, Volume 94, Issue 1, pp 102–109 | Cite as

Island/mainland body size differences in Australian varanid lizards

  • Ted J. Case
  • Terry D. Schwaner
Original Papers


Island varanids seem to be an exception to the rule that territorial vertebrate taxa often become gigantic relative to mainland relatives when on islands, whereas non-territorial species become dwarfed (Case 1978). However, no systematic island/mainland studies have examined the empirical size trends in this group of carnivorous lizards. We perform such an analysis for the Australian region and critically evaluate various selective agents that might be responsible for size changes in several island populations. Insular gigantism occurs at least four times among the island populations examined. The magnitude of size change is positively correlated to prey abundance on the islands (as indirectly measured through a condition index of the lizards, essentially a measure of how fat they arc) and the size of prey: islands with large prey have large varanids and vice versa. Since the island population with the largest size change, the Reevesby Varanus rosenbergi, was introduced less than 100 years ago, these size changes can be quite rapid. This might indicate that selective coefficients are strong; however, we can not exclude the possibility that these size differences have no genetic component and simply reflect environmental differences in growth rate and shifts in age structure between island and mainland locations.

Key words

Lizards Islands Gigantism Varanus 


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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • Ted J. Case
    • 1
  • Terry D. Schwaner
    • 2
  1. 1.Department of Biology, C-016University of California at San DiegoLa JollaUSA
  2. 2.Alabama School of Mathematics and ScienceMobileUSA

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