|Scientific Name:||Dicrostonyx unalascensis|
|Species Authority:||Merriam, 1900|
Dicrostonyx groenlandicus Merriam, 1900 subspecies unalascensis
Dicrostonyx stevensoni Nelson, 1929
|Taxonomic Notes:||This species formerly was recognized as a subspecies of D. groenlandicus. It has distinctive pelage and craniodental characteristics, and apparently uniquely among Dicrostonyx, it lacks specialized nival pelage and foreclaws (see Musser and Carleton in Wilson and Reeder 2005).
Dicrostonyx taxonomy is complex and not well resolved. The complex was regarded as part a single circumpolar species, D. torquatus, until the 1970s when karyological and breeding studies indicated the possible existence of a superspecies complex among North American Dicrostonyx (Rausch and Rausch 1972, Rausch 1977; see also Krohne 1982). Former subspecies occurring in western Canada and Alaska were recognized as separate species based mainly on karyotypes (Rausch and Rausch 1972; Rausch 1977; Krohne 1982; Honacki et al. 1982; Jones et al. 1986, 1992). Musser and Carleton (in Wilson and Reeder 2005) reviewed these and subsequent studies and provisionally recognized eight Dicrostonyx species, six of which (groenlandicus, hudsonius, nelsoni, nunatakensis, richardsoni, and unalascensis) occur in North America; this is the taxonomy adopted here. Baker et al. (2003) recognized D. exsul, D. kilangmiutak, and D. rubricatus as species, but Musser and Carleton recognized exsul as a synonym of D. nelsoni, and kilangmiutak and rubricatus were treated as synonyms of D. groenlandicus.
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor(s):||Linzey, A.V. & NatureServe (Garibaldi, A. & Hammerson, G.)|
|Reviewer(s):||Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)|
Listed as Data Deficient, because its extent of occurrence is less than 5,000 km², and it is known from only two islands, which is under the criterion for Endangered, however, further information on population status and the nature and extent of any threats to the species are needed to determine if it is declining.
|Range Description:||The species' range includes Umnak and Unalaska Islands, in the Aleutian Archipelago, Alaska, United States (Musser and Carleton, in Wilson and Reeder 1993, 2005). Umnak Island is approximately 85,920 hectares and Unalaska Island is 137,849 hectares (total 2,238 square kilometers).|
Native:United States (Alaska, Aleutian Is.)
|Range Map:||Click here to open the map viewer and explore range.|
No population estimates are available (Jarrell 1997), but the total adult population size (though variable) presumably exceeds 10,000. Each of the two occupied islands could be regarded as a single occurrence or subpopulation.
No population trend information is available. Although Fay and Murie did not believe that lemming populations on Umnak Island are cyclic (Fay pers. comm.; Murie 1959, in Fay and Sease 1985), they noted that populations fluctuate widely from scarce to abundant. However, according to Stenseth and Ims (1993), "Lemmings are characterized by, and known for, their pronounced density cycles combined with shifts in habitat use both at a local and regional scale." They discussed reasons for controversy over accepting cyclicity in lemmings and possible ways to account for this phenomenon. No information has suggested a positive or negative population trend, so the population may be stable.
|Habitat and Ecology:||This species is an Arctic tundra inhabitant, but specific ecological information is sparse.|
|Major Threat(s):||The restricted range of this species increases its vulnerability to outside threats (e.g., rat introduction). Effects from the development of Nikolski village, Umnak Island, appear to be insignificant (Fay and Sease 1985). This is an important prey species for red fox and predatory birds on both islands (Fay and Sease 1985; Peterson 1967); however, red fox is native to these islands (not introduced) so the Dicrostonyx population may be able to tolerate fox predation. The effects of Norway rat, house mouse, and ground squirrel introductions on Unalaska Island and European hare introduction on Umnak Island are unknown. The Arctic fox was introduced on Unalaska Island in 1922 but has since disappeared (Bailey 1993).|
No known protection measures are in place for this species. Lemmings are listed as unclassified game by the U.S. Fish and Wildlife Service with no closed season and bag limit. No protection measures currently are needed; however, populations should be monitored to ensure that protection needs do not change.
Research needs include: 1) Genetic analysis to substantiate species status of Dicrostonyx unalascensis. 2) Determine factors that affect cyclicity of lemming populations on Unalaska and Umnak islands. 3) Study habitat preferences and ecosystem structure involving lemmings. 4) Determine effects of winter breeding and reproductive patterns in relation to cyclicity. 5) Determine the impact of introduced species on the populations.
|Citation:||Linzey, A.V. & NatureServe (Garibaldi, A. & Hammerson, G.) 2008. Dicrostonyx unalascensis. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 29 May 2015.|
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