38. Dial, K.P. and J.M. Marzluff. 1988. Are the smallest organisms the most diverse? Ecology 69:1620-1624.
Blog Author: Ben Clinch
Blurb Author: Alison G. Boyer
-Former Postdoc, Bioinformatics, Yale University
-Research Assistant Professor, Department of Ecology and Evolutionary Biology, University of Tennessee
-ORNL DAAC Chief Scientist
-Research interests- global change ecology, biogeography, biodiversity
Paper Author: Kenneth P. Dial
-Flight Lab Founder & Director, University of Montana
-Professor Emeritus, University of Montana
-B.S. Loyola Marymount University, M.A. California State University, Ph.D. Northern Arizona University
-Research interests: evolutionary questions in animal design, transitional stages of locomotordevelopment, allometry of behavior, life history biology and ecology
Blog Author: Ben Clinch
Blurb Author: Alison G. Boyer
-Former Postdoc, Bioinformatics, Yale University
-Research Assistant Professor, Department of Ecology and Evolutionary Biology, University of Tennessee
-ORNL DAAC Chief Scientist
-Research interests- global change ecology, biogeography, biodiversity
Paper Author: Kenneth P. Dial
-Flight Lab Founder & Director, University of Montana
-Professor Emeritus, University of Montana
-B.S. Loyola Marymount University, M.A. California State University, Ph.D. Northern Arizona University
-Research interests: evolutionary questions in animal design, transitional stages of locomotordevelopment, allometry of behavior, life history biology and ecology
Main Question: Are the smallest organisms the most diverse? Is there a model of evolution
that explains the right-skewed body-size distribution?
-Background: Body size has historically been a correlate to diversity. Previous research on this
topic argued that diversity is higher among the smallest organisms because smaller organisms
can divide any environment into finer niches, allowing more species to occupy one area.
However, previous research shows a lack of species in the smallest size bins- this piece aimed to
explore the reason for the right-skew of the distribution. Previous researchers pinned this skew
due to lack of sampling in the smallest taxa.
-Assumptions: Three taxonomic terms to discuss diversity: subunit (species), unit (genus), and
assemblage (family). The range of body sizes measured within an assemblage represents the true
range for the assemblage.
Methods:
Methods:
-Meta data compilation of published body size datasets for 46 assemblages- only assemblages for
which body sizes were known for nearly all members (>90%)
invertebrates
-Included mammals, birds, fish, reptiles, amphibians, plants, insects, and marine
-Used most representative sizes for subunits- mean body masses of mammals and birds, median
of a length distribution of invertebrates and plants, and maximum lengths of fish.
Results:
-Monotonic relationship between body size and diversity doesn’t exist. On average, the most
diverse unit was 38% larger than other units in the assemblage.
diverse unit was 38% larger than other units in the assemblage.
-Only 13% of assemblages dominated by smallest unit, only 11% dominated by largest unit.
Small to medium sizes more likely to dominate.
Conclusions:
Conclusions:
-Smallest organisms not the most diverse taxonomic members. Only in carnivorous mammals are
the smallest members the most diverse.
-In assemblages where small to medium organisms don’t dominate, it may be due to how
different taxa respond to spatial and temporal changes. Very small or very large may be at an
advantage in these variable conditions.
-Evolutionary model- high extinction rates of very small and very large taxa coupled with high
speciation of small taxa lead to the observed right-skewed body-size distribution.
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Comments/Questions:
-Are researchers mainly concerned with body size when questioning diversity? How often are
other phenotypic traits considered?
-Was the evolutionary mechanism for the distribution tested by subsequent autho
-Was the evolutionary mechanism for the distribution tested by subsequent autho
-Was there a reason to refer to species, genuses, and families as subunits, units, and assemblages?
-Pretty straight forward paper, easy to read and understand
-Pretty straight forward paper, easy to read and understand
Overall, I found this paper very easy to grasp and read. The paper only focused on their one research question, which greatly aided to its readability. To weigh in on some of Ben's questions, other phenotypic traits are researched and considered on topics of diversity, but doing so narrows the possible scope of that research. In this paper, the authors looked at relative body size within the groups, therefore the fact that mammals, birds, fish, inverts, and plants all may have different established methods of determining body mass. When other traits are considered, like diet or locomotion, the research is limited as to potential comparisons. While you can compare locomotion of bats and birds, you can't for other orders of mammals. Comparisons across larger taxonomic branches become fuzzier for phenotypic traits. There are plenty of papers out there that look at various traits, but we've been focused on larger-scaled papers.
ReplyDeleteBody size is relatively easy trait to measure in extant and extinct species and have a great impact on many of the other phylogenetic traits associated with the animals like range size and life habits. So I think body size would usually be considered when looking at diversity.
ReplyDeleteI liked how straightforward and easy to read this paper was too. About the reason to address to units, subunits and assemblages, in table 1 it is shown the different taxa they included in their analyses. Not all taxa have the same information regarding their diversity in the species level, as it is know for mammals and birds. So to make it comparable and easier to explain, I think, they took whatever diversity information was available to a taxa, be it in terms of genus withing a family (as in most vertebrates) or in terms families within an order, subfamilies within families and so on, as is available for invertebrates.
ReplyDeleteI am still curious about the sampling effort would even affect the distribution even more. The paper is pretty short and the points were made pretty straightforward. It is interesting to see the extinction frequency over body size. Body size variable is chosen because it is the most fundamental measurement to take when species have been found or described. Body size represents lots of scenarios and functions of evolution and their impacts. Phenotypic traits used to be considered all the time and it should be but nowadays, the molecular approach is getting popular. However, I still believe that phenotypic traits are still valid and have very important information of the past and present because we cannot forget the formula "phenotype=genotype+environment".
ReplyDeleteThis paper is pretty easy to read. I like that they clarify the consumption that the smallest organisms are not the most diverse, and the small-medium ones are. This really helps make sense the graphs from my assignment 1. The extinction rate of stable environment vs variable environment graphs at the end of the paper are interesting. The graphs show that environment fluctuations lead to extinction of very large or small size. So wouldn't medium sized animals survive the most? I remember in class we talked about how evolutionary changes do not favor medium-sized organisms. So this is where I get kind of confused...
ReplyDeleteA very straightforward paper. I like that they chose to test a particular assumption, compiled a dataset, and tested the assumption, without adding in a bunch of other things to discuss or explore. It's the relatively simple papers, with one clear message, that make the most impact, at least to me.
ReplyDeleteI think is interesting the wide range of organisms analyzed (vertebrates, invertebrates and even plants) which results in strong evidence for the generality of the pattern.
ReplyDeleteFrom what we have read, there are ecological and evolutionary reasons behind the characteristic distribution of body sizes for many groups, it would be interesting to see if there is any study assessing both at the same time.
I enjoy how this paper was a lot easier to read than some of our other math heavy papers. Ben brought up a good question about how often are phenotypic traits considered? I feel like a lot of the papers we read are based off of the genotype and I don’t understand why we never consider phenotypes.
ReplyDelete