Why Does Species Number Decrease with Smaller Body Mass?

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Discussion Overview

The discussion centers on the relationship between species number and body mass, particularly why the number of species decreases for organisms with body mass smaller than 100g. It explores implications for microbial species and the challenges in estimating species diversity.

Discussion Character

  • Exploratory, Debate/contested, Conceptual clarification

Main Points Raised

  • One participant notes a trend where the number of species increases with smaller body sizes but questions why this trend decreases for organisms under 100g, suggesting a potential assumption that it should continue to increase.
  • Another participant raises the issue of missing species, particularly in microbes, arguing that many are difficult to culture, implying that undiscovered species may exist.
  • A different participant counters that the original graph pertains to animals, not microbes, and suggests that the advent of metagenomics mitigates the issue of unculturable microbes for understanding species distribution.
  • One participant expresses difficulty accessing the graphs and inquires about the representation of size variation among dogs.

Areas of Agreement / Disagreement

Participants express differing views on the implications of missing species and the relevance of microbial diversity to the discussion. There is no consensus on the reasons behind the observed trends in species number relative to body mass.

Contextual Notes

Limitations include potential missing assumptions regarding the definitions of species and the scope of the graphs, as well as unresolved questions about the applicability of findings to microbial organisms.

farful
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# of species vs body mass

Here are some graphs:

http://en.wikipedia.org/wiki/File:Intercontinental_land_mammals.png
http://en.wikipedia.org/wiki/File:North_american_land_mammals_graph.png
http://en.wikipedia.org/wiki/File:May_slope_-2_line.png

It's obvious why the number of species that have smaller body sizes are greater in number.
However, once we get into organisms with mass smaller than 100g, it seems to decrease. Why? One would assume it'd keep increasing, no?
Furthermore, would the trend continue for microbials?

Edit: Thanks DaveC, links have been fixed
 
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There may be a problem with missing species. Most microbes are impossible to culture in lab (or at least we haven't figured out how to yet), so there are likely a great number of undiscovered microbial species.
 


Ygggdrasil said:
There may be a problem with missing species. Most microbes are impossible to culture in lab (or at least we haven't figured out how to yet), so there are likely a great number of undiscovered microbial species.

The graph is for animals, not microbes, so I can't imagine there being missing species.

Also, with the advent of metagenomics, not being able to culture microbes is not a problem to get a distribution of species in an environment.
 
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I couldn't see the graphs... does it mention the wide range of the size of dogs?
 


farful said:
Edit: Thanks DaveC, links have been fixed
Uh, that's DaveC426913. I hate nicknames... :-p
 

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