Blurb Authors: James H. Brown and Brian A. Maurer
James H. Brown (retired)
- PhD from University of Michigan, 1967
- Emeritus Distinguished Professor of Biology, University of New Mexico
- Research Interests: "Science is driven by curiosity about the diversity of life." Conducts research in biogeography, scaling and metabolic theory of ecology, macroecology, and biocomplexity.
- current whereabouts: retired to Monterey Bay, CA
Brian A. Maurer (deceased)
- PhD from University of Arizona
- Professor in Department of Geography and Department of Fisheries and Wildlife at Michigan State University
- Research Interests: "My interest focuses on the largest spatial and longest temporal scales studied by ecologists. To understand the importance of processes at geographical scales, it is important to understand how they connect to local scale processes. Thus, I am interested in modeling population and community dynamics in a geographical context. "
Paper Authors: James H. Brown and Brian A. Maurer - (see above)
Summary/Main points
1. Main Question:
- background: They were interested in trying answer questions about the abundance and distribution of birds in an area where field work wasn't really a good option. They realized that new datasets that were being published would allow them to ask questions about bird abundance and distributions in a different way that didn't rely on field work.
- They were also interested in understanding how to compare among small scale and experimental approaches to understand which were demonstrating general rules in ecology and which were simply unique to a particular study system.
- assumptions: data are ecologically relevant.
- body mass tells you something about the energetic requirements of an organism,
- local population density is an accurate measure of the number of individuals that can be sustained in a given area,
- size/shape of species range is an accurate representation of their distribution.
- main question: What are the processes that characterize the assembly of continental biotas of mammals and birds in North America? How are "the physical space and nutritional resources of large areas divided among diverse species?"
2. Methods:
- data:
- study organisms: NA breeding land birds and nonvolant mammals
- traits: body size, local population density, area and shape of geographic range
- methods:
- multivariate analyses
- compare among many species
- define sets of species taxonomically - this helps control for phylogenetic effects, but ignores others such as ecological interactions - trophic interactions, competition, etc.
- examined relationships among the traits for birds and mammals (e.g., body size distributions, relationship between population density and body mass, geographic range size and body mass, energy use and body mass, dispersal distance and body mass, and range shape).
3. Results:
- body size patterns:
- birds and mammals have similar body size distributions: right-skewed, unimodal, with a mode between 50 and 100 g
- shape of body size distributions flattens with smaller spatial scales (shown with mammals only)
- geographic range area is related to body size, only small species have small ranges, large species have large ranges
- population density scales with body size in two ways: species <100g show a decrease in population density with size, species >100 g show a decrease in population density with size, peak occurs around 100 g.
- relative energy use increases with body size
- geographic range size/shape:
- In North America, small ranges are elongated north-south
- In North America, large ranges are elongated east-west
- different pattern for Europe
4. Conclusions/Inference
- body size patterns:
- small bodied species should be more specialized than large bodied species
- this pattern is a result of energetic constraints
- interspecific competition drives changes in shapes of body size distributions at different spatial scales
- large bodied species are more vulnerable to extinction over long time scales
- geographic range size/shape:
- species with small ranges are limited by habitat and topographic features
- species with large ranges are limited by climate and biomes.
5. Questions:
- How does this differ from traditional ecology?
- What did you think about the way they built a case and made inferences rather than setting up experiments to test hypotheses?
- How might you test the 3 hypotheses they outline for body size patterns?
I like the part where the authors mention how macroecology can be integral to conservation. Until recently, conservationists focused solely on small-scale preservation, but large-scale conservation could be so much more effective.
ReplyDeleteI'm questioning several statements made on page 17 (second page of the article. It seems he is suggesting in his second point that larger mammals are more likely to go extinct due to the amount of resources needed, lower densities and larger territories. This idea has since been debated against that larger animals have the same chance of extinction as a smaller-bodied animal.
ReplyDeleteIn the third point, they suggest that larger bodied animals consume lower quality food and digest longer. This seems like a vast exaggeration. In carnivores, larger sized carnivores eat higher quality food and cover more area (organs). Smaller carnivores consume lower quality food (bones, fur, skin etc.).
I agree with Maria, I also like how they pointed how conservation efforts should be focused in a macro scale point of view, instead of a specific small scale.
ReplyDeleteAlso, it caught my attention when they mention how smaller mammals tend to have a more specialized diet and smaller habitats that translated into more movements between their distant foraging sites. And later they mention that they expect that the patterns described would also be present in other taxa. I wonder if this would be true for arthropods though, as they are mostly small animals, some have a very broad diet and a very wide distribution. Will this pattern of smaller body size-specialized diet-small habitat-increased displacements also be true in this taxa? I suppose it is something that has been addressed in other papers after this was published, but is something that came to my mind while I was reading this.
I have read a summary related to this topic in Mammalogy class. It is a very logical interpretation of these results. However, these kinds of research involve large data sources and the results depend on the data processing before the analysis which can cause error or bias interpretation or even can lead to different outcomes. It is complex. I like the conservation effort section, "above comments" specifically to conserve the functional groups, biodiversity, ecosystem (large scale)! It also has lots of political and geographic challenges.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteI'm just amazed at the rapid increase in macroecological interest in the past 20 years. I think human ecology sounds especially interesting, I'd like to learn more about that.
ReplyDeleteI hadn´t read or though before about how energetic constraints on habitat selection for small organisms could result in higher dispersal distances. I would like to read more about it and see if the pattern holds for other types of organisms and datasets. This pattern would also help to explain the low number of species under certain size threshold at continental scale as species with higher dispersal distances will probably have lower allopatric speciation rates. I wander if this has been explored further.
ReplyDeleteI also agree with Maria, the use of a macroecological approach in conservation seems as a logical step given the broad scale impact of humans on biodiversity. I know there has been search in the area, but I don´t know how much of the conservation and management suggestions have been or will be implemented given the broad scale of the analysis (how easy is to scale it down to local actions)
In ecology and evolution we spent some time learning about interspecific competition and we touched briefly on differential extinction. I don't remember learning about energetic constraints. Is it possible for us to go over it a little bit more in class?
ReplyDeleteSide note: I think it's cool that macroecology combines other sciences such as climatology and biogeograpy to get it's information and theories.