[CINC] Island Rule, Hobbits, and Island Biogeography

[WhaleBear at cs.com]

The discussion of the "island rule" raises some interesting issues.

For most of us over 40, the island rule, as Kate Faulkner states, is a 
general principle that small animals tend toward larger size on islands (less 
predation/competition being one reason) and larger animals tend toward smaller 
size (in part because of less food availability).  While often true, this 
is a gross oversimplification and is subject to influence by a number of 
factors.  A good starting point for reading about the topic is Carlquist (1974); 
although this reference is of some age, it is written by one of the great 
biologists of the twentieth century and has aged well.  While you're at it, 
you may wish to read further about island biogeography in general.  Another 
two references that have held their age well are Wilcox, writing in Power 
(1980) (brief summary of island biogeography with particular pertinence to 
reptiles) and MacArthur and Wilson (1967) (the classic in the field).  More 
recently, Whittaker and Palacios (2007) and Losos and Ricklefs (2009) have built 
excellent volumes on this foundation.

The "optimal body size" hypothesis, that large clades have a single, 
optimal body size, (although sometimes quoted as a rule, this is inappropriate) 
has been bandied about for some decades and still enjoys wide currency.  It is 
questionable on both theoretical and technical grounds.  Raia, Carotenuto, 
and Meiri (2010), quoted in an earlier posting, is merely the latest study 
to provide evidence against it.  The article cited by Kate (Case, 1978) and a 
more recent article by Meiri, Simberloff, and Dayan (2005) offer further 
evidence against this hypothesis.

The "Hobbit of Indonesia," or Homo floresiensis, is not a good fit for this 
discussion.  The 2004 National Geographic press release quoted in a 
previous posting is both somewhat sensationalistic and grossly in error.  It was 
initially believed that H. floresiensis was a descendent of H. erectus, and 
its small size was attributed to insular dwarfism.  Ongoing analysis has shown 
the bulk of the complete H. floresiensis skeleton to be structurally much 
closer to the australopitecine lineage than to the genus Homo; only the 
cranial elements place it within the Homo lineage. It predates H. erectus.  
Interestingly, its small braincase may be a mild example in insular dwarfism; 
there is good evidence that the brain size of some insular mammals decreases to 
a degree greater than that predicted by standard scaling models.  The 
subject of  "the hobbit" is quite complex but is well-summarized in a recent 
Scientific American article by Wong (2009).

The articles and texts I've cited are both interesting and should be 
accessible to a group with the intelligence of the Naturalist Corp.  Good starting 
points in seeking them out would be the Santa Barbara Museum of Natural 
History, the Santa Barbara Botanic Garden, and any of the local universities.

I will be positing shortly on the blow of whales and the possible effect of 
seismic activity on marine mammals.  In August, I will begin a biweekly 
commentary on recent marine mammal articles in the literature.  

Be well,

Chuck Rennie

Literature cited:

Carlquist, Sherwin (1974).  Island Biogeography.  New York:  Columbia 
University Press, 

Case, Ted J (1978).  A General Explanation for Insular Body Size Trends in 
Terrestrial Vertebrates.  Ecology 59:  1-18.

Losos,Jonathon B and R E Ricklefs (2009).  The Theory of Island 
Biogeography Revisited.  Princeton:  Princeton University Press.

MacArthur, Robert H and E O Wilson (1967).  Island Biogeography.  
Princeton:  Princeton University Press.

Meiri, Shai, D Simberloff, and T Dayan (2005).  Insular Carnivore 
Biogeography:  Island Area and Mammalian Optimal Body Size.  American Naturalist 165: 
 505-514.

Raia, Pasquale, F Carotenuto, and S Meiri. (2010).  One size does not fit 
all:  no evidence for an optimal body size on islands.  Global Ecology and 
Biogeography 19.

Whittaker, Robert J and J M Fernandez-Palacios (2007).  Island 
Biogeography:  Ecology, Evolution, and Conservation.  New York:  Oxford University Press.

Wong, Kate (2009).  The Hobbits of Indonesia.  Scientific American 301:  
66-73.

Wilcox, Bruce (1980).  Species Number, Stability, and Equilibrium Status of 
Reptile Faunas on the California Islands.  In The California Islands:  
Proceedings of a Mulitdisciplinary Symposium (ed Dennis Power) pp 551-564.  
Santa Barbara:  Santa Barbara Museum of Natural History.</HTML>