THE STUNNING SERPENT
How would you like it if we destroyed your home?
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The very specific nesting requirement of the endemic San Francisco Garter Snake makes survival in a constantly changing world increasingly difficult. The snakes must live in densely vegetated ponds with water no more than 2 inches deep so they are able to hunt, near open, sparsely vegetated hillsides which provide upland habitat suitable for thermoregulation. Ephemeral ponds provide an ideal habitat for frog hunting, as that is where many frogs choose to reproduce (San Francisco Garter Snake, 2010).
Home page photo retrieved from https://www.youtube.com/watch?v=vL5vXk_OEHc
Retrieved with permission from Tammy Lim
As these ponds dry and the frogs retreat to wooded areas, San Francisco Garter Snakes move to more permanent aquatic areas, or head up hill. These hillsides offer rodent burrows for the snakes to take refuge in to hide from predation during their hibernation (San Francisco Garter Snake, 2010).
Due to the rising human population in the San Francisco Bay Area in the past 100 years, the delicate wetland habitats relied upon by the snake and its co-evolved prey is not only fragmented, but in many cases destroyed.
In addition to its highly specific needs, the San Francisco Garter Snake, as the name implies, has an extremely restricted range to only the small 744 square mileage of San Mateo County (Roberson, 2004). If the San Francisco Garter Snake becomes extinct in San Mateo County, it will not only become locally extinct, but it will be gone from our planet forever. The range of the snake has not drastically diminished but within that range individual populations have been extirpated and others seem to be declining (San Francisco Garter Snake, 2010).
When the recovery plan for this species was written the snake population faced extinction. The gene pool was comprised of a dwindling 400 individuals that had been captured, marked, and released back into the wild as of 1985, which provided space in the food chain for the bullfrogs to take control of the snake’s niche (US Fish and Wildlife Service, 2017). The population has shown promising recovery since then because of the conservation efforts used, but still only about 1000-2000 individuals live in the wild and the San Francisco Garter Snake nowhere near being removed from endangerment (Center for Biological Diversity, 2017).
The carnivorous San Francisco Garter Snake is a crucial specialist species in the Bay Area’s wetlands food chain.
Like all animals, it is part of a complex food web. It preys upon and controls the population size of the California Red-Legged Frog, Rana draytonii. In return, it is preyed upon by larger predators such as birds and the invasive bullfrogs, Rana catesbeiana, which often eat the ovoviviparous animal’s eggs. There are endangered, anadromous fish such as the coho salmon, which also rely on the ecosystem that the SFGS lives in (US Fish and Wildlife Service, 2017).
The snake’s highly specific food requirement of the native frog makes the snake’s survival a constant struggle because its main food source, the California red-legged frog, is also endangered.
The San Francisco Garter Snake can reproduce once a year with a litter of 12-24 snakes, making their biotic potential fairly high, but young snakes quickly become prey of the bullfrog (San Francisco Garter Snake, 2010). Hopeful scientists say that mature San Francisco Garter Snakes also feed on young nonnative bullfrogs, helping to restrain the bullfrog’s out of control population (Swenty, 2016).
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One amazing characteristic of the San Francisco Garter Snake is that, because of coevolution, it is able to eat California Newts, Taricha torosa, a salamander that exudes a poison on its skin that is toxic to most other snakes (Roberson, 2004). It is one of the only predators of the toxic California Newt, making it crucial to the control of the newt population (Swenty, 2016). The newt necessary overeats detritivores, such as worms and slugs, as well as the eggs of amphibians like the SFGS and the California red-legged frog. If the newt’s population is not controlled by their snake predator these natural services will be lost forever (National Parks Service, 2015).
Snakes also serve as pest control for rats which helps to control disease because rodents often carry illness that can infect local communities of people and animals alike (Grant, 2014).
Decomposition of dead snakes of course contribute to nutrient cycling even though many are eaten by predators; moreover, shedding of snake skin contributes large amounts of energy to the nutrient cycling that occurs within the serpent’s community. Snakes across the United States produce about 1.6 billion pounds of shed skin per year which contain 3.6 trillion calories of energy, so each pound of skin returns 2,250,000 calories of energy to the soil. The plants, as producers, use nutrients from the soil and sequester carbon from the air to grow and start the food chain over, while helping to remove carbon from the atmosphere that would be contributing to climate change and global warming (Durso, 1970).
The San Francisco Garter Snake’s role in its wetland food chain is crucial to keeping prey populations in check, supporting the animals it falls prey to, and sustaining the cycling of nutrients and energy. Without the important link that this snake serves in the food chain, the balance of the ecosystem would be thrown off and become unstable.