King Kong did live on an island...

I have always thought the fact that small animals tend to be larger on islands, and large animals tend to be smaller is very interesting, especially as it related to other "island-like" environments. I did my Masters work on springtails found in caves. It is often said that caves are "island-like" in that cave-obligate species are isolated from other populations even if they are located nearby. I think that you could also argue that many caves are "island-like" in their lack of resources and in low levels of competition. Although my research was more focused on the genetic side of things, I noticed that as I sorted many individuals collected from both cave and surface populations I never saw any signs of a larger size of the cave-dwelling springtails. It struck me as interesting, though I never gave it too much thought. I assumed that either the populations I was sampling from had not existed in the caves long enough for the change in size to occur or whatever really drove the increase on islands was not found in the "island-like" caves.


Although it has been a while since I completed that research, I was reminded of it when I saw this article on some new research. The study showed that the "island rule" holds in "island-like" deep sea environments. The large isopod pictured above is an example of larger body size that has evolved in the deep ocean. So, if the island rule holds for islands and the deep ocean, does it hold for caves as well? If it does, why did I find no qualitative evidence of it in cave springtails? My Google searching for applications of the island rule to caves turned up many articles on the Homo floresiensis remains found a few years back, but nothing much further specifically related to size. A few sites made reference to "cave arthropods showing 'typical adaptations' such as ... changes in size ..." but did not back up the claim with data or citations. There were a couple of hits that looked promising, but did not allow me access from my non-university based computer. There are times that I really miss being connected to a university library, on-line journals and search options.

So, were my observations just an anomaly, a result of populations being too young for the change to have occurred? How long would they need to really show the change? If I could go back, I would have extended my research to examine these questions. How old where the populations I was studying? I know the caves themselves are quite old, but that really says nothing about the populations inside. There are not too many times that I miss grad school, but every once in a while I am struck by a question that I wish I could research. Maybe if I could just get myself to a good library I would find out that someone else already knows the answer. Unfortunately, that is never quite as satisfying as figuring it out yourself.