Keystone Species

Ever come home at the end of a long week at work, wondering how the place could function without you? It might feel like you’re the only one holding it all together, like a keystone. This week we’ll take a look at the keystone that holds an ecosystem together- keystone species. Without the keystone species, the ecosystem would collapse, or at least be severely altered.

Examples of keystone species are the gray wolf, limber pine, and sea otters. We’ll take a quick return trip to the lava fields of Idaho, then the kelp forests of the Pacific coast to see how limber pines and sea otters are the keystones of their neighborhoods. We learned about the gray wolf and the good work they do at Yellowstone back in September here.

The limber pine is one of the few trees I saw growing at Idaho’s Craters of the Moon National Monument and Preserve. Back in September I spotlighted Craters of the Moon in “Volcanic Idaho”. In that blog post, I mentioned the diverse ecosystem found there. Much of it centers around the limber pine. Limber pine is a pioneer, one of the first to colonize an area following a disturbance, such as a volcanic eruption in Idaho. Its seeds, needles, and sap feed a multitude of mammals, insects, and birds. Without the limber pine, those critters would have to live elsewhere in Idaho, maybe even Utah or Wyoming.

Limber pine at Craters of the Moon

Off the Pacific coast, one of the most important marine habitats is the kelp forest. The kelp hosts many species of fish, somewhat resembling a coral reef (sans coral, of course). The kelp also absorbs storm surge and carbon dioxide. However, kelp tastes delicious, at least according to sea urchins. Lucky for the kelp, sea otters think sea urchins are delicious. Without the otters keeping the urchins in check, the kelp forest becomes an undersea clear cut. Local biodiversity plummets.

River otters (Marine Mammal Commission)

Kelp forest with and without sea otters (Sea Otters.com)

This week's information comes from Great Ecology's blog on limber pines and Sea Otters.com

What Otter Is This?

Otters are terribly cute little critters. There are several species worldwide, but in North America we have the river otter and the sea otter. Other than one living in a river and one living in the sea, what are the differences? If you should happen to see an otter near the coast, how do you know which one it is?

It might seem silly to not know what otter you are looking at, but coastal river otters will swim into the ocean. Now that you can’t always rely on the type of water to tell the otters apart, what do you do?

You probably won’t have the two otters side by side for a comparison, but the sea otter is much larger, twice or even three times the size of the river otter. The sea otter’s tail is shorter and flatter, while the river otter’s tail is about half the length of its body. River otters have a more rounded nose than sea otters, and the river otter’s nose farther above the mouth. The sea otter’s nose is slightly pointed at the top and the bottom comes to the mouth much like a cat’s. The sea otter has very dense fur, which is why they were hunted to near extinction. The river otter has a course fur and a layer of fat.

Sea otters at sea (Marine Mammal Commission)

River otter swimming

Movement is a good indicator of which otter you’re looking at. Sea otters swim almost exclusively on their backs, using their bellies as a dinner table. River otters swim on their bellies (riding very low in the water) and usually eat on land. On land, river otters move quite well, running with an arched back or sliding downhill on snow. Sea otters rarely come ashore, and when they do, they are clumsy critters that waddle more than they walk.

Sea otter ashore (Oregon Zoo)

River otter on land (Smithsonian National Zoo)

Hopefully you will be lucky enough to find yourself in a position that you see an otter and wonder what kind it is. Sea otters live exclusively on the West Coast and are a threatened species so you will be lucky indeed to find one. River otters have suffered in the past due to hunting and trapping pressures just as their seafaring cousins, but have had a more successful recovery thus far and enjoy no special federal protection.

So you’re far more likely to see a river otter based on population and range. Still, seeing a river otter is a special event. I’ve come across them in the wild twice, and both times it was an unexpected delight. The first otter was in my pond while I was surveying amphibian egg masses. The second was in Capitol Lake in Olympia, WA where I was joining a group for an evening bat program. Check your local waterways; you may be in for a pleasant surprise too!

This week's otter information comes from the Seattle Aquarium. Don't forget to follow Nature Minute on Facebook!