The islands of Mexico’s Gulf of California or Sea of Cortez support numerous plants and animals that are endemic, found there and nowhere else on earth. Endemic Baja species and subspecies occur on many of the more than 50 isolated islands, some formed over 5 million years ago during the separation of Baja California from mainland Mexico. When small populations of organisms become isolated, any beneficial genetic mutation that develops within the species may be selected for and become part of the genetic material. Through long periods of time, isolated species experience genetic drift. Their gene pool changes enough to become significantly different and over time, a new endemic subspecies can evolve. If this process continues, a population may even become a new endemic species.
A critical component of the process of genetic drift is isolation. Without total isolation the original genetic material may re-enter the gene pool. This is sometimes called the rescue effect and may slow down or stop genetic drift. In the Sea of Cortez the islands close to the Baja California Peninsula or the Mexican mainland have lower incidences of endemism, because there is a higher likelihood of immigration of species on floating debris. A land connection may have also occurred when the sea level was lower during glacial times. An interesting variation is in killer whales. New research shows there are now several genetically identifiable species. Although they may use the same waters and there is no physical separation, they never cross-breed because of behavioral isolation due to different diets, habits, and sounds used for communication.
Genetic drift takes time. Not all mutations are beneficial. Some may be lethal, and others may not result in improvements that could be selected in survival. Isla Santa Catalina has been separated for millions of years and is 16 miles from the Baja Peninsula. Seventy percent of this island’s snakes and lizards are endemic species, including a rattlesnake that has lost its rattles. There are no mammalian predators that pose a threat so rattles offer no advantage.
Although many of the hundreds of endemics have subtle differences or are hard to find, there are some spectacular examples of plants and animals you would probably love to see. Small Baja Mexico cruise ships do make it to a few of these great destinations within Mexico’s Sea of Cortez. Isla Santa Catalina and several other gulf islands have massive barrel cactuses that can reach 3 feet in diameter and up to 12 feet in height. There is also an unforgettable side-blotched lizard with turquoise spots along the top of its body and a bright malachite-colored tail. Isla San Estéban in the Midriff Islands is inhabited by a giant chuckwalla that can reach 16 inches in length from the nose to the tip of its tail. It has a plump body with light orange and gray, granular scales.
The Sea of Cortez is a treasure trove for island biogeographers, biologists who study isolated island populations and how they evolved. Baja California has many islands with different ages, locations, sizes, and topography all available to see on a cruise in Mexico. These features are invaluable in testing theories and hypothesis of island biogeography. For this and many other reasons, the conservation of the islands within the Sea of Cortez is critical. Fortunately, this importance has been internationally recognized, and the Gulf of California islands have been given the status of a World Heritage Site. Some are also protected as a part of a National Park or Biosphere Reserve. Hopefully these designations and the continued isolation of these biological gems will protect the rare and unique endemics that survive within Mexico’s Sea of Cortez.
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