Xantusia riversiana

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	REPTILIA	SQUAMATA	XANTUSIIDAE

Scientific Name:

Xantusia riversiana

Species Authority:

(Cope, 1833)

Common Name/s:

English

–

Island Night Lizard

Synonym/s:

Klauberina riversiana

Assessment Information [top]

Red List Category & Criteria:

Least Concern ver 3.1

Year Assessed:

2007

Assessor/s

Hammerson, G.A.

Evaluator/s:

Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)

Justification:
Listed as Least Concern because, although its extent of occurrence is much less than 5,000 km², it is common and occurs in a habitat that is not under significant threat.

History:

1996	–	Vulnerable (Baillie and Groombridge 1996)
1994	–	Rare (Groombridge 1994)
1990	–	Rare (IUCN 1990)
1988	–	Rare (IUCN Conservation Monitoring Centre 1988)
1986	–	Rare (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description:	The entire range is on the California Channel Islands in the southwestern United States. The species occurs on San Clemente and Santa Barbara islands (subspecies reticulata) and on San Nicolas Island (subspecies riversiana). It also occurs on a small islet (Sutil Island) 1.3 km offshore from Santa Barbara Island (Bezy et al. 1980). Old records for Santa Catalina Island are erroneous. San Clemente Island, at 145 sq. km, is the largest inhabited island (San Nicolas = 57 sq. km, Santa Barbara = 16 sq. km).
Countries:	Native: United States (California)
Range Map:	(click map to view full version)

Population [top]

Population:	Each island can be regarded as a distinct, single occurrence. Hence there are just a few occurrences or subpopulations. The total adult population size is unknown but greater than 10,000 and perhaps exceeds 100,000. At the time of listing, the population on San Clemente Island was estimated at 800 to 1300 per ha of prime habitat; the San Nicolas Island population was estimated at 14,800; and the Santa Barbara Island population was thought to be 550 to 700 (Matthews and Moseley 1990). However, Fellers and Drost (1991) determined that the total population on Santa Barbara Island was at least 17,600 and concluded that the population is not threatened with extinction as was previously thought. Also Mautz recently found healthy populations on San Clemente Island. USFWS (1990) categorized the status as "stable."
Population Trend:	Stable

Population:

Each island can be regarded as a distinct, single occurrence. Hence there are just a few occurrences or subpopulations. The total adult population size is unknown but greater than 10,000 and perhaps exceeds 100,000. At the time of listing, the population on San Clemente Island was estimated at 800 to 1300 per ha of prime habitat; the San Nicolas Island population was estimated at 14,800; and the Santa Barbara Island population was thought to be 550 to 700 (Matthews and Moseley 1990). However, Fellers and Drost (1991) determined that the total population on Santa Barbara Island was at least 17,600 and concluded that the population is not threatened with extinction as was previously thought. Also Mautz recently found healthy populations on San Clemente Island. USFWS (1990) categorized the status as "stable."

Population Trend:

Stable

Habitat and Ecology [top]

Habitat and Ecology:	This lizard inhabits grassland, chaparral, oak savanna, clumps of cactus and boxthorn, dry sandy or rocky streambeds, cliffs, and rocky beaches (Stebbins 2003). It occupies areas of thick, low-lying vegetation growing on rocky soil and certain types of rock habitat; dominant plants include patches of prickly pear, matted thickets of boxthorn, and thickets of non-native Australian saltbush (Fellers and Drost 1991, Matthews and Moseley 1990). Individuals are often found under cover of rocks, driftwood, and fallen branches (Stebbins 2003), and they also use burrows.
Systems:	Terrestrial

Habitat and Ecology:

This lizard inhabits grassland, chaparral, oak savanna, clumps of cactus and boxthorn, dry sandy or rocky streambeds, cliffs, and rocky beaches (Stebbins 2003). It occupies areas of thick, low-lying vegetation growing on rocky soil and certain types of rock habitat; dominant plants include patches of prickly pear, matted thickets of boxthorn, and thickets of non-native Australian saltbush (Fellers and Drost 1991, Matthews and Moseley 1990). Individuals are often found under cover of rocks, driftwood, and fallen branches (Stebbins 2003), and they also use burrows.

Systems:

Terrestrial

Threats [top]

Major Threat(s):	The inhabited islands and their native inhabitants have been negatively affected by habitat alteration and predation resulting from introduction of alien species (e.g., feral cats, goats, pigs, and rabbits). However, according to the Channel Islands Species Recovery Plan of 1984, habitat on the islands "probably has not been altered to the detriment of the [island night] lizards by grazing mammals". Goats and pigs have recently been removed from San Clemente Island. Today, the Island Night Lizard is regarded as not significantly threatened.

Major Threat(s):

The inhabited islands and their native inhabitants have been negatively affected by habitat alteration and predation resulting from introduction of alien species (e.g., feral cats, goats, pigs, and rabbits). However, according to the Channel Islands Species Recovery Plan of 1984, habitat on the islands "probably has not been altered to the detriment of the [island night] lizards by grazing mammals". Goats and pigs have recently been removed from San Clemente Island. Today, the Island Night Lizard is regarded as not significantly threatened.

Conservation Actions [top]

Conservation Actions:	Santa Barbara Island is part of the Channel Islands National Park. The entire island of San Clemente, used for military training, has been designated as Critical Habitat. The species is federally listed as threatened, but delisting may occur in the near future.

Conservation Actions:

Santa Barbara Island is part of the Channel Islands National Park. The entire island of San Clemente, used for military training, has been designated as Critical Habitat. The species is federally listed as threatened, but delisting may occur in the near future.

Citation:	Hammerson, G.A. 2007. Xantusia riversiana. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 02 December 2008.
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