Week 9: Abundances and Distributions
Paper for Tuesday: Geographic Ranges of North American Terrestrial Mammals (1977)
Commentary author: Christy M. McCain
Christy McCain got her PhD from the University of Kansas in 2003 and is now an associate professor in the Ecology and Evolutionary Biology department at University of CO Boulder, as well as the Curator of Vertebrates at the university’s museum. McCain is interested in ecological organizations and studies these through species, population, and community-level interactions. She worked on a postdoc at UNM in 2007.
Paper author: Sydney Anderson
Information on S. Anderson was tough to find, but based on his many published papers he is interested in a wide range of topics in ecology, from range size distributions to faunal evolutionary patterns. As far as I know, he is still a Curator Emeritus of Vertebrate Zoology and Mammalogy at the American Museum of Natural History. He, too, got his PhD from the University of Kansas. Along with working as curator at the AMNH, Anderson also taught at U of Kansas, New York University, and City University of New York. He served as the president of the American Society of Mammalogists from 1974-1976.
Cliffnotes:
For this study, Anderson is considering the frequency distributions of range sizes for different species in a fauna. In this preliminary paper, Anderson first uses “North American mammals” as his example fauna (McCain points out in her commentary that Anderson subsequently performed similar tests on birds, fishes, amphibians, and reptiles). His goal is to form a general theory that would predict the distribution of species within a fauna in a certain space.
Anderson first makes it very clear that this specific question has never been looked at before. However, he does cite some important works leading up to his own study: Willis and his “hollow curve” pattern; MacArthur and Wilson, with their important work on island biogeography; May, who applies the “central limit theorem” to species abundance distributions; and Rosenzweig, who finds a correlation between increased bat species numbers and decreased range size.
Anderson describes different levels of space occupation: alpha-area is the space an individual takes up; beta-area is the home range of the individual; gamma-area is the composite of all individual ranges in a population; and delta-area is the total species range – this is the area that Anderson deals with in the paper. Ranges were estimated based on previously published maps and newer range and taxonomy info. Historical information was used only to avoid human impact.
I'm a little confused on Anderson's results and interpretations. The most solid conclusions I can see are that each group gets less concentrated in their range as the range goes up in order of magnitude, and that the distribution seen in the results does not match any pattern suggested by the previous work Anderson cited in the beginning of his paper. He concludes by stating that more work should (and will) be conducted.
I have many questions. For now, I'll just ask a few broad ones: Should single-locality samples be used for a study like this? What do you think of Anderson's estimation that single-locality species equal around 10 km2? Also, someone help me out with island biogeography: why would more insular species result from the presence of more diverse fauna (p. 10 of the paper)? Would this go back to Rosenzweig's suggestion of increasingly intense habitat selection with more species?
My key-board is broken, so I'm typing with the onscreen keyboard. My main question relates to a theme we've gone over several times in macroevolution, namely, how do you define a population, and how do you distinguish it from a species? How much gene flow do you need to have before two 'populations' should just be considered one population? Do all ecologists agree on a universal method of determining what is and is not a population? This all comes down to the question of what is the difference between beta and gamma area, and what that means for conservation. Can you get legal protection for an endangered population in the first place, or is it a 'species-level-or-bust' dealio? I'm also curious about the population definition business in general because, at least according to my momentarily favorite species concept, speciation only occurs when species = population. I realize this is mostly a sidenote, sorry for the diversion and any awkward spelling, etz kybrdz.
ReplyDeleteI think that Anderson had an interesting macroevolutionary question in mind… What is the size-distribution range of species in a larger scale and why? This is an interesting idea but I feel that the methodology to approach that idea wasn’t the best at the time… Towards the end of the paper he talks about the error in the measurement of the area where in some cases can be up to 20%. Also, he spends some time at the beginning of the paper defining the different biologically meaningful areas, but then he never comes back to it. I think that Anderson’s fundamental question is good but it's probably too early to approach the idea with the right tools to obtain robust results.
ReplyDeleteI think the question about the insular species may be more present in the diverse fauna is because Anderson is looking at mammals, which tend to conform to Bergmann's Rule. This would mean that mammals may become limited by range size of the island they would be on. It also could me a sampling bias, as he is only looking at North America, and most of the island data would come from the hyper-diverse Carribbean, while other island groups like the Alexander Archipelago in SE Alaska would be exceptionally under sampled (it still is today, let alone in 1977). I wonder also if that pattern is partially what drives part of the latitudinal diversity gradient (how much of the pattern results from mainland species, and how much is from insular species).
ReplyDelete