Chamberlain et al. 2005- Pleistocene to recent dietary shifts in California Condors
Pleistocene to recent dietary shifts in California Condors
Chamberlain et al. 2005 PNAS
Baby and Adult California Condor (Gymnogyps californianus). Beauty is in the eye of the beholder.
During the
Pleistocene, the California condor (Gymnogyps
californianus) used to live across the USA, but when Europeans occupied the
western USA, condors were only observed living on the west coast. Now, condors are an endangered species and
live in California, Arizona, and Baja California. All historical accounts such
as Lewis and Clark, Captain Clark, and Taylor, observed the condor, a
scavenger, feeding on whale and sea lion carcasses. However, in the present,
condors are spotted feeding on livestock cattle. Chamberlain et al. developed a
hypothesis that the California condor shifted their diet from a combination of
terrestrial and marine mammals in the Pleistocene and historical record to only
terrestrial mammals in the present.
Bone
collagen and feather and hair keratin were measured for ∂13C and ∂15N
(stable isotopic analysis) of the condors and their food sources. The bone
collagen was analyzed from 10 Pleistocene condors (36,000 to 11,000 years
before present), 10 historical condors (1904 to 1965 C.E.), and 10 modern
condors (1993 to 2001 C.E.). Bone collagen of Pleistocene bison (Bison antiquus) and Pleistocene horse (Equus occidentalis) was examined using
stable isotopic analysis. Also, a literature review of published data of
Holocene pinnipeds (Northern Fur Seals, CA Sea Lions, and Harbor Seals) and 20th
century whales (Odontocetes and
Mysticetes) bone collagen was used for this study. The keratin from
condor feathers was analyzed from 50 historical condors in museum collections
(1797 to 1965 C.E.) and 12 modern condors (1993 to 2001 C.E.) and the keratin
from hair of 20th century mule deer, feral pigs, range fed cattle,
feedlot cattle and pinnipeds was measured using stable isotopic analysis.
To test the
differences in food sources based on bone collagen and keratin a few isotopic
characterizations are known. Marine food webs have higher ∂13C and ∂15N
values than terrestrial food webs. Most of California’s wild terrestrial
animals eat C3 plants and have lower ∂13C values (∂13C
= -26.7 + 2.7%) compared to domesticated cattle, which are fed corn, a C4
plant, and have higher ∂13C values (∂13C = -12.5 +
1.1%). Also, carnivores have higher ∂15N values than primary
producers. There are some caveats to Chamberlain et al.’s study including that
∂13C and ∂15N isotopic values vary within individual
condor feathers and the feathers are dependent on what the condors are eating
during that time. Also, birds have higher ∂13C and ∂15N
trophic enrichment. Typically, ∂13C and ∂15N values shift
from 1% to 3% between each trophic level, but in birds ∂13C and ∂15N
values could shift up to >3% to 4%. For their analysis, they used trophic
level fractionations of +1 for ∂13C and +4 ∂15N. They
used an IsoError isotopic mixing model to determine C3 and C4
proportions in the condors.
During the
Pleistocene, condors ate both terrestrial (C3 mean = 68.2) and
marine mammals (mean = 31.8). During the historic record, condors ate a greater
proportion of terrestrial animals (C3 mean = 85.2), but also ate
some marine (mean = 13.9) and some livestock cattle (C4 mean = 0.9).
However, during the present, there is an equal proportion diet between wild terrestrial
mammals (C3 mean = 52.3) and livestock cattle (C4 mean =
47.7).
Chamberlain
et al. postulate that humans caused the Pleistocene condors to be restricted to
the marine realm because of the Quaternary mega fauna extinction. Then in the
historic record, humans caused a decline in marine mammals and this caused the
condors to shift their diet to strictly terrestrial. Also, humans introduced
livestock in the late 1700s and condors began to scavenge on livestock. Since
condors are an endangered species, it is important to determine what their food
sources are so they can be self-sufficient and thrive in a changing world
caused by humans.
Questions:
1. How
did the California condor become endangered?
2. What
is keratin? Why measure both bone collagen and hair and feather keratin for
stable isotope analysis (SIA)?
3. Why
is there a decrease in 13C due to the burning of fossil fuels?
4. Why
is there an isotopic trophic shift for condors? Why it is 4% instead of 3%
shift for ∂15N?
5. Do
you believe humans would cause the switch from terrestrial to marine to
terrestrial diet?
6. Do
you think condor population should be reintroduced even though pinniped
populations are just starting to stabilize?
We welcome your own questions! These questions are here to just start the scientific conversation flowing.
Picture from: https://www.wired.com/images_blogs/wiredscience/2012/01/30d-chick-Joseph-Brandt-Wikimedia-Commons.jpg
While I think it's a good idea to work on increasing the populations of endangered species, that will possibly have an adverse effect on pinniped populations that are not healthy. If both populations can be helped then I would support reintroducing condor populations. However, if the only way to do that is at the expense of pinniped populations then I think it should be stalled until either the pinniped population is stable and healthy enough to support the reintroduction of condors or until it can occur without causing harm to another sensitive population. I think the authors make a valid point in their conclusion as they state that humans could have caused condors to switch from a marine to a terrestrial food source. Humans do have a tendency to collapse population numbers causing other animals to switch food sources when they are in competition for food.
ReplyDelete4) There is a trophic shift for condors because of their position as a high-protein consumer. Previous research has shown birds of prey on a high protein diet to have a 4% rather than 3% enrichment in ∂15N.
ReplyDelete5) I suspect humans likely caused the switch from marine to terrestrial diet in part because of the data we read regarding Fur Seal populations in Newsome et al. (2007). At around the same time Condors are switching from a marine to terrestrial diet source along the west coast (the late 1700s), the Northern Fur Seal population had dropped off around AD 1750 from the Californian and Pacific Northwestern coast. We had previously discussed how humans were most likely the driving factor behind their regional collapse. If condors had been relying heavily on marine resources (seals being a component of this) at this time, then humans may likely indirectly caused this shift. Based on the initial terrestrial to marine shift, due to the Pleistocene extinction, there is precedence for the adaptability of Condors to major shifts in their dietary composition with human predation as an indirect factor.
The researchers were wise to measure different biologic molecules (keratin/ bone collagen) as they have different formation/equilibration times so it may be possible to reconstruct a dietary life history of the animal in question.
ReplyDeleteThe hypothesis that humans could alter the diet of the condors seems solid, especially since the ranchers were using cattle primarily for leather. This increased the general waste of meat, which the scavenging condors largely benefitted from.
I do not think that the condors should be reintroduced into the population until there is more stability in order to ensure their survival. If condors are reintroduced too soon then they could become extirpated leaving them right where they started, a community without condors. I definitely did not fully understand why there was a 4% change in 15N rather then a 3% change, but Asia cleared that up for me in a simple way. Thank you.
ReplyDeleteThe article indicates that, typically, feathers are replaced every two years, and that it takes about four months for these feathers to form. Given this, I found myself wondering about the accuracy of using these feathers as an indicator of condor diet in light of a limited sample size of ten condors per each time range. That is, since individual feathers are replaced every two years they only represent the carbon and nitrogen isotope values associated with the diet of a particular condor over those two years. In comparison, I would think that an assessment of bone isotope values would give a more comprehensive view of the feeding preferences of the condors over their lifetime. Given this, should there be cause for concern as to the accuracy and representation of differing dietary preferences in condors as presented by the data associated with the feather isotope values? Relatedly, were the feather isotope values only collected to further confirm the accuracy of the bone isotope values?
ReplyDeleteIn response to question six, I do not think that the condor population should be reintroduced until the pinniped population has stabilized and can properly support the burden that would be placed on the pinniped population by the reintroduction of condors.
The California condor has shown how it is able to adapt throughout the Pleistocene to historic time to modern time which leads to think that it is a strong possibility that the population of California Condors can be increased with help. With that in mind since the condor is an obligate scavenger it shouldn’t affect the nearly stabilized pinniped population too much since that species will be preying on dead animals. I believe that humans could have caused the switch of California condor diet due to its overkilling of marine animals for oils and other uses as well as the introduction of cattle changing the possible food sources that the condors could scavenge from over time. This leads to the problem of why they are endangered today since humans are messing with the available food that the condors can eat changing the amount and the availability with different farming techniques and marine hunting today. Lastly to address the keratin question, keratin is a type of protein that is formed in hair, feathers and other tissue outside the main vertebrae. This shows why it makes sense for them to measure bone collagen and feather keratin for SIA because feathers fall out and are replaced like Andrew stated making it more of a snapshot of what the diet consisted of whereas the collagen was more of a broad proxy for the condor’s diet.
ReplyDeleteI think that Condor's should be reintroduced into the population because as previously mentioned it would not interfere or compete too heavily with the pinniped population since Condor's preferentially feed on the carcass of already dead animals. I am a little confused when discussing trophic shifts and what significance there is between 4% and 3%.
ReplyDeleteI think Asia brings up an interesting point when discussing the probability of humans being the ultimate causation for the shift in diet amongst Condor populations. It seems that humans are typically the root cause for many important shifts we study so it would be interesting to read studies that looked more closely at what impact humans had on Condor populations during the Pleistocene extinction.
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ReplyDeletePersonally, this article was a bit confusing. While it is stated that the geographic range of Condors has become restricted compared to that of the Pleistocene, I didn't get a sense that the Condors themselves had become endangered. It is understandable that the Condor diet would become restricted after the Pleistocene extinction and their diet then shifted to marine mammals and then it was then further restricted by the hunting of pinnipeds, for example, in historical times. However, it seems that dairy calves and cattle provide a stable food source for the Condor...at least that was my belief after reading this article. What is the purpose increasing a widespread availability of marine animals as an additional food source for the Condor? Is it to increase their geographic range or to have them then be less dependent on humans in an indirect way since our farming practices provide a stable food source for them? What implications would reintroducing a marine diet for the Condors have for the marine ecosystem if any?
ReplyDeleteBeing a scavenger the California condor does seem to adapt quite well throughout time. Feeding on mostly dead animal material I wouldn't expect there to be a lack in food sources for this animal. Although based on the data presented in this paper we can see a preference for terrestrial animals. Taking that into account the Pleistocene extinction of megafauna could disrupt that preference leading the condors to find alternate sources such as marine life as shown in the shift during the Pleistocene. In response to the fifth question presented, I believe there could be evidence that humans, increasing their fishing and invasion of marine life, caused a shift in the condors diet but with the data is shows consistency in their diet across time. I assume that modern humans wouldn't use the entire marine animal leaving most of animal on the shore, which would leave food for the condor. Although the introduction of livestock due to humans was apparent based on the data provided by this study.
ReplyDeleteI worry about any analysis of an organism which undoubtedly has a wide range in diet via a strictly two-dimensional scale. In this case, the diet of an organism that probably ate anything and everything is being constrained by a simple 'greater or lesser' isotope value. I see no reason why it should be considered more likely that the condors in plot A on figure 1 have eaten more feedlot cattle or more pinnipeds or indeed, more of some other organism altogether unconsidered in this study - than their ancestors. The small number of ancient inland condors was also troubling to me, although I suppose some things cannot be helped.
ReplyDeleteThe use of feather to perform isotopic analysis may not be the best for this experiment as it is replaced and is not like human hair that can go back years. So Why not use their bones? Were they not available? this study analyzed the isotopic data of not only historic and modern condors but covered its base by analyzing what were/ are potential food to this birds. One thing I wish the experiments would have included evidence for in their paper are condors opportunist or are they generalist? Do they eat carcass as it is available or are make developed to use of what is in their habitat?
ReplyDeleteCondors are scavengers; their reintroduction shouldnt have an averse effect on the local ecosystem; they feed on already dead carcasses. The shift from terrestrial to marine foodsources are an adaptation to human activity. At the same time constant manipulation of natural selection isnt a good idea either. Humans have done enough with that as it is
ReplyDeletei would suspect the introduction of scavengers to any population would be beneficial as it would prevent remains from being left to rot for extended periods of time. leaving rotting flesh out i suspect would decrease the overall health of the population living in proximity to the carrion. perhaps i am wrong but i also see no possibility of these birds having any adverse effect on the existing population living on the shores. however as i commented on the previous article, what is stopping these birds from naturally moving to fill these vacated niches? is human intervention and movement into these extirpated habitats necessary? wouldn't providing a safe habitat be sufficient to coax these birds back into areas where they once lived?
ReplyDeleteI believe that the evidence for human involvement for the change in the condor's diet is strong and I would not doubt that humans wasted a large portion of meat and this benefited the condors. They were simply adapting to their new environment that was constructed by humans.
ReplyDelete1) I think that the California condor became endangered because of human activity. Human hunting limited out the condor's primary food source, big game, so the ones that were not close to marine environments were not able to adapt and survive. The only ones that were able to adapt by eating marine life were the ones closest to bodies of water and this number could have been quite small compared to the original population.
ReplyDelete5) Yes, I do believe that humans caused the sift in the Condor's diet from terrestrial to marine to terrestrial diet. Since humans usually hunt big game we were most likely the cause of their first shift by killing off large quantities of bison and other big animals causing a shortage in the carcasses that the condors could scavenge. Then humans started farming and ranching, introducing cattle into the environment which gave the condors terrestrial carcasses to scavenge on again.
6) I do not see a problem with introducing Condors back into the wild as long as we are sure they have enough food to eat. Since they are so close to extinction one more human caused shift could cause them to become extinct entirely.
1) I think that the California condor became endangered because of human activity. Human hunting limited out the condor's primary food source, big game, so the ones that were not close to marine environments were not able to adapt and survive. The only ones that were able to adapt by eating marine life were the ones closest to bodies of water and this number could have been quite small compared to the original population.
ReplyDelete5) Yes, I do believe that humans caused the sift in the Condor's diet from terrestrial to marine to terrestrial diet. Since humans usually hunt big game we were most likely the cause of their first shift by killing off large quantities of bison and other big animals causing a shortage in the carcasses that the condors could scavenge. Then humans started farming and ranching, introducing cattle into the environment which gave the condors terrestrial carcasses to scavenge on again.
6) I do not see a problem with introducing Condors back into the wild as long as we are sure they have enough food to eat. Since they are so close to extinction one more human caused shift could cause them to become extinct entirely.
1) and 5) The condor may have became endangered largely because of humans as there was a big decrease in their food sources. Marine populations decreased due to humans which may have caused the switch from marine to terrestrial food sources for the condors.
ReplyDelete4) Condors have been known to have high protein diets enriched with 15N. So where else can they get their high protein diet if not marine? Terrestrial. But endangered possibly because they aren't getting enough protein they need for survival.
6) I think that the condor population should be re introduced as they are endangered, but only when other populations stabilize to allow a balance between the predator and prey.
I think it is extremely important to reintroduce not only this condor but all native species that are on the brink of extinction because of humans. I think large breeding programs would need to be the first step because introducing genetic diversity is going to be a difficult task. If you get independent breeders from around the country you could add to the gene pool of the wild population.
ReplyDeleteI do believe the Condor should be reintroduced as it will not be actively hunting the pinniped population as it is a scavenger. In the paper they discussed how hair and feather keratin could vary which would make sense as hair and feathers can grow out/fall out and would reflect a more long term record of what the organism is eating, I assume bone collagen was used as it could show a more direct and recent reading on what the organism is consuming. Not sure though, I may have missed something in the reading, so any input is nice.
ReplyDeleteThe Condor became endangered from over-harvesting for museum collections and from lead poisoning due to lead bullets. Keratin is a protein found in vertebrate animal hard parts such as beaks, horns and claws.There is a decrease in Carbon-13 due to the burning of fossil fuels because introduced large amounts of Carbon-14 into the atmosphere. There is a trophic shift because Marine ecosystems have more trophic levels than terrestrial systems and thus shifting from one to the other shifts isotopic values. I believe humans played a large role in the shifts due to their first hunting large terrestrial megafauna and then large aquatic fauna.I believe that condor populations should be reintroduced to select areas where there is enough carrion, whether terrestrial or aquatic, to support healthy populations.I am curious to see how DDT might have affected Condors as biomagnification would concentrate high amounts of the compound in the large carrion that they prefer to eat.
ReplyDeleteThe California condor became endangered for a couple reasons one being that people hunted them to stuff and but in museum and also habitats change and so did their food source, this is a probably since they have such a long lifespan it's hard to adapt rapidly to quick changing conditions. The use of keratin and dating it is useful because it can tell us about how that animal has grown over it life and if it got good nutrients from its diet. With habitat humans could definitely change the way they feed for instance we feed them cows and dead animals now so they are already starting to make that transition back to terrestrial.
ReplyDelete