Catalina Island Home to at Least 60 Species found Nowhere Else
Catalina Island Conservancy
From the tiny Catalina Island fox to one of the world's rarest butterflies, Catalina Island is home to at least 60 plants and animals found nowhere else. Known as endemic species because they are found exclusively in one geographic area, their survival is essential to preserving the world's genetic diversity. Catalina's endemics are also one more feature of this island that fascinates our visitors.
Endemic species are fairly common on remote islands where isolation limits the addition of new individuals and can offer protection from destructive mainland forces.
Some endemics evolve from ancestors that arrived thousands of years ago. Over the generations, individuals carrying traits that make them more successful under island conditions become more numerous.
Those carrying other traits produce fewer young, and some features die out over time. Selection pressures come from changes in the resources available. Those include food, water, materials, or space. Resource changes can also affect mate selection and alter competition with and predation by other species.
For example, the Catalina Island fox, known to science as Urocyon littoralis cataline, likely evolved to become a smaller version of its ancestor, the gray fox, for three reasons. Space on the island is limited, menu options are reduced compared with the mainland, and larger competitors, such as coyotes and wolves, are absent.
Other endemics were once widely distributed on the continent or even globally. Since colonizing the island in the distant past, their populations elsewhere have disappeared due to changing climate or interactions with other plants and animals.
Meanwhile, the island populations are protected from those pressures and continue to survive. A local example is the Catalina ironwood, also known as Lyonothamnus floribundus floribundus. It once had a broad distribution across North America and can now be found only on Catalina.
Catalina’s endemic animals are a varied group, represented by five mammals, three birds and more than 45 species of invertebrates (mostly insects). They’re each genetically distinct from their ancestors as confirmed by DNA analysis. Some, like the fox, also have visible, physical differences that set them apart.
Among the rarest of the endemic species is the Avalon hairstreak (Strymon avalona), a one-inch gray butterfly with faint yellow marking on its hind wings. It is considered to be vulnerable to extinction because it occupies such a limited range. Yet its closest relative, the gray hairstreak (Strymon melinus), is one of the most widespread butterflies in North America.
Eight plants are thought to be endemic to Catalina Island, including the Trask’s yerba santa, Eriodictyon traskiae var. traskiae. Another, the Trask’s monkeyflower, Mimulus traskiae, is presumed to be extinct because it hasn’t been seen on Catalina since 1901.
It’s important to note that the field of taxonomy, or the classification of organisms, is an ever-changing science, thanks especially to DNA analysis. As further research is conducted, organisms that were once considered to be the same as their mainland counterpart may end up getting re-classified as endemic species, or vice versa.
The protection of endemics is a high priority for conservation groups because these plants and animals are truly irreplaceable. Our efforts to remove introduced species particularly benefit our rare plants and animals. By preserving Catalina endemics, we are maintaining the planet’s genetic diversity, supporting ecosystem function and ultimately improving human welfare.
By Alexa Johnson
Alexa Johnson is the Catalina Island Conservancy’s outreach and naturalist training specialist. For more information, please visit catalinaconservancy.org.