Week 2 - Introduction to Macroecology and Predation Through Time
Week 2 Readings:
Brown, James H. 1995. Macroecology. University of Chicago Press, Chapters 1 & 2
Huntley, John Warren and Michal Kowalewski. 2007. Strong coupling of predation intensity and diversity in the Phanerozoic fossil record. Proceedings of the National Academy of Sciences 104:15006-15010.
In the first chapter of Macroecology, Brown gives an example of a macroecological study. In this study, he and his grad student estimated how many species of small mammals would go extinct on mountain tops in the Great Basin due to global warming, using the predicted decrease in area due to the treeline’s increase in elevation, the species-area curve, and the nested subset structure found in the mountaintop communities. (Discussion thoughts: How does this compare to a “microecological” approach to the same problem? How would you have gone about answering the same question?)
In the second chapter, Brown defines macroecology as “a way of studying relationships between organisms and their environment that involves characterizing and explaining statistical patterns of abundance, distribution, and diversity.” He discusses complex systems and points out that it is impossible to reconstruct a complex system from reductionist knowledge about the components and interactions within that system – for example, no one has successfully created a living organism from the molecules required for life. Microecology examines the components of ecosystems, while macroecology allows us to study the whole system. Brown then outlines the characteristics and goals of macroecology, and discusses examples of past and current macroecological research. (Discussion thoughts: What are your thoughts on the different methods and goals of macroecology vs. reductionist ecology? What are some examples of macroecological studies you’ve read or heard about? Do you have any ideas for research that would be considered macroecological?)
The journal article for this week is a study by Huntley and Kowalewski, in which the authors made a database of fossil predation traces in various taxa throughout the Phanerozoic (please reference the Wikipedia article on the geological time scale if you need a refresher on this.) They compare instances of predation to diversity, to get at the age-old question: do ecological interactions contribute to diversity? Many of you have probably heard of the Red Queen Hypothesis, which suggests that competition and predation between species leads to increasing adaptation of those species, just so they can continue to compete with each other. This and later hypotheses on the subject predict that increased predation should lead to increased diversity, which is, indeed, what the authors of this study find. However, they suggest alternate hypotheses to explain this pattern: 1) a long-term coupling of diversity and predation results in an ecological signal of increasing predation with diversity, 2) greater species diversity leads to a greater variety of predation strategies, or 3) both our species diversity curve and abundance of predator traces are correlated with sampling efficiency. Check out the supplementary information for this article to see more information about methods. Some discussion thoughts: Which hypothesis do you support? What are some other ways the hypotheses could be tested? Do you think the species/genera and predation traces studied are sufficient to answer the question? Do you have any questions about how the study was carried out?
Leave your thoughts on the reading in the comments. I’ll try to get the authors to take a look and respond. Looking forward to seeing you tomorrow!
First.
ReplyDeleteOkay, I'll be honest, I haven't read the book yet because I've been a frantic mess all week. I'll have more to say on it by the time class rolls around because it will be read by then.
ReplyDeleteI have lots to say on this paper. First, I'm going to say that I'm kind of a pessimist when it comes to preservational biases, and that was the first thing that popped into my brain when I started reading this paper.
I really liked that this paper included multiple hypotheses that could be equally valid for the patterns they observed. IF the pattern is real, then I like hypothesis #2 because of its explanatory power. The pattern that was observed could support this idea that whole ingestion is primitive; it also provides an explanation for the coincidence of the Mesozoic Marine Revolution and post-Jurassic diversification.
I will also note that not all periods are equally represented by lithological types, and not all lithological types are equally "good" at preserving things. I would like to see some kind of analysis that shows this pattern isn't somehow linked to rock availability.
ReplyDeleteIn the supplemental materials they note that their analysis was restricted to drilling and repair scars. I understand that this was done because these traces are unambiguous, but I feel like they missed an opportunity to identify any patterns in increased or decreased modes of feeding/predation.
Is the answer to their initial question, "Do ecological interactions matter over evolutionary timescales"... maybe? What constitutes an "evolutionary" time scale. I've been doing some recent reading that implies that evolutionary time scales may be on par with ecological time scales. Do they mean "geologic" time scales? Is this a matter of semantics?
Well, for starters I really enjoyed the preface and first chapter. Brown gives a really wonderful overview of the book and a nice beginning to bring us into ecology on the macro level, but I really enjoyed how he doesn't separate macroecology from the other fields of study in biology and in general. In a way I think it is the mother of all studies.
ReplyDeleteThe second chapter was more in depth into this study; again it was thoroughly interesting and enjoyable. The way that we can put this study together from such a broad array of studies helps calm me down about how much there is out there. I agreed in every way when Brown discussed how putting the pieces together to create the big picture is necessary, and I also loved the gas analogy when thinking about patterns. It is easy as whatever-ists to become tunnel-visioned and not think of the whole globe, or at least more than one species. I can tell this book is only going to get better, and it makes me enjoy it even more because we really need to know more about all the components of each system, but large scale, in order to save these ecosystems and even world.
I haven't read the paper yet, as soon as I do I will surely leave a comment for you guys!
The paper was interesting in it's overall contribution to knowledge we have on the earth's long history of life. However, I am slightly biased in some sense and also agree with some of what Mel said. I am biased mainly because I'm not sure the marks on the fossils they were using are completely valid? But, I suppose this is one of the woes of paleoecology, using the past remains aren't necessarily 100% accurate, or at least it is hard to know exactly what happened? Realistically, nothing is completely accurate due to the fact that there is always room for error and we can just make educated guesses and test hypothesis. I am also biased because it makes sense that as diversity increases, predation, along with many other aspects of species would increase, right? I may be completely off about this paper, I did find it intriguing and a good Thursday evening read!
ReplyDeleteWhat I found really fascinating about this paper is how it suggests that frequency of predation increased by the Ordovician and not later. Further, in Fig. 1 it shows that - despite a mass extinction - rates of predation continue to increase.
ReplyDeleteI would like to see if with increased diversity if a) predator diversity increased and b) if predator attack method also diversified.
To me it seems macroecology is about trends and tendencies that govern life. I have always had problems with reductionism, mainly because I find it too narrow and confined. This paper provided a great way to see how a macroecological approach can be used to support a ecological theory.
Right, so I have done the assigned book reading and can now comment. It seems to me that some of the most interesting paleoecological studies are, by necessity, macroecological. The funny thing is, very few paleontologists that I know use the term. Part of the problem may be the disconnect between biology/ecology and paleo which is compounded by biology/ecology's tendency to be microecologically focused.
ReplyDeleteIn my own research I have thought of the idea of using the fossil record of extant organisms to identify which species are more likely to go extinct with future climate change. The fact that this idea has existed for the past 20 or so years in macroecology, and that I haven't read about it until just now, demonstrates this disconnect.
Perhaps what is more sad is that macroecological approaches could be used to develop really effective conservation strategies; they just have yet to be implemented.
I'm sorry for posting so late, but here you go. I still don't have the text, so I wasn't able to read the chapter for the week, but you all make it sound interesting.
ReplyDeleteBoth Mel and Natalya noted that they were a little uncomfortable with the method of measuring predation only by scars and drilling, and I had the same thought as I read the paper. It would seem to me that the ability of a predator to drill would be a pretty specialized adaptation, and I would think the earliest predators would use more primitive techniques like smashing or prying apart prey with hard shells.
Furthermore, as a hard shell would be an adaptation against predation, I would expect early hard-shelled organisms to be preyed on less than their soft-bodies counterparts that I presume would not fossilize well. This would lead to data skewed to show that there was less predation in early history of hard-bodied organisms.
I am not well-versed on animal history, so you all will have to tell me if these are viable concerns to this study.
I'm not sure I like hypothesis #1: I would think predation would be proportional to prey availablity. Hypothesis makes sense to me if (like Mel said) the trend in this paper is true.
I have to agree that this paper did a very good job in evaluating potential explanations with multiple hypotheses. As well am I inclined to agree with hypothesis (ii), if these data are correct. I am not fully aware of sampling procedure, spatial relevance and the overall diversity of sampling technique evaluated in the paper. (I could have dug in more, but you can see I have stretched my time fairly thin as it is). That is to say I would like to know the confidence level in these data from a historic sampling stand point and where they came from. I do feel the results of this paper would be greatly supplemented with the author’s suggestion of a meta analysis of benthic marine environments. I am always a fan of comparative studies, even if they’re separated by an epoch or two.
ReplyDeleteHi all
ReplyDeleteI would just point out that you need to remember a bit of evolutionary history to put this all into context. For a predator to smash or pry apart a prey item may require unique body parts (e.g., maybe jaws, claws etc ...) that weren't around early in the Paleozoic. Sounds like we need to post the evolutionary cheat sheet to when various forms of life evolved.
Felisa
Apologies for the lateness of the post, but I was having too much fun reading what everyone else thought. I too questioned the validity of the fossilized predation marks; it would have been useful to include some sort of image so we could really see what the authors were speaking about. There are many things that create drill holes in bivalves, gastropods and other shelled aquatic species, not all of them are predators.
ReplyDeleteI also found it interesting that there was no mention of competition in the paper. Whenever there is increased diversity we should expect to see increased competition, which could lead to any number of problems with collecting data on fossil specimens. Starvation due to competition can inhibit the proper formation of shells, sudden extinction of former prey items changes the behavior of predators, etc.
Overall, I felt the article was interesting enough, although I would have preferred some more in-depth explaination of the predation marks.
I was glad that the paper offered different potential hypotheses for future research to explore. As with others in the class I had doubts about measuring predation by using drill holes and repair scars. I'm still not very certain that I would agree with one hypothesis more than the other. I also agree that it might not be completely accurate to call all drill holes and scars as predations marks. It seems that its possible to have a lot of uncertainty in certain case so this might skew the data. The authors also did not really specify what they were considereing.
ReplyDeleteHi Felisa,
ReplyDeleteGlad to hear your class enjoyed our arm waver. Actually, I am really not committed to any of those ideas. I think intellectually I like number 2 best (more complex behavior are likely to show up when diversity is higher), the other two are much more vague (1. Some linkage between predation and diversity and 3. Some bias that makes them appear correlated). But I do not think there are solid data of a type needed to distinguish between those ideas with confidence. I know that you probably wanted something more specific, but I am, and have always been, an intellectual coward.
Hope all is well in New Mexico,
Michal
I guess it goes without saying that he was kidding about the last part ...
ReplyDelete