Grad Core Week 3: Macroecology & more macroecology
Hi Folks. Thoughts/comments/responses to the papers for this week? The application to human macroecology is fairly recent, and still, fairly controversial.
p.s. Jim responded to your comments - see towards end of posts in this section
Brown and Maurer, 1989
ReplyDelete"large animals can cover a larger area, ingest more food relative to their requirements... extract a greater fraction of the energy and nutrients than small animals"
Some "small" mammals have size plasticity within species. Does this passage apply to larger individuals within species, or does it have to be an order of magnitude difference in size?
Can anybody find the Brown et al. Bioscience, in press. article?
ReplyDeleteBrown and Maurer, 1989
This article is pretty straight forward, I am surprised by the fact that this is a relatively new way of approaching ecology. One thing that I found interesting was the decrease in maximum population density with smaller body mass. Also, I think that the distribution of space and resources should be studied 3-dimensionallly. A 3-D analysis would likely show some interesting variation in productuvuty, distribution, and niche partitioning that would otherwise not be shown in traditional "flat" data. This is especially true for forest and aquatic habitats.
Smith et al. 2008.
This was a great overview of the macroecology approach. I enjoyed the many examples of work that has been done, and predictions for future applications. I think it is important to remember that macroecology is an "approach" and not a field.
DeLong et al. 2010
What an interesting paper! I liked their unique approach to predicting a steady state of human population. I wonder what the predictions would be for beyond 2050? I am still confused as to how extra energy leads to decreased fecundity. Also, I don't understand the negative correlation between growth rate and energy use. Perhaps someone can explain these assumptions and than the paper will make more sense. Lastly, the assumption for Figure 3 rests on shifting enery use from developed to developing countries... Do you think this is likely to happen?
Moses and Brown, 2003.
Using the term fertility makes it seem like energy use affects the ABILITY to get pregnant, not number of births.
While biological constraints may affect human fecundity, I wonder what other non-biological factors scale negatively with fecundity with a trade-off for investment aswell. Education? Income?
Brown & Maurer 1989-- I find it interesting that there is a body size 'tipping point' (~100g) in those two taxa where abundance no longer increases w/a decreasing body size. Could a similar 'tipping point' be present in other taxa? (although it may not be 100g) Has anyone tried to find it?
ReplyDeleteSmith et al. 2008-- Another one of those 'wow, wish I would have seen this earlier'/'all the subjects should have a nice background intro like this' paper. I'm sensing a pattern. :-) It is encouraging to see that people have attempted to do some large-scale management & conservation analysis-- this is an interest of mine, and I may be trying to do a related project.
Ernest et al. 2003-- How nice it is to finally be able to read and understand what's going on! I liked that the data analysis covered MULTIPLE taxa, and not just mammals and/or birds like the majority of the papers we have read so far seem to be. I always seem to be left with 'but what about the OTHER taxa?', but not after this one.
Damouth 1981-- I think the small size of the article unfortunately led to not as much analysis as I would have liked about the various habitat types & patterns they exhibited, but Fig. 1 was a clear example of the pattern he was trying to support.
Brown, OIKOS 1999
ReplyDeleteSince this article was posted in Jim's file for this week, I assume we're supposed to read and discuss it as well.
"The promise of macroecology is that very general statistical patterns provide clues to the operation of equally general mechanistic processes which govern the structure and dynamics of complex ecological systems." A really important statement. I don't know how many times I've had lay-people question something scientific because a subject seems "too complex" and, therefore, impossible to understand. It's good to point out that there are basic principles that apply, even to complex systems, and people forget that.
DeLong et al.: I followed the same line of thought as Alyssa -is there a minimum to fecundity? That is, is there a point at which malnutrition prevents reproduction? I do wonder why it should be that with more resources, there is less reproduction.
ReplyDeleteI wonder if the negative correlation between growth rate and energy use could be a combination of the negative correlation of fecundity and per capita power consumption as well as the tendency for more developed nations to have more efficient energy use.
Brown OIKOS 1999, cont.
ReplyDelete"...many of the statistical patterns of body size, abundance, distribution, and diversity over space and time can be attributed ultimately to the effects of limited energetic and other resources."
Okay, yes. But my inclination is that these things also have some kind of geologic memory. Events of the past (such as extinctions or natural disasters) shape communities rapidly, and gradually they come back into equilibrium some time afterward. That equilibrium point isn't always the same as it was pre-disturbance. Do the statistics which people compute (slopes, intercepts, limitations, etc.) remain constant through geologically meaningful periods of time (say, the lifetime of a species)? I know that people consider these things and take them into consideration, but I haven't explicitly seen this in too many of the readings for the class.
Brown 1999 (Oikos) and Smith et al. 2008 both resonate the main idea that macroecology has come a long way but still has much more room for expansion and growth. The most important thing for future progress is the elucidation of the underlying mechanisms of observed patterns rather than simply identifying the patterns. As the examples of metabolic scaling and other instances show, it will not be an easy or uncontroversial undertaking, but the results can be extremely fruitful.
ReplyDeleteI think the Table in the Brown paper showing the links between patterns and processes is very interesting/informative and should serve as a basic blueprint for future research.
Melissa, in response to your very first post here, I think you raise an interesting point about natural selection and body size. If the statement does apply to plasticity in species, it seems like there should be a significant advantage to getting larger. Not that it would always be advantageous, but it's still an intriguing notion...
Moses and Brown, 2003
ReplyDeleteThe decrease in human fertility with increased use of energy conflicts with life-history theory. So then does the same pattern in non-humans in figure 3 also conflict with this theory, or did I read this wrong?
"Here we additionally propose that the perceived energetic investment (including material goods and education) required for a child to be competitive in a given society is greater in more consumptive societies."
Would it be reasonable, then, to predict a reduction in the quality of child rearing as our energy use increases?
DeLong et al 2010
ReplyDeleteI'm with Meghan and Alyssa on this one. I don't really understand how increased energy use (and with that availability) would lead to a decrease in fertility. Hopefully this is something that can be explained in class today!
Moses and Brown 2003
"...parents have as many children as they can afford to provision with the energetic resources expected in their society"
All the data that is presented in this paper is by country, not by "societies". Most countries have societal groups that are very different from one another (India's caste system for example, or a little closer to home, the American socio-economic groups). How does the scaling change when looking at societies instead of just countries?
Brown et al in press
This paper was a great reminder that humans are just another animal, with a few oddities thrown in. I also really enjoyed the macroecology-multidisciplinary approach. It showed just how interesting collaborations with different fields can be. Most of this paper was presented at Jim's brown bag, but I thought the paper was an easy to read synthesis of the concerns raised in the talk.
Allometry of human fertility and energy use
ReplyDeleteFertility decreases as energy consumption increases. Does low fertility rate cause high energy consumption per capita or does high energy consumption per capita cause low fertility rate? It seems that the paper assumed parents would have as many children as they can afford the energy consumption, or do I misunderstand?
I think he main point of the DeLong and Moses papers is that the more energy a society uses the higher the cost of reproducing. So the fact that there is more energy available to reproduce is not what defines the relationship, but the fact that it cost more to be a parent in societies that use more energy is.
ReplyDeleteThe scary bit about this (as was brought up in the Brown et al paper)is what will happen if we discover cheaper unlimited energy sources? Will population growth no longer decrease with increased energy consumption? This could be the case if solar technology is advanced and becomes more wide spread.
Note: the more money parents need to participate (= consumption of energy) in the culture/society they are part of the fewer kids they have.
This comment has been removed by the author.
ReplyDeleteMoses and Brown 2003: Human facility
ReplyDeleteClarify the cause and effect
This paper shows a clear solid relation between human fertility decisions and extrametabolic energy consumption. Thus with limited energy, the higher the energetic invested in each offspring, the lower number of children could be raise. I think this is not the source of the problem. The first step should be that the energy one spent on children would decrease the energy used to benefit current generation. In order to obtained higher level of living standard, some people would choose to give birth later or never have a child. The impact of the result of this choice would rise up the average energy consumption, which in turn affect other people’s decision of how many children to have.
It’s amazing to look through the sociology phenomenon from the standpoint of Macroecology. I like the open circles in Figure 1 that reasonably distinguish the major oil producers out as outliers, which objectively reflect the true situation.
Two things I thought of during discussion today but didn't get a chance to get in:
ReplyDelete1. If it were somehow possible lower the energy consumption of the wealthiest nations (Fig 3 Brown et al in press) while maintaining a similar standard of living, would it effectively be the "sustainable" way of living people are searching for?
2. What role might localization of commerce, agriculture, etc have on this?
Any thoughts/comments on this?
Well in regards to the Smith et al. Macroecology paper there is continual emphasis on studying Taxa through time. The only way to do this is through systematics, yet systematics (as usual) is overlooked and underestimated (despite it being used more and more) and is only mentioned once in the article as one of the disciplines that uses a macro view and could be incorporated into macroecology. I think that further emphasis should've been placed on some of the areas of science that could assist in macroecology. It appears that systematics will be essential to any macroecological studying looking at taxa through time.
ReplyDeleteOn the Moses Brown paper:
ReplyDeleteI would like to if religion was considered in the variables for this analysis, especially with the Middle East being systematically diviant from the regression line. Religion is an important aspect of human society and governs a major aspect of human choice. I am wondering how religion would compare to energy use in this analysis.
Damuth: I think I'm finally understanding the full implications of "energy equivalence". I like the author's suggestion at the end that competition and environmental fluctuations act over evolutionary time to keep species energy use about level. This may be why things like invasive species cause such large disruptions in communities, because they throw the energy balance off, leading to extinctions or changes in abundance at least.
ReplyDeleteErnest et al: This paper is getting at the mechanisms behind what many community ecologists have understood for some time: that energy flow and allocation is a fundamental driver of community structure and interactions. Really cool paper!
Response from Jim:
ReplyDeleteThis is very good. Looks like you are understanding much of what macroecology ahs done and has promise to do in both human and "other" ecology.
If any of you want to talk about aspects of this that you would like clarified or might want to pursue, come around. Kathie Thannish keeps my schedule and can help find a mutually good time.
You might be interested to know thatstrid, Richard Sibly, and I are working on a multi-authored book on "metabolic ecology" which will hopefully explore many of the relevant topics and make progress in elucidating mechanisms. Richard Sibly (U Reading, UK) will be here and in the PiBBs space Mon thru Thur next week. He is a nice guy, very broad physiological/behavioral ecologist, and likes to talk to students. So look him up if you are interested. The "publications" on my website have PDFs of several papers co-authored with Richard.
Cheers,
Jim
Macroecology:The Division of food and space among species on Continents
ReplyDeleteI found it interesting that this paper states such a wide estimation for all the species on Earth (10-50 million). There is so much yet to be found that it is interesting to see an estimation of any sort for the number of species that currently exist. This paper places focus on large scale explanations for wide-ranging patterns found across the globe, such as diversity, allocation, and abundance. The question of how a diverse group of organisms split up the land and nutrients around them. It was intriguing to see the similarities of log scaling for the frequency distributions of body masses among birds and land mammals on the same continent. This was found to be the results of three mechanisms; interspecific competition, differential extinction, and energetic constraints. This paper places focus on resource allocation without taking into account human impact. Humans are the most widely distributed and use the most solar energy. The authors state that diversity will lessen, wild species will become extinct, and population sizes will decrease. In the conclusions, this article strives to stress the importance of conservation and appropriate reservations.
Body Size, Energetics, and Evolution
ReplyDeleteThe main focus of this paper is to answer the questions of why organisms evolve a certain size, and what the ecological and evolutionary consequences and tradeoffs are of each. I found this paper interesting from the beginning because it notes the body size range over more than three orders of magnitude, also how body mass of organisms is extended when considering extinct species. It is rare that I get to read papers that include both insects and extinct species. Biological functions such as metabolic rate also change in a predictive way like body size. Energy is not only dependant on size, but the temperature of an organism (whether it is endo or ectothermic). This paper states rules which are observable patterns able to be explained by statistics. Bergmanns rule states that larger animals are most likely to be found in colder environments as smaller are in warmer environments. The island rule states that larger vertebrates on isolated islands become smaller, and the opposite is true for smaller vertebrates. Copes rule states that lineages of organisms tend to get bigger over time. This may be a sampling error or investigator bias. This paper ends with the definition of macroecology, which I found very helpful, “the statistical study of broad, consistent patterns between organisms and their environment.”