EPOW - Ecology Picture of the Week

Two of a Different Kind

top:  Van Dyke's Salamander (Plethodon vandykei), Family Plethodontidae
bottom:  Cascade Torrent Salamander (Rhyacotriton cascadae), Family Rhyacotritonidae
Cascade Mountains, Washington USA

Explanation:  Welcome to the southern Cascade Mountains of Washington State, USA.  Along a narrow stream gorge we find these two salamanders in sympatry (living together).  Although they look alike, they belong to different species and, in fact, to entirely different families.  

On the top is the ultra-rare Van Dyke's Salamander, whom we met in a previous EPOW episode.  Van Dyke's Salamanders occur only in Washington State in 3 separate populations.  In the Cascade Mountains portion of their range, they associate with steep rocky streams with some cover afforded by vegetation, down wood, and rocks.  Their genetics may bear further study, given their spotty distribution in the state.

At the bottom, though, is a beast of a different kind.  This is a Cascade Torrent Salamander which occurs only on the west side of the Cascade Mountains in Washington and Oregon, so it also is a regional endemic.  Largely active at night, Cascade Torrent Salamanders are poorly studied but do occur in some of the same habitats as Van Dyke's Salamanders.  They generally need cool mountain streams or seeps in steep mountain country.

How do these seemingly similar species coexist?  They likely occur together when there is sufficient invertebrate prey and cover objects to support both populations, but how they further differentiate their niches is not well known.

Interestingly, both of these species persisted in some locations impacted by the 1980 eruption of Mount St. Helens.

The IUCN Red List of Threatened Species lists the Cascade Torrent Salamander as "Near Threatened" although the rarer Van Dyke's Salamander is listed as a species of "Least Concern."  The justification is that the latter "has a presumed large population" and is "unlikely to be declining fast enough to quality for listing in a more threatened category," but the Cascade Torrent Salamander has a narrow geographic range and its "habitat is in decline" ... even though they both share some common habitat.  This ecologist respectfully suggests that more study is needed of population size, density, and trend, and habitat associations, of both species...