January 13, 2012
The Channel Islands are a chain of eight islands in Southern California off the Santa Barbara Channel. Santa Catalina Island – often referred to as just “Catalina” – is located roughly 20 miles directly opposite Torrance and Palos Verdes and is one of the larger islands in the Channel Island chain (76 sq. mi.). Catalina exhibits a mild, sub-tropical climate year-round and is composed mainly of a quartz base. The vegetation resembles that of a desert/ chaparral climate, and noteworthy landmarks include Echo Lake and Black Jack Mountain.
Catalina is an oceanic island that was formed by tectonic activity as opposed to being a continental island that separated from the mainland many years ago. This marine history was proved by the presence of fossils from plankton skeleton called diatoms. The material created by the presence of diatoms, called diatomite, is white and looks somewhat chalky. Continental islands’ native species often evolved from ancestral species that occupied the land before it broke away from the mainland, but oceanic islands are populated by immigrating species. Catalina Island is relatively close to the mainland, and the island’s biodiversity reflects this proximity. This follows the theory that larger islands will have higher levels of biodiversity than smaller islands, and islands that are closer to the mainland will have higher levels of biodiversity than those that are far away. Over time, animals have rafted, flew, and swam across the channel to the island to populate Catalina and the other islands. Once there, many have evolved to adapt to their new habitats.
Geological records are not necessarily conclusive, but it is possible to estimate species’ introduction to the island via remains and chart their arrival and extinction. Additionally, researchers have noticed that many plant and animal species closely resembled species on the mainland, but their physical appearances differ slightly. When species are separated from the mainland, and competitors or predators are removed, different physical traits may be selected over features that proved successful previously.
There are varying theories regarding the means of transportation taken by founder species and the reasons that species have changed in physical appearance. The Island Fox, a species on six of the eight Channel Islands, is thought to have been introduced thousands of years ago when Native Americans brought them over as domesticated pets.
Present day feral cats and dogs were also introduced as pets, but are now wild. More recent introductions, such as the Bison, have persisted on Catalina and have adapted to island life by evolving into ‘dwarf bison.’ The origin of the bison on Catalina is a funny one. In the 1920s, fourteen bison were brought to Catalina for the filming of a movie. After the movie was finished, the crew left the bison on the Island and their population grew quickly, now amounting to almost 600 across the whole Island.
The island fox also exhibits a similar case to the bison of dwarfism and appears smaller than the average mainland fox. The quail and squirrel, on the other hand, have become larger, exhibiting signs of gigantism. It has been proposed that some smaller animals were able to grow larger over generations due to the lack of stress presented by predators and competitors, while once-large animals became smaller because there were not sufficient resources to keep them well nourished. In addition, due to differences in environment and competition, some shrubs undergo ‘arborescence,’ which leads them to look more like trees after many generations. On Catalina, this is true of the Toyon and Island Scrub Oak. Species that can only be found in one place or region are called ‘endemic species,’ and Catalina Island contains eight such plant species and eight animal species as well as eight species of invertebrates. According to the Catalina Conservancy, which managed 88% of the island, two of the plant species are still under review regarding whether or not they are truly endemic. An interesting case study is that of the Island Ironwood trees. Many island endemics are often grouped as subspecies of mainland plants, but the Island Ironwood is the only species that is actually differentiated on the genus level from the parent species. The Santa Catalina Ironwood (Lyonothamnus floribundus, floribundus) differentiates from the Island Ironwood (Lyonothamnus floribundus, aspleniifolius) in that the Catalina Ironwoods have significantly longer and wider leaves.
This post was authored by Nina Gordon-Kirsch ’12 an Environmental Studies major (BS) with a minor in marketing; and Annie Guo ’12 an Environmental Studies major (BS) with a minor in International Relations.
For more information about Santa Catalina Island, feel free to visit the Catalina Island Conservancy’s website.