EPOW - Ecology Picture of the Week

Isla San Esteban Chuckwalla (Sauromalus varius), Family Iguanidae
San Esteban Island, Gulf of California, Mexico

Explanation:   Chuckwallas are large, stubborn lizards of the desert southwest U.S. and Mexico.  The Common Chuckwalla (Sauromalus ater) is the one you're most likely to encounter in the inland deserts.  But this species -- the San Esteban Island (or Piebald) Chuckwalla -- is unique.  It is found only on the arid islands of San Esteban and Isla Roca Lobos in the Sea of Cortez (Gulf of California) off Baja California, Mexico.

Various aspects of the ecology of this species also make remarkable stories.  First, how it got there and evolved into a separate species is a lesson in island biogeography, the study of organisms in remote and isolated locations.  The islands of the Sea of Cortez, which I have explored on diving expeditions (and on which I was once stranded, but that's another story), are host to other rare and endemic life forms of plants and animals.  For example, another rare and endemic species found only on San Esteban Island is the San Esteban Island Rattlesnake (Crotalus estebanensis).  The Isla San Esteban Chuckwalla might have been originally brought from the mainland in prehistoric times by local people as a source of food, and over time evolved to its unique island form, but this is speculation.  We just don't know how it got there.  Islands can be amazing places for the evolution of unique life.

Another fascinating aspect of the ecology of this species is its relative tameness.  Wildlife on islands that are isolated from human contact and mainland predators are often incredibly unwary and seemingly naive.  They either lost their fear of predators when they became isolated or never evolved the fear response.  This is one of the attractions of wildlife on the Galapagos Islands of Ecuador where human visitors can wander among colonies of seabirds and marine mammals and reptiles as if invisible.  The conservation challenge is how to keep such islands free from introduced predators (including, in some cases, humans).

There is a viable breeding colony of the species that has been introduced and fostered for more than 20 years at the Arizona- Sonora Desert Museum outside Tucson (where I took this photo).  The Museum is studying the species' behavior and breeding biology.  
  

Information:
    Delibes, M., and M. C. Blazquez. 1998. Tameness of insular lizards and loss of biological diversity.  Conservation Biology 12(5):1142-1143.