Grad Core Week 1: Paleoecology
Hi Folks. Please post thoughts about the readings for this week.
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Jason Lau
Defaunation & Biological Annihilation
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This article was interesting in that it attempted to bring to paleontology what many ecologists have adopted- a science that is based on testable hypotheses and experimental studies. Acknowledging that controlled experiments may not be possible, some aspects of this process may be achievable. Sample size and representativeness of the sample being among the most important pointed out.
ReplyDeleteI am skeptical that the fossil record contains an accessable large sample size(at least for many species)that is representative of the community at a particular time, but perhaps at large timescales patterns of community composition and dynamics can be studied...Macroecology.
Sorry, the article was "What can we learn about ecology
ReplyDeleteand evolution from the fossil record?"
"Dead delta's former productivity..."
ReplyDeleteThis article addresses techniques that are very relevant to conservation issues. I often find that management and conservation agencies try to "preserve" ecosystems and communities, but often struggle to define a reference point. Using similar paleontological and ecological techniques, many management agencies may be able to identify natural conditions that not only pre-date urbanization, but may also pre-date human colonization of an area. I was really impressed with the integrated approach the authors used in addressing the case.
Just one question... what is the reservoir effect in Figure 1? It's described in the legend, but I still didn't understand.
In response to Alyssa's comment on "What can we learn about ecology
ReplyDeleteand evolution from the fossil record?", there have been studies that specifically address whether the fossil record adequately approximates the biological communities that they originate from. Box one of the article references several of these studies. In particular, the study by Liz Hadley on the fidelity of the fossil record found that some terrestrial fossil assemblages do show a high degree of fidelity to the actual biotic communities from which they originate. I'm also aware of the research done by a woman by the name of Rebecca Terry who also found this to be true with caves and deposits that accumulated as a result of owl pellet deposition. In these cases, the assemblages actually do a BETTER job of censusing small mammal communities than do people physically trapping animals. A little time averaging and the right preservation conditions produce data sets that are as robust as those collected via trapping by "neoecologists".
Fossil data sets for the aquatic ecosystems are usually robust enough for rigorous analyses as well.
If one is ultimately interested in changes over geologically meaningful periods of time, the fossil record has more than adequately large datasets to accomplish this, for many taxa.
I also want to comment on the Wilf et al. paper, though admittedly I haven't read it in a while. Most of my commentary is actually based off of conversations with Dr. Wilf and talks he has given that I have attended.
ReplyDeleteIt's funny that this paper uses plant fossils that historically would have been considered "junk", because some insect came along and "ruined" the leaf. One of the important things that Peter has beat into my head is that through some of these specimens you actually get a snapshot of the activities of multiple trophic levels within a community. I've seen some of these fossils, and many have multiple types of insect damage in one specimen: you can see in some where parasitic wasps have left evidence of laying eggs within other galls created by other insects, in addition to mining, etc. It's kind of amazing that no one had considered these to be valuable specimens until relatively recently.
It's also kind of neat that you can get an idea of the relative insect diversity without any actual insect fossils.
"Insect herbivory, plant defense, and early Cenozoic
ReplyDeleteclimate change"
I agree, what a brilliant idea to use an indirect approach to study organisms for which there are few fossils. This study is fascinating because it seems that a majority of paleontological work involves systematics, and long-term ecology, but less frequently (in my limited experience) do these studies address behavior or interspecific interactions.
Contrary to my previous post, I was impressed with the sample size and number of species included (n= 2435 and 58 species).
I wonder if researchers would be able to classify the herbivory damage as having occurred while the leaf was living, or after the leaf had fallen which may provide more information on the niches filled by the insects. (post abscission may indicate decomposing insects). The galls would be indicative of damage while connected to the plant, but maybe other damage types are indicative of different stages?
The authors note that other variables may have influence plant growth, particularly soil quality. I am curious about the prospects of determining soil quality from the sediments that the plants are fossilized in.
The conclusion about the two life strategies for herbivory defence was very interesting. They concluded that herbivory was reduced by short leaf lifespan with reduced defence or long lived leaves with increased defecnces for insect damage.
In regards to the Jackson and Erwin paper when then they state that one of the problems, when they ask 'what does it mean for communities to be similar or different in taxonomic composition, and where do we draw the line'. Because it is entirely dependent upon which rank you are viewing things from i.e. the specific, generic, ordinal, or even at the level of Phylum.
ReplyDeleteI completely agree with the authors in that regard.
ReplyDelete"Pleistocene to Recent Dietary Shifts In California Condors"
ReplyDeleteI found this article very straightforward and with sound methods (it was especially understandable after Wolf's lectures on isotopes). I am curious to know if there are any physiological, life history, behavioral, etc costs associated with variations in nutrition, besides an inland movement of their range.
Chamberlain et al.: I think one of the most important aspects about paleoecology is that you can see how species functioned in the past, and how communities were structured. It’s cool to see how plastic condors are in their diet. One question I have to ask about this paper is what is the goal of reporting Condor past diet if it does not put it into an ecological context? That is, what ecological function did condors serve? Is that niche even open right now? And, if the purpose is to protect this species, how will making it reliant on the coast help?
ReplyDeleteKowalewski: It is always cool to bring to light history.
Wilf et al. : I really like how this paper took an approach that I don’t think I would have. Rather than looking at how insects respond to plant defenses, the paper puts it into an environmental context and shows how that then affects insects.
Jackson & Erwin: I liked how positive this paper is. I think a lot of people only hear the drawbacks of paleobiology work and don’t see all the cool applications it has.
In response to Mel and the Wilf paper. I also had a chance to see Wilf speak at KU and I am happy that the paper added a bit of a grain of salt to the end. Because it is true that the leaf damage can give you an idea of some of the insect diversity that was there however it is a very faint idea at most. It is difficult to estimate the true diversity since numerous taxa create similar damage (i.e. galling thrips and wasps) as well as typical mandibulate chewing (beetles and grasshoppers). Wilf did compare modern leaf damage to get an idea of the taxa that caused it, and he was quite convinced that they were able to identify the insects quite specifically. I was not so convinced upon seeing his talk and some of his identifications. This is further exacerbated by the fact that we don't have any direct fossil evidence for the insect fauna of the area. I do however greatly appreciate his effort towards any insect related knowledge and it is definitely a starting and could give an idea of some (i emphasize the some part) of the insect diversity especially where the direct fossils are not present.
ReplyDeleteGrey - not only what rank you are looking at, it also depends when in time. A lot of the geological record is divided into seminal events, as mentioned in class. However, these events in themselves are subjective (i.e., sometimes only referring to one taxa). So, if you are going to look at changes in taxonomic composition, when do you start -at the seminal event? Is that starting point going to be relevant for all taxa?
ReplyDeleteGrey. I totally agree. I was skeptical myself, although I am willing to concede that in increase in damage types probably reflects an increase in insect types. In the absence of insect body fossils, this is a good starting point.
ReplyDeleteChamberlian et al:
ReplyDeleteI don't quiet understand the implications of the last paragraph of the article, particularly the following: "Efforts to establish a self-sustaining condor population may be enhanced, however, by the widespread availability of marine mammals as an additional food source." Are they suggesting that we provide marine mammals carcasses to the condors? I'm hoping that I'm reading it incorrectly, because that is the feeling I'm getting, and while the condors are in need of assisted living via food supply, it seems like killing a reestablishing pinniped population to feed the condors is a bad idea.
Jackson and Erwin:
I found this article to be really interesting, especially since I've had no exposure to paleoecology prior to this class (or in the details provided by this paper). I had not thought about the ancient environment, other than in an evolutionary context, and I think this sort of thinking is in fact critical to biology as a whole.
Kowalewski et al.:
This paper was interesting, but it raises a question that I'm having a hard time wrapping my head around. It discusses a skew in age distribution toward younger age classes of shells. However, it is noted that the skew doesn't represent an actual difference. It is just an artifact of the "exponential decay of older shells". I don't get how any answers can be determined if we don't have the evidence there. I understand that modeling is used, but I still can't quiet figure it all out. So how do paleoecologists determine what was there at the time compared to the records we have?
Wilf et al:
The fact that the end-games of defense strategies have been around for over 10 million years, dependent of the host species is really cool!
Hi Everyone, since I was out visiting in your department a few years ago and had a wonderful time, and Felisa is the coolest prof there could ever be, I feel comfortable taking up her invitation to participate in this. Thanks for the interesting comments, always appreciated. A few responses to Grey:
ReplyDelete“ Because it is true that the leaf damage can give you an idea of some of the insect diversity that was there however it is a very faint idea at most. It is difficult to estimate the true diversity since numerous taxa create similar damage (i.e. galling thrips and wasps) as well as typical mandibulate chewing (beetles and grasshoppers).”
Absolutely true, it is an idea of relative diversity, not absolute insect diversity which it has never been suggested to be. But the unpublished Panama canopy crane work you saw me discuss at KU, designed to address this very question, is showing us that on a host-plant basis, there is indeed a very robust, almost 1:1 correlation of #damage types and #insect species making the damage, despite mouthpart convergence and all the other issues. This strongly supports the fossil studies by connecting damage diversity of each host plant to its real insect diversity.
“Wilf did compare modern leaf damage to get an idea of the taxa that caused it, and he was quite convinced that they were able to identify the insects quite specifically. I was not so convinced upon seeing his talk and some of his identifications.”
It’s always reasonable to be skeptical of taxonomic assignments for trace fossils. I did not claim we could identify all the damage makers, but rather a few that leave particularly diagnostic marks that are very convincing, in my view. Those that I have been involved in are: 1. Mines of leaf-mining flies on Paleocene sycamores from Montana. These are extensively documented and formally described in a new article in J. Paleontology (Isaac Winkler et al. 2010). 2. Damselfly oviposition on a variety of Eocene leaves from Argentina, also extensively and formally described in J. Paleontology (Laura Sarzetti et al. 2009). 3. Feeding marks of rolled-leaf hispine beetles on Cretaceous and Eocene ginger leaves, formally described in a 2000 Science cover article (Wilf et al 2000). These have been questioned in a few papers, but the alternative culprits proposed lack the diagnostic characteristics of living rolled-leaf hispine damage that we described in the fossils. I am in the process of redescribing these fossils, a necessary step because the illustrations in the Science article were too little. But I have observed many examples of living rolled-leaf hispines and discussed this with several experts, and so far there is no other group that makes the damage as we described it. Anyhow, I’d appreciate hearing what you find unconvincing about these examples.
“This is further exacerbated by the fact that we don't have any direct fossil evidence for the insect fauna of the area.”
Insects from the Green River Formation lake beds (the youngest of the three units studied in that paper) are quite abundant and many of them have been described, which I should have mentioned in the paper. Nevertheless, the key point is that insect fossils alone do not provide direct trophic information about what and how they were eating (they blow out in the lake and die, they fossilize in isolation and not in the act of eating) and thus could not directly answer the questions raised in the paper, whereas insect damage shows us direct trophic interactions.
Anyhow, thanks again for reading this paper!
In response to Rachel:
ReplyDeleteI think the point the authors were trying to make was that a successful pinniped population may help to naturally maintain a successful condor population. In this broad ecological sense, the conservation of one species greatly benefits another. In this case, it is that pinniped carcasses, as they die naturally, will provide a reliable food source for condors if the pinniped population is in reasonable health.
Dead Deltas former productivity
ReplyDeleteThis paper estimates the deltas productivity during the 1k.y. directly proceeding the artificial shut down of the river in 1930. It was found that current beaches have 2x10^12 shells, and ages ago had about 6x10^9. This was written to provide insight into human impact on coastal ecosystems. The problem with human irrigation and water divergenve comes from the resulting decrease in sediment and nutrients. This paper went well into detail about sampling efforts and provided reasoning behind the methods. I felt that the methods used for conducting this experiment were well thought out to lessen biases. The authors also noted an increase in pollutants as part of the resulting decrease in productivity. I liked this paper beacuse of the novel approach for studying an already well studied area, looking into the past for answers rather than the present or even the future.
Pleistocene to recent dietary shifts in Calif. Condors
ReplyDeleteIsotopic analysis provides the insight for this paper. This paper says that the condors went from marine food to land food, and that if this were restored a bit, so would the population. The isotopic analysis is very thorough, and is written about in detail in this paper. I think that if I were interested in using stable isotope analysis, this paper would be a great methods reference. I enjoyed the explaination of sample preparation to obtain collagen and keratin. This paper also gave a lot of insight into how to use stable isotopes, and then how to properly avoid caveats when interporating them. This study also describes places to hunt for obtaining good results like feather samples and collagen in bones. The results of this study included a change in condor diet twice from marine to more terrestrial, in addition to potential past distribution.