Paper 38: ARE THE SMALLEST ORGANISMS THE MOST DIVERSE? – K. P. DIAL AND J. M. MARZLUFF (1988)

Alison G. Boyer – Commentary author  

Dr. Boyer is a quantitative macroecologist interested in the interaction between humans and natural systems. She works for the Climatic Change Science Institute (NASA – biogeochemical dynamics) to understand and predict global change and prevent biodiversity lost due to anthropogenic causes. She is also a Joint Faculty Assistant Professor in the Department of Ecology and Evolutionary Biology at University of Tennessee, Knoxville. Alison got her PhD in 2008 at University of New Mexico under Dr. Brown’s supervision. During that time, she also helped as a Graduate Curator for the Museum of Southwestern Biology, University of New Mexico.

27 publications and 934 citations (ResearchGate).

Kenneth P. Dial – Author

Dr. Dial is a Professor Emeritus at University of Montana. In general, he is interested in the origin and evolution of birds, most particularly the flight animal design using 3-D motion analysis, high speed movie film, recording system and other various techniques. He is also interested in the mechanistic foundations differences in locomotion between small and large animals.

He is member of the Flight Laboratory at the UM Field Station at Fort Missoula. Natalie Wright (ex-student at UNM, Chris Witt lab) is a Post-doctoral with him.

63 publications and 3016 citations (ResearchGate).

John Marzluff – Author - http://tedxseattle.com/talks/crows-smarter-than-you-think-john-marzluff-at-tedxrainier/

Dr. Marzluff is a professor of Wildlife Science at University of Washington. He is interested in human-bird relationships (birds-feeders) and how this may impact wildlife conservation. He is particularly interested in crows (how crow view its captor using brain imaging).

130 publications 6772 citations (ResearchGate).

Cliff Notes of the paper:

Before this paper came out, scientist thought that smaller body size species had higher diversity than larger body sized species. The reasoning behind that was that small body size species have more space to fit more species, subdivide and speciate to avoid extinction. Robert May (1978, 1986) also believed in this general pattern of “strong, inverse, monotonic relationship between diversity and relative body size within a taxonomic assemblage” even though his distributions didn’t show that pattern. May justified this incongruence between his data and his conclusions to an insufficient sampling of the smallest body-size categories.

Later on, Dial and Marzluff compiled body-size data for 46 assemblages (invertebrate, vertebrate and plant taxa) and they calculated the relative body size for each taxonomic unit. They used relative body size values to be able to compare distantly related groups.

In conclusion, their results show that most diverse species were constrained in the smallish-medium body size range: right-skewed modal distribution [Fig. 1]. This conclusion disproved what May thought it was an underrepresentation of the smallest body size groups.

Towards the end of this paper, Dial and Marzluff also provided a conceptual model to understand the evolution through time of body size distribution including speciation and extinction rates. They assumed speciation to be the highest in small body sized groups and extinction to be high in the smallest or large body size groups [Fig. 2].

As the commentary author points out, this paper has been the foundation to multiple subsequent studies based on species diversity and body size.

One of the main questions that came to my mind when I was reading the paper is: Is this general pattern applicable to the fossil record with the data the we have today?