Tarsier

(vagabondish.com)

I thought it would be a good idea to give a real-life example of matched-pairs nested comparisons, and this paper by Gittleman and Purvis (1998), published by the Royal Society is a great example. 

They use this technique to overcome the pitfalls in examining body size with species richness in mammals.  They collected data on body mass for 175 primate and 240 carnivore species.  They used the technique outlined in my previous blog (along with other statistical methods to test the body mass-species richness hypothesis) and found amongst high levels of heterogeneity between clades, no significant relationship exists in the primates, and a significant (but weak negative) relationship in the carnivores (especially canids), as in figure 1a  (top) and b (bottom).   

 

Figure 1 a)       Large-bodied carnivore clades tend to be significantly less species rich that small-bodied clades (black circles represent mustelids, procyonids, Ailurus, and pinnipeds), white circles are others.  b)  No significant pattern described in primates.  Least square regression line through origin. 

These are the overall trends, but certain clades e.g. the fox-like and cat-like carnivores show a stronger relationship than closer relatives.  The authors explain that the associations highlighted by this technique are like to reflect differential extinction because both clades have suffered size-selected extinctions (e.g. extant primates on Madagascar are smaller than their extinct relatives).  This study shows that body size might be important in diversification within clades (i.e. foxes), but not among them (i.e. primates).  This technique is now used to assess extinction risks, and will be discussed later.  

Reference:   Gittleman, J., Purvis, A. (1998).  Body size and species-richness in carnivores and primates.  Proceedings from the Royal Society London, 265, 113-119