups, the YOY. The change in temperatures could have resulted in less food available. It was mentioned that the stranded and scavenged seals that were taken by the Native Americans were in a starved state. The later population decline could have been due to the over hunting by man, but also could have been due to other factors, such as a lower amount of available food because of changing climate factors.
The decline of the NFS 800 years ago, before the introduction to human hunting by Europeans, was probably due to problematic climate conditions, unlike the collapse of NFS that happened 200 years ago. Climatic conditions like drought in western North America seemed to play a big role in the declines of NSF populations, especially in this time period where human hunting wasn’t a likely reason for the collapse. In order to survive unfavorable conditions, NSF adapted their reproductive and lactation strategies in order to survive.
ReplyDeleteWhat I would like to know is how compatible this study is to other marine populations. Since it’s apparent that the climate is changing currently, will the NFS able to continue to conform to rapid environmental changes through behavioral modifications?
It would be interesting to see what kind of information can be found in the next few years about the potential environmental impacts that may have decimated the northern fur seals of Central and Northern California. It does seem to be the most probable hypothesis as to why these populations died out so much earlier than the other populations, though as noted in the paper, more data on the El Niño-Southern Oscillation is needed to corroborate this idea since the paleoceanographic records don't show record of any major upheaval. Hopefully, the information garnered from both the effects of climate and human predation can be used to conserve the modern populations of northern fur seals so they may continue to contribute to their ecosystem.
ReplyDeleteI thought it was interesting that one could find the organic isotopes of the Northern fur seals to compare the diet to today. Knowing or should I say having an educated guess that the YOY were weaned off at an older age leads to have given assumptions that the food was scared in that era making the best outcome for survival to delay YOY weaning. This relates to the factors of indigenous hunting and El Nino effects that could have disrupted the environment making living harsh on the Northern fur seals. Determining that as well as the other ecological findings shows how ecological shifts tend to take place and very well could be a template for other marine animal research for this purpose.
ReplyDeleteWith respect to the question concerning isotopic distinctions among seals of differing regions, in the scope of confirming prehistoric NFS from California as exclusive residents of temporal latitudes, as opposed to the being immigrants from regions of higher latitudes:
ReplyDeleteThe paper indicates there are isotopic differences in phytoplankton which vary with respect to temperate and high-latitude ecosystems. Relatedly, there are differences in the isotope values found in NFS that vary as a function of location, (northern group, southern group, and western group). Using this information, the prehistoric NFS from California were determined to not be immigrants from higher latitudes because they did not show evidence of isotope values consistent with those expected in NFS of higher latitudes. Thus, they must have been year-round residents of more temperate latitudes.
According to the paper, the best explanation as to the differences in nitrogen 15 values of historic populations of NFS as compared to modern NFS populations, can be attributed to differences in the age at which NFS pups were weaned from their mothers. These differences in weaning age are likely in response to different environmental pressures that are imposed on NFS as a result of differences in climate, given the varying latitudes that NFS occupied.
It was interesting to read about the prolonged and gradational weening strategy that the Otariids have employed. The paper suggested that this behavior was likely to encourage a smoother transition for the young into increasingly unfavorable environments. The increased pressure from colonial hunting on these populations gave a great perspective into early anthropogenic-caused disturbances. It would be interesting to see if other populations of various pinnipeds (such as those in the southern hemisphere ) have responded similarly to excessive hunting practices.
ReplyDeleteweening young at an older age suggests that environmental stress was increasing as time progressed. seeing as how the shift only occurred after colonization likely indicates that infant mortality was increasing due to human interactions. the paper doesn't give a clear reason why colonization would negatively effect NFS but does allude to the possibility of excessive hunting. another possible cause may be the introduction of harmful diseases which NSF where not previously exposed to. this would make sense as young NFS would be least equipped to deal with virus' leading to higher infant mortality. this would trigger a behavioral adaptation to feed their young milk at an older age to ensure good health and improve infant mortality. this is all speculation but may be the topic of future research.
ReplyDeleteThe fact that we can compare diets of today to the past is helpful in so many ways. Diets can tell so much about a species, where they lived, what food sources were around. Which leads me to discussing the way lactation has changed to allow the pups to survive when there isn't as many resources for the mother to feed her pups.
ReplyDeleteThe paper specifies that there was strong selection for early weaning due to severe winter conditions, i'm just curious how this is beneficial to the pup? With human populations in natural environments weaning for humans doesn't occur till 5 to 7 years of age due to poor nutrition allowing for human children to have extra supplement to their diets which encourages growth and development, Is early weaning detrimental to the survival rates of pups?
ReplyDeleteVery interesting paper. It makes me wonder if the seals in the southern range where in fact a subspecies of the northern seals based on their prolonged nursing strategy, which is likely to deal with occasional El Ninos. It does puzzle me how the Northern and Central California populations went extinct some 800 years B.P. Could the Native Americans have put enough pressure on the populations to decrease Genetic Variability and thus make them more vulnerable to El Nionos? Or was some other biotic or abiotic factor at work? With this in mind, would it really be feasible to attempt to repopulate the southern range with breeding stock originating from the north where nursing strategies are meant to key in on a short window of opportunity when productivity is high rather than to endure tough times?
ReplyDeleteI found it very interesting in this paper how such weather events such as El Nino could have such a drastic effect on the ecological community of these seals, also how they adapted over time to even deal with these weather patterns was very interesting as well but besides nursing what else could did they adapt to survive?
ReplyDeleteThis paper shows a strong correlation between seal pup and the age they are weaned, with the possible explanation being that they were weaned longer in regard to the environmental challenges being faced. This led me to the question of nature vs. nurture. The paper revealed that the seals range locality or a bottleneck. Does it have to be either or, why not both?
ReplyDelete