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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

128: Death Valley

Major Habitat Type:

xeric freshwaters and endorheic (closed) basins

Author:

Text modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment. Island Press, Washington, DC, USA.

Countries:

United States

Boundaries:

Death Valley comprises the southwest corner of the Great Basin and dominates central southern California and reaches into southwestern Nevada. Included in the ecoregion are the eastern slopes of the southern portion of the Sierra Nevada Mountains and the northeastern slopes of the Transverse Range.

Drainages flowing into:

Death Valley is an endorheic basin defined by the drainages of the Owens, Amargosa, and Mojave rivers (Sada et al. 1995).

Main rivers or other water bodies:

This area has few large lakes or perennially flowing rivers and streams, but abundant springs rising along faults instead provide much of the habitat available to freshwater species. Water flowing from these springs is 8,000-12,000 years old and originates in southern and eastern Nevada (Minckley et al. 1986).

Topography:

North-south trending mountains and valleys with numerous faults characterize this landscape (Minkley et al. 1986). While most of the Mojave region lies between 610 and 1,220 m, Badwater Basin lies at - 86 m, the lowest point in North America (Ricketts et al. 1999).

Climate:

Death Valley is part of the Mojave high desert and is characterized by a warm temperate climate, receiving low annual precipitation ranging between 65 and 190 mm (Ricketts et al. 1999). Temperatures typically range between 10 – 24 °C, although summer temperatures can exceed 49 °C and winter temperatures dip below 7 °C in the valleys (McNab & Avers 1994).

Freshwater habitats:

This ecoregion contains some of the most extreme conditions inhabited by freshwater life and its biota has been extensively studied. Ash Meadows, covering an area of about 756 km2, is of particular interest, as its more than 30 springs and seeps create an oasis in the middle of the desert (Williams et al. 1985). Devils Hole is the highest in elevation of these springs, at 732 m. With increasing elevation, springs have been isolated from each other for a longer time, and springs only a kilometer apart may have been isolated for thousands of years (Williams et al. 1985). In this arid area groundwater recharge is so slow that the aquifers supplying springs such as Devils Hole contain fossil water (Pister 1990).

Terrestrial Habitats:

Xeric shrublands and desert vegetation characterize much of this ecoregion, with saltpans devoid of vegetation in the lowest elevations to sub-alpine habitats on mountain peaks. Dominant plants include creosote bush (Larrea tridentata), all-scale (Atriplex polycarpa), brittlebush (Encelia farinosa), desert holly (Atriplex hymenelytra), white burrobush (Hymenoclea salsola), and Joshua tree (Yucca brevifolia) (Turner 1994).

Fish Fauna:

Like other arid ecoregions of North America, Death Valley exhibits low species diversity but extraordinarily high endemism.

Description of endemic fishes:

Within the ecoregion, there are five endemic fish species. The number of endemic fish forms increases if subspecies are included, as some authors argue is appropriate given the degree of differentiation observed in forms associated with distinct, persistent water bodies (Minckley et al. 1986; Sada et al. 1995). With the exception of the fish in the Owens River and Mojave River basins, all of the endemic freshwater species in this ecoregion are associated with springs or spring margins. Given the minute amount of freshwater available in this ecoregion, this biodiversity is truly impressive.

The endemic fish come from four families, with subspecies of two minnows (Rhinichthys osculus and Gila bicolor), one sucker species (Catostomus fumeiventris), the extinct Ash Meadows killifish (Empetrichthys merriami), and four pupfish (Cyprinodon radiosus, C. diabolis, C. nevadensis, and C. salinus). Of these, five subspecies of C. nevadensis and two of C. salinus are recognized, as are three subspecies of speckled dace (R. osculus) (Sada et al. 1995). The Devil’s Hole pupfish (C. diabolis) is distinguished by having the smallest range of any vertebrate species—23 square yards in a spring-fed, limestone cavern in Ash Meadows (Williams et al. 1985; Sada et al. 1995). The species is tiny, rarely exceeding 20 mm standard length, and populations fluctuate seasonally from between 150 and 400 individuals (Williams et al. 1985). The two forms of the Salt Creek pupfish (C. salinus) live between 180 and 240 feet below sea level, where temperatures can reach 130 °F (Sigler & Sigler 1994).

Other noteworthy aquatic biotic elements:

The ecoregion also hosts over twenty endemic mollusks (all snails) and more than five endemic aquatic insect species.

Evolutionary phenomena:

Death Valley is considered continentally outstanding for its higher taxonomic endemism, including one fish genus (Empetrichthys), and for its high beta-diversity among sites (Abell et al. 2000).

Justification for delineation:

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).

References/sources:

Abell, R., Olson, D., et al. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.

Maxwell, J. R., Edwards, C. J., et al. (1995) "A hierarchical framework of aquatic ecological units in North America (Nearctic Zone)". St. Paul, MN. North Central Forest Experiment Station, USDA Forest Service.

Minckley, W. L., Hendrickson, D. A., et al. (1986)"Geography of western North American freshwater fishes: Description and relationships to intracontinental tectonism" In Hocutt, C.H.;Wiley, E.O. (Ed.). The zoogeography of North American freshwater fishes. New York: John Wiley.

Pister, E. P. (1990). "Desert fishes: an interdisciplinary approach to endangered species conservation in North America" Journal of Fish Biology 37 183-187.

Ricketts, Taylor H. Dinerstein Eric Olson David M. Loucks Colby J. (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.

Sada, D. W., Britten, H. B., et al. (1995). "Desert aquatic ecosystems and the genetic and morphological diversity of Death Valley System speckled dace" American Fisheries Society Symposium 17 350-359.

Sigler, J. W.,Sigler, W. F. (1994)"Fishes of the Great Basin and Colorado Plateau: Past and present forms" In Harper, K.T.;St. Clair, L.L.;Thornes, K.H.;Hess, W.M. (Ed.). Natural history of the Colorado Plateau and Great Basin. Niwot: University of Colorado Press.

Turner, J.T. (1994)"Great Basin Desertscrub" In Brown, D.E. (Ed.). Biotic communities in southwestern United States and northwestern Mexico. (pp. 145-155) Salt Lake City, UT: Univerisity of Utah Press.

Williams, J. E., Bowman, D. B., et al. (1985). "Endangered aquatic ecosystems in North American deserts with a list of vanishing fishes of the region" Journal of the Arizona-Nevada Academy of Sciences 20 1-62.

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